Download Ataxia..Telangiectasia and Cellular Responses

(CANCER RESEARCH55. 5991-6001. December 15, 19951
Review
Ataxia..Telangiectasia
and Cellular Responses to DNA Damage'
M. Stephen Meyn2
Departments of Genetics and Pediatrics, Yale University School of Medicine, New Haven, connecticut 06510
Abstract
Ataxia-telangiectasia
(A-T) is a human disease characterized by high
cancer risk, immune defects, radiation sensitivity, and genetic instability.
Although A-T homozygotes are rare, the A-T gene may play a role in
sporadic breast cancer and other common cancers. Abnormalities of DNA
repair, genetic recombination,
chromatin structure, and cell cycle check
elevated frequencies of spontaneous and induced chromosome aber
rations, high spontaneous rates of intrachromosomal recombination,
aberrant immune gene rearrangements, and inability to arrest the cell
cycle in response to DNA damage (3—6)].
The
nature
speculation;
of the A-T
defect
most hypotheses
has been
the subject
of much
focus on the radiation sensitivity
of
point control have been proposed as the underlying defect in A-T; how
A-T cells. Early reports that A-T fibroblasts were unable to excise
ever, previous
radiation-induced
DNA adducts prompted suggestions that the
radiation sensitivity of A-T cells was due to an intrinsic defect in
DNA repair (7). However, subsequent work indicated that not all
models cannot
satisfactorily
explain
the plelotropic
A-T
phenotype.
Two recent observations help clarify the molecular pathology of A-T:
(a) inappropriate
p53-mediated apoptosis is the major cause of death in
A-T cells irradiated in culture; and (b) ATM, the putative gene for A-T,
has extensive homology to several celi cycle checkpoint genes from other
organisms. Building on these new observations, a comprehensive model is
presented in which the ATM gene plays a crucial role in a signal trans
duction network that activates multiple cellular functions In response to
DNA damage. In this Damage Survefflance Network model, there is no
intrinsic defect in the machinery of DNA repair in A-T homozygotes, but
their lack of a functional ATM gene results In an Inabifity to: (a) halt at
multiple cell cycle checkpoints in response to DNA damage; (b) activate
damage-inducible
DNA repair; and (c) prevent the triggering
of pro
grammed cell death by spontaneous and induced DNA damage. Absence
of damage-sensitive
cell cycle checkpoints and damage-induced repair
disrupts immune gene rearrangements and leads to genetic instability and
cancer. Triggering of apoptosis by otherwise nonlethal DNA damage is
primarily responsible for the radiation sensitivity ofA-T homozygotes and
results in an ongoing loss of cells, leading to cerebellar ataxia and neuro
logical deterioration,
as well as thymic atrophy, lymphocytopenla,
and a
paucity of germ cells.
Experimental
evidence supporting the Damage Surveffiance Network
model
is summarized,
ATM-dependent
followed
by a discussion
signal transduction
network
of how
defects
in the
might account for the A-T
phenotype and what insights this new understanding of A-T can offer
regarding DNA damage response networks, genomic instability, and can
cer.
Previous Models for A-T3
A-T is an autosomal recessive disease with a pleiotropic phenotype
that includes progressive cerebellar ataxia, cellular and humoral im
mune defects, progenc changes of the skin, endocrine disorders,
gonadal abnormalities, and a high incidence of cancer; the relative risk
of developing some tumors (e.g. , lymphoma) is several hundredfold
higher than normal ( 1, 2). Heterozygote carriers are also at increased
risk for cancer, particularly breast carcinoma (2). A-T cells are sen
sitive to the killing
effects
of ionizing
radiation,
and they exhibit
in
vivo and in vitro abnormalities consistent with a defect involving
DNA metabolism
and/or maintenance
of genomic integrity [e.g.,
Received 8/2 1/95; accepted 10/16/95.
The costs of publication of this article were defrayed in part by the payment of page
A-T fibroblasts
have a defect
in DNA adduct excision
(8), and that
the kinetics of repair of DNA breaks and chromosome
aberrations
is grossly normal (reviewed in Ref. 3). Functional abnormalities of
specific repair enzymes have been proposed [e.g. , topoisomerase
II
(9) and poly(ADP-ribosylase) (10)], but conclusive evidence of
repair enzyme defects in A-T is lacking. Structural abnormalities
of chromatin, subtle defects in DNA repair that affect repair
quality, and abnormalities of differentiation also have been offered
as explanations for the A-T phenotype (11—15).
Several investigators have suggested that a defect in genetic recom
bination, resulting in an inability to productively rearrange and repair
genes, would provide a unifying explanation for radiation sensitivity,
immune defects, and karyotypic abnormalities in A-T (5, 6, 16—18).
However, a defect in genetic recombination is difficult to resolve with
reports of near-normal frequencies of extrachromosomal recombina
lion (4, 19, 20) and the observation
that spontaneous
rates of chro
mosomal recombination in A-T fibroblast lines are 30- to 200-fold
higher than normal (4). Other investigators, struck by the inability of
irradiated A-T cells to temporarily halt DNA replication and cell cycle
progression, have proposed that A-T cells cannot recognize or respond
to DNA damage (1 1, 12, 21—23).In these models, the radiation
sensitivity of A-I cells generally is assumed to result from an inability
to delay the cell cycle to allow sufficient time to repair DNA damage.
These models could explain why A-T cells are radiation sensitive
despite grossly normal DNA repair, but they cannot readily account
for several studies in which experimental
temporarily
irradiated
conditions
that prolonged
or
halted the cell cycle did not improve the survival of
A-I cells (24—26). Neither
do these models
explain
another
puzzling feature of A-I: unlike most normal mammalian cells, fatally
irradiated A-I cells typically die before they can complete the first
postirradiation mitosis (113—1
15).
The finding that the radiosensitivity of A-I cells in culture is
primarily the result of inappropriate apoptosis, together with recent
observations regarding the role that the p53 tumor suppressor protein
plays in mediating cellular responses to DNA damage, has led to the
development of a new model regarding the nature of the A-I defect.
charges. This article must therefore be hereby marked advertisement in accordance with
Initial analysis of the A-T disease gene supports this model, which is
18 U.S.C. Section 1734 solely to indicate this fact.
related to previous proposals in which the A-T gene product normally
mediates cellular responses to DNA damage (e.g., see Ref. 22), but
overcomes the objections to those models, cited above, while provid
ing a unifying explanation for the pleiotropic manifestations of the
disease.
I This
work
has
been
supported
by
grants
from
the
NIH
and
the
A-I
Children's
University
School
Project.
2 lo
whom
requests
for
reprints
should
be addressed,
at Yale
Medicine, 333 Cedar Street, P.O. Box 208005, New Haven. CI 06520-8005.
3 The
abbreviations
used
are:
A-I,
ataxia-telangiectasia;
LOH,
ICR, I-cell receptor;P13-kinase.phosphatidylinositol3-kinase.
loss of heterozygosity;
of
5991
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECTASIA
Ihe Damage Surveillance Network Model
a critical role. The detection of certain types of spontaneous or induced
DNA damage triggers this signal transduction network, resulting in the
Biological organisms are not passive targets ofDNA-damaging agents;
activation of a group of cellular functions that promote genetic stability
they actively respond to DNA damage [e.g., the SOS system in Esche
by temporarily arresting the cell cycle and enhancing DNA repair. At the
richia coli (30)]. A growing body of evidence indicates that the response
of mammalian cellsto DNA damage iscomplex,perhapsinvolving same time, the A-I-dependent network promotes cellular survival by
several interrelated signal-transductionnetworks that detect DNA dam
inhibiting execution of damage-induced programmed cell death. In ad
age, activate DNA repair, and alter the cell cycle (22, 27—29).Fig. IA
depicts a damage response network in which the A-T gene product plays
dition to the five responses
illustrated
in Fig. 1A, there also may be other,
asyetundefined,
A-I-dependent
functions.
A. NormalIndividuals
Activated
DNARepair
@
@GADD45
,t
p21
‘t'@@
GuS
p53
Spontaneous and
Checkpoint
f
Induced
@
@
DNADamage
ImmuneGene
Rearrangments
@.
ssandds
DNAbreaks
\
S phase
Checkpoint
___________
ATM
I
ShortTelomeres
p53
GRIM
Checkpoint
B. A-T Homozygotes
No enhanced reactIvation
‘V d2
D
@
air
@GADD45
@
/@ p21
increased genomic instability
chromosomal translocations
epithelial cells with micronudel
aneuploid cells in muftipletissues
alleleloss in erythrocytes
ICR transrearrangements
recombination between repeated genes
p53
Spontaneousand
I
Induced
@
@
DNADamage
ImmuneGene
Rearrangments
ShortTelomeres
55 and ds
DNAbreaks
@.
of Irradiated virus
No enhanced mutagenesis
of irradiated virus
induced chromosome
solid tumors
*-
Disruption of Immune gene rearrangement
Lowlevelsof lgA, IgE, g02 and lgG4
Lowproportionof I cells expressingW@3
TCRs
Frequent translocatlons near immune genes
9@PQk@t
%4@
aberrations
Increased risk of lymphoma and leukemia
p53
C
ck
nt
Abnormal cell cycle kinetics following DNAdamage
RadioresistantDNAsynthesis
Programmed
Cell Death
Increased spontaneous cell death
progressive loss of neurons
thymic hypoplasia and lymphocytopenia
depletion or absence of germ cells
hypoplastic thyroid and adrenals
progeric changes in skin and hair
cirrhosis and elevated serum AFP
Increased mutagen-lnduced cell death
Marked sensitivity to killingby:
Ionizing radiation
radiomimetic drugs
Fig. I . A, a DNA Damage Surveillance Network. As part of this signal transduction network, the ATM protein activates at least five cellular functions in response to the detection
of spontaneous or induced DNA damage. In B, the DNA damage surveillance network is defective in A-I homozygotes. A-I homozygotes cannot activate ATM-dependent functions
in response to DNA damage. resulting in the pleiotropic A-I phenotype.
5992
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECTASIA
in S phase, resulting in the phenomenon of radioresistant DNA syn
thesis (11). The G2-M checkpoint appears to be defective in A-T cells
The primary abnormality in A-I homozygotes presumably creates
a defect in this network that prevents the activation of these cellular
functions in response to strand breaks, shortened telomeres, and other
DNA lesions (Fig. 1B). This inability to respond to spontaneous and
induced DNA damage results in increased genomic instability, as well
as well, in that both A-T fibroblasts and lymphocytes irradiated in 02
fail to undergo the initial radiation-induced 02-M delay seen in
normal cells (46, 47, 113).
as in an unusually low threshold for the triggering of p53-mediated
Lack of Damage-activated DNA Repair. Exposing human cells
apoptosis by otherwise nonlethal DNA damage. These abnormalities
lead, in turn, to the multiple in vivo and in vitro abnormalities seen in
A-I homozygotes (Fig. 1B). Although they are not as severely af
fected as homozygotes, A-I heterozygotes may not have a fully
functional damage response network, because they express subtle
abnormalities in their cellular responses to ionizing radiation (3) and
to low doses of radiation before infection of irradiated virus improves
viral survival and increases the number of mutant viruses recovered
(48). These effects, termed “enhancedsurvival―and “enhancedmu
tagenesis,― have been demonstrated using both single-stranded and
double-stranded DNA viruses (48—50),but they are not as striking as
the analogous phenomena in bacteria, Weigle reactivation and Weigle
have an increased relative risk of cancer (2).
mutagenesis (30).
