Involvement of the Interaction between p21 and Proliferating Cell Nuclear Antigen for the Maintenance of G2/M Arrest after DNA Damage

Abstract

Although a major effect of p21, a cyclin-dependent kinase inhibitor, is considered to be exerted during G1 phase of the cell cycle, p21 gene knock-out studies suggested its involvement in G2/M checkpoint as well. Here we demonstrate evidence that p21 is required for the cell cycle arrest at G2 upon DNA damage. We found that expression of wild-type p21 (p21WT), not mutant p21 (p21PCNA-) lacking the interaction with proliferating cell nuclear antigen (PCNA), caused G 2 cell cycle arrest in p53-deficient DLD1 colon cancer cell line after the DNA damage by treatment with cis-diamminedichloroplatinum (II). We also found that p21WT was associated with Cdc2/cyclin B1 together with PCNA. Furthermore, coimmunoprecipitation experiments revealed that PCNA interacted with Cdc25C at the G2/M transition, and this interaction was abolished when p21WT was expressed presumably due to the competition between p21WT and Cdc25C in the binding to PCNA. These findings suggest that p21 plays a regulatory role in the maintenance of cell cycle arrest at G2 by blocking the interaction of Cdc25C with PCNA.