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 a nd the induction of proliferation in various cell types although its e xact function is still unknown. The p22/PRG1 promoter region contains a 20 bp sequence matching the consensus binding motif for the tumor su ppressor protein p53, Gel shift assays demonstrated that p53 specifica lly binds to an oligonucleotide derived from the p53 binding site of t he p22/PRG1 promoter. Chloramphenicol acetyltransferase (CAT) reporter gene assays confirmed that this site confers p53-dependent transcript ional activity to the p22/PRG1 promoter. In Hela cells, p22/PRG1 promo ter constructs induced CAT expression only when cotransfected with an expression plasmid for wild-type, but not for mutant p53, Similarly, C AT expression was inducible at the permissive (31 degrees C) but not a t the non-permissive temperature (39 degrees C) in the rat embryo fibr oblast-derived cell line clone-6 that expresses a temperature-sensitiv e mutant p53, Conversion of this mutant p53 to a functional p53 at the permissive temperature was accompanied by a significant increase of e ndogenous p22/PRG1 mRNA level in this cell line. gamma-irradiation of rat splenocytes or doxorubicin-treatment of Hela cells increased p53 l evels followed by transcriptional activation of p22/PRG1 and p21/Waf1 in parallel. Our data demonstrate that p22/PRG1 transcription is induc ed by p53 during p53-dependent cell cycle arrest and apoptosis, Theref ore, p22/PRG1 represents a novel target for transcriptional activation by p53.