A-I Homozygotes Lack DNA Damage-activated Functions
repair pathway in bacteria; similarly, one or more damage-activated
Weigle reactivation results from induction of an error-prone DNA
Absence of Cell Cycle Checkpoints. In normal eukaryotic cells,
the cell cycle halts temporarily after the induction of strand breaks in
cellular DNA by a variety of agents, including ionizing radiation,
radiomimetic drugs, restriction enzymes, and topoisomerase inhibitors
(reviewed in Refs. 23 and 29). There are at least three damage
sensitive cell cycle “checkpoints―
in mammalian cells: one at the G1-S
border, one in S phase, and one at the G2-M boundary. These check
points also may restrain the cell cycle in response to the generation of
strand breaks, shortened telomeres, and other DNA damage that
occurs spontaneously during the course of normal DNA metabolism
(e.g. , site-specific gene rearrangements, genetic recombination, and
repair of replication errors). Given the viability of yeast and mamma
han mutants that lack functional damage-sensitive cell cycle check
points (31—33),these checkpoints probably are not invoked during
most cell cycles. The relative timing of DNA replication, DNA repair,
genetic recombination, and cell division ensures that genomic integ
rity is restored before the cell cycle reaches a checkpoint (23, 29).
The tumor suppressor protein p53 plays a key role in activating the
DNA repair processes could be responsible for enhanced survival and
enhanced mutagenesis in mammalian cells. At least some form of
damage-activated repair may be p53 dependent in human cells. Smith
et aL (51) recently demonstrated that loss of p53 function in human
cells was associated with modest decreases in clonogenic survival, as
well as reduced repair of UV-damaged reporter plasmids. Activation
of excision DNA repair, as measured by an in vitro assay, also was
decreased in p53@ cells (52). The p53 protein role in damage
activated repair might occur either by direct interaction with repair
enzyme complexes (52) and/or by activation ofGADD45, which itself
has been shown to bind to proliferating cell nuclear antigen and
stimulate DNA excision repair in vitro (53). Although not extensively
studied, damage-activated DNA repair appears to be impaired in A-I
homozygotes because A-T fibroblasts have been shown to lack the
enhanced survival and enhanced mutagenesis expressed by control
human cells for irradiated H-l parvovirus and adenovirus 2 (49, 50,
54).
29; e.g., mammalian cells increase intracellular levels of p53 protein
Low Threshold for Triggering Programmed Cell Death after
DNA Damage. A growing body of evidence documents that low
doses of ionizing radiation kill some types of mammalian cells in vivo
shortly
and in vitro by activating apoptosis, a well-characterized
G1-s checkpoint after certain types of DNA damage [reviewed in Ref.
after exposure
to many agents that induce DNA strand breaks,
form of
and functional p53 protein typically is required for activation of the
programmed cell death (reviewed in Ref. 55) that can be carried out
Gl-s checkpoint after ionizing radiation exposure (22, 34, 35)]. G1-S
in both cycling (56) and noncycing cells (57).
cell cycle arrest occurs via p53-mediated transcriptional activation of
the p21 (WAF-JICIPJISDIJ) gene, which codes for a protein that
binds to cyclin-dependent kinase-cyclin complexes and inhibits their
kinase activities (22, 36, 37). The p21 protein may be involved in the
S-phase checkpoint as well because it can bind to proliferating cell
nuclear antigen/replication factor C/pol 6 complexes in vitro and
block the elongation step of DNA polymerization (38, 39). The
S-phase checkpoint may be p53 independent because cells lacking
functional p53 can express a radiation-induced S-phase checkpoint, as
indicated by normal suppression of DNA synthesis after irradiation
Although researchers have only recently begun to focus on the
possible role of programmed cell death in the A-I phenotype, several
in vivo and in vitro findings support such a possibility. Histological
analyses of cerebella taken from A-T homozygotes at autopsy docu
ment a high frequency of abnormal Purkinje and granule cells that
exhibit the highly condensed, pyknotic nuclei expected from pro
grammed cell death in neurons (58—60).An in vitro flow cytometric
study that examined the effects of the radiomimetic drug streptomgrin
on A-T fibroblasts described changes in the DNA content of treated
A-I cells that are consistent with apoptosis (61).
(40). In mammalian
cells,theG2-Mdamage-activated
checkpoint Following up on these observations, we recently demonstrated that
probably is also p53 independent (e.g., see Ref. 41); however, rela
lively little is known about its genetics and biochemistry. In contrast,
at least 10 yeast genes are involved in controlling the G2-M check
point (31, 32, 42, 43).
fibroblasts and lymphoblasts representing all A-I complementation
groups undergo apoptotic death in culture after exposure to low
checkpoint, and the kinetics of p53, p21, and GADD45 induction by
ionizing radiation are abnormal in the cells of A-I homozygotes (22,
radiation and streptomgrin doses that do not induce appreciable ap
optosis in control cells (62).@This inappropriate apoptosis appears to
be mediated by p53, in that it is suppressed in A-T fibroblasts, the p53
protein of which has been functionally inactivated by transfection
with either a dominant-negative p.53 gene or a human papilloma virus
A-I homozygotes lack the p53-mediated G1-S damage-sensitive
44, 45). These observations led Kastan et aL (22) to propose that the
E6 gene.
A-T gene product(s) functions upstream of p53 in a damage-respon
survival of control fibroblasts, but transfected A-I cells acquired
sive pathway that leads to Ge-S arrest. This pathway is incorporated
in the Damage Surveillance Network model as one branch of the
near-normal resistance to ionizing radiation, suggesting that p53-
ATM-dependent network (Fig. 1A). A-I cells do not have the S-phase
checkpoint, because they fail to arrest DNA synthesis when irradiated
4 M.
Iransfection-induced
S. Meyn,
L
Strasfeld,
loss of p53 function
and C. Allen.
p53-mediated
apoptosis
did not affect
is the primazy
of radiosensitivity in ataxia-telangiectasia, manuscript in preparation.
5993
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
cause
A COMPREHENSIVE
MODEL
FOR
ATAXIA-TELANGIECTASIA
mediated apoptosis is the major cause of radiosensitivity in A-I cells
also have marked elevations in the frequency of I lymphocytes
in culture (62).@
expressing y/13, ‘SIP,
aTh, or y/6 heavy-chain ICRs as a result of
aberrant interlocus gene rearrangements (5, 6) and a high frequency of
B and I lymphocytes carrying chromosome translocations involving
Initial Analysis of the ATM Gene Supports the Damage
Surveillance
Network Model
Earlier this year, Savitsky et a!. (63) positionally cloned a gene
from the 1lq23.l A-I locus that is mutated in A-I patients from all
complementation groups. The gene, termed ATM (A-I, mutated), is
conserved in vertebrates and codes for a I2-kb transcript that is
abundantly expressed in multiple tissues in vivo. As shown in Fig. 2,
the carboxy terminus of the putative AIM protein is homologous to
that of at least four checkpoint proteins from other organisms: Dro
sophila melanogaster MEI-41, Schizosaccharomyces pombe Rad3,
Saccharomyces cerevisiae MEC1p, and S. cerevisiae TEL1p (63—65).
The region of strongest homology between these five proteins contains
a phosphatidylinositol 3-kinase domain, suggesting that proteins are
involved in signal transduction.
The ATM gene shares phenotypic similarities with these genes as
well. Like A-I homozygotes, mei-41, rad3, and med mutants are
X-ray sensitive and lack damage-induced cell cycle checkpoints (42,
43, 65). In addition, A-I, mei-41, rad3, and tell homozygotes express
increased chromosomal instability and have high spontaneous rates of
mitotic recombination (1, 4, 64—66).Taken together, the physical and
phenotypic similarities between these checkpoint genes and ATM
suggest that the ATM gene activates multiple cellular functions in
response to spontaneous and induced DNA damage.
Lack of Damage-activated Functions Explains the Phenotype of
A-T Homozygotes
sites on chromosomes 2, 7, and 14 near the immunoglobulin super
gene family genes (reviewed in Ref. 17).
The Damage Surveillance Network model for A-I explains these
clinical findings by assuming that the gene rearrangements necessary
for immunoglobulin
switch recombination and ICR heavy-chain re
arrangements frequently trigger the A-I damage surveillance network
and its cell cycle checkpoints, perhaps in response to the creation of
double-strand breaks during immune gene recombination. Normal
cells halt the cell cycle temporarily to allow completion of these
immune gene rearrangements
(69), but cells of A-I homozygotes
cannot activate cell cycle checkpoints. Hence, A-I cells that are
undergoing switch recombination or ICR heavy-chain rearrangement
may attempt to replicate their DNA and/or proceed past the G2-M
checkpoint into mitosis before resolving these recombination com
plexes. Manipulation of the immune recombination complexes during
DNA replication, chromosome condensation, and/or mitosis then dis
rupts the complexes, creating chromosomes that contain free DNA
ends generated during abortive immune gene rearrangement. These
free ends are highly recombinogenic and could serve as foci for
illegitimate recombinational events that lead to interlocus gene rear
rangements and chromosome translocations. The final result is an
abnormally high frequency of lymphocytes carrying translocations
near immune genes or expressing aberrantly recombinant ICRs. DNA
damage resulting from disrupted immune gene rearrangements also
may trigger apoptosis in A-I lymphocytes (see below), which, by
Lack of damage-activated functions in A-I homozygotes due to a
defect in a signal transduction network that monitors genomic integ
eliminating cells undergoing immunoglobulin switch or ICR recom
bination, would contribute to the selective immunoglobulin deficien
rity, as proposed in the Damage Surveillance Network model de
scribed above, could explain the pleiotropic nature of the clinical and
cies and paucity of a/@3ICR-expressing I cells seen in A-I homozy
gotes.
Unlike A-I homozygotes,
laboratory abnormalities associated with the disease. Fig. lB summa
rizes the consequences of lack of damage-activated functions in A-T
homozygotes,
Damage
along with the resulting phenotypic effects. How the
Surveillance
Network
model accounts
for each aspect of the
A-I phenotype when previous models cannot is discussed below.
p53-null mice do not exhibit aberrant
immune gene rearrangements, nor do their peripheral lymphocytes
express the type of chromosome translocations characteristic of A-I
lymphocytes (33, 70). This suggests that loss of the p53-mediated
G1-S checkpoint is not as disruptive to immune gene recombination as
Cell Cycle Checkpoint Defects Disrupt Immune Gene Rear
rangements. The immunoglobulinheavy-chaingene and ICR genes
loss of the S-phase
and G2-M checkpoints.
undergo site-specific gene rearrangements during normal develop
ment, resulting in production of IgA, IgE, IgG2, and IgG4 by B
lymphocytes and in expression of a/j3 heavy-chain ICRs by I lym
phocytes (67, 68). A-I homozygotes have deficiencies in these spe
stability. Cells that lack functional p53 protein fail to halt at the G1-S
border after irradiation, but will arrest the cell cycle in S phase and at
cific immunoglobulin classes, as well as a relative lack of I lympho
cytes expressing a/@3heavy-chain TCRs (reviewed in Ref. 3). They
point but not the S-phase or G2-M checkpoints. Several studies have
Cell Cycle Checkpoint Defects Cause Spontaneous Genetic In
the G2-M border (34, 35, 40). Hence, cells that are defective for p53
function have a specific defect in the G1-S damage-sensitive
check
demonstrated spontaneous genetic instability in mammalian cells that
Protein
@
Length (a.a.)
