Nitric oxide stimulates COX-2 expression in cultured collecting duct cells through MAP kinases and superoxide but not cGMP.

Collecting ducts are a major site of renal production and action of both prostaglandins and nitric oxide. Experiments were undertaken to examine whether nitric oxide regulates cyclooxygenase (COX)-2 expression and PGE₂ release in cultured collecting duct cells. In mlMCD-K2 cells, sodium nitroprusside (SNP) in the 50- to 800-μM range induced a marked dose- and time-dependent increase in COX-2 protein levels, determined by immunoblotting, and the induction was detectable at 4 h. This was preceded by induction of COX-2 mRNA as determined by real-time-RT-PCR. The COX-2 induction was accompanied by a significant rise in PGE2 release as determined by enzyme immunoassay. S-nitroso-N-acetylpenicillamine (SNAP) had a similar stimulatory effect on COX-2 expression and PGE₂ release. 8-bromo-cGMP (200 μM) had no effect on COX-2 expression. The SNP-stimulated COX-2 expression was not affected by the guanylyl cyclase inhibitor methylene blue or the protein kinase G inhibitor KT-5823 (2.0 μM). In contrast, the SNP-stimulated COX-2 expression was significantly reduced by either the Erk1/2 inhibitor PD-98059 or the P38 inhibitor SB-203580 and was abolished by combination of the two kinase inhibitors. The stimulation was also significantly blocked by the SOD mimetic tempol. Thus we conclude that NO stimulates COX-2 expression in collecting duct cells through mechanisms involving MAP kinase and superoxide, but not cGMP. [ABSTRACT FROM AUTHOR]