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Oncogenes et Gènes Suppresseurs de
Tumeurs Introduction
I. Les Conditions de la Prolifération
Cellulaire Les Conditions Normales Sénescence I
nhibition de Contact, Adhérence et Facteurs de
Croissance Transformation Cellulaire,
Définitions Le Développement Tumoral

II. Les Gènes Impliqués Dans les Contrôle
Cellulaire Anomalies Génétiques Oncogènes et
Gènes Suppresseurs de Tumeurs Hypothèse de
Knudson L Exemple de Rb
III. Découverte des Oncogènes Le Virus du
Sarcome de Roux Découverte de lAgent
Transformant src Les Protéines Cellulaires
Equivalentes Mode d Action des Oncogènes
L Exemple de T
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Tumeurs
Mutations
Mutations
?
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Facteurs de Croissance Seuls
Adhérence Seule
Le déclenchement de la Prolifération Cellulaire
Nécessite l Apport De Deux Signaux
Complémentaires
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Adhérence Seule
Facteurs de Croissance Seuls
Absence de Signal
Le déclenchement de la Prolifération Tumorale
Peut se Faire Spontanément, Avec Un Seul
Facteur, etc...
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MULTISTEP CARCINOGENESIS (TISSUE VIEW)
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What is an immortalized cell?
Immortalized
crisis (cell death)
senescence (G1 arrest)
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Initial Research

• Leonard Hayflick first to recognize that normal
  cells have finite replicative capacity
• Interpreted as a manifestation of human aging at
  the cellular level
• Recognized relationship between population
  doubling potential and maximum lifespan of
  species cells were taken from

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Hayflick Limit

• Hayflick Limit is the maximum number of times
  that normal cells can undergo replication before,
  as seen in culture, entering growth arrest
• Discovered replicometer,
• later known to be telomeres,
• located in nucleus

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Hayflick Limit

• Young cells after 20 population doublings (PDs)
• Older cells entering a senescent phase after 50
  population doublings

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Morphology

• Senescent cells become flattened, enlarged and
  have increased ?-galactosidase activity
• Increased size of nucleus and nucleoli
• Increased number of multinucleated cells
• Increased number of lysosomes, Golgi
• and cytoplasmic microfilaments

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What is senescence?

• Replicative senescence is the progressive
  shortening of telomeres at chromosome ends
• Critically short telomeres trigger activation of
  cell cycle checkpoints/arrest
• Permanent cell cycle growth arrest due to
  activated cell cycle checkpoints, similar to
  those activated upon double strand breakage
• Cells metabolically active but cannot continue to
  divide, unlike quiesence

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• Genomic instability
• Cells that can still divide (loss of p53/pRb)
  AND have lost their telomeres will develop an
  unstable genome

Mort Cellulaire (mitose)
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Cellular Senescence A Gatekeeper Tumor
Suppressor Induced by potentially oncogenic
stimuli Most tumor cells acquire mutations that
abrogate the senescence response Controlled by
p53 and pRB -- tumor suppressors inactivated in
most tumors
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Cellular Senescence Induced by Potentially
Cancer-Causing Events
Stress/ Signals
Chromatin Instability
Irreversible arrest of cell proliferation
DNA Damage
Oncogenes
Short/dysfunctional telomeres (REPLICATIVE
SENESCENCE)
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Telomeres

• The key to immortality
• Loss of telomeres leads to genomic instability
• Re-extension of telomeres leads to immortality