ATM
3056
DNA-PK@5
4096
MEI-41
2357
TEL1p
2787
RAD3
2386
MEC1p
2368
kinase
domain
Fig. 2. Block alignment of predicted protein products for the ATM (146), DNA-PK@@(130), mei-41 (65), TELl (64), radY (146), and MECI (147) genes. (U. P1-3 kinase domains
that show 60—70%similarity between all family members; (I]), regions of 40—50%similarity. Alignments were generated using BLAST@analysis (148). a.a, amino acids.
5994
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECFASIA
lack the G1-S checkpoint as a result of mutations in the p53 gene.
Fibroblasts from p53-null mice and patients with Li-Fraumeni syn
drome, as well as cell lines that have lost wild-type p53 alleles or
harbor
dominant-negative
p53
mutations,
lack
functional
p53 and
show increased frequencies of chromosome loss, chromosome aber
rations, intrachromosomal genetic recombination, and/or gene ampli
fication events (33, 62, 71—73).Given the genetic instability of cells
that lack a -S cell cycle checkpoint because of loss of p53 function,
the G1-S cell cycle checkpoint defect is likely to contribute to the high
spontaneous frequencies of chromosome aberrations, genetic recom
bination. aneuploid cells, and allele loss seen in different A-I cell
types
in Vit'() and in vitro
( I 7. 74—77). Inability
to arrest
at the S-phase
and G2-M DNA damage checkpoints also may contribute to sponta
neous chromosome instability in A-T cells, in that S. cerevisiae rad9
mutants that have lost the G,-M damage-sensitive checkpoint show
marked increases in the frequency of spontaneous chromosome loss at
mitosis (78).
The spontaneous genetic instability seen in nonimmune A-I cells
may be due to a mechanism similar to that outlined above for the
immune system@an inability to activate cell cycle checkpoints in the
face of spontaneous DNA damage allows A-T cells to attempt to
replicate DNA (G1-S and S-phase checkpoints) or enter mitosis
(G,-M checkpoint) before completion of repair of the damage. Rep
lication or mitosis then results in breaks and gaps in chromosomal
DNA that promote the formation of acentric chromosome fragments,
facilitate generation of aneuploid daughter cells through missegrega
tion, and serve as substrates for chromosome translocations and mi
totic recombination.
The AIM-dependent damage surveillance network may monitor
telomeres as well, preventing the propagation of cells containing
chromosomes with short telomeres by triggering cell cycle check
points when telomeres fall below a critical size. In this scenario, short
telomeres would be unable to arrest cell division in cells from A-I
homozygotes, leading to the gradual accumulation of cells with short
ened telomeres. This would explain why A-I cells in culture have
shorter
telomeres
and fewer
telomeric
hybridization
signals
than do
control cells (79). Aberrant telomeres, in turn, may cause telomere
telomere associations, which are a characteristic karyotypic feature of
both A-I cells and senescing cells from normal individuals (17, 80).
Short telomeres also may contribute to the overall genomic instability
of A-I cells through their tendency to provoke chromosome
rearrangements.
Cell Cycle Checkpoint Defects Contribute to Induced Chromo
some Aberrations. The S. cerevisiae rad9 and S. pombe rad3 mu
tants exhibit high levels of chromosome aberrations after irradiation,
presumably as a result of defective G1-S and G2-M damage check
points (43, 8 1). Defective cell cycle checkpoints could contribute to
the high residual frequency of radiation-induced chromosome and
chromatid aberrations seen in A-I cells when assayed at the first
postirradiation mitosis (82, 83). Although the kinetics of DNA break
repair are grossly normal in A-I cells, the lack of checkpoint restraint
on forward progress of the cell cycle into DNA synthesis and mitosis
effectively gives A-I cells less time in which to remove DNA breaks
before they give rise to chromosome aberrations (irradiation in
and chromatid aberrations (irradiation in G,).
Cell Cycle Checkpoint Defects Lead to Cancer. A growing body
of evidence indicates that multiple genetic changes resulting in loss of
function at tumor suppressor genes and gain of function at oncogenes
are critical to the development of cancer (29, 84). Accumulation of
these changes is more likely to occur in cells from individuals with
constitutional genetic instability. Hence, it is not surprising that can
cers occur at high frequencies in A-I homozygotes (85). G@-S, S
phase, and G,-M cell cycle checkpoint defects may contribute to the
increased incidence of solid tumors in A-I homozygotes by increas
ing the occurrence of spontaneous and induced chromosome aberra
tions, mitotic recombination, and LOH.
A-I homozygotes face a 250- to 700-fold increased risk of devel
oping leukemia and non-Hodgkin's lymphoma (2, 85), tumors that
frequently harbor chromosome rearrangements involving immuno
globulin supergene family genes ( 17). Kastan et a!. (22) noted that
both A-I homozygotes and p53-null mice have a predilection for
immune system tumors and suggested that an abnormal response to
DNA strand breaks may be responsible for the high incidence of
lymphoid tumors in both cases. In the Damage Surveillance Network
model, this abnormal response would be an inability to trigger the A-I
damage surveillance network and activate its cell cycle checkpoints.
A-I lymphoid cells would become malignant as a consequence of the
activation of cellular oncogenes by chromosome translocations result
ing from disruption of the normal rearrangement and repair of im
mune gene DNA. The specific increase in lymphoid tumors seen in
A-I homozygotes suggests that the initial production of strand breaks
and other DNA damage is a rate-limiting step in oncogenesis, even in
cells that are genetically unstable because of a lack of DNA damage
sensitive cell cycle checkpoints.
Lack of Damage-activated DNA Repair Prevents Enhanced
Survival and Mutagenesis. Heightened ability to repair DNA dam
age resulting from radiation exposure to host cells is the putative
cause of enhanced survival and enhanced mutagenesis of irradiated
viruses in mammalian cells. The contribution of damage-activated
repair to cellular survival after DNA damage is less certain. Loss of
damage-activated repair is associated with a modest increase in UV
sensitivity but does not appreciably affect the clonogenic survival of
X-irradiated cells (5 1, 7 1, 86, 87). This differential effect on UV
damage may be due to the fact that damage-activated repair is pri
manly a form of enhanced excision repair (5 1). The Damage Surveil
lance Network model assumes that, whatever its mechanism, this
enhanced ability to repair DNA damage can be activated by normal
cells but not by A-I cells or cells without functional p53.
Lack of damage-activated repair does not appear to be a major
factor in the X-ray sensitivity of A-I cells (see below), but it may be
partially responsible for the mild UV sensitivity seen in some A-I
cells (3). Lack of damage-activated repair also could contribute to the
higher than normal residual level of double-strand breaks seen in
X-irradiated A-I cells (82, 88). Alternatively, the residual double
strand breaks in A-I cells could be due to initiation of apoptosis
mediated nucleolytic degradation of genomic DNA.
Dysfunctional Programmed Cell Death Leads to Spontaneous
Cell Loss. Autopsies of A-I homozygotes have documented chronic
spontaneous loss of Purkinje cells and granule cells in the cerebellum,
as well as depletion of other neurons in the central nervous system of
older patients (reviewed in Ref. I). Other tissues reported to be
atrophic and/or hypoplastic in A-I homozygotes include the thymus,
gonads, thyroid, and adrenals ( 1). Cirrhotic changes have been seen in
the livers of A-I homozygotes, together with patches of regenerating
hepatocytes, which may be the cause of their high serum levels of
a-fetoprotein (1, 89). Taken together, these autopsy findings indicate
that chronic spontaneous cell death occurs throughout the tissues of
A-I homozygotes.
Cell cycle checkpoint defects cannot easily account for this ongoing
in vivo cell loss. Homozygous p53-null mice do not have detectable
neurological abnormalities, immune defects, or sterility (33, 70).
Hence, the G1-S checkpoint defect does not appear to be the cause of
the cerebellar, immunological, and gonadal defects in A-I. Defective
S-phase and G2-M checkpoints could cause a small part of the loss of
dividing cells in vivo, as well as contribute to the high frequency of
aneuploid giant cells found in A-I homozygotes (60, 76), a prediction
5995
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECTASIA
based, in part, on the high frequency of spontaneous aneuploidy
associated with the G2-M checkpoint defect in rad9 mutant yeast (78).
However, although defective S-phase and G2-M checkpoints may kill
some dividing cells, they cannot cause the death ofcells arrested in G0
(e.g., Purkinje cells and other neurons) in A-I homozygotes. In this
regard, it seems significant that the cell types most affected by in vivo
degeneration in A-I are those that, in normal individuals, are most
sensitive to radiation-induced apoptotic cell death [e.g., lymphocytes,
spermatogonia, and neurons in the developing cerebellum (reviewed
in Ref. 90)].
The Damage Surveillance Network model predicts that the primary
cause of spontaneous loss of both dividing and nondividing cells in
tissues of A-I homozygotes is inappropriate activation of pro
grammed cell death by DNA damage that occurs spontaneously
during normal DNA metabolism and as the result of ordinary envi
ronmental insults. In the Damage Surveillance Network model,
chronic cell loss due to programmed cell death depletes Purkinje cells
and other neurons
from the central
nervous
system,
I-cell
and B-cell
precursors from the immune system, and germ cells from the gonads.
These losses account for the progressive cerebellar ataxia and intel
lectual arrest seen in A-I homozygotes, as well as their thymic
atrophy, reduced numbers of circulating lymphocytes, and paucity of
germ cells (1).
Dysfunctional Activation of Programmed
Cell Death Causes
Mutagen Sensitivity. The striking sensitivity of A-I cells to killing
by ionizing radiation and radiomimetic drugs has been a long-standing
puzzle that has not been adequately
explained
in the past.
Multiple biochemical studies have failed to detect gross abnormal
ities in the kinetics of single-strand and double-strand break repair in
A-I cells (e.g., see Ref. 91, 92). Other reports have found no evidence
that A-I cells are functionally defective in DNA repair (93—95).On
the other hand, several studies found slight increases in the fraction of
breaks left unrepaired in irradiated A-I cells (82, 88), as well as
abnormalities in the rejoining of restriction enzyme breaks in plasmids
transfected into A-I fibroblasts (13, 14). To account for the seeming
disparity between the various functional and biochemical studies of
irradiated A-I cells, it has been suggested that the repair defect in A-I
is subtle, perhaps the result of impaired accuracy in strand rejoining
(13, 14) or an inability to repaira smallbut critical fractionof
double-strand breaks
Subtle but critical
radiation sensitivity
number of persistent
(82, 96—98).
defects in DNA repair might contribute to the
of A-I cells and help to explain the increased
chromosome aberrations observed in irradiated
A-I cells at the first postirradiation
mitosis
(82, 83). However,
DNA
repair defects alone cannot readily account for the cell cycle abnor
malities observed in A-I cells. To explain both radiosensitivity and
cell cycle abnormalities, several investigators have proposed that the
enzymatic machinery for DNA repair and recombination is essentially
intact in A-I but that the in vivo and in vitro radiosensitivity of A-I
cells is due to inability to activate cell cycle checkpoints in response
to DNA damage (1 1, 12). Experimental evidence suggests, however,
that the effects of checkpoint defects on the survival of irradiated A-I
cells are minor.
