Differential inhibition of mesangial MAP kinase cascade by cyclic nucleotides

The agents which increase intracellular cyclic AMP (cAMP) or cyclic GMP (cGMP) have been found to counteract the effects of the vasoconstrictive agents such as endothelin-1 (ET-1). To clarify the mechanism of this interaction, we evaluated the activities of mitogen-activated protein kinase (MAPK) cascade, one of the important signal transduction system of ET-1. Beraprost sodium, an analogue of PGI2, and adrenomedullin, a cAMP-raising agent, inhibited ET-1-induced activation of MAPK. Dibutyryl cAMP (Bt2-cAMP) and 8-bromo-cGMP (8-Br-cGMP), cell permeable analogues of cAMP and cGMP, were also able to inhibit the activation of MAPK and MAPK kinase (MAPKK) by ET-1 without interfering basal activities. In contrast, phorbol 12, 13-dibutylate (PDBu)-induced activation of MAPK and MAPKK was inhibited by Bt2-cAMP but not by 8-Br-cGMP. Interestingly, atrial natriuretic peptide (ANP) partially inhibited PDBu-induced activation of MAPK and MAPKK. These results indicate that cAMP and cGMP inhibit ET-1-induced activation of MAPK in cultured mesangial cells at different steps; the former might inhibit at a step downstream of PKC and the latter prior to PKC. The data also suggest that ANP might have cGMP-independent effect on MAPK.