Mort Cellulaire (mitose)
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1. Overexpress telomerase (htert) limitless
replicative potential
Mathon et al., Nature Reviews Cancer, 2001
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Les Etapes du Développement Tumoral
 The Hallmarks of Cancer   Robert Weinberg
Cell, 2000, 100 57
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Genes involved in cancer
Oncogenes Activated from protooncogenes Usually
enhance cell proliferation Tumor suppressor
genes Inactivated by mutation or deletion Usually
arrest cell proliferation Genes regulating
apoptosis Control cell survival Overexpression,
mutation or deletion can enhance cell
survival Genes regulating metastasis Control
cell motility and interaction with the
environment Both activating and inactivating
mutations
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MULTISTEP CARCINOGENESIS (TISSUE VIEW)
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1. Overexpress telomerase limitless replicative
potential 2. Inactivate RB insensitivity to
anti-growth signals 3. Inactivate p53 evasion
of apoptosis
Mathon et al., Nature Reviews Cancer, 2001
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Sénescence
Sénescence
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RétroContrôle de la Voie PI3Kinase/Akt/PKB
La Phosphatase PTEN Déphosphoryle les Lipides
Membranaires
Déphosphorylation
La Déphosphorylation Elimine les Sites
d Accrochage De Akt à la Membrane
Inactivation
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Le Gène Suppresseur de Tumeur PTEN
Dans les Gliomes (Tumeurs Cérébrales), PTEN est
Inactivée PTEN est un Gène Suppresseur de Tumeurs
Conditions Normales
Tumeurs Gliales PTEN -/-
Activation PI3 Kinase
Activation PI3 Kinase
Prolifération Protection Apoptose
Prolifération Protection Apoptose
Activation Akt
Activation Akt
Déphosphorylation Lipides Membranaires par PTEN
Tumeurs
PTEN
Extinction du Signal Rétrocontrôle
Extinction du Signal Rétrocontrôle
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Detection of Oncogenes in Human Tumors
DNA transfections
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DNA TRANSFECTION STUDIES TO IDENTIFY ONCOGENES
ISOLATE TUMOR DNA
TUMOR CELL
NORMAL CELL
ISOLATE TUMOR DNA AND CHARACTERIZE TRANSFERRED
DNA
TUMOR CELL
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Activation of ras Oncogenes by Point Mutations
1 2 3 4 5 6 7 8
9 10 11 12 13

• Ras mutations in tumors usually involve codons
  12, 13, 59 and 61.
• Mutated ras is found in 50 of colorectal cancers
  and 95 of pancreatic cancers.

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TWO FUNCTIONS OF GENES ASSOCIATED WITH CANCER

• ONCOGENES
• - ACTS IN A POSITIVE FASHION
• - SEEMS TO INFLUENCE GROWTH STIMULATION

• TUMOR SUPPRESSOR GENES
• - ACTS IN A NEGATIVE FASHION
• - SEEMS IMPORTANT FOR GROWTH CONTROL

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Functions and Mechanisms of Activation of
Proto-oncogenes Products

• Protein phosphorylation.
• Can activate kinase activity of the protein.
• Can generate docking sites to recruit target
  proteins.
• Signal transmission by GTPases.
• Signal transduction.
• Ras family proteins are prototypical members.
• Proteins localized in nucleus.
• Control of progress through cell cycle.
• Involvement in DNA replication.
• Proteins that regulate cell death (apoptosis).

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From the Growth Factor to the Cell Cycle
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Les Etapes du Développement Tumoral
 The Hallmarks of Cancer   Robert Weinberg
Cell, 2000, 100 57
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MULTISTEP TUMORIGENESIS NOT ALWAYS IN THE
SAME ORDER
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TISSUE HOMEOSTASIS
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DYSREGULATED HOMEOSTASIS CAN PROMOTE
TUMORIGENESIS
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MULTISTEP TUMORIGENESIS OF HEAD AND NECK
CARCINOMAS
Other alterations
3p
9p
17p
11q
GENETIC ALTERATIONS
loss
loss
loss
amplification
?
p16/p15
p53
CCND1
GENOMIC INSTABILITY
ADJACENT NORMAL
DYSPLASIA
TUMOR
METASTASIS
HYPERPLASIA
PCNA
EGFR
p53
CCND1
RAR?
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GENETIC INSTABILITY DURING TUMORIGENESIS
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DNA Damage Signaling in Early Bladder Cancer
?-H2AX staining in early bladder lesions

• Observations
• Chk expressed throughout transition, but Chk2
  becomes activated in early stages
• ATM and downstream pathway substrates become
  activated in early stages
• Levels of Chk2 and ATM activation seem decrease
  at later stages.

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CHROMOSOME INSTABILITY AND CANCER
RISK ASSAYING GENOMIC INSTABILITY IN ORAL
LEUKOPLAKIA
HIGH INSTABILITY GROUP
PROBABILITY OF CANCER
LOW INSTABILITY GROUP
YEARS SINCE BASELINE BIOPSY
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