It is unlikely that the G1-S checkpoint defect plays a significant role
in the sensitivity of A-I cells to the lethal effects of induced DNA
damage. Cells lacking the G1-S checkpoint as a result of defects in
p53 expression or function are not radiosensitive (e.g. , see Refs. 40
and 71), and drug treatments that delay DNA replication in irradiated
A-I
cells
(e.g.,
see Ref. 99) do not enhance
survival.
The S-phase
restoration of normal survival after X-irradiation but still express
radioresistant DNA synthesis, indicating that their S-phase check
points remain defective. Fusion of HeLa cells to an A-I fibroblast line
resulted in heterodikaryons that exhibited normal survival after irra
diation, despite the lack of an S-phase checkpoint, as measured by
radioresistant DNA synthesis (40). Further evidence for the lack of
concordance between S-phase checkpoint abnormalities and increased
sensitivity to the lethal effects of radiomimetic agents is provided by
Mirzayans and Paterson (2 1), who found that fibroblasts from one
A-I patient were hypersensitive
to the killing effects
of the mutagen
4NQO but exhibited a normal S-phase checkpoint after 4NQO expo
sure, whereas fibroblasts from another A-I patient had normal sur
vival after 4NQO treatment but demonstrated complete lack of a
4NQO-induced S-phase checkpoint.
Yeasts that lack a functional G2-M damage-sensitive checkpoint
because of mutations in the RAD9, RAD1, or RAD24 genes are
sensitive to the killing effects of ionizing radiation (102), presumably
because these mutations effectively shorten the postirradiation cell
cycle, thereby giving cells less time to complete repair before mitosis.
The behavior of the yeast G2-M checkpoint mutants suggests that the
radiation sensitivity of A-I cells could be due to unchecked progres
sion into mitosis before repair of potentially lethal DNA damage.
However, a defective G2-M damage checkpoint cannot explain an
unusual aspect of radiation sensitivity in A-I, the lack of “liquid
holding―recovery. In both prokaryotes and eukaryotes, experimental
manipulations that delay entry into the cell cycle or slow progression
of the cell cycle normally enhance the survival of irradiated cells (e.g.,
see Ref. 103), a phenomenon that usually is demonstrated in mam
malian cells by their recovery of colony-forming ability after a po
stirradiation period of growth inhibition. As might be expected, treat
ments that prolong or temporarily halt the postirradiation cell cycle
are especially
effective
in increasing
the survival
of mutants
that lack
a functional G2-M damage checkpoint [e.g., the S. cerevisiae rad9
mutant (104) and the S. pombe radl mutant (105)]. In marked con
trast, several studies have found that holding A-I fibroblasts in G0 for
up to 7 days after irradiation does not significantly improve their
survival (24—26).This lack of liquid holding recovery in A-I fibro
blasts argues against G2-M damage-sensitive checkpoint defects play
ing a major role in determining the survival of A-I cells after
irradiation.
Another aspect of the A-I phenotype that is not explained by
previous A-I models is the circumstances under which irradiated A-I
cells die. It is well established that the lethal effects of ionizing
radiation are associated with the production of double-strand breaks in
chromosomal DNA (reviewed in Ref. 106), and it has been estimated
that an average of 40 unrepaired double-strand breaks is sufficient to
kill a normal diploid human cell (107). It is unlikely that so few breaks
introduced at random would directly damage a gene necessary for cell
survival.
Instead,
unrepaired
double-strand
breaks
are thought
to kill
dividing mammalian cells because they give rise to acentric frag
ments, dicentrics, and other chromosome aberrations (108, 109).
These chromosome aberrations then can undergo missegregation at
mitosis, resulting in daughter cells with partial monosomies and
tnsomies, the unbalanced karyotypes of which eventually prove fatal
(1 10, 1 1 1). This conclusion
is supported by observations
that, for most
mammalian cells, radiation-induced death is not immediate but typi
cally occurs in the first- and second-generation offspring of irradiated
cells (summarized in Ref. 112).
Previous models for the A-I defect have assumed that, like normal
cells, irradiated A-I cells die as a result of genomic imbalance caused
by persistent radiation-induced chromosome aberrations (82, 83).
However, there is in vitro and in vivo evidence to the contrary. Unlike
checkpoint defect also has been dissociated from cell survival in A-I
cells by gene transfer and cell fusion studies. After transfection of the
A-I fibroblast line AT5BIVA with normal human genomic DNA,
other mammalian cells, fatally irradiated A-I fibroblasts do not divide
clones have been isolated that have partial (100) or complete (101)
5996
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECTASIA
several times before death. Instead, the majority arrest in G2 before
their first postirradiation mitosis (1 13—1
15). While arrested in G2,
they undergo apoptosis (62)@ before any radiation-induced chromo
some aberrations can missegregate. Several case reports document the
extreme sensitivity of A-I homozygotes to the neurotoxic effects of
central nervous system irradiation given as treatment for cancer (116,
117). Central nervous system neurons in children are nondividing
cells, suggesting that at least part of the neurotoxicity of radiation
therapy in A-I homozygotes is the result of neurons being killed
while in G0. Because irradiated A-I fibroblasts and neurons die before
any induced chromosome aberrations can lead to genomic imbalance,
other causes must be sought to explain their radiation sensitivity.
The Damage Surveillance Network model predicts that, because
A-I cells lack a functional ATM gene, they cannot prevent the
initiation of programmed cell death by radiation-induced DNA lesions
(Fig. 1B). As a result, radiation damage that would be nonlethal in
normal cells triggers programmed cell death in A-I cells, which then
is carried out in G0 in noncycling cells and at the first postirradiation
mitosis in actively dividing cells. In this way, the Damage Surveil
lance Network model overcomes objections to previous cell cycle
based A-I models and accounts for why (a) both cycling and non
cycling A-I cells are radiosensitive despite having only minor defects
in DNA repair; (b) irradiated A-I fibroblasts do not undergo liquid
holding recovery; and (c) irradiated A-I cells die before the first
postirradiation cell division.
Discussion and Predictions
The Damage Surveillance Network model for A-I proposes that the
A-I defect results in an inability to activate a group of diverse cellular
functions in response to DNA damage. It offers a unifying explanation
of how a single-gene defect can cause the pleiotropic phenotype seen
in A-I homozygotes and explains several puzzling aspects of the
disease. The model assumes that the enzymatic machinery for DNA
repair and genetic recombination is essentially intact, and it empha
sizes the contribution of defective cell cycle checkpoints to genetic
instability and immune defects, two cardinal features of A-I. By
ascribing the disruption of immunoglobulin switch recombination and
transduction network is not certain. However, consideration of a
related human protein, DNA-PK€@5,
may be instructive in this regard.
DNA-PK@5 is the catalytic subunit of DNA-PK, a DNA-dependent
protein kinase (122). Ku70 and Ku80, the other subunits of DNA-PK,
form a heterodimer that binds without sequence specificity to double
strand DNA breaks, gaps, and short hairpins (123). Once bound to
DNA ends by the Ku polypeptides, DNA-PK activates its DNA-PK@5
subunit, which then can phosphorylate a variety of proteins in vitro,
including p53 (122). This ability of the DNA-PK holoenzyme to
phosphorylate proteins when bound to damaged DNA suggests that
DNA-PK not only may have a direct role in promoting the repair of
certain types of DNA damage but also may serve as the front end of
a signal transduction pathway that activates cellular responses to DNA
damage. Further experimental support for a role in cellular damage
responses for DNA-PK€@5
is provided by recent evidence that a
mutation in the DNA-PK@5 gene is responsible for the immune
deficient SCID mouse (124, 125), and that mutant DNA-PK@@,ku7O,
and ku8O genes are associated with radiosensitivity, defects in double
strand break repair, and abnormalities of VDJ recombination (126—
129). Although ATM and DNA-PK€.@5
proteins share strong sequence
homology in their P1-3 kinase domains (130), their mutant phenotypes
differ (e.g., see Ref. 126). In addition, A-I fibroblasts have normal
intracellular amounts of the kulO, ku8O, and DNA-PK€.@5
polypep
tides, and the DNA-PK enzymatic activity of A-I cell extracts is
normal (129). Taken together, these observations suggest that ATM
and DNA-PK€.@5
act early and independently in separate signal trans
duction pathways that respond to DNA damage. The similarities
between ATM and DNA-PIQ5 suggest that, like DNA-PIQ5 the
ATM protein may be directly involved in the recognition of DNA
damage, perhaps serving as the protein kinase subunit of a functional
complex that also includes ku7O- and ku8O-like polypeptides.
The Damage Surveillance Network model assumes that a major
function of ATM protein is signal transduction. It is not yet clear how
this occurs. However, initial sequence analysis of the ATM protein
indicates that it has a P13-kinase domain (63). Similar PI3-kinase
domains are found in the DNA-PK@5, MEI-4l, MEC1, RAD3, and
TELl proteins, as well as TOR1 and IOR2, two yeast proteins that
help to regulate normal progression of the cell cycle from G@into S
ICR rearrangements to cell cycle checkpoint abnormalities, and pos
(63—65, 130—132).These cell cycle control genes also share their
tulating that disruptions of immune gene rearrangements and of repair
P13-kinase domains with the mammalian PI3-kinase, which mediates
of spontaneous DNA damage lead to generation of recombinogenic
signal transduction pathways that control growth factor-dependent
breaks and gaps in DNA, the Damage Surveillance Network model
mitogenesis, membrane ruffling, and glucose uptake (reviewed in Ref.
explains why immunoglobulin switch recombination and ICR rear
133). The existence of a PI3-kinase domain in the ATM protein raises
rangement appear to be defective in A-I homozygotes, whereas
the possibility that a phosphoinositide might serve as a secondary
spontaneous rates of recombination between directly repeated nonim
messenger for the ATM signal transduction network. However, al
mune genes in A-I fibroblasts are markedly higher than normal (4).
though the ATM protein has a PI3-kinase domain, its enzymatic
The model can also account for the observation that chromosomal
activity is unknown, and it is far from certain that phosphoinositols are
translocations in A-I lymphocytes cluster near immune genes,
the biologically relevant targets for its putative phosphotransferase
whereas translocations in A-I fibroblasts appear to involve random
activity. The most closely related mammalian protein, DNA-PIQ@,
sites throughout the genome (1 18). By assuming that the damage
has no detectable phosphinositol kinase activity in vitro but can
surveillance network normally monitors telomere integrity, the model
phosphorylate many proteins (130). The mammalian PI3-kinase and
explains telomenc abnormalities seen in A-I cells.
