p53 Extra Reading

Question 1

Tumour associated alterations in p53 result in what types of mutations that can be stabley expressed in tumours?

Answer 1

Missense mutations, single aa substitution, which occur most commonly in the DNA binding region of p53 which leads to reduction in wild-type p53 activity.

p53 normally acts as a tetramer so that mutant proteins may also function as dominant negative inhibitors over any remaining wildtype p53.

Question 2

Mutations to p53 occur most commonly where?

Answer 2

Missense mutations, single aa substitution, which occur most commonly in the DNA binding region of p53 which leads to reduction in wild-type p53 activity.

p53 normally acts as a tetramer so that mutant proteins may also function as dominant negative inhibitors over any remaining wildtype p53.

Question 3

What impact does p53 acting as a tetramer have?

Answer 3

Missense mutations, single aa substitution, which occur most commonly in the DNA binding region of p53 which leads to reduction in wild-type p53 activity.

p53 normally acts as a tetramer so that mutant proteins may also function as dominant negative inhibitors over any remaining wildtype p53.

Question 4

What does the p53 gene actually encode for?

Answer 4

Family of isoforms, cross-talk can occur through protein-protein interactions and this can have a major impact on their biological function.

Question 5

How is p53 regulated by MDM2?

Answer 5

Kept at low levels thought ubiquitylation and proteosomal degradation mediated by MDM2 (murine double minute 2).

MDM2 and p53 act within a negative-feedback loop in which p53 transactivates MDM2 expression.

Question 6

How does p53 provide a barrier to the development of cancer? (brief)

Answer 6

Blocking proliferation or eliminating cancer cells.

p53 is inactivated in 50% of all cancers.

Question 7

What are the ways in which loss of normal p53 function can occur? (4)

Answer 7

1. Mutations to the DNA binding region due to aa substitutions.
2. Mutations that lead to incorrect structure or prevent correct folding or oligomerisation.

3 Mutations that cause overexpression of MDM2 or MDMX.

4. Mutations in upstream regulators that prevent p53 activation.

Question 8

What are three target genes of p53?

Answer 8

Cyclin-dependent kinase inhibitor (p21) - mediates cell cycle arrest at G phase.

GADD45 (growth arrest and DNA-damage-inducible protein 45)

PUMA (p53 up-regulated modulator of apoptosis)

Question 9

What is p21?

Answer 9

Cyclin-dependent kinase inhibitor (p21) is a target gene of p53, it mediates cell cycle arrest at G phase.

Question 10

What is GADD45?

Answer 10

GADD45 ( growth arrest and DNA-damage-inducible protein 45) is a target gene of p53.

Question 11

What is PUMA?

Answer 11

PUMA (p53-upregulated modulator of apoptosis) is a taget gene of p53.

Question 12

What types of cancer have an earlier onset, those with a complete loss of p53 function/expression or those with expression of mutated forms of p53?

Answer 12

Mutated forms have earlier onset.

Many mutant proteins can acquire new oncogenic functions.

Question 13

How can GOF p53 mutants contribute to cancer development?

Answer 13

1. Upregulation of genes involved in cellular growth: p53 mutants can upregulate expression of EGFR.
2. Downregulation of pro-apoptotic receptors: CD95.
3. Promote specific protein activity: NRF2 upregulates anti-apoptotic protein Bcl-2 which prevents cellular apoptosis.
4. Interacting with other p53 family members, suppress p63 and hence its anti-metastasis activity.

Question 14

Receptor upregulated by mutant GOF p53 that can cause cell growth

Answer 14

EGFR

Question 15

Pro-apoptotic receptor downregulated by GOF mutant p53

Answer 15

CF95

Question 16

A protein which GOF mutant p53 can promote

Answer 16

NRF2 causing upregulation of anti-apoptotic protien BCL-2.

Question 17

How can we convert mutant p53 to WT p53?

Answer 17

PRIMA-1 - small molecule, which promotes protein folding of the mutant p53s and restores p53 function.

Addition of zinc, due to TW p53 needing the metal ion zinc to fold correctly. Link this to loss of ZIP1 in prostate cancer and hence more energy.

Question 18

How can we promote the degradation of mutated p53?

Answer 18

It has been demonstrated that MDM2 and CHIP are important for mutant p53 degradation. To be stabilised, mutant p53 interacts with the HSP70 and HSP90 chaperone complex that requires interaction with HDAC6 for proper functioning.

Prevention of HDAC6 binding results in the dissociation of heat shock proteins from mutant p53 and allows for mutant p53 degradation by MDM2 and CHIP.

HDAC inhibitors show promise in destabilising mutant p53 by preventing HDAC6 from interacting with HSP90.

Question 19

In order to be stabilised, mutant p53 must interact with what?

Answer 19

HSP70 and HSP90, both of which need HDAC6.

We can inhibit this via HDAC inhibitors.

Question 20

How can we target mutated p53 regulated pathways, as opposed to mutated p53 itself?

Answer 20

Large numbers of mutant p53s interact with and inhibit the p63 and p73 interaction.

RETRA is a SMI that can destabilise the p73 and mutant p53 interaction.

Question 21

What is RETRA?

Answer 21

Large numbers of mutant p53s interact with and inhibit the p63 and p73 interaction.

RETRA is a SMI that can destabilise the p73 and mutant p53 interaction.

Question 22

What is cyclotherapy with regards to mutant p53?

Answer 22

Normal cells surrounding a tumour can be placed into a transient cell cycle arest by the activation of functioning p53 via MDM2 inhibitors.

p53-mutant tumour cells will be unaffected and continue to proliferate.

Use PLK1 inhibitor, or any other mitotic inhibitor to target these still proliferating cancer cells.

Bypass side effects of normal chemo: hair loss, WBC decrease etc.

Question 23

What is MI888?

Answer 23

Inhibitor of MDM2/MDMX

Question 24

What is RO-2443?

Answer 24

Inhibitor of MDM2/MDMX