Cell Cycle 9 Flashcards
Where does MDM2 bind on p53?
In the transactivation domain - blocks the recruitment of other TF.
What happens when MDM2 binds to p53?
It acts as ubiquitin ligase and tags it for degradation by the proteasome.
Describe the MDM2-p53 feedback loop.
At high levels of p53, it will switch on MDM2 expression.
What does ARF do?
Binds to MDM2, sequestering it and preventing it from degrading p53.
What does ARF stand for?
Alternative reading frame
What protein is also transcribed from the ARF gene region?
p16
What exons is p16 made up of?
Exon 1a, 2 and 3
What exons is ARF made up of?
Exon 1B, 2 and 3
Why do ARF and p16 have no sequence homology?
They use different reading frames.
Do ARF and p16 both respond to oncogenic activation by Ras?
Yes
What type of radiation causes single stranded breaks?
UV
What type of radiation causes double stranded breaks?
Ionising
Which proteins deal with single and double stranded breaks?
ATR - single
ATM - double
What type of enzymes are ATR and ATM?
Serine/threonine kinase
Briefly describe 3 ways ATM is activated by DNA damage.
- Association with chromatin, causes trans-auto-phosphorylation between dimer, when dsDNA break occurs, activating monomers.
- MRN binds to dsDNA breaks, this undergoes conformational change - causing trans-auto-phosphorylation of dimer –> activated monomers.
- Oxidative damage causes disulphide bonds to form between monomers, resulting in transautophosphorylated –> active dimer.
Which of the mechanisms of ATM activation is most likely correct?
They are all likely to be correct.
What are the downstream effects of ATM?
Phosphorylates Ser15 on p53 (insufficient to activate) and phosphorylates Chk2.
Chk2 phosphorylates Ser20 on p53 - activating it.
Name 4 things that can affect the decision for arrest/apoptosis in p53 signalling.
- Strength of signal.
- Promoter affinity.
- PTMs
- Other regulators.
Give an example of a regulator that effects p53 downstream pathway.
ASPP2 causes p53 to bind to the Bax promoter and activate apoptosis.
Name two things that are involved in pushing the equilibrium of p53 degradation in favour of MDM2.
- Wip1 - dephosphorylates p53 in the MDM2 binding site.
2. Akt - phosphorylates MDM2, making it more efficient at p53 degradation.
Name two other proteins in the p53 family?
p63 and p73
Where is the second promoter in p63 and p73?
Between exon 3 and 4
Why can the truncated forms of p63 and p73 inhibit transcription/dampen p53 response?
They can occupy promoters, but have no transactivation domain, as this is in exon 1-3.
Are p63/p73 often mutated in cancer?
No
Describe the function of the drug, Nutlin.
Nutlin binds to MDM2 and prevents degradation of p53 - WT p53 re-activation.
Describe the function of the drug, NSC319726.
Binds to the structural p53 mutant R175H (DBD) and reactivate it.
