H2O2 induces a transient multi-phase cell cycle arrest in mouse fibroblasts through modulating cyclin D and p21Cip1 expression

To defend against the potential damages induced by reactive oxygen species, proliferating cells enter a transient cell cycle arrest. We treated mouse fibroblasts with H2O2 and found that sublethal doses of H2O2 induced a transient multi-phase cell cycle arrest at the G, S, and G. phases but not the M phase. Western blot analysis demonstrated that this transient cell cycle arrest is associated with the down-regulation of cyclins D1 and D3 and up-regulation of the CKI p21(Cip1) expression. We also demonstrate that the induction in p21(Cip1) expression by H2O2 is at least partially mediated at the transcriptional level and can occur in the absence of p53 function. Further immunoprecipitation kinase and immunodepletion assays indicated that in response to H2O2 treatment, the down-regulation of cyclin Ds expression are associated with repression of cyclin D-CDK4, whereas the accumulation of P21(Cip1) is responsible for the inhibition of cyclin E and A-CDK2 activity and associated with the down-regulation of cyclin B-CDC2 activity. These data could account for the cell cycle arrest at the G(1), S, and G(2) phases following H2O2 stimulation. Deletion of p21(Cip1), restoration of cyclin D expression, or overexpression of cyclin E alone is insufficient to effectively overcome the cell cycle arrest caused by sublethal doses of H2O2. By contrast, overexpression of the human Herpesvirus 8 K cyclin, which can mimic the function of cyclin D and E, is enough to override this transient cell cycle arrest. On the basis of our findings, we propose a model in which moderate levels of H2O2 induce a transient multi-phase cell cycle arrest at least partially through up-regulation of P21(Cip1) and down-regulation of cyclin D expression.