Lecture 9

Question 1

What is the “double action” of E2F?

Answer 1

It’s a transactivator and repressor

Question 2

What’s RB’s relationship to E2F?

Answer 2

RB represses E2F

Question 3

What kind of gene is RB?

Answer 3

A tumor suppressor

Question 4

How is RB inhibited?

Answer 4

When Cyclin D is bound to CDK1, CDK1 phosphorylates RB, preventing it from binding E2F, activating E2F

Question 5

What does p16 do in the RB-E2F pathway?

Answer 5

p16 inhibits CDK r/6’s phosphorylation/inhibition of RB, allowing RB to inhibit E2F

Question 6

What’s unique about RB?

Answer 6

RB is the first tumor suppressor gene which causes hereditary(tendency) tumors

Question 7

What is LOH?

Answer 7

Loss of Heterozygosity - when cell divides, both mutated copies go to the same daughter cell

Question 8

Why does Rb lead to retinoblastoma and usually not another type of cancer?

Answer 8

Theory is that the eye has fewer protective mechanisms - can’t die in response to damage, we need those cells

Question 9

Where are E1A and E1B found?

Answer 9

in adenoviruses

Question 10

Where are E7 and E6 found?

Answer 10

In HPV

Question 11

What does Large T do?

Answer 11

It’s a SV40 protein that inhibits RAB and p53

Question 12

What are the 3 ways to activate E2F?

Answer 12

RB phosphorylation by CDK4/CyclinD, RB mutation, E1A binding RB

Question 13

What are 2 permanent ways to activate E2F?

Answer 13

RB mutation, E1A

Both are pathological

Question 14

What does permanent activation of E2F cause?

Answer 14

Unlimited Proliferation, Cancer

Question 15

What would be a cure for a tumor caused by loss of RB?

Answer 15

Loss of E2F

Question 16

In general, what is E2F?

Answer 16

A sequence-specific transcription factor

Question 17

3 categories of E2F-regulated genes

Answer 17

1. DNA synthesis
2. Nucleotide Metabolism
3. Origin of Replication

Question 18

Ribonucleotide reductase

Answer 18

Turns RNA nucleotides to DNA nucleotides

Question 19

What does E2F co-regulate?

Answer 19

Multi Subunit complexes

Question 20

What type of multisubunit complexes does E2F coregulate?

Answer 20

Related to DNA replication

Question 21

What does RB bind other than E2F?

Answer 21

Proteins that modify histones and cause compression of DNA

Question 22

How does E2F act as a “two-faced” transcription regulator?

Answer 22

It’s an activating transcription factor and a DNA-binding subunit of a repressor.

Question 23

E2F family structure *7 domains

Answer 23

DNA binding domain
Transactivation domain
Dimerization domain
Cyclin A binding domain
NLS
NES
RB family binding

Question 24

E2F is active as a

Answer 24

Heterodimer

Question 25

What are p107 and p130?

Answer 25

Part of RB family, bind E2F and repress

Question 26

What’s the difference between pRB and p107/p130?

Answer 26

pRB binds activating E2Fs, p107 and p130 bind repressing E2Fs

Question 27

p107 and p130 are unable to

Answer 27

Replace pRB in the case of pRB inactivation in cancer

Question 28

What is DP?

Answer 28

Dimerization Partner - E2F creates dimers with other E2Fs, can be other types from the same family

Question 29

Cyclins controlled by E2F

Answer 29

Cyclins A and E

Question 30

Steps of the cell cycle

Answer 30

G0
G1
S
G2

Question 31

What states is E2F in throughout the cell cycle? (bound to which proteins, and low or high promoter activity)

Answer 31

G0-early G1:
Bound to RB and DP , low level promoter activity

Late G1-early S: Bound to DP, high level of promoter activity

Late S-G2: Bound to DP, low level of promoter activity

Question 32

What causes low levels of E2F promoter activity later in the cell cycle?

Answer 32

After E2F is active and has upregulated Cyclin A, Cyclin A/CDK2 binds E2F, phosphorylating DP and lowering E2F’s affinity to DNA

Question 33

Why do E2F need a NLS?

Answer 33

They’re transcription factors, work in the nucleus

Question 34

NES

Answer 34

Nuclear Export Signal

Question 35

Why does E2F expression go up and then down?

Answer 35

When there’s a lot of E2F not bound to RB, bind the promoters for E2F.

Question 36

What are E2F 4 and 5?

Answer 36

Repressors

Question 37

How are E2F 4 and 5 Regulated?

Answer 37

Localization - during G0 and early G1 are in nucleus. At restriction point, go out to cytoplasm for rest of cycle.

Question 38

At what levels are E2F 4 and 5 expressed throughout the cell cycles?

Answer 38

constant level

Question 39

which E2Fs have NLS and which have NES?

Answer 39

4,5 have NES, 1,2,3 have NLS

Question 40

How do E2F4,5 get to the nucleus without a NLS?

Answer 40

They’re bound to p107/p130 (Rb’s “cousins”) which do have NLS

Question 41

What activates E2F7 and 8?

Answer 41

E2F 1,2,3

Question 42

Which E2Fs close the transcription of E2F?

Answer 42

E2F7,8

Question 43

E2F activates what kind of genes?

Answer 43

Proliferation (G1/S transition)

Apoptosis (p53-dependent and independent)

Question 44

Why does E2F have 2 opposite jobs?

Answer 44

A built-in cancer mechanism - same transcription factors that induce proliferation will induce apoptosis if they are deregulated