Download Grant IGA MZČR 8563-5/2005 Genetický profilů genů metabolismu

Chromosomes
and tumors
RNDr Z.Polívková
Lecture No 523
course: Development of cells and tissues
Cancers = heterogenous diseases – initiation
and progression are promoted by
aberrant function of genes, that regulate
DNA repair, genome stability, cell
proliferation, cell death, cell adhesion,
angiogenesis, invasion and metastasis –
so called „ cancer genes“
Gene functions can be influenced by:
• gene polymorphisms
• alteration of copy number (amplifications, deletions,
duplications, changes in chromosomal number)
• changes of gene structure, chromosome structure
(translocations, inversions etc.)
• gene mutations (substitution, deletion, insertion in coding
sequences, on boundary of exons and introns)
• epigenetic modifications (imprinting, DNA methylation and
histone modification – histone acethylation/deacethylation,
methylation or phosphorylation)
Activation of oncogenes (change of protooncogene to
oncogene) through:
• mutation
• structural rearrangement (reciprocal translocation, inversion)
• amplification (double minutes or HSR=homogenously staining regions)
• epigenetic changes
• virus insertion
Inactivation of tumor suppressor genes through:
• mutation
• deletion
• epigenetic modification
• mitotic recombination
CHA and tumors
1.
Specific CHA in tumors - CHA is primary event in tumor origin
rearrangement in neighborhood of protooncogenes:
consequences: - abnormal activity of product
- abnormal gene expression
rearrangement only in tumor cells (e.g.chronic myelogenous leukemia,
Burkitt lymphoma)
- deletion of tumor suppressor genes
in tumor cells or present as constitutional aberrations (heterozygosity)
(e.g. retinoblastoma)
2.
Heritable syndromes with increased chromosome breakage
defect of reparation or replication  high risk of malignancies
Chromosomal study in tumors:
Role: - diagnosis and subclassification of haematologic malignancies
- rational selection of therapy, targeted therapies
- prognostic informations
- monitoring of treatment effect, residual leukemia ..
- study of mechanism of carcinogenesis
CHA in tumors:
balanced without loss or gain of material :
translocations, inversions
unbalanced: with loss of material: deletions, monosomies
with gain of material: duplications, trisomies, polyploidies,
amplifications
Primary changes connected with initiation of malignant process
Secondary changes – connected with progression of disease
Chromosomal aberrations as primary changes connected
with initiation of malignancy
Translocations – 2 types of translocations
1. Translocations leading to fused genes (genes with function in cell
division regulation or differentiation)
Ph1 chromosome in chronic myelogenous leukemia (CML)
=abnormal chrom. 22
from reciprocal translocation 46,XX or XY, t(9;22)(q34;q11)
protooncogen abl transfered from 9q to 22q near the gene bcr 
fused gene bcr/abl  abnormal product = chimeric protein
with stable tyrosinkinase activity – breaks in introns of genes
Ph1 in CML good prognosis
during blastic crisis another chromosome changes
In ALL (acute lymphoblastic leukemia):other site of break in bcr, Ph1 in ALL= bad prognosis
Cme.medscape.com
Fused gene
brc/abl
Wysis 1996/97
Other examples of fused genes:
ALL
t(1;19)
good prognosis
der(19)t(1;19)
bad prognosis
t(12;21)
good prognosis
acute promyelocyt.leu (M3)
t(15;17)
good prognosis
acute myelocytic leu (M2)
t(8;21)
good prognosis
ALL and AML
t(4;11)
bad prognosis
2. Translocation of protooncogenes to position, where they are
abnormally stimulated to transcription
Burkitt lymphoma (BL) – B lymphocytes
t(8;14)(q24;q32) - present also in other lymphomas
protooncogen myc transfered from 8q to 14q – near genes for heavy
chains of immunoglobulins  abnormal stimulation of gene activity 
abnormal amount of normal product
similar translocations: t(8;22) or t (2;8) – light chains of Ig (on chrom.2 and 22)
T-lympho malignancies - breaks near genes for T-cells receptors
Restricted to cells in which genome undergoes somatic rearrangement (e.g.VDJ
recombination of Ig genes) as a part of process of maturation of effector cells
(B,T lymphocytes)
ncbi.nlm.nih.gov
Translocation produces premalignant clone – probably other genetic
changes (mutations, epigenetic changes..) are necessary for full
malignancy
Translocations (balanced) are relatively frequent cause of
malignancies
Most of translocations or inversions were detected in haematologic
malignancies,
In solid tumors translocations are less frequent (and rearrangements are
more complex)
Fused genes encoding:
• transcription
