Cell Cycle 5 Flashcards
When was p16 discovered?
1993
How did they discover p16?
2 yeast hybrid with cdk4
What is the structure of p16?
4 Ankyrin repeats
What are family members of p16?
p15, p18, p19
What mutation made p16 unable to bind?
P114L
R87P
What happens when p16 bind cdk (structurally)?
Rotation of beta strand (N) lobe by 15˚. Misaligns ATP binding site that lies between C and N lobes
Why is p16 a potent inhibitor of cell cycle?
p16 displaces p21, p27 and p57 which can thenbind other cdks/cyclins
Can p16 promoter be methylated?
Yes - to silence it
p16 is promoter methylated or deleted in 20% of cancers
Give an example of oncogene induced senescence?
Injection of Ras isn’t proliferative because it activates expression of p16 - halting proliferation
What is replicative senescence?
DDR (arrest) induced because of shortening of telomeres
What is the nucleotide telomere sequence repeat?
TTAGGG
Why do cancerous cell not under replicative senescence?
Have telomerase action, or homologous recombination 10% of the time.
How many bases are typically lost in replication?
50/200
How long is the average telomere?
5-25Kb in humans
What healthy endogenous cells have telomerases?
Germline cells and stem cells
Why do most somatic cells not require telomerases?
They do not replicate
Are we pombe cells?
We are not - they have circular DNA and so do not require telomerases
Why were ciliated protozoa key in discovery of telomerases?
They have many small chromosomes and can’t not go into replicative senescence because they are single celled organisms
What is the catalytic domain of telomerase?
hTERT
How does telomerase work?
Uses RNA strand to catalyse the addition of DNA to the other DNA strand. DNA polymerase fill in the other strand
Why is the replicative senescence 6-9 days after addition of telomerase inhibitor peculiar?
Would not expect telomer to be a at a critical length after 6-9 replications, hence telomerase must affect some other pathway
What is the function of AZT?
Thymidine analogue - has no -OH 3’ and so can not be extended - prevents action of telomerase
What are the side affects of AZT?
Infertility, reduced blood circulation (stem cells unable to replenish)
Other than telomerase, how can telomeres be maintained in cancer?
ALT pathway (homologous recombination)
