Lecture 7

Question 1

What is PTEN?

Answer 1

A tumor suppressor protein

Question 2

When is the loss of PTEN not a problem?

Answer 2

When EGF (a growth signal) is gone

Question 3

What can an EGFR mutation lead to?

Answer 3

To an oncogene, whjch signals without needing EGF binding

Question 4

What is the Knudson’s two-hit hypothesis?

Answer 4

When you need a mutation in both TSG for it to lead to cancer

Question 5

Why is familial cancer different then normal cancer?

Answer 5

Familial cancer is more frequent and occurs earlier as there is only one additional mutation needed

Question 6

What is haploinsufficieny?

Answer 6

Some TSG only need one mutation, eg p53

Question 7

Which cancers belong to the proteins RB1, p53, APC and BRCA

Answer 7

RB1 = retinoblastoma
p53 = Li-Fraumeni
APC = colorectal cancer
BRCA = breast and ovarian cancer

Question 8

How can E2F be released from Rb?

Answer 8

Release via phosphorylation

Question 9

What is E2F needed for?

Answer 9

For transcription

Question 10

Which factors can lead to no cell cycle regulation (by E2F)?

Answer 10

When pRB is lost, when there is a mutation in the pocket region of pRB, hyperphosphorylation of pRB (common) and binding of an oncogene virus to pRB

Question 11

What are upstream activators of p53?

Answer 11

There is deregulation: eg DNA damage, oncogene activation and cell stress (are sensors)

Question 12

What are downstream effects of p53?

Answer 12

There is restauration or suicide: eg cell cycle arrest, DNA repair, apoptosis, inhibit angiogenesis (are effectors)

Question 13

What does p53 do to work?

Answer 13

It has to form tetrameres

Question 14

Which four domains can be found in a p53 gene?

Answer 14

Tetramerization domain, DNA binding domain (promoter), transactivation (transcription) and MDM3 (inhibits p53) domain and regulatory domain (cofactor binding)

Question 15

What is the effect of p53 binding to MDM2?

Answer 15

It drives the export of p53 out of the nucleus, then ubiquitination and degradation of p53, so usually p53 has lower levels

Question 16

What drives the expression of MDM2?

Answer 16

p53

Question 17

What is the effect of stress on p53?

Answer 17

It leads to production of more p53, which has a fast and strong effect and eventually there will also be more MDM2

Question 18

What happens after DNA damage and cell stress?

Answer 18

Kinases are activated, which phosphorylate p53 to dislodge MDM2

Question 19

What happens after oncogene activation?

Answer 19

This activates molecules that bind to MDM2 with a higher affinity than p53, which frees p53

Question 20

How does p53 introduce cell cycle arrest?

Answer 20

By binding of p53 to p21, which binds to a cyclin inhibitor, which binds to pRB. This means that pRB cannot be phosphorylated, thus E2F cannot be released

Question 21

How does p53 introduce intrinsic apoptosis?

Answer 21

It releases cytochrome c from the mitochondria and suppresses anti-apoptotics (eg BCL2)

Question 22

How does p53 introduce extrinsic apoptosis?

Answer 22

Via FasL

Question 23

What other molecule does p53 work on?

Answer 23

miRNA

Question 24

Which p53 factors target gene selectivity?

Answer 24

Amount, modification, co-factor of promoter or p53

Question 25

How does the difference in promoter binding affinity influence the gene selectivity?

Answer 25

eg p21 has a high affinity for p53, anti-apoptotics have a low affinity

Question 26

How do cofactors binding to the promoter influence the gene selectivity?

Answer 26

By eg MIZ-I binding to the promoter of p21

Question 27

How do cofactors binding to p53 influence the gene selectivity?

Answer 27

ASPP binds to p53 and increases the affinity for pro-apoptotic promoters

Question 28

What is the function of Myc oncogenes (in cancer) do to prevent p53 activation?

Answer 28

It binds to MIZ-I with a higher affinity than p53

Question 29

In which domain can about 90% of the mutations be found?

Answer 29

In the DNA binding domain

Question 30

What other way is there to prevent p53 apart from mutations?

Answer 30

By inhibiting other proteins, either endogenous or viral

Question 31

What is a dominant negative p53 mutation?

Answer 31

This mutated p53 can form a tetramer with the WT, but when one mutated protein is in the tetramer it becomes transcriptionally inactive. There is p53 accumulation, as less MDM2 is produced

Question 32

What is a gain-of-function mutation in p53?

Answer 32

p53 binds to promoters that contribute to carcinogenesis and it activates them

Question 33

What does the viral DNA do with Rb and E2F

Answer 33

One protein inhibits RB + release of E2F and a second protein blocks p53, so it cannot go into cell cycle arrest and produce new viral DNA

Question 34

Which proteins of HPV inhibit what?

Answer 34

E7 inhibits RB, E6 inhibits p53

Question 35

Which proteins of Adenovirus inhibits what?

Answer 35

E1A inhibits RB, E1B inhibits p53

Question 36

What is needed for the maintenance of cancer?

Answer 36

The continues inhibition of p53

Question 37

How can p53 be used for cancer treatment?

Answer 37

Restoring the activity of p53

Question 38

Which ways are there of using p53 activity as treatment?

Answer 38

Introducing functional p53, restore protein conformation, oncolytic adenovirus introduction, inhibitor of MDM2

Question 39

What is the problem with the introduction of functional p53?

Answer 39

It is hard to introduce it into all the cancer cells

Question 40

Which molecules can be used to restore protein conformation?

Answer 40

PRIMA-1 or APR-246

Question 41

How can oncolytic adenovirus be used to restore p53 activity?

Answer 41

It is introduced without E1B, so it will not kill normal cells, but it will cancer cells

Question 42

How can an inhibitor be used to restore p53 activity?

Answer 42

MDM2 binds to the inhibitor (eg nutlin) when p53 is still active