TRANSCRIPTIONAL ACTIVATION OF THE HUMAN PROLIFERATING-CELL NUCLEAR ANTIGEN PROMOTER BY P53

Proliferating-cell nuclear antigen (PCNA) is a DNA damage-inducible pr otein that performs an essential function in DNA replication and repai r as an auxiliary factor for DNA polymerases delta and epsilon. Examin ation of the human PCNA promoter DNA sequence revealed a site with hom ology to the consensus DNA sequence bound by p53. PCNA promoter fragme nts with this site intact bound p53 in vitro and were transcriptionall y activated by wild-type p53 in transient expression assays in SAOS-2 cells. The resident p53-binding site could be functionally substituted by a previously described p53-binding site from the ribosomal gene cl uster. A plasmid expressing a mutated version of p53 derived from a pa tient with Li-Fraumeni syndrome failed to activate the PCNA promoter i n the cotransfection assay. In different cell types, activation of the PCNA promoter by the p53-binding sequence correlated with the status of p53. Activation of the PCNA promoter by wild-type p53 depends upon the level of p53 expression. This concentration dependence and cell ty pe specificity reconciles the observations presented here with prior r esults indicating that wild-type p53 represses the PCNA promoter. Thes e findings provide a mechanism whereby p53 modulates activation of PCN A expression as a cellular response to DNA damage.