Repression of CDK1 and other genes with CDE and CHR promoter elements during DNA damage-induced G(2)/M arrest in human cells

Entry into mitosis is controlled by the cyclin-dependent kinase CDK1 and ca n be delayed in response to DNA damage. In some systems, such G(2)/M arrest has been shown to reflect the stabilization of inhibitory phosphorylation sites on CDK1. In human cells, full G(2) arrest appears to involve addition al mechanisms. We describe here the prolonged (>6 day) downregulation of CD K1 protein and mRNA levels following DNA damage in human cells, This silenc ing of gene expression is observed in primary human fibroblasts and in two cell lines with functional p53 but not in HeLa cells, where p53 is inactive . Silencing is accompanied by the accumulation of cells in G(2), when CDK1 expression is normally maximal. The response is impaired by mutations in ci s-acting elements (CDE and CHR) in the CDK1 promoter, indicating that silen cing occurs at the transcriptional level. These elements have previously be en implicated in the repression of transcription during G(1) that is normal ly lifted as cells progress into S and G(2). Interestingly, we find that ot her genes, including those for CDC25C, cyclin A2, cyclin B1, CENP-A and top oisomerase II alpha, that are normally expressed preferentially in G(2) and whose promoter regions include putative CDE and CHR elements are also down regulated in response to DNA damage. These data, together with those of oth er groups, support the existence of a p5.3-dependent, DNA damage-activated pathway leading to CHR- and CDE-mediated transcriptional repression of vari ous G(2)-specific genes. This pathway may be required for sustained periods of G(2) arrest following DNA damage.