Download Consequences of aneuploidy.

Consequences of aneuploidy.
Angelika Amon
Massachusetts Institute of Technology
Howard Hughes Medical Institute
Consequences of aneuploidy.
Part 1: Introduction.
Part 2: The effects of aneuploidy
on cell physiology.
Part 3: Disease implications.
Definition of aneuploidy:
Chromosome composition that is not a
multiple of the normal chromosome
composition.
Aneuploidy comes in many
different flavors.
Aneuploidy comes in many
different flavors.
Two types of aneuploidy:
• Mosaic aneuploidy: some cells in the organism are
aneuploid; caused by mitotic chromosome missegregation.
• Constitutional aneuploidy: the entire organism is
aneuploid; caused by meiotic chromosome missegregation.
How does aneuploidy arise?
Chromosome
segregation problems
2N+x
2N-x
The study of aneuploidy has a
long tradition.
Marcella O Grady s and Theodore Boveri s
famous 1902 experiment.
The study of aneuploidy has a
long tradition.
In 1929 Barbara McClintock described the
first aneuploid corn plants.
The study of aneuploidy has a
long tradition.
In 1959 Jerome Lejeune showed that Down
Syndrome was due to trisomy 21.
Consequences of aneuploidy in
humans:
•  All autosomal monosomies and most autosomal trisomies
are lethal.
•  Aneuploidy is the leading cause of mental retardation in
humans.
•  Aneuploidy is the leading cause of miscarriages: 35% of
all clinically recognized spontaneous abortions have an
incorrect chromosome number.
•  Associated with cancer: 90% of solid tumors are
aneuploid.
Summary:
The consequences of aneuploidy.
•  Aneuploidy is detrimental at the organismal level.
•  Chromosome losses are more detrimental than
chromosome gains.
•  The severity of the phenotypes correlates with the degree of
aneuploidy.
The questions and conundrums.
•  Single gene effects or additive effects of many genes,
which on their own have little or no effect, or both?
The questions and conundrums.
•  Single gene effects or additive effects of many genes,
which on their own have little or no effect, or both?
•  Case study: Aneuploidy in humans.
•  Single gene effects: APP duplication in Down syndrome
The questions and conundrums.
•  Single gene effects or additive effects of many genes,
which on their own have little or no effect, or both?
•  Case study: Aneuploidy in humans.
•  Multi gene effects: Down Syndrome critical region cannot
account for the phenotypes of Down Syndrome.
The cancer conundrum.
•  Single chromosomal abnormalities are highly detrimental
for the organism, yet cancer, a disease characterized by
unrestricted growth is associated with high-level
aneuploidy.
What are the consequences of
aneuploidy on cellular physiology?
Consequences of aneuploidy.
Overview:
Part 1: Historical review of the
study of aneuploidy.
Part 2: The effects of aneuploidy
on cell physiology.
Part 3: Disease implications.
The effects of aneuploidy on cell physiology.
•  Models to study the effects of aneuploidy
on cells.
•  Gene-specific effects of aneuploidy.
•  General effects of aneuploidy: The
aneuploidy stress response .
Two systems to study the effects of
aneuploidy on cell physiology:
log2 ratios
Defined, low complexity aneuploidies:
•  20 yeast strains carrying one or two extra
chromosomes.
Two systems to study the effects of
aneuploidy on cell physiology:
Defined, low complexity aneuploidies:
• 4 primary MEF lines carrying an extra
chromosome.
Two systems to study the effects of
aneuploidy on cell physiology:
Random heterogeneous high complexity aneuploidies:
• Meiotic non-disjunctions obtained as progeny of triploid
meiosis.
• Mitotic non-disjunctions caused by interference with
chromosome segregation machinery.
Gene-specific effects of aneuploidy.
Selmecki et al., 2006
Torres et al., 2007
General effects of aneuploidy: The
aneuploidy stress response .
•  Aneuploidy causes proteotoxic stress.
•  Aneuploidy causes a transcriptional
response.
•  Aneuploidy causes a G1 delay.
Evidence for proteotoxic stress in yeast
and mammals:
•  Compromising proteasome function with chemicals or
genetic manipulations impairs the growth of aneuploid yeast
cells more than of euploids.
•  All aneuploid yeast cells are cycloheximide and temperature
sensitive.
•  Aneuploid mouse cells are sensitive to the authophagy
inhibitor chloroquine (Tang et al., 2011).
