Involvement of the interaction between p21 and proliferating cell nuclear antigen for the maintenance of G(2)/M arrest after DNA damage

Although a major effect of p21, a cyclin-dependent kinase inhibitor, is con sidered to be exerted during G(1) phase of the cell cycle, p21 gene knock-o ut studies suggested its involvement in G(2)/M checkpoint as well. Here we demonstrate evidence that p21 is required for the cell cycle arrest at G(2) upon DNA damage. We found that expression of wild-type p21 (p21(WT)), not mutant p21 (p21(PCNA-)) lacking the interaction with proliferating cell nuc lear antigen (PCNA), caused G2 cell cycle arrest in p53-deficient DLD1 colo n cancer cell line after the DNA damage by treatment with cis-diamminedichl oroplatinum (II). We also found that p21(WT) was associated with Cdc2/cycli n B1 together with PCNA. Furthermore, coimmunoprecipitation experiments rev ealed that PCNA interacted with Cdc25C at the G(2)/M transition, and this i nteraction was abolished when p21(WT) was expressed presumably due to the c ompetition between p21(WT) and Cdc25C in the binding to PCNA. These finding s suggest that p21 plays a regulatory role in the maintenance of cell cycle arrest at G(2) by blocking the interaction of Cdc25C with PCNA.