Prostaglandin E2 stimulates p53 transactivational activity through specific serine 15 phosphorylation in human synovial fibroblasts

Cyclooxygenase-2 (COX-2) overexpression has been linked to cell survival, transformation, and hyperproliferation. We examined the regulation of the tumor suppressor gene p53 and p53 target genes by prostaglandin E-2 (PGE(2)) in human synovial fibroblasts (HSF). PGE(2) induced a time-dependent increase in p53 Ser(15) phosphorylation, with no discernible change in overall p53 levels. PGE2 dependent Ser(15) phosphorylation was apparently mediated by activated p38 MAP kinase as SB202190, a p38 kinase inhibitor, blocked the response. Overexpression of a MKK3 construct, but not MKK1, stimulated SB202190-sensitive p53 Ser15 phosphorylation. PGE2-stimulated [phospho-Ser(15)] p53 transactivated a p53 response element(GADD45)-luciferase reporter in transiently transfected HSF (SN7); the effect was compromised by overexpression of a dominant-negative mutant (dnm) of p53 or excess p53S15A expression plasmid but mimicked by a constitutively active p53S15E expression construct. PGE2, wtp53 expression in the presence of PGE2, and p53S15E suppressed steady-state levels of MEKK1-induced MMP-1 mRNA, effects nullified with co-transfection of p53 dnm or p53S15A. MEKK1-induced MMP-1 promoter-driven luciferase activity was largely dependent on a c/EBP beta-NF-kappa B-like enhancer site at - 2008 to - 1972 bp, as judged by deletion and point mutation analyses. PGE2, overexpression of p53wt with PGE2, or p53S15E abolished the MEKK1-induced MMP-1 promoter luciferase activity. Gel-shift/super gel-shift analyses identified c/EBP beta dimers and c/EBP beta/NF-kappa B p65 heterodimers as binding species at the apparent site of MEKK1-dependent transactivation. PGE2-stimulated [phospho-Ser15] p53 abrogated the DNA binding of c/EBP beta dimers and c/EBP beta/NF-kappa B p65 heterodimers. Our data suggest that COX-2 prostaglandins may be implicated in p53 function and p53 target gene expression.