the yeast Vps34p P13-kinase also phosphorylate proteins (134, 135),
The range of DNA lesions that might trigger the ATM network is reinforcing the possibility that the true targets of the phosphotrans
uncertain, although strand breaks and gaps containing modified 3'
ferase activity of the ATM protein may be proteins.
termini are likely to play a major role, given the sensitivity of A-I
Phenotypic and sequence similarities between the ATM gene and
homozygotes to physical and chemical agents that induce strand
cell cycle checkpoint genes from Drosophila (mei-41) and yeast
breaks and small gaps containing 3' phosphoglycolates (119—121). (MECJ and radfl support the central assumption of the Damage
Short telomeres also may activate the ATM network, suggesting that
Surveillance Network model that the ATM gene controls a signal
the ends of abnormally short telomeres may be structurally similar to
transduction network that activates cell cycle checkpoints and other
DNA breaks generated by these agents. As indicated in Fig. 1, the
cellular functions in response to certain types of DNA damage.
same lesions that activate A-I dependent cellular functions may also
However, there are phenotypic differences between the genes [e.g.,
trigger p53-mediated programmed cell death.
unlike A-I homozygotes, MECJ and rad3 mutants do not have
How far upstream of p53 the ATM protein functions in the signal
telomere abnormalities (64)]. Sequence analysis carried out by Green
5997
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECFASIA
well et al. (64) indicates that TELl, another S. cerevisiae gene, is more
closely related to ATM than either MEC] or rad3@. Like A-I homozy
gotes, TEL] mutants have shortened telomeres, elevated rates of
recombination between repeated genes, and increased frequencies of
aberrant chromosomal segregation (64). However, the TELl pheno
type does not completely overlap with the A-I phenotype. TELl
mutants are not X-ray sensitive, nor do they have obvious defects in
DNA damage-induced cell cycle checkpoints (64).@As suggested by
Greenwell et al. (64), this may be due to the presence of redundant
signal transduction systems in yeast that can partially mask the effect
of a defective TELl protein. Alternatively, the ATM gene and its
signal transduction network may be the functional equivalent of
several different yeast damage response pathways.
A novel feature of the Damage Surveillance Network model is that,
in response to DNA damage, the ATM protein activates cellular
functions that promote genetic stability and survival, whereas it sup
presses any tendencies to commit cellular suicide via apoptosis. Ap
Optosis is a normal process that is widely used by multicellular
organisms to regulate the growth, development and maintenance of
individual organs (55). This innate ability to commit cellular suicide
may have been incorporated into the repertoire of DNA damage
responses because it offers a means by which mammals and other
multicellular organisms can eliminate cells that have sustained genetic
damage that threatens the survival of the organism. In this context, the
increased spontaneous and DNA damage-induced cell loss in A-I
homozygotes can be seen as the result of lowering the threshold for
triggering an otherwise normal mammalian response to DNA damage.
Recently, p53 was shown to be required for the induction of
apoptotic cell death in peripheral mouse lymphocytes by ionizing
radiation (86, 87). This finding suggests that, in addition to its “guard
ian of the genome― role in activating the G1-S damage-sensitive
checkpoint (136), p53 also acts as a “guardianof the organism―by
mediating cellular decisions to trigger programmed cell death in the
face of DNA damage. If this is true, then a normal function of the
wild-type ATM protein may be to promote survival in cells that have
sustained DNA damage by physically interacting with the p53 protein
in a way that inhibits p53-mediated activation of apoptosis. Alterna
tively, the ATM protein may counteract p53-mediated apoptosis in
directly, perhaps by inhibiting a step in apoptosis that is downstream
of p53. PI3-kinase is required for prevention of apoptosis in rat
pheochromocytoma cells deprived of nerve growth factor (137) and
may protect against apoptosis in B cells (138). Perhaps the ATM
protein, through its kinase domain, acts as a general inhibitor of
apoptosis, whether apoptosis is triggered by DNA damage or by lack
of trophic factors. It is also possible that the ATM protein does not
directly prevent DNA-damage induced apoptosis, but that functional
loss of the ATM signal transduction network in A-I homozygotes
results in the activation of a set of backup cellular damage responses
that includes p53-dependent apoptosis.
Although inactivation of the ATM gene may be favored during
functions that prevent DNA damage from causing genetic instability.
Acquisition of a genetic instability phenotype is a frequent event in
tumorogenesis (136, 140, 141). Therefore, one might expect that the
ATM gene, like p53 and p21, would function as a tumor suppressor
gene. If so, inactivation of the ATM gene might occur during tumor
progression and be detectable as LOH of markers near the ATM gene
on 1lq23. This prediction is supported by multiple studies that found
that LOH at llq22—23 loci is a frequent event in sporadic breast,
ovarian, colon, and cervical cancers (142—145).For example, in an
analysis of 62 sporadic breast cancers, 39% of the tumors had lost
llq23 markers, with the common overlapping region ofLOH defining
an —@20-cm
region that includes the A-Tlocus (143). The LOH studies
suggest that loss of ATM function is not just the cause of a rare
genetic disease but that it also plays a role in the development of many
common tumors. With the recent isolation of the ATM gene, confir
mation of these LOH studies should be forthcoming in the near future,
and a more accurate picture of the role of ATM gene inactivation in
tumorogenesis will emerge.
The A-I-dependent DNA damage-sensitive signal transduction net
work appears to be only one of an overlapping and partially redundant
web of intracellular networks that are involved in genetic homeostasis
in mammalian cells. We are now entering a period of intense study of
the roles played by the ATM, p53, p21, and DNA-PK@5 genes in cell
cycle checkpoints, genetic instability, and programmed cell death.
These studies should test the predictions of the Damage Surveillance
Network model, further our understanding of these basic biological
processes, and shed light on the origin and development of cancer.
Acknowledgments
I thank Drs. C. F. Arlett, R. Gatti, M. F. Lavin, M. C. Paterson, Y. Shiloh,
and C. M. R. Taylor for helpful discussions; Drs. D. E. Brash, L. B. K.
Herzing, and R. J. Monnat, Jr. for critical review of the manuscript; and Drs.
C. W. Anderson, R. S. Hawley, T. Petes, and T. Pandita for sharing their
unpublished results. This paper is dedicated to A-I patients and their families.
References
tumor progression because loss of ATM gene function could contrib
ute to genetic instability, the Damage Surveillance Network model
predicts that such a loss also may render a cell sensitive to being killed
by DNA damage-induced apoptosis. Hence, inactivation of ATM or
related genes may explain the sensitivity of many tumor cells to
induction of apoptosis by ionizing radiation, radiomimetic chemicals,
and topoisomerase inhibitors (139), a sensitivity exploited by many
cancer
treatments.
The Damage Surveillance Network model predicts that a major
function of the ATM gene product is to activate multiple cellular
5 T.
Petes,
personal
1. Sedgwick, R. P., and Boder, E. Ataxia-telangiectasia. Handb. Clin. Neurol., 16:
347—423,1991.
2. Swift, M., Reitnauer, P. J., Morrell, D., and Chase, C. L. Breast and other cancers
in families with ataxia-telangiectasia. N. EngI. J. Med., 316: 1289—1294, 1987.
3. Cohen, M. M., and Levy, H. P. Chromosome instability syndromes. Adv. Hum.
Genet., 18: 43—149,1989.
4. Meyn, M. S. High spontaneous intrachromosomal
recombination
rates in ataxia
telangiectasia. Science (Washington DC). 260: 1327—1330,
1993.
5. Kobayashi, Y., Tycko, B., Soreng, A. L., and Skiar, J. Transrearrangements between
antigen receptor genes in normal human lymphoid tissues and in ataxia telangiec
tasia. J. Immunol., 147: 3201—3209, 1991.
6. Lipkowitz, S.,Stem,M. H., andKirsh, I. R. Hybrid T-cell receptorgenesformedby
interlocus recombination in normal and ataxia-telangiectasia lymphocytes. J. Exp.
Med., 172: 409-418, 1990.
7. Paterson, M. C., Smith, B. P., Lohinan, P. H. M., Anderson, A. K., and Fishman, L.
Defective excision repair of y-ray-damaged DNA in human ataxia-telangiectasia
fibroblasts. Nature (Lond.), 260: 444—446, 1976.
8. Paterson, M. C., and Smith, P. J. Ataxia telangiectasia: an inherited human disorder
involving hypersensitivity to ionizing radiation and related DNA-damaging chem
icals. Annu. Rev. Genet., 13: 291—318,1979.
9. Singh, S. P., Mahamed, R., Salmond, C., and Lavin, M. F. Reduced DNA topo
isomerase II activity in ataxia-telangiectasia cells. Nucleic Acids Res., 16: 3919—
3929, 1988.
10. Edwards, M. J., and Taylor, A. M. R. Unusual levels of ADP-ribose and DNA
synthesis in ataxia telangiectasia cells following -y-ray irradiation. Nature (Lond.),
287: 745—774,1980.
11. Painter, R. B., and Young, B. R. Radiosensitivity in ataxia-telangiectasia: a new
explanation. Proc. Nail. Acad. Sci. USA, 77: 7315—7317. 1980.
12. McKinnon, P. J. Ataxia-telangiectasia: an inherited disorder of ionizing-radiation
sensitivity in man. Progress in the elucidation of the underlying biochemical defect.
Hum. Genet., 75: 197—208,
1987.
13. Debenham, P. 0., Webb, M. B., Stretch, A., and Thacker, J. Examination of vectors
with two dominant, selectable genes for DNA repair and mutation studies in
mammalian cells. Mutat. Res., 199: 145—158,1988.
communication.
5998
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECTASIA
14. Cox, R., Masson, W. K., Debenham.
P. G., and Webb, M. B. T. The use of
recombinant DNA plasmids for the determination of DNA-repair and recombination
43. Jimenez, G., Yucel, J., Rowley, R., and Subramani, S. The rad3' gene of Schizo
saccharomyces pombe is involved in multiple checkpoint functions and in DNA
repair. Proc. Natl. Acad. Sci. USA, 89: 4952—4956,1992.
44. Khanna, K. K., and Lavin, M. F. Ionizing radiation and UV induction of p53
in cultured mammalian cells. Br. J. Cancer, 46 (Suppl. VI): 67—72,1984.
15. McFarlin, D. E., Strober, W., and Waldmann, T. A. Ataxia-telangiectasia. Medicine
(Baltimore), 51: 281—314,1972.
16. Carbonari, M., Cherchi, M., Paganelli, R., Giannini, G., Galli, E., Gaetano, C.,
Papetti, C., and Fiorilli, M. Relative increase ofT cells expressing the ‘jIB
rather than
the a/f3 receptor in ataxia-telangiectasia. N. Engl. J. Med., 322: 73—76,1990.
17. Kojis, T. L.. Gatti, R. A., and Sparkes, R. S. The cytogenetics of ataxia telangiec
protein by different pathways in ataxia-telangiectasia
cells. Oncogene, 8: 3307—
3312,1993.