factors necessary for haematopoetic differentiation –
chimeric product of fused gene increases or represses
transcription of genes involved in differentiation
• tyrosine kinases (regulators of proliferation) – fused gene product =
chimeric protein - uncontrolled cellular proliferation
CLINICAL UTILITY OF TRANSLOCATIONS:
Targeted therapy:
ex. imatinib = tyrosin kinase inhibitor - good response to treatment in patients
with bcr/abl fusion (t 9/22)
„ Fragile sites“ and tumors
„Fragile sites“ (FS)
• sites of genome instability on chromosomes
• late replicating
• nonrandom loci – disposed to breaks and exchanges
• manifested as gap or break under condition of replicative stress (i.e.inhibition of
DNA synthesis by aphidicoline, 5.azacytidine, BUdR)
FS – common
- rare in < 5% of population (connected with expansion of triplet repeats,
ex.FRAXA)
In sites of common FS tumor supressor genes and protooncogenes
are located
Common FS = target site of mutagenes/carcinogenes action, site of
integration of oncogenne viruses
52% of all translocations in tumors have sites of breaks in FS (Burrow et al. 2009)
CHA as primary event in initiation of malignancy:
Deletions of tumor suppressor genes
Retinoblastoma (Rb) – eye cancer of children
heritable type (familiar or „de novo“ origin) - AD (with reduced
penetrance)
sporadic type – nonheritable – usually afects only one eye
• heritable Rb – 1st step - germinal mutation or deletion in all cells of body
= heterozygote (constitutional abnormality)
2nd step: somatic mutation in one cell of retina = loss of
heterozygosity (LOH)
loss of heterozygosity by somatic recombination
del(13)(q141-142)
• sporadic Rb – both mutations somatic in one cell of retina
Heterozygosity for mutation or deletion =
predisposition to tumor
Imprinting of tumor suppressor gene =
only single functional copy
Retinoblastoma
Mutation of second
allele in one somatic
cell = loss of
heterozygosity
heterozygote
Heritable
RB/rb or RB/Mutation or
deletion
Sporadic
Loss of function:
mutation, deletion,
loss of whole
chromosome, mitotic
recombination
→
→
→
Mutation of both alleles consecutively in one somatic cell
Heterozygosity in daughter cells
replication
mitotic
recombination
chromatid
segregation
In mitosis
+
heterozygosity
Loss of heterozygosity by mitotic
recombination
+
Loss of heterozygosity
Interstitial deletion 11p
Wilms tumor = nephroblastoma
WT1 locus on 11p13 mutation or deletion
Wilms tu = isolated or a part of
syndrome - WAGR association
(Wilms, aniridia, urogenital anomaly,
mental retardation)
Gain of material
Amplification of oncogenes:
„double minutes“ = amplified circular oncogenes
(extrachromosomal)
HSR (homogenously stainin regions) =
amplification and recombination of oncogenes to
chromosome tandemly or to different sites
Amplification present especially in solid tumors:
e.g.: N-myc in neuroblastoma, cyclin D1 in many tumors (carcinoma of
oesophagus), cyclin D2 in ovarian and testicular cancers
Targeted therapy: Herceptin =monoclonal antibody against ERBB2
oncogene (=Her2/Neu= tyrosin-kinase receptor) in women with breast cancer
and amplification of oncogene
Chromosomal changes as a consequences of carcinogenic
process:
caused by deregulation of genes resposible for segregation of chromosomes
or cytokinesis = consequences of chromosomal instability
Gains of genetic material: intragene duplications, duplications of genes,
groups of genes, chromosomal parts or whole chromosomes
Duplication, trisomy : e.g.+8 in blastic crisis in CML, ANLL, MDS
Hyperdiploidiy, polyploidy – hyperdiploidy in ALL = good prognosis
but hypodiploidy = bad prognosis
Loss of genetic material: deletions inside genes, deletions of whole genes,
groups of genes, chromosomal parts or whole chromosomes - deletions of
tu su genes, loss of noncoding genes (e.g.micro RNA –role in
posttransctriptional regulation of gene expression)
- Loss of genetic material = loss of tumor suppressor genes
- Gain of genetic material = gain of (proto)oncogenes
Oncogene Her-2/neu amplification in breast cancer – FISH method
Trisomy and tetrasomy in cells of breast tumor
Chromosome loss in cells of breast tumor
New methods of chromosomal study in tumors:
FISH, comparative genomic hybridization and variants of
these methods
Array CGH: comparison of tested and normal DNA, both stained
by different fluorochromes – mixture of both is applied to a slide
with thousands of spots of reference DNA sequences to hybridize
- gains and losses of genetic material are detected as spots of
different colours by computor
!! Complex, multiple changes = bad
prognosis, bad response to treatment !!
