The proliferation-associated early response gene p22/PRG1 is a novel p53 target gene

The novel early response gene p22/PRG1 is linked to cell cycle entry and the induction of proliferation in various cell types although its exact function is still unknown. The p22/PRG1 promoter region contains a 20 bp sequence matching the consensus binding motif for the tumor suppressor protein p53. Gel shift assays demonstrated that p53 specifically binds to an oligonucleotide derived from the p53 binding site of the p22/PRG1 promoter. Chloramphenicol acetyltransferase (CAT) reporter gene assays confirmed that this site confers p53-dependent transcriptional activity to the p22/PRG1 promoter. In Hela cells, p22/PRG1 promoter constructs induced CAT expression only when cotransfected with an expression plasmid for wild-type, but not for mutant p53. Similarly, CAT expression was inducible at the permissive (31°C) but not at the non-permissive temperature (39°C) in the rat embryo fibroblast-derived cell line clone-6 that expresses a temperature-sensitive mutant p53. Conversion of this mutant p53 to a functional p53 at the permissive temperature was accompanied by a significant increase of endogenous p22/PRG1 mRNA level in this cell line. γ-irradiation of rat splenocytes or doxorubicin-treatment of Hela cells increased p53 levels followed by transcriptional activation of p22/PRG1 and p21/Waf1 in parallel. Our data demonstrate that p22/PRG1 transcription is induced by p53 during p53-dependent cell cycle arrest and apoptosis. Therefore, p22/PRG1 represents a novel target for transcriptional activation by p53.