18. Molecular Sensors Detecting DNA Damage And Completion Of DNA Replication During The Cell Cycle

Question 1

DNA damage inhibits which components

Answer 1

-G1/S, S, M-cdk
Unreplicated DNA inhibits M-cdk
-activation prot. Kinase ATR(Ataxia Telangiectasia and Rad3 related prot); activated by dsDNA breaks, ATR (Ataxia Telangiectasia Mutated); responding to a variety of DNA dmg most likely in a ssDNA
-p53 inducing p21 WAF1 which inhibits all cdk-cyclin complex
-TGF beta

Question 2

P53 domain structure

Answer 2

N-TransActivation Domain(TAD)-Proline rich domain(PRD)-DNA binding domain(DBD)-Nuclear localization signal(NLS)-Tetramerization domain(TET)-C terminal domain(CTD)-C

TAD : where corepressor & coactivator can attach to turn the whole structure into repressor or activator
TET : check if other transcription fawctors has arrived as well in order to form tetramer and it has also Nuclear Export Signal (NES) which allows p53 to go out of nucleus to cytosol

Question 3

Post translational modification of p53

Answer 3

Inactive p53 is rapidly degraded in the cytoplasm (5~20min)
phosphorylation and other modification of p53 in response to DNA damage greatly increase its ability to activate transcription of specific genes that help the cell cope with DNA dmg.
-Ser/Thr kinase(e.g. Chk1,2, ATM, ATR, PKC,PKR,AMPK..) phosphorylate TAD and CTD, which hinders MDM2 domain and prohibits p53 ubiquitination & also hides NES of TET
-phosphorylations favors p300 and P300 (transcriptional coactivator histone acetyl transferase) that not only acetylates histone but also acetylates NLS(exposing) and CTD of p53
-MDM2 (ubiquitin ligase/ E3 ligase having ring domain) binds to TAD and polyubiquitinates CTD which decreases the half-life drastically

*after p300 acetylation, activated p53 protein forms stable DNA associated homotetramer and transcript MDM2 (self regulation; neg. feedback)

Question 4

Affect of accumulation of p53 upon stress

Answer 4

Cell cycle arrest
Apoptosis induction
Enhanced DNA repair
Reinforced antioxidant defense
Hindered vascularization
Senescence
MDM2

Question 5

Affect of TGF beta as an inhibitor of proliferation

Answer 5

Inducing p15, p21, p27

Lowering production of cdk4, cdc25, c-Myc (stopping G1 phase)