INHIBITION OF SMOOTH-MUSCLE CELL-