Lecture 16 & 17 (TSGs)

Question 1

2 best studied tumour suppressor proteins

Answer 1

Rb and p53

Question 2

What happens when tumour suppressor proteins are implicated in cancer?

Answer 2

They have lost their function - no longer able to negatively control cellular growth

Question 3

Many tumourigenic DNA viral oncoproteins sequester…

Answer 3

Rb and p53

Question 4

Tumorigenic DNA viral oncoproteins that interact with Rb (under-phosphorylated)

Answer 4

• SV40 large T
• Adenovirus E1A
• HPV E7 antigen

Question 5

Tumorigenic DNA viral oncoproteins that interact with p53

Answer 5

• SV40 large T
• Adenovirus E1B55K
• HPV E6 antigen
• EBNA-1

Question 6

How does Rb negatively control cellular growth?

Answer 6

• by repressing expression of genes that stimulate cell proliferation through its ability to bind E2F transcription factors & inhibit their activity
• by activating expression of genes that inhibit proliferation

Question 7

Two Rb-related proteins

Answer 7

p107 and p130 (pocket proteins)

Question 8

Where do most mutations which inactive Rb occur?

Answer 8

in its pocket region

Question 9

Rb pocket domains shown strong homology to which 2 general transcription factors?

Answer 9

TBP and TFIIB

Question 10

How can transcriptional regulation by Rb be mediated?

Answer 10

1. E2F (transcriptional activator)
2. ATF (nuclear oncoprotein)
3. RCE (retinoblastoma control element) sites

Question 11

What transcription factor is implicated in Rb control of transcription from RCE sites?

Answer 11

SP-1

Question 12

How does Rb function in terminal differentiation of muscle cells?

Answer 12

by preventing binding of MyoD dimers to DNA

Question 13

The overall structure of the Rb protein depends on its __ state

Answer 13

phosphorylation

Question 14

Most frequently implicated gene in human cancers

Answer 14

p53 (found inactivated - deleted/mutated)

Question 15

p53 is a nuclear transcription factor that’s particularly active in response to…

Answer 15

cellular stress

Question 16

Normal function of p53

Answer 16

To sense if problems are occurring within the cell (e.g. if there’s extensive nucleic acid damage, p53 will induce expression of genes involved in DNA repair and if this is unsuccessful, p53 will induce expression of genes involved in apoptosis)

Question 17

p53 functions as a __ and is subject to __

Answer 17

tetramer
phosphorylation

Question 18

~50% of ovarian cancer tumours have a __ mutation

Answer 18

p53

Question 19

Motif for p53 binding

Answer 19

5’ Pu-Pu-Pu-C-(A/T)-(A/T)-G-Py-Py-Py 3’

Question 20

4 domains of p53

Answer 20

• N-terminal transactivation domain
• DNA-binding domain (contains a zinc ion)
• Oligomerisation domain
• C-terminus regulatory domain

Question 21

How many different promoter regions can p53 bind?

Answer 21

~300

Question 22

p53 is normally present in __ levels in cells

Answer 22

low

Question 23

p53 is typically bound to __ , which regulates its turnover

Answer 23

MDM2

Question 24

Examples of events that will lead to the activation of p53

Answer 24

• lack of nucleotides
• UV radiation
• ionising radiation
• oncogene signalling
• hypoxia
• metabolic stress
• blockage of transcription

Question 25

How does MDM2 regulate p53 turnover?

Answer 25

MDM2 expression is controlled by p53 (auto-regulatory loop). When MDM2 is expressed, it will associate with p53 and flag it for degradation. If problems arise within the cell, MDM2 will separate from p53 to liberate p53 activity.

Question 26

What is MDM2?

Answer 26

a ubiquitin ligase

Question 27

Activation of which kinases (due to DNA damage) leads to p53 phosphorylation, preventing it from binding to MDM2?

Answer 27

ATM and DNA-PK

Question 28

Examples of stress-activated kinases that perturb p53/MDM2 association

Answer 28

- ATR - Casein kinase II

Question 29

Activated oncogenes such as Ras can induce the activity of another tumour suppressor protein called __ , which can bind MDM2

Answer 29

p14 ARF

Question 30

3 ways to prevent p53 degradation by MDM2

Answer 30

- activated kinases - activated oncogenes - auto-regulatory loop

Question 31

p53 elicits cell cycle arrest in response to DNA damage through transcriptional induction of a gene called __

Answer 31

p21

Question 32

What does p21 inhibit?

Answer 32

several cyclin-CDK complexes

Question 33

p53, p21 and __ act together to sense DNA damage, halt cell cycle and repair DNA

Answer 33

PCNA

Question 34

What is NF-1?

Answer 34

a GTPase activating protein (GAP) for Ras

Question 35

NF-1 is __ when it's implicated in cancer (neurofibromatosis)

Answer 35

inactivated (unable to stimulate Ras to hydrolyse GTP)

Question 36

How can overexpression of Rev-1 reverse Ras-induced transformation?

Answer 36

believed to do so by abortively sequestering Ras effector proteins like Raf and PI3K

Question 37

Genes implicated in hereditary breast and ovarian cancer (HBOC) syndrome

Answer 37

BRCA1 and BRCA2

Question 38

Tumour suppressor protein implicated in many colorectal cancer cases

Answer 38

APC

Question 39

What is PTEN?

Answer 39

a phosphatase that dephosphorylates PIP3 back into PIP2