Tumour Suppressors Flashcards
What is haploinsufficiency?
Loss of one copy of a gene is sufficient to permit the development of the disease
What cell cycle checkpoint is Rb present at?
G1/S phase
What cell cycle checkpoint is p53 present at?
G1/S phase
S phase
G2/M phase
What is the function of Rb?
To block E2F-DP1 complex and therefore inhibitors transcription of genes required for DNA synthesis
What cyclin does the MAPK signalling family produce?
Cyclin D1
In terms of Rb, what is the function of cyclin D1?
It phosphorylates it which inhibits its function
Acts as an oncogene
Name the domains of p53
Transcription transactivating domain (TAD) -1 and 2 DNA binding domain Tetramerisation domain (TET) Regulatory domain (Reg)
How often is p53 mutated in cancer?
~50% of the time
What are the 2 main mutational hotspots of p53 and which domain are they in?
273 and 248
DNA binding domain
How does p53 normally bind to the promoter?
As a tetramer
What is p300?
Histone acetyl transferases
What p53 domains bind to p300?
TAD
What are the subunits of p300?
Taz1
KIX
Taz2
IBiD
What does p300 induce?
acetylation of histones and transcription
What does p53 induce?
Apoptosis Growth arrest Repair Metabolism Angiogenesis block
How is p53 auto-regulated?
By inhibition by Mdm2, causing it to be targeted for degradation by the proteasome, to make sure it is at low levels until required
What is MDM2?
an E3 ubiquitin ligase
Genes produced by p53 involving growth arrest
p21
GADD45
14-3-3sigma
Reprimo
Genes produced by p53 involving apoptosis
PIDD Bax Fas PIG3 KILLER p53 AIP1 PERP NOXA Scotin
Genes produced by p53 involving repair
p53R2
Genes produced by p53 involving angiogenesis block
Maspin
TSP1
PAI1
GD-AIF
Genes produced and inhibited by p53 involving metabolism
Inhibit G6PDH
Inhibit PGM
Sestrins
TIGAR
How does p53 inhibit the cell cycle at G1/S?
Activates p21 which inhibits Cyclin/CDK
How does p53 inhibit the cell cycle at G2/M?
It inhibits genes which normally cause the movement through the cell cycle : - CDC25C - Cyclin B1 - CKS1 - CDC2 - Topo II - PLK1 It activates genes which inhibit the cell cycle: - p21 - GADD45 - 14-3-3 sigma - Reprimo
What is the warburg effect?
That most cancer cells produce energy through high rate glycolysis, followed by lactic acid fermentation in the cytosol
Name 3 pathways involved in the activation of p53
Arf pathway
DNA damage pathways
Nutlin
Name some stresses which activate p53
Telomere erosion DNA strand breaks UV radiation Transcriptional failure ROS Ribosomal stress Nutrient deprivation Viral infection Oncogenes Hypoxia Mitotic catastrophe
How does Mdm2 and p53 work in a negative feedback loop?
Increase Mdm2 -> ubiquitylate and target p53 for degradation
Increase p53 -> stimulates transcription of Mdm2
What is etoposide?
A chemotherapy drug
causes DNA damage and activates p53 and increases its expression
What is nutlin?
A drug which induces p53 without DNA damage
Blocks the interaction between Mdm2 and p53
How does p53 stop being to Mdm2 and bind to p300 instead?
Through phosphorylation of p53
How does the ARF pathway promote p53?
Oncogenes stimulate ARF production -> ARF inhibits Mdm2 and p53 binding
What is the phenotype of p53 KO mice?
They grow to adulthood normally but are more susceptible to cancer
What is the phenotype of Mdm2 KO mice?
They die in utero at day 5
What is the phenotype of p53 and Mdm2 KO mice?
They are viable but get cancer
Indistinguishable from p53 KO mice
Why do Mdm2 KO mice die in utero?
Since there is too much p53 and therefore there is uncontrolled apoptosis
What is the most common p53 mutation?
Missense (>75%) - gain of function
Phenotype of p53 oncogenes
They increase metastatic potential and invasiveness
They are resistant to killing
How do p53 mutants become oncogenes?
Missense mutations in the DNA binding domain so instead of binding to p21, they bind close to promoters which drive the cell cycle through undergoing a conformational change
What transcriptional proteins does mutant p53 bind to and what does it cause?
Ets2 - metastasis
NF-Y - proliferation
Mre11 - inhibits ATM-mediated DNA repair
NF-kappaB - Inflammation
MLL1 and MLL2 (methyltransferases) and MOZ (acetyltransferases) - chromatin re-modelling
How do pathologists detect that p53 and mp53 is accumulating?
The increase in MDM2 since it doesn’t bind to p53
Apart from mutation, how else can you get mp53?
Inactivate ARF and ATM
How does HPV induce cervical cancer?
The E7 protein will inhibit p53 binding to the E2F-DP1 complex, causing hyperproliferation, which would normally produce ARF and cause p53-mediated apoptosis. However, p53 is inhibited by an E6 uquitin ligase and therefore p53 is degraded instead promoting apoptosis
What is the issue with p53 based drugs?
Effects normal cells - genotoxic effects
Name an p53 based therapy and what cancer it targets
Gendicine
Head and neck squamous cell carcinoma
How does gendicine work?
Triggers apoptosis
What is the effectiveness of gendicine?
64% of patients shows complete regression after 8 weeks of the drug in combination with radiotherapy
Name 4 drugs which restore p53 activity
Nutlin-3
PRIMA-1
RITA
PhiKan083
Describe Nutlin-3
competitive inhibitor of p53, it binds to Mdm2
No genotoxicity
What does PRIMA-1 do?
Restores mp53 through altering the covalent modifications
What does RITA do?
Binds to p53 and blocks the interaction with Mdm2
what does PhiKan083 do?
Binds to p53 Y220C mutant