•  Basal levels of autophagy are increased in trisomic MEFs
and following chromosome mis-segregation (Tang et al.,
2011).
•  Aneuploid mouse cells are sensitive to the Hsp90 inhibitor
17-AAG (Tang et al., 2011).
Evidence for proteotoxic stress in yeast:
Hsp104 foci accumulate in cells.
Autophagy is induced upon
chromosome mis-segregation.
Where is this proteotoxic
stress coming from?
Is the proteotoxic stress due to proteins
made from additional chromosomes?
The additional chromosomes are active.
DNA
(CGH)
Chr I
Chr V
Chr XVI
Chr I
Chr V
Chr XVI
Chr I
Chr V
Chr XVI
RNA
(array)
Protein
(SILAC)
In collaboration with
Noah Dephoure and Steve Gygi
The shared phenotypes are due to the
additional chromosomes being active.
Chromosome size human or
mouse DNA does not cause
adverse phenotypes.
DNA
(CGH)
Chr I
Chr V
Chr XVI
Phenotypes in 1N+1 are more
severe than in 2N+1.
RNA
(array)
Chr I
Chr V
Chr XVI
Chr I
Chr V
Chr XVI
Protein
(SILAC)
Hypothesis:
Aneuploidy leads to excess protein
production.
This causes, among other deleterious
outcomes, proteotoxic stress because
overproduction of certain proteins
saturates protein quality control
pathways.
How do you get saturation of protein
quality control?
1.  Proteins that require protein quality
control systems for function are
overproduced in aneuploids.
i.e. Protein kinases, WD40 repeat proteins,
Tubulin, Actin
How do you get saturation of protein quality
control?
2. Protein stoichiometry imbalances
B-A
Chr 1 Chr 2
A
A
A
A
B
B
B
B
[A]
Neutralized by protein
quality control pathways
and sometimes feedback
controls of gene expression
Examples of this type of control:
Alpha and beta tubulin,
Ribosomal subunits,
Histones
How do you get saturation of protein quality
control?
B-A -A
[A]
A
A
A
A
B
B
B
B
A
Increased burden on protein
quality control pathways
and other phenotypes
(increased need for energy,
cell cycle delay, etc)
Chr 1 Chr 2 Chr 2
A
A
A
A
Consequences of aneuploidy.
Overview:
Part 1: Historical review of the
study of aneuploidy.
Part 2: The effects of aneuploidy
on cell physiology.
Part 3: Disease implications.
•  Aneuploidy as a therapeutic target in
cancer.
•  Aneuploidy in neurodegenerative
disease.
Compounds that selectively impair
proliferation of aneuploid mouse cells.
Targeted screen identifies AICAR (energy
stress inducer) and 17-AAG (proteotoxic stress
inducer).
Trisomy 13
Trisomy 1
AICAR inhibits the accumulation of trisomic MEFs.
Mediated by p53-dependent apoptosis
Do AICAR and 17-AAG show
efficacy in aneuploid cancer cells?
Analysis of MIN and CIN colon cancer cell
lines.
Highly aneuploid CIN lines but not near euploid
MIN lines are sensitive to AICAR+17-AAG
AICAR and 17-AAG inhibit CIN tumor cell
growth in Xenografts
PBS
HCT15
SW620
AICAR+17-AAG
HCT15
SW620
PBS
LoVo
AICAR+17-AAG
HT29
LoVo
HT29
Conclusions:
Aneuploidy could be a potential target in
tumor therapy.
Implications for cancer.
•  Aneuploidy causes a proliferation disadvantage.
• The proliferative disadvantage caused by aneuploidy needs
to be overcome during transformation.
• Cancer cells may more heavily depend on mechanisms
helping cells deal with stress associated with aneuploidy for
their survival.
• The phenotypes shared by aneuploids may provide new
therapeutic targets (i.e. AICAR).
Aneuploidy and
neurodegenerative diseases.
- 10% of adult neurons in the brain are aneuploid (Chun et
al.).
- Aneuploidy is increased in Alzheimer s patients.
The proteotoxic stress caused by aneuploidy could
contribute to protein aggregation characteristic of
neurodegenerative diseases such as polyQ expansion
diseases, Alzheimer s Diseases and Parkinson s
Disease.
PolyQ-aggregates form more readily
in many disomes.
Prion conversion rates are increased in
disomic yeast strains.
Eduardo Torres
Bret Williams
Jason Sheltzer
Ana Oromendia
Stefano Santaguida
Yun-Chi Tang