Mechanisms of G2 arrest in response to overexpression of p53

Overexpression of p53 causes G2 arrest, attributable in part to the loss of CDC2 activity. Transcription of cdc2 and cyclin BI, determined using repor ter constructs driven by the two promoters, was suppressed in response to t he induction of p53. Suppression requires the regions -287 to -123 of the c yclin B1 promoter and -104 to -74 of the cdc2 promoter. p53 did not affect the inhibitory phosphorylations of CDC2 at threonine 14 or tyrosine 15 or t he activity of the cyclin-dependent kinase that activates CDC2 by phosphory lating it at threonine 161. Overexpression of p53 may also interfere with t he accumulation of CDC2/cyclin B1 in the nucleus, required for cells to ent er mitosis. Constitutive expression of cyclin B1, alone or in combination w ith the constitutively active CDC2 protein T14A Y15F, did not reverse p53-d ependent G2 arrest. However, targeting cyclin B1 to the nucleus in cells al so expressing CDC2 T14A Y15F did overcome this arrest. It is likely that se veral distinct pathways contribute to p53-dependent G2 arrest.