Excessive release of nitric oxide (NO) by mesangial cells contributes to the pathogenesis of glomerulonephritis. Prostaglandin E2
(PGE2) produced at inflammatory sites regulates the release of NO through its downstream signaling. In glomerular mesangial cells
(MES-13 cells), PGE2 modulated NO production mainly through EP4 receptor in a cAMP-dependent manner. Lipopolysaccharide
and interferon-c (LPS + IFNc)-induced NO production, inducible nitric oxide synthase (iNOS) gene and protein expression were greatly
inhibited by AH23848, an EP4 antagonist. Further investigation indicated that AH23848 attenuated endogenous cAMP accumulation in
MES-13 cells and modulated NO production through declination of iNOS gene expression and acceleration of iNOS protein degradation.
AH23848 downregulated the iNOS protein in MES-13 cells through protein kinase A (PKA) since KT5720, a PKA-specific inhibitor,
reduced iNOS protein stability. A short exposure of activated MES-13 cells to okadaic acid augmented iNOS activity. AH23848 and
KT5720 attenuated serine/threonine phosphorylation of iNOS protein in LPS + IFNc-stimulated MES-13 cells. The results of this study
led us to speculate that cAMP might regulate iNOS-stimulated NO synthesis through posttranslational mechanisms. Attenuation of
cAMP signaling and the phosphorylation status of the iNOS protein may account for the effect of AH23848 in accelerating iNOS protein
degradation in MES-13 cells.
