P21 DISRUPTS THE INTERACTION BETWEEN CDK2 AND THE E2F-P130 COMPLEX

In nonproliferating or growth-arrested cells, the transcription factor E2F remains bound to the retinoblastoma-related protein p130. Accumul ation of this E2F-p130 complex correlates with an arrest of the cell c ycle progression. Progression through G(1) phase is associated with a cyclin-dependent binding of the cyclin-dependent kinase cdk2 to the E2 F-p130 complex. By fractionating mouse L-cell extracts, we have obtain ed a partially purified preparation of the E2F-p130 complex that also contains cdk2. Incubation of this complex with recombinant p21 results in a disruption of the interaction between cdk2 and the E2F-p130 comp lex. We have also analyzed the interaction between cdk2 and the E2F-p1 30 complex in extracts of a cell line that expresses a temperature-sen sitive mutant of p53. Incubation at the permissive temperature (32 deg rees C) results in an induction of p21 synthesis. An increase in the l evel of p21 in these cells correlates with a loss of cdk2 from the cdk 2-containing E2F-p130 complex. We also show that the expression of a r eporter gene containing E2F sites in the promoter region is reduced by the coexpression of p21. Since p21 is believed to be a mediator of p5 3, we speculate that the p21-mediated disruption of the cdk2-containin g E2F-p130 complex plays a role in the growth suppression function of p53.