Goljan questions on p53

[MudPhud20XX]

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Inactivation of the p53 suppressor gene is associated with which of the following cell cycle alterations?
A. Unrestricted passage of the cell from the G1 into the S phase
B. Decreased synthesis of cyclin D in the G1 phase
C. Inactivation of cyclin D-dependent kinase
D. Decrease in the mitotic rate of the cell
E. Inhibition of the Rb suppressor gene

So A is the answer. C is wrong b/c inactivation of p53 will lead to the activation of cyclin D dependent kinase that will phosphorylate the Rb and allow the cells to enter the S phase right?

Many thanks....

 

[StIGMA]

p53 activation leads to primarily G1 arrest and G2/M arrest (or apoptosis). "A" should be the answer, although "unrestricted" should really be removed from the answer choice. That is not technically correct although it is commonly quoted.

p53 leads to arrest primarily through upregulation of p21 (aka CDKN1A) that inhibits multiple CDK complexes including those that activate cyclin D- so p53 inactivaton would increase cyclin activity, not decrease it.

 

[Psai]

I think cyclin d dependent kinase allows it to keep going through the cell cycle.

 

[seminoma]

I think cyclin d dependent kinase allows it to keep going through the cell cycle.

Yeah, cyclinD/cdk4 is responsible for phosphorylating Rb -> activation of E2F -> cell goes into S phase.