45. Canman, C. E., Wolff, A. C,. (len, C. Y.. Fornace, A. J., Jr., and Kastan, M. B. The
p53-dependent G, cell cycle checkpoint pathway and ataxia-telangiectasia. Cancer
Res., 54: 5054—5058, 1994.
tasia. Cancer Genet. Cytogenet.. 56: 143—156,
1991.
18. Peterson, R. D. A., and Funkhouser, J. D. Speculations on ataxia-telangiectasia:
defective regulation of the immunoglobulin gene superfamily. Immunol. Today, 10:
313—315,
1989.
19. Dasgupta. U. B., and Summers, W. C. Genetic recombination of herpes simplex
virus, the role of the host cell and UV-irradiation of the virus. Mol. & Gen. Genet.,
178:617—623,
1980.
20. Timme, T. L., Wood, C. M., and Moses, R. E. Intermolecular plasmid recombination
46. Zambetti-Bosseler, F., and Scott. D. Cell death, chromosome damage and mitotic
delay in normal human, ataxia telangiectasia and retinoblastoma fibroblasts after
X-irradiation. mt. i. RadiaL Biol., 39: 547—558,1980.
47. Rudolph, N. S., and Laft, S. A. Flow cytometric analysis of X-ray sensitivity in
ataxia telangiectasia. Mutat. Res., 211: 31—41,1989.
48. Summers, W. C., Sarkar, S. N., and Glazer, P. M. Direct and inducible mutagenesis
in mammalian cells. Cancer Sun'., 4: 517—528,1985.
49. Hilgers, G., Abrahams, P. J., Chen, Y. Q., Schouten, R., Comelis, J. J., Lowe, J. E.,
in fibroblasts from humans with DNA damage-processing defects. Plasmid, 22: 1—9,
1989.
21. Mirzayans, R., and Paterson, M. C. Lack of correlation between hypersensitivity to
cell killing and impaired inhibition of DNA synthesis in ataxia telangiectasia
fibroblasts treated with 4-nitroquinoline 1-oxide. Carcinogenesis (Lond.), 12: 19—
23,1991.
22. Kastan, M. B., Zhan, Q., el-Deiry, W. S.. Carrier, F., Jacks, T., Walsh, W. V.,
Plunkett, B. S., Vogelstein,
van der Eb, A. J., and Rommelaere, J. Impaired recovery and mutagenic SOS-like
responses in ataxia-telangiectasia cells. Mutagenesis, 4: 271—276,1989.
50. Jeeves, W. P., and Rainbow, A. J. An aberration in y-ray-enhanced reactivation of
irradiated adenovirus in ataxia telangiectasia fibroblasts. Carcinogenesis (Lond.), 7:
381—387.
1986.
51. Smith, M. L., Chen, I. T., Than, Q., O'Connor, P. M., and Fomace, A. J., Jr.
Involvement of the p53 tumor suppressor in repair of u.v.-type DNA damage.
Oncogene, 10: 1053—1059,
1995.
B., and Fomace, A. J., Jr. A mammalian cell cycle
checkpoint pathway utilizing p53 and GADD45 is defective in ataxia-telangiectasia.
Cell, 71: 587—597.1992.
23. Murray. A. W. Creative blocks: cell-cycle
checkpoints
52. Wang, X. W., Yeh, H., Schacifer, L., Roy, R., Moncollin, V., Egly, J-M., Wang, Z.,
Friedberg, E. C., Evans, M. K., Taffe, B. G., Bohr, V. A., Weeda, G., Hoeijmakers,
J. H. J., Forrester, K., and Harris, C. C. p53 modulation of TFIIH-associated
nucleotide excision repair activity. Nat. Genet., 10: 188—195,1995.
and feedback controls.
Nature (Lond.), 359: 599—604,1992.
24. Masson, W. K., Weichselbaum,
R. R., Nove, J., and Little, J. B. The repair of
53. Smith, M. L., Chen, I. T., Than, Q., Bae, I., Chen, C. Y., Gilmer, T. M., Kastan,
potentially lethal damage in X-irradiated cultures of normal and ataxia telangiectasia
human fibroblasts. mt. i. Radiat. Biol., 39: 357—365.1981.
25. Little, J. B., and Nagasawa, H. Effect of confluent holding on potentially lethal
damage repair. cell cycle progression, and chromosomal aberrations in human
M. B., O'Connor, P. M., and Fomace, A. J., Jr. Interaction of the p53-regulated
protein Gadd4S with proliferating cell nuclear antigen. Science (Washington DC),
266: 1376—1380,1994.
54. Bennett, C. B., and Rainbow, A. J. Delayed expression of enhanced reactivation and
normal and ataxia-telangiectasia fibroblasts. Radiat. Res., 101: 81—93,1985.
26. Arlett, C. F., and Priestley, A. Defective recovery from potentially lethal damage in
some human fibroblast cell strains. mt. j. Radiat. Biol., 43: 157—167,1983.
27. Fomace, A. J., Jr., Jackman, J., Hollander, M. C., Hoffman-Liebermann, B., and
Liebermann, D. A. Genotoxic-stress-response
genes and growth-arrest genes.
GADD, MyD, and other genesinducedby treatmentseliciting growth arrest.Ann.
NY Acad. Sci., 663: 139—153,1992.
28. Kaini, B., Stein, B., Schtinthal. A., Rahmsdorf, H. J., Ponta. H., and Herrlich, P. An
uptake ofthe mammalian UV response: gene regulation and induction ofa protective
function. Life Sci., 182: 652—664,1990.
29. Hartwell, L. H., and Kastan, M. B. Cell cycle control and cancer. Science (Wash
ingtonDC), 266: 1821—1828,
1994.
30. Battista, J. R., Donnelly, C. E., Ohta, T., and Walker, G. C. The SOS response and
induced mutagenesis. Prog. Clin. Biol. Res., 340A: 169—178,1990.
3 1. Weinert, T. A. Dual cell cycle checkpoints sensitive to chromosome replication and
DNA damage in the budding yeast Saccharomyces cerevisiae. Radiat. Res., 132:
141—143,1992.
32. al-Khodairy, F.. and Carr, A. M. DNA repair mutants defining G2 checkpoint
pathways in Schizosaccharomyces pombe. EMBO J., 11: 1343—1350,1992.
33. Donehower, L. A., Harvey, M., Slagle. B. L., McArthur, M. J., Montgomery, C. A.,
Jr., Butel, J. S., and Bradley, A. Mice deficient for p53 are developmentally normal
but susceptible to spontaneous tumors. Nature (Lond.), 356: 215—221,1992.
34. Kuerbitz, S. J., Plunkett, B. S., Walsh, W. V., and Kastan, M. B. Wild-type p53 is
a cell cycle checkpoint determinant following irradiation. Proc. NatI. Acad. Sci.
decreased mutagenesis of UV-irradiated adenovirus in UV-irradiated ataxia telan
giectasia fibroblasts. Mutagenesis, 3: 389—395,1988.
55. Tomei, L. D., and Cope, F. 0. (ads.). Apoptosis: The Molecular Basis of Cell Death.
Cold Spring Harbor, NY: Cold Spring Harbor Laboratory, 1991.
56. Kruman, I. I., Matylevich, N. P., Beletsky, 1. P., Afanasyev,
7-irradiation. J. Cell. Physiol., 148: 267—273,1991.
57. Yamada, T., and Ohyama, H. Radiation-induced interphase death of thymocytes is
intemally programmed apoptosis. mt. J. Radiat. Biol., 53: 65—75,1988.
58. Boder, E., and Sedgwick, R. P. Ataxia-telangiectasia.
A familial syndrome of
progressive cerebellar ataxia, oculocutaneous telangiectasia and frequent pulmonary
infection. Pediatrics, 21: 526—554,1958.
59. Amromin G. D., Boder, E., and Teplitz, R. Ataxia-telangiectasia
60. Agamanolis, D. P., and Greenstein, J. I. Ataxia-telangiectasia: report of a case with
Lewy bodies and vascular abnormalities within cerebral tissue. J. Neuropathol. &
Exp. Neurol., 39: 475—489,1979.
61. Schimke, R. T., Kung, A. L., Rush, D. F., and Sherwood, S. W. Differences in
mitotic control among mammalian cells. Cold Spring Harbor Symp. Quant. Biol.,
56: 417—425,1991.
62. Meyn, M. S., Strasfeld, L., and Allen, C. Testing the role ofp53 in genetic instability
and apoptosis in ataxia-telangiectasia. mt. J. Radiat. Biol., 66: 141—149,
1994.
63. Savitsky, K., Bar-Shira, A., Gilad, S., Rotman, 0., Ziv, Y., Vanagaite, L., Tagle,
D. A., Smith, S., Uziel, T., Sfez, S., Ashkenazi, M., Pecker, I., Frydman, M.,
Hamik, R., Patanjali, S. R., Simmons, A., Clines, G. A., Sartiel, A., Gatti, R. A.,
Chessa, L., Sanal, 0., Lavin, M. F., Jaspers, N. G. J., Taylor, A. M. R., Arlett,
C. F., Miki, T., Weissman, S. M., Lovett, M., Collins, F. S., and Shiloh, Y. A
0.. Sidransky, D., Vogelstein, B., and Craig, R. W.
Participation of p53 protein in the cellular response to DNA damage. Cancer Res.,
51:6304—6311,
1991.
36. el-Deiry, W. S., Harper, J. W., O'Connor. P. M., Velculescu, V. E., Canman, C. E,
Jackman. J., Pietenpol, J. A., Bw@el1,M., Hill, D. E, and Wang, Y. WAFJICIPJ is
induced in p53-mediatedG, arrest and apoptosis.Cancer Res., 54: 1169—1174,
1994.
37. Dulic, V., Kaufmann, W. K.,
Elledge, S. J., and Reed, S. I.
activities in human fibroblasts
1023, 1994.
38. Flores-Rozas, H., Kelman, Z.,
Wilson, S. J., Tlsty, T. D., Lees, E., Harper, J. W.,
p53.dependent inhibition of cyclin-dependent kinase
during radiation-induced G, arrest. Cell, 76: 1013—
single ataxia telangiectasia
gene with a product similar to P1-3 kinase. Science
(Washington DC), 268: 1749—1753,1995.
64. Greenwell, P. W., Kronmal, S. L., Porter, S. E., Gassenhuber, J., Obermaier, B., and
Petes, T. D. TELl, a gene involved in controlling telomere length in Saccharomyces
cerevisiae,is homologousto the humanataxia telangiectasia(ATM) gene.Cell, 82:
823—830, 1995.
65. Had, K. L., Santerre, A., Sekelsky, J. J., McKim, K. S., Boyd, J. B., and Hawley,
R. S. The mei-41 gene of Drosophila melanogaster is a structural and functional
homology of the human ataxia telangiectasia gene. Cell, 82: 815—822,1995.
Dean, F. B., Pan, Z. Q., Harper, J. W., Elledge, S. J.,
O'Donnell, M., and Hurwitz, J. cdk-interacting protein I directly binds with prolif
crating nuclear antigen and inhibits DNA replication catalyzed by the DNA polym
erase 6 holoenzyme. Proc. NatI. Acad. Sci. USA, 91: 8655—8659, 1994.
