The cell cycle II

Question 1

What cyclin/CDK pairs controls G1?

Answer 1

Association of D-type cyclins (D1, D2 or D3) with CDK4 and CDK6

Question 2

What cyclin/CDK pairs controls G1 after the R point?

Answer 2

E-type cyclins (E1 and E2) with CDK2

Question 3

What does cyclin E/CDK2 mediate?

Answer 3

The phosphorylation of substrates required for ENTRY into the S phase

Question 4

What cyclin/CDK pairs controls the beginning of S phase?

What mediates S phase later on?

Answer 4

A-type cyclins (A1 and A2) replace cyclin E in complex with CDK2

Cyclin A/Cdc2 later on in S phase

Question 5

What is Cdc2 also known as?

Answer 5

CDK1

Question 6

What cyclin/CDK pairs controls G2?

Answer 6

B-type cyclings with Cdc2 (CDK1)

Question 7

What does cyclin B/Cdc2 trigger?

Answer 7

Mitosis

Question 8

What is the G0 –> G1 transition mediated by?

Answer 8

Cyclin C/CDK3 complex

Question 9

Describe the levels of cyclin E in G1

Answer 9

Low during most of G1

Rapid increase after the R point

Question 10

When do cyclin A levels increase?

Answer 10

In concert with entrance to the S phase

Question 11

What happens to cyclin B levels in the cell cycle?

Answer 11

Increases with anticipation into mitosis

Levels drop once mitosis has finished

Question 12

How do cycling levels decrease?

Answer 12

Degradation of the protein by ubiquitination

Question 13

What ensures that the cell cycle only occurs in one direction?

What is the exception to this?

Answer 13

Cyclins GRADUALLY accumulate and are RAPIDLY degraded

Cyclin D is the exception - levels don’t change during the cell cycle

Question 14

How is cyclin D regulated?

Answer 14

By EXTRACELLULAR signals:

1) Growth factors
2) Integrin-mediated ECM attachment

Question 15

What is the function of cyclin D?

Answer 15

To convey messages from the EXTRACELLULAR environment to the CELL CYCLE CLOCK

Question 16

Where is the cell cycle clock present?

Answer 16

In the NUCLEUS

Question 17

How does cyclin D achieve its function?

Answer 17

Cyclin D is synthesised in the cytoplasm and transported to the nucleus (where the cell cycle clock is present)

ONLY when the environment is right to undergo CELL PROLIFERATION

Question 18

How does cyclin D fluctuate?

Answer 18

NUCLEAR cyclin D fluctuates (but the amount of cyclin D in the cell doesn’t)

Question 19

What occurs in G1, before the R point?

Answer 19

Cells asses their environment and decide if the environment is right to divide or not

Question 20

What is the decision to divide or not in G1 taken by?

Answer 20

Controlling the activity of cyclin D

Question 21

What happens is cyclin D goes into the nucleus in G1?

Answer 21

It associates with CDK4/6 and triggers the cells THROUGH the R point

Question 22

What happens if cyclin D is not localised in the nucleus in G1?

When might this happen?

Answer 22

Cell cycle cannot proceed

In the ABSENCE of GF
When the cell is not attached to the ECM

Question 23

What is the only cyclin that is regulated by extracellular signals?

Answer 23

Cyclin D

Question 24

What are the cyclins NOT dependant on after the R point?

What are they dependant on instead?

Answer 24

NOT dependant on extracellular signals

Dependant on autonomous, intracellulr signals

Question 25

What do cyclin/CDKs activate? Inhibit? What does this ensure?

Answer 25

Active the formation of the complexes in the subsequent phases Inhibit the complexes in the previous phase Ensures that the cell cycle only occurs in 1 direction

Question 26

What activates cyclin A? What does cyclin A do following this activation?

Answer 26

Activated during the G1/S phase by cyclin E/CDK2 Replaces cyclin E in the complex and leads to the inactivation of cyclin E Cyclin A-CDK2 complex then ACTIVATES the cyclin B/Cdc2, which inactivates the synthesis of cyclin A

Question 27

What are CKIs?

Answer 27

CKD inhibitors

Question 28

How many CKIs are there?

Answer 28

7

Question 29

What are the 2 groups of CKIs? What are the members of these groups?

Answer 29

1) CKIs that inhibit the cyclin D/CDK4/6 complex but has NO activity towards the other complexes (4 x INK4 proteins) 2) CKIs that inhibit the other cyclin/CDK complexes (E,A, B) but has no activity towards cyclin D (P57^Kip2, P27^Kip1 P21^Cip1)

Question 30

What does TGFb play a role in? How?

Answer 30

The pathogenesis of many carcinomas Plays a different role in the different stages of cancer: Early stages - Arrests the growth of many cell types Late stages - Contributes to tumour invasivness and metastasis

Question 31

What does TGFb control?

Answer 31

- Cell growth - Cell differentiation - Apoptosis - Cellular homeostasis

Question 32

What is the process of TGFb superfamily signalling?

Answer 32

1) Ligand binds type II receptors 2) Recruits type I receptor which DIMERISES and activates type II 3) Type II phosphorylates type I and leads to the overall activation of the receptor 4) Activated receptor phosphorylates specifics receptor-regulated SMAD proteins (r-SMADs) , which recruits SMAD4 (coSMAD) to form a complex 5) This complex acts as a TF and translocates into the nucleus to regulate gene expression

Question 33

What are the genes that are controlled by the R-SMAD/coSMAD complex? What does this cause?

Answer 33

CDI: - Strongly INCREASES levels of P15^INK4B - Causes the inhibition of cyclinD/CDK4/6 - Cells don't reach the R point - Cells don't proliferate - Weakly induces p21^Cip1

Question 34

When is P21^Cip1 more strongly induced by TGFb signalling? What does this cause? Why?

Answer 34

Upon DNA damage Inhibition of most cyclin/CDK complexes - to HALT the cell cycle whilst repair takes place

Question 35

How do GF/mitogenic factors promote the advancement of the cell cycle? Process?

Answer 35

They MUTE the action of CKI: - Bind to the receptors - Activate the P13 pathway - Leads to the activation of Akt (PKB) 1) Akt/PKB phosphorylates p21^Cip in the NUCLEUS, causing its translocation to the cytoplasm 2) Akt/PKB phosphoylates p27^Kip in the CYTOSOL, PREVENTING the translocation to the nucleus - p27 and p21 cannot function in the cytosol - cyclin-CDK complexes can trigger the progression of the cell cycle (not blocked)

Question 36

How can the effect of Akt/PKB be seen in the cell?

Answer 36

When they are stained with an antibody marker

Question 37

What is seen in constitutively active Akt/PKB?

Answer 37

Most p21^Cip is in the cytosol No blockage of cyclin-CKD complexes

Question 38

What is seen in dominant-negative Akt/PKB?

Answer 38

Most p21^Cip in in the nucleus Blocks cyclin-CDK complexes

Question 39

What is the difference between patients that have breast cancer that have P27^Kip in the nucleus or in BOTH the nucleus and the cytoplasm?

Answer 39

In the nucleus - Higher survival rate In the nucleus and the cytoplasm - Lower survival rate

Question 40

In patients with breast cancer, what does Akt activation correlate with?

Answer 40

Cytoplasmic p27^Kip No blockage of cell growth

Question 41

What can the localisation of p27^Kip be used as? BUT, what doesnt this mean?

Answer 41

A prognostic marker to identify which kind or tumours are more likely to progress and become more aggressive DOESN'T mean that cytoplasmic p27^Kip causes breast cancer