INDUCTION OF PROSTAGLANDIN ENDOPEROXIDE SYNTHASE-2 BY SERINE-THREONINE PHOSPHATASE INHIBITION

Regulation of prostaglandin endoperoxide synthase-2 (PGHS-2) mRNA leve ls by serine-threonine phosphatases was examined in murine fibrosarcom a methylcholanthrene-101 cells. Okadaic acid (OA), a serine-threonine phosphatase inhibitor, induced PGE(2) production and a significant inc rease in PGHS-2 immunoreactive protein. A specific PGHS-2 inhibitor, N -(2-cyclohexyloxy-4-nitrophenyl) methanesulphonamide, completely aboli shed the OA-mediated increase in PGE(2) production, which suggests tha t the PGE(2) formed in response to OA was derived from PGHS-2. OA-medi ated PGHSP mRNA accumulation was observed at 1 hr, remained elevated f or 24 hr and was blocked by actinomycin D, which indicates that OA inc reases PGHS-2 gene transcription. A significant post-transcriptional m echanism also contributed to the increased PGHS-2 mRNA accumulation, b ecause the mRNA half-life was approximately 4 to 5 h in OA-stimulated cells. Tumor necrosis factor-alpha, but not OA, activated transcriptio n factor nuclear factor-kappa B in methylcholanthrene-101 cells, as de monstrated by translocation of the nuclear factor-kappa B complex to t he nucleus and disappearance of the cytoplasmic inhibitory protein, I kappa B-alpha. We conclude that inhibition of serine-threonine phospha tases contributes to the up-regulation of PGHS-2 expression in an NF-k appa B-independent manner.