39. Waga, S., Hannon, G. J., Beach, D., and Stiliman, B. The p21 inhibitor of cyclin
with a 32 year
survival. A dlinicopathologicalreport. J. Neuropathol. & Exp. Neurol., 38: 621—643.
1979.
USA, 89: 7491—7495,1992.
35. Kastan, M. B., Onyekwere,
V. N., and Umansky,
S. R. Apoptosis of murine BW 5147 thymoma cells induced by dexamethasone and
66. Phipps, J., Nasim, A., and Miller, D. R. Recovery, repair, and mutagenesis in
Schizosaccharomyces pombe. Adv. Genet., 23: 1—72,1985.
67. Harriman, W., Volk, H., Defranoux, N., and Wabl, M. Immunoglobulin class switch
dependent kinases controls DNA replication by interaction with PCNA. Nature
(Lond.), 369: 574—578, 1994.
40. Komatsu, K., Okumura, Y., Kodama, S., Yoshida, M., and Miller, R. C. Lack of
recombination. Annu. Rev. Immunol., II: 361—384,1993.
68. Strominger, M. L. Developmental biology of T-cell receptors. Science (Washington
DC), 244: 943—950,1989.
correlation between radiosensitivity and inhibition of DNA synthesis in hybrids A-T
x HeLa. mt. J. Radiat. Biol., 56: 863—867,1989.
69. Robey, E., and Fowlkes, B. J. Selective events in T-cell development. Annu. Rev.
Immunol., 12: 675—705,1994.
41 . Russell, K. J., Wiens, L. W., Demers, G., W., Galloway, D. A., Plon, S. E., and
Groudine, M. Abrogation of the G2 checkpoint results in differential radiosensiti
70. Purdie, C. A., Hamson, D. J., Peter, A., Dobbie, L., White, S., Howie, S. E., Salter,
D. M., Bird, C. C., Wyllie, A. H., and Hooper, M. L Twnour incidence,spectrumand
zation of the G, checkpoint-deficient and G, checkpoint-competent cells. Cancer
Res., 55: 1639—1642, 1995.
42. Weinert, T. A., Kiser, 0. L., and Hartwell, L. H. Mitotic checkpoint genes in
budding yeast and the dependence of mitosis on DNA replication and repair. Genes
& Dcv., 8: 652—665,1994.
ploidy in mice with a large deletion in the p.53 gene. Oncogene, 9: 603—609,1994.
71. Bischoff, F. Z., Yim. S. 0., Pathak, S., Grant, G., Siciliano, M. J., Giovanella, B. C.,
Strong, L. C., and Tainsky, M. A. Spontaneous abnormalities in normal fibroblasts
from patients with Li-Fraumeni cancer syndrome: aneuploidy and immortalization.
Cancer Res., 50: 7979—7984,1990.
5999
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA.TELANGIECTASIA
72. Livingstone. L. R., White, A., Sprouse, J., Livanos, E., Jacks, T., and Tlsty, 1. D.
Altered cell cycle arrest and gene amplification potential accompany loss of wild
type p53. Cell, 70: 923—935,1992.
73. Yin, Y., Tainsky, M. A., Bischoff, F. Z., Strong, L., and Wahl, G. M. Wild-type p53
restores cell cycle control and inhibits gene amplification in cells with mutant p53
alleles. Cell, 70: 937—948,1992.
74. Hecht. F., Koler, R. D., Rigas, D. A., Dahnke, G. S., Case, M. P., Tisdale, V., and
Miller, R. w. Leukaemia and lymphocytes in ataxia-telangiectasia. Lancet, 2: 1193,
1966.
75. Rosin, M. P., Ochs, H. D., Gatti R. A., and Boder, E. Heterogeneity of chromosomal
breakage levels in epithelial tissue of ataxia-telangiectasia homozygotes and het
erozygotes. Hum. Genet., 83: 133—138,1989.
76. Aguilar, M. J., Kamoshita, S., Landing, B. H., Boder, E., and Sedgwick, R. P.
Pathological observations in ataxia-telangiectasia. A report on 5 cases. J. Neuro
pathol. & Exp. Neurol., 27: 659—676, 1968.
77. Bigbee, W. L., Langlois, R. G., Swift, M., and Jensen, R. H. Evidence for an
elevated frequency of in vivo somatic cell mutations in ataxia-telangiectasia. Am. J.
Hum. Genet.. 44: 402—408, 1989.
78. Weinert, T. A., and Hartwell, L. H. Characterization of RAD9 of Saccharomyces
cerevisiae and evidence that its function acts posttranslationally in cell cycle arrest
after DNA damage. Mol. Cell. Biol., 10: 6554—6564, 1990.
79. Pandita, T. K., Pathak, S., and Geard, C. Chromosome end associations, telomeres
and telomerase activity in ataxia telangiectasia cells. Cytogenet. Cell Genet., 71:
86—93,1995.
80. Counter, C. M., Avilion, A. A., LeFeuvre, C. E., Stewart, N. G., Greider, C. W.,
Harley, C. B., and Bacchetti S. Telomere shortening associated with chromosome
instability is arrested in immortal cells which express telomerase activity. EMBO J.,
11:1921—1929,
1992.
81 . Hartwell, L. H. Twenty-five years of cell cycle genetics. Genetics, 129: 975—980,
1991.
82. Cornforth, M. N., and Bedford, J. S. On the nature of a defect in cells from
101. Green, M. H., Lowe, J. E., Arlett, C. F., Harcourt, S. A., Burke, J. F., James, M. R.,
Lehmann, A. R., and Povey, S. M. A ‘y-ray-resistantderivative of an ataxia
telangiectasia cell line obtained following DNA-mediated gene transfer. J. Cell Sci.
Suppi.,
6: 127—137,
1987.
102. Kunz, B. A., and Haynes, R. H. Phenomenology
and genetic control of mitotic
recombination in yeast. Annu. Rev. Genet., 15: 57—89,1981.
103. Hahn, G. M., and Little, J. B. Plateau-phase cultures of mammalian cells: an in vitro
model for human cancer. Curr. Topics Radiat. Res. Q., 8: 39—83,1972.
104. Weinert, 1. A., and Hartwell, L. H. The RAD9 gene controls the cell cycle response
to DNA damage in Saccharomyces cerevisiae. Science (Washington DC), 241:
317—322,
1988.
105. Rowley, R., Subramani, S., and Young, P. G. Checkpoint controls in Schizosaccha
romyces pombe: rod!. EMBO J.. 1!: 1335—1342,1992.
106. Iliakis, G. The role of DNA double strand breaks in ionizing radiation-induced
killing of eukaryotic cells. Bioessays, 13: 641—648, 1991.
107. Elkind, M. M. DNA damage and cell killing: cause and effect? Cancer (Phila.), 56:
2351—2363, 1985.
108. Natarajan, A. T., and Obe, G. Molecular mechanisms involved in the production of
chromosomal aberrations III: restriction endonucleases. Chromosoma (Berl.), 90:
120—127,1984.
109. Bender, M. A., Griggs, H. G., and Bedford, J. S. Mechanisms of chromosomal
aberration production. III. Chemicals and ionizing radiations. Mutat. Res., 23:
197—212,
1974.
110. Bedford, J. S., Mitchell, J. B., Gnggs, H. G., and Bender, M. A. Radiation-induced
cellular reproductive death and chromosome aberrations. Radiat. Res., 76: 573—586,
1978.
111. Carrano, A. V. Chromosome aberrations and radiation-induced cell death. II. Pie
dicted and observed cell survival. Mutat. Res., 17: 355—366,1973.
112. Hopwood, L. E., and Tolmach, L. J. Manifestations of damage from ionizing
radiation in mammalian cells in the postirradiation generations. Adv. Radiat. Biol.,
8: 317—362,
1978.
individuals with ataxia-telangiectasia. Science (Washington DC), 227: 1589—1591, I 13. Beamish, H., and Lavin, M. F. Radiosensitivity in ataxia-telangiectasia: anomalies in
1985.
radiation-induced cell cycle delay. Int. J. Radiat. Biol., 65: 175—184,
1994.
83. Nagasawa, H., Latt, S. A., Lalande, M. E., and Little, J. B. Effects of X-irradiation
114. lmray, F. P., and Kidson, C. Perturbations of cell-cycle progression in Y-irradiated
on cell-cycle progression, induction of chromosomal aberrations and cell killing in
ataxia telangiectasia and Huntington's disease cells detected by DNA flow cyto
ataxia telangiectasia AT fibroblasts. Mutat. Res., 148: 71—82,1985.
metric analysis. Mutat. Res., 112: 369—382,1983.
84. Carbone, D. P., and Minna. J. D. Antioncogenes and human cancer. Annu. Rev.
Med., 44: 451—464, 1993.
85. Hecht, F., and Hecht, B. K. Cancer in ataxia-telangiectasia patients. Cancer Genet.
Cytogenet., 46: 9—19,1990.
86. Lowe, S. W., Schmitt, E. M., Smith, S. W., Osborne, B. A., and Jacks, T. p53 is
required for radiation-induced apoptosis in mouse thymocytes. Nature (Land.), 362:
847—849,1993.
87. Clarke, A. R., Purdie, C. A., Harrison, D. J., Morris, R. G., Bird, C. C., Hooper,
M. L., and Wyllie, A. H. Thymocyte apoptosis induced by p53-dependent and
independent pathways. Nature (Lond.), 362: 849—852, 1993.
88. Blocher, D., Sigut, D., and Hannan, M. A. Fibroblasts from ataxia telangiectasia AT
and AT heterozygotes show an enhanced level of residual double-strand breaks after
low dose-rate y-irradiation as assayed by pulsed field gel electrophoresis. tnt. J.
Radiat. Biol., 60: 791—802, 1991.
89. Zerbini, C., Weinberg, D. S., Hollister, K. A., and Perez-Atayde, A. R. DNA ploidy
abnormalities in the liver of children with hereditary tyrosinemia type I. Correlation
with histopathologic features. Am. J. Pathol., 140: 1111—1
119, 1992.
90. Allan, D. J. Radiation-induced apoptosis: its role in a MADCaT mitosis-apoptosis
differentiation-calcium toxicity scheme of cytotoxicity mechanisms. Int. J. Radiat.
Biol., 62: 145—152,1992.
91. Taylor, A. M. R., Harnden, D. G., Arlett, C. F., Harcourt, S. A., Lehmann, A. R.,
Stevens, S., and Bridges, B. A. Ataxia telangiectasia: a human mutation with
abnormal radiation sensitivity. Nature (Lond.), 258: 427—428, 1975.
92. Lehman, A. R., and Stevens, S. The production and repair of double strand breaks
in cells from normal humans and from patients with ataxia telangiectasia. Biochim.
Biophys. Acta, 474: 49—60, 1977.
93. Eady, J. J., Peacock, J. H., and McMillan, T. J. Host cell reactivation of y-irradiated
adenovirus 5 in human cell lines of varying radiosensitivity. Br. J. Cancer, 66:
113—118,1992.
94. Sikpi, M. 0., Freedman, M. L., Dry, S. M., and Lurie, A. G. Mutation spectrum in
‘y-irradiatedshuttle vector replicated in ataxia-telangiectasia lymphoblasts. Radiat.
