Cancer 4: cellular control 2

Question 1

What is the main controller of the cell cycle?

Answer 1

Control of the entry into the cycle is very important
Thats done by c-myc -its transiently expressed (very quick peak-8h after growth factor)-alawys happen just before S-phase-causes it

multiple genes combine in reality to produce this effect-also C-jun

Question 2

How do RTKL activate and activate other proteins?

Answer 2

dimerise when binding a ligand-autophopshorylate and create docking points to which adaptor proteins will bind-helps create the scaffold on which signalling proteins can bind - moldular structure (and can have

Targetted a lot in cancer-to immediatly stop it-eg: Her2/EGFR

Question 3

Describe Grb2 structure and role?

Answer 3

2SH3 and 1 SH2 (Src homology domain)
SH3-recognise proline rich domains -provides a binding target
SH2-bind phosphorylated tyrosines + specific AA sequence (Grb2-bind EGFR)-

Activates Ras (GTPase) via SOS

Question 4

How does RAS get activated?

Answer 4

its a GTPase-activates when it binds GTP-
self GTPase activity ->GDP and inactivate the protein on its own (resting state-only activated via signalling)

SOS-will facilitate the exchange of GDP for GTP

RAS can be oncogenically activated so that it prevents any inactivation -prevent GAP binding and GTP hydrolysis

Question 5

How do EGFR/GRb/RAs/SOS work together?

Answer 5

EGFR activated-Grb2 adaptor protein binds and SOS can bind GRB2 (via SH3 domain)-this activates it and allows it to help activate Ras
Ras HAS to bind to the memrbrane to be active-so spacially close to SOS -receptor bound

Question 6

What is the role of Ras? what does it activate and cause?

Answer 6

Ras is bound to the plasma membrane-activates kinases (recruit) –ERK/MAPK (starts with raf (MAPKKK), MEK (MAPKK)-ERK (MAPK) => MAPK will then either change protein activity or gene expression
-> includes c-myc

Myc and Ras are common oncogenes

Question 7

What are Cyclins (and role in cell cycle)?

Answer 7

Cdk’s are cyclin depedent kinases
cyclins are the main regulatory element-transiently epxressed (and destroyed) –different cyclin/Cdk complexes will trigger different effects
eg: 1 mitotic cyclin will bind to Cdks to start M-phase
Leaves at G1
Then before S phase, another Cyclin binds Cdks and initates cel cycle

Question 8

How do cyclins induce actiavtion of CDks? When?

Answer 8

CDK1 for ex: Binds cyclin B-forms inactive MPF-then be phosh by CDk activating cascade (CAK) AND Wee1 inactivating
d (BOTH)
and then cdc25 phosphatase, when active, removed the Wee1 inhbitory phosphae-activating the complex

also feedback loop from activated MPF-upregulated Cdc25 topush forward

Signals from fully attatched kinetochores cause cyclin B to be degrades-CDk1 inactivated,-then mitosis is allowed to progressed

the cyclins also change how the Cdks bind targets-so depending on which cycling bound ckds-different downcellular targets

Question 9

how does EGFR signalling activate cyclin production?

Answer 9

c-myc production will lead to production of Cyclin D-and start the process of G1 (leaving Go) -promote entry to cell cycle

Question 10

How does cyclin levels/Cdk activity change during a cell cycle?

Answer 10

G1-c-myc production-> at end Cdk4+CyclinD peak-
S phase-CDK2+Cyclin E -peak nearly all through out
Middle of S to mitosis-CDK2+A (slow rise and peak during metaphase)
then during all of mitosis-peak-Cdk1+Cyclin B

All activation require the previous one to be activated-

Question 11

How is the timing for Cdk activation regulated?

Answer 11

Cdks and cyclins can bind to form MPF as soon as produced, but are only activated when right phosph
Different cyclins (eg: CyclinB+Ckd1)-will target proteins that lead to cell wall degradation
Or activation of retinoblastoma (RB)
Rb-naturally active binds E2F-stops e2F from working-
when cell proliferates, CDK4+ cyclin D ->inactivates Rb protein-releases E2F-> increase gene expresssion (like cyclin E)

Question 12

How does retinoblastoma protein regulate the cell cycle? What genes end up expressed

Answer 12

in activation of retinoblastoma (RB)
Rb-naturally active binds E2F-stops e2F from working-
when cell proliferates, CDK4+ cyclin D ->inactivates Rb protein-releases E2F-> increase gene expresssion (like cyclin E)

E2F-also actiavtes many oncogenes, cell cycle and DNA synthesis => important to not have bad regulated

Each MTF will inactivate/phospho pRB-whcih releases E2F
Cdk4+D activates first, then when E+Cdk2 active-rephosph pRB-release more E2F- then Cdk2+A-more and more

Question 13

how are Cdk’s downregulated? What types of these are there?

Answer 13

can be deactivated
but also inhbitors-CKD inhbitors (CKI) -binds the whole MTF complex and hold it inactive

2 CKI family-INK4 (g1 phase CKI-displace Cyclin D) and the CIP/KIP family (S Phase CKI-inhbit by binding whole Cdk/Cyc complex))

must be degraded to allow cycle progression

Question 14

So what kind of mutations of cell cycle proteins cause cancer?

Answer 14

Loss of p16 (a CKI) is quite often lost in cancer (like pancreas)-
Overproduction of CDk4/CycD- 50% of breast cancer, 90% mantle cell lymphomas
Loss of pRB-80%small cell lung cancer/and non small cell

Its oncogenes-HER2/Ras/Cyclin D1/bRaf/Cmyc-overexpressed => but can be inhbited therapeutically-at least in theory

Or tumour supressing genes (Rb, P27/CKI)-downregulatory
harder to replace