Karyotype of breast cancer cell
Chromosome instability syndromes
Common features:
• AR inheritance
• increased sensitivity to UV light (sun light)
• hyper or hypopigmentation
• small stature
• defects of immunity
• increased sensitivity to radiation, chemical mutagens (breaks,
chromosome exchanges, sister chromatid exchanges)
• increased spontaneous level of chromosome aberrations or
increased level of CHA after induction by mutagenes
• increased risk of malignancy !!!
error in DNA reparation or replication
Fanconi anemia (FA)
panmyelopathy with bone marrow failure leading to pancytopenia
skeletal anomalies (thumb, radius), growth retardation
hyperpigmentation
microcephaly, defect of thumb and radius - in 50% of patients
CHA: breaks and chromatid exchanges (multiradials, komplex changes)
heterogenic: several genes (7genes FANCA-G)
- defect in DNA repair activation
Bloom syndrome (BS)
low birth weight, stunted growth
sun sensitivity of the skin
immunodefect (B-lymphocytes)
facial butterfly-like lesions with telangiectasia
most families of Ashkenazi Jewish origin
CHA: breaks, exchanges between homologs, increased level of sister chromatid
xchanges (SCEs)
defect of replication, DSB reparation (DNA helicase-gene BLM)
Ataxia teleangiectasia (AT - Louis-Bar syndrome)
progressive cerebellar ataxia, growth retardation
sensitivity to radiation
oculocutaneous teleangiectasia
immune deficiency (cell immunity)
„café au lait“ spots on skin
CHA: rearrangement of chromosomes Nos 7, 14 or 2,22
= sites of T-cell receptors genes and Ig heavy chains genes
defect of DNA repair (ATM gene – protein kinase regulates TP53,
signal recognition)
Xeroderma pigmentosum (XP)
erythema after UV irradiation of the skin - atrophy,
teleangiectasias
sensitivity to UV and ionizing radiation
skin cancer
CHA: spontaneous level not increased, increased respons to induction of aberrations (UV)
defect of DNA repair (excision, postreplication repair,
repair of DNA strand breaks ) 7types: genes XPA-G + XPV
Nijmegen breakage sy
growth retardation, mental retardation
microcephaly, atypic facies
immunodefect
CHA: rearrangement of chromosomes Nos 7, 14
Rearrangement→failure to produce fully functional immunogluobulins
and T-cell receptors → immunodeficiency
Error in reparation of DNA double strand breaks
gene NBS1 (nibrin)
Syndromes connected with premature aging
Werner sy
Cataracts, subcutaneous calcification, changes of skin, premature hair greying,
premature arteriosclerosis
defect of exonuclease and helicase activity, gene WRN
Cockayne sy
Stunted growth, mental retardation, deafness, premature senility
defect of DNA excision repair (NER)
http://dl1.cuni.cz/course/view.php?id=324 presentation
http://dl1.cuni.cz/course/view.php?id=324 supplementary text to
cytogenetics
Thompson &Thompson: Genetics in medicine, 7th ed.
Chapter 16: Cancer genetics and genomics: Oncogenes, Tumorsuppressor genes (including Retinoblastoma,Caretaker genes in
autosomal recessive chromosome instability syndromes,
Cytogenetic changes in cancer, Gene amplification)
Chapter 6: Principles of clinical cytogenetics:Mendelian disorders
with cytogenetic effects, Cytogenetic analysis in cancer
+ informations from presentation