Effect of cyclic AMP and prostaglandin E₂ on the induction of nitric oxide- and prostanoid-forming pathways in cultured rat mesangial cells

Cyclic AMP (cAMP) represents an important cellular signalling molecule. We analysed the effect of dibutyryl cAMP (db-cAMP), a cell-permeable and stable derivative of cAMP, on the regulation and expression of cyclo-oxygenase 2, inducible NO synthase and argininosuccinate synthetase. We observed different transcriptional regulation of these enzymes depending on the db-cAMP concentration used. Low concentrations of db-cAMP in the range 10-50 μM elevated levels of cyclo-oxygenase 2 mRNA, protein and activity, but not the respective mRNA and protein concentrations of the inducible NO synthase or argininosuccinate synthetase. At higher concentrations a massive induction of the latter two enzymes was also apparent. Expression of prostacyclin synthase and argininosuccinate lyase, secondary enzymes of NO-and prostanoid-forming pathways, was not stimulated by db-cAMP. Prostaglandin E₂, known to be an intracellular physiological trigger of cAMP formation, stimulated only cyclo-oxygenase 2 expression and activity at a concentration of 10 μM, and not inducible NO synthase. The induction of the mRNA for the transcription factors JunB and p65, a component of the NFĸB complex, by prostaglandin treatment of the cells might be a possible mechanistic explanation for this observation.