lecture 15- cell checkpoints 1

Question 1

what is the point of cell cycle checkpoints

Answer 1

only allow cells to proceed if prerequisite step has been completed

Question 2

what are the 5 checkpoints of the cell cycle

Answer 2

R- growth vs. G0

G1/S- entrance to S blocked if genome damaged

S checkpoint - DNA replication halted if genome is damaged

G2/M checkpoint - entrance to M blocked if DNA replication not completed

spindle checkpoint - anaphase blocked if chromatids not assembled

Question 3

how can cancer cells replicate if there are checkpoints stopping them

Answer 3

have one or more checkpoints inactivated

Question 4

what is pRb

Answer 4

retinoblastoma protein- governor of R point

Question 5

what occurs when pRb is activated

Answer 5

unphosphorylated
E2Fs bound
cells dont go through R point

Question 6

what occurs when pRb is deactivated

Answer 6

early/ mid G1 -> cyclin D cdk 4/6 initiate phosphorylation

hypopolarisation occurs which is necessary but not sufficient

cyclin E cdk 2 mediate hyperphosphorylation

E2Fs released

transcription of genes mediating G1/S transition

Question 7

what happens to E2Fs in s phase

Answer 7

cyclin A / CDK2 target them for ubiquination

Question 8

how is positive feedback shown in pRb

Answer 8

E2Fs promote cyclin E transcription

Cyclin E/ CDK2 mediate phosphorylation if own inhibitor (p27 kip)

Question 9

what are the 3 ways pRb can be inactivated in cancer

Answer 9

Rb1 mutations -> no protein expressed (retinoblastomas)

deregulated phosphorylation -> E2F removed (breast cancer/melanoma/colon)

viral protein interaction -> displaces E2F (cervical)

Question 10

what does cyclin D/E overexpression cause

Answer 10

pRb phosphorylation and inactivated

cell proliferation

Question 11

what is palbociclib

Answer 11

CDK 4/6 inhibitor
competes with ATP
inhibits breast cancer cell growth but not normal growth

Question 12

how can resistance to palbociclib occur

Answer 12

activation of upstream effectors

inactivating mutations in pRb

overexpression of CDK6

bypass pathways (cycline E/CDK2)

Question 13

why is the cyclin E pathway activated in resistance to palbociclib

Answer 13

treatment causes increased c myc
this increased cyclin E levels

Question 14

what are the three different ways to inhibit CDKs

Answer 14

just CDK inhibitor

multiple CDK inhibitor

drug combinations

Question 15

describe the drug combinations used to inhibit CDKs

Answer 15

taxol ( DNA damaging chemotherapy) followed by palbociclib reduces pancreatic cell growth

NOT P of P->T

Question 16

what is the DNA damage response

Answer 16

network of signalling pathways which monitor DNA integrity

Question 17

how are DDRs related to cancer

Answer 17

DDR inactivation is a hallmark of cancer

but the cancer relies on what is left of the DDR to survive

Question 18

What two components is DDR controlled by

Answer 18

ATM and ATR

ATM- activated by double strand breaks
activates G1/S checkpoint

ATR - activated by single strand breaks
mediates S and G2/M checkpoints

Question 19

what is WEE1 activated by and what does it activate

Answer 19

CDKs
activates S and G2/M checkpoints

Question 20

what is replicative stress

Answer 20

slowing of replication forks

Question 21

what is replicative stress caused by

Answer 21

activation of oncogenes ->stimulates G1/S transition -> premature S stimulation

inactivation of TSGs -> promote G1/S transition

Question 22

what is CHK1 and what is it activated by

Answer 22

cell cycle checkpoint kinase 1

activated by ATR

Question 23

How can CHK1 be used to target neuroblastomas

Answer 23

in neuroblastoma -> MYC overexpression -> replicative stress -> ATR-CHK1 response

CHK1 is expressed at higher levels in MYCN amplified tumours compared to normal tumours

so we can develop CHK1 inhibitors

Inhibiting CHK1 in stressed neuroblastoma cells → accumulated DNA damage → apoptosis.