Res., 130: 331—339,1992.
95. Muriel, W. J., Lamb, J. R., and Lehmann, A. R. UV mutation spectra in cell lines
from patients with Cockayne's syndrome and ataxia telangiectasia, using the shuttle
vector pZl89. Mutat. Res., 254: 119—123,1991.
96. Pandita, T. K., and Hittelman, W. N. The contribution of DNA and chromosome
repair deficiencies to the radiosensitivity of ataxia-telangiectasia. Radiat. Res., 13!:
214—223,
1992.
97. Taylor, A. M. R. Unrepaired DNA strand breaks in irradiated ataxia-telangiectasia
lymphocytes suggested from cytogenetic observations. Mutat. Res., 50: 407—418,
1978.
98. Taylor, A. M. R., Metcalfe, J. A., and McConville, C. Increased radiosensitivity and
the basic defect in ataxia telangiectasia. tnt. J. Radiat. Biol., 56: 677—684, 1989.
99. Smith, P. J., and Paterson, M. C. Effect of aphidicolin on de novo DNA synthesis,
DNA repair and cytotoxicity in y-irradiated human fibroblasts. Implications for the
enhanced radiosensitivity in ataxia telangiectasia. Biochim. Biophys. Acts, 739:
17—26,1983.
100. Kapp, L. N., Painter, R. B., Yu, L-C., van Loon, N., Richard, C. W., III, James,
M. R., Cox, D. R., and Murnane, J. P. Cloning of a candidate gene for ataxia
telangiectasia group D. Am. J. Hum. Genet., 5!: 45—54,1992.
115. Seyschab, H., Chindler, D., Friedl, R., Barbi, G., Oltshauser, E., Fryns, J. P.,
Hanefeld, F., Korinthenberg, R., and Krageloh-Mann, I. Simultaneous measurement,
using flow cytometry, of radiosensitivity and defective mitogen response in ataxia
telangiectasia and related syndromes. Eur. J. Pediatr., 15!: 756—760,1992.
116. Foledano, S. R., and Lange, B. J. Ataxia-telangiectasia and acute lymphoblastic
leukemia. Cancer (Phila.), 45: I675—1678, 1980.
117. Eyre, J. A., Gardner-Medwin, D., and Summerfield, G. P. Leukoencephalopathy
after prophylactic radiation for leukaemia in ataxia telangiectasia. Arch. Dis. Child.,
63: 1079—1093,1988.
118. Kojis, T. L., Schreck, R. R., Gatti, R. A., and Sparkes, R. S. Tissue specificity of
chromosomal rearrangements in ataxia-telangiectasia. Hum. Genet., 83: 347—352,
1989.
119. Nelson, W. G., and Kastan, M. B. DNA strand breaks: the DNA template alterations
that trigger p53-dependent DNA damage response pathways. Mol. Cell. Biol., 14:
1815—1823,1994.
120. Shiloh, Y., Tabor, E., and Becker, Y. Abnormal response of ataxia-telangiectasia
cells to agents that break the deoxyribose moiety of DNA via a targeted free radical
mechanism. Carcinogenesis (Lond.), 4: 1317—1322,1982.
121. Burger, R. M., Drlica, K., and Birdsall, B. The DNA cleavage of iron bleomycin. J.
Biol. Chem., 269: 25978—25985, 1994.
122. Anderson, C. W. DNA damage and the DNA-activated protein kinase. Trends
Biochem. Sci., 18: 433—437, 1993.
123. Gottlieb, T. M., and Jackson, S. P. The DNA-dependent protein kinase: requirement
for DNA ends and association with Ku antigen. Cell, 72: 131—142,1993.
124. Kirchgessner, C. U., Patil, C. K., Evans, J. W., Cuomo, C. A., Fried, L. M., Carter,
T., Oettinger, M. A., and Brown, J. M. DNA-dependent kinase (p350) as a candidate
gene for the murine SCID defect. Science (Washington DC), 267: 1178—1
183, 1995.
125. Blunt, T., Finnie, N. J., Taccioli, G. E., Smith, G. C., Demengeot, J., Gottlieb, T. M.,
Mizuta, R., Varghese, A. J., Alt, F. W., Jeggo, P. A., and Jackson, S. P. Defective
DNA-dependent protein kinase activity is linked to V(D)J recombination and DNA
repair defects associated with the murine scid mutation. Cell, 80: 813—823, 1995.
126. Van Buul, P. P., Dc Rooij, D. G., Zandman, I. M., Grigorova, M., and Van
Duyn-Goedhart, A. X-ray-induced chromosomal aberrations and cell killing in
somatic and germ cells of the acid mouse. Int. J. Radiat. Biol., 67: 549—555, 1995.
127. Troelstra, C., and Jaspers, N. G. Recombination and repair. Ku starts at the end.
Curr. Biol., 4: 1149—1151,1994.
128. Taccioli, G. E., Gottlieb, T. M., Blunt, T., Priestley, A., Demengeot, J., Mizuta, R.,
Lehmann, A. R., Alt, F. W., Jackson, S. P., and Jeggo, P. A. Ku80: product of the
XRCCS gene and its role in DNA repair and V(D)J recombination. Science (Wash
ington DC), 265: 1442—1445,1994.
129. Lees-Miller, S. P., Godbout, R., Chan, D. W., Weinfeld, M., Day, R. S., III, Baron,
G. M., and Allalunis-Tumer. J. Absence of p350 subunit of DNA-activated protein
kinase from a radiosensitive human cell line. Science (Washington DC), 267:
1183—1186,
1995.
130. Hartley, K. 0., Gell, D., Smith, G. C. M., Thang, H., Divecha, N., Connelly, M. A.,
Admon, A., Lees-Miller, S. P., Anderson, C. W., and Jackson, S. P. DNA-dependent
protein kinase catalytic subunit: a relative of phosphatidylinositol 3-kinase and the
ataxia telangiectasia gene product. Cell, 82: 849—856, 1995.
131. Helliwell, S. B., Wagner, P., Kunz, J., Deuter-Reinhard, M., Henriquez, R., and
Hall, M. N. TOR1 and TOR2 are structurally and functionally similar but not
6000
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
A COMPREHENSIVE MODEL FOR ATAXIA-TELANGIECTASIA
identical phosphatidylinositol
kinase homologues in yeast. Mol. Biol. Cell, 5:
105—118,
1994.
132. Kunz, J., Henriquez, R., Schneider, U., Deuter-Reinhard, M., Movva, N. R., and
Hall, M. H. Target of rapamycin in yeast, TOR2, is an essential phosphatidylinositol
kinase homolog required for G, progression. Cell, 73: 585—596,1993.
133. Kapeller, R., and Cantley, L. C. Phosphatidylinositol 3-kinase. Bioessays, 16:
565—576,1994.
134. Dhand, R., Hiles, I., Panayotou, G., Roche, S., Fry, M. J., Gout, I., Totty, N. F.,
Truong, 0., Vicendo, P., Yonezawa, K., Kasuga. M., Courtneidge, S. A., and
Waterfiel, M. D. P1 3-kinase is a dual specificity enzyme: autoregulation by an
intrinsic protein-serine kinase activity. EMBO J., 13: 522—533,1994.
135. Stack, J. H., and Emr, S. D. Vps34p required for yeast vacuolar protein sorting is a
multiple specificity kinase that exhibits both protein kinase and phosphatidylinosi
tol-specific P1 3-kinase activities. J. Biol. Chem., 269: 31552—31562, 1994.
136. Lane, D. P. Cancer: p53, guardian ofthe genome. Nature (Lond.), 358: 15—16,1992.
137. Yao, R., and Cooper, G. M. Requirement for phosphatidylinositol-3 kinase in the
prevention of apoptosis by nerve growth factor. Science (Washington DC), 267:
2003—2006,1995.
I38. Knox, K. A.. and Gordon, J. Protein tyrosine kinases couple the surface immuno
globulin of germinal center B cells to phosphatidylinositol-dependent
and -mdc
pendent pathways of rescue from apoptosis. Cell Immunol., 155: 62—76,1994.
I39. Dive, C., Evans. C. A., and Whetton, A. D. Induction of apoptosis: new targets for
cancer chemotherapy. Semin. Cancer Biol., 3: 417—427,1992.
140. Loeb. L. A. Mutator phenotype may be required for multistage carcinogenesis.
Cancer Res., 5!: 3075—3079, 1991.
141. Hartwell, L. Defects in a cell cycle checkpoint may be responsible for the genomic
instability of cancer cells. Cell, 71: 543-546, 1992.
142. Keldysh, P. L, Dragani, T. A., Fleischman, E W., Konstantinova, L. N.,
Perevoschikov, A. 0., Pierotti, M. A., Della Ports, G., and Kopnin, B. P. 1lq
deletions in human colorectal carcinomas: cytogenetics and restriction fragment
length polymorphism analysis. Genes Chromosomes & Cancer, 6: 45—50,1993.
143. Carter, S. L, Negrini, M., Baffa, R., Gillum, D. R., Rosenberg, A. L., Schwartz,
G. F., and Croce, C. M. Loss of heterozygosity at I lq22—q23in breast cancer.
Cancer Res., 54: 6270—6274,1994.
144. Pejovic, T. Genetic changes in ovarian cancer. Ann. Med., 27: 73—78,1995.
145. Hampton, G. M., Penny, L. A., Baergen, R. N., Larson, A., Brewer, C., Liao, S.,
Busby-Earle, R. M., Williams, A. W., Steel, C. M., Bird, C. C., Stanbridge, E. J., and
Evans, G. A. Loss of heterozygosity in cervical carcinoma: subchromosomal
local
ization of a putative tumor-suppressor gene to chromosome I 1q22—q24.
Proc. Nail.
Acad. Sci. USA, 91: 6953—6957, 1994.
146. Savitsky, K., Sfez, S., Tagle, D. A., Ziv, Y., Sartiel, A., Collins, F. S., Shiloh, Y., and
Rotman, G. The complete sequence of the coding region of the ATM gene reveals
similarity to cell cycle regulators in different species. Human Molec. Genet., 4:
2025—2032,1995.
147. Kato, R., and Ogawa, H. An essential gene, ESRI, is required for mitotic cell growth,
DNA repair, and meiotic recombination in Saccharomyces cerevisiae. Nuclear Acids
Res., 22: 3104—3112, 1994.
148. Altschul, S. F., Gish, ‘W.,
Miller, W., Myers, E. W., and Lipman, D. J. Basic local
alignment search tool. I. Mol. Biol., 215: 403—410, 1990.
6001
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.
Ataxia-Telangiectasia and Cellular Responses to DNA Damage
M. Stephen Meyn
Cancer Res 1995;55:5991-6001.
Updated version
E-mail alerts
Reprints and
Subscriptions
Permissions
Access the most recent version of this article at:
http://cancerres.aacrjournals.org/content/55/24/5991
Sign up to receive free email-alerts related to this article or journal.
To order reprints of this article or to subscribe to the journal, contact the AACR Publications
Department at [email protected].
To request permission to re-use all or part of this article, contact the AACR Publications
Department at [email protected].
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1995 American Association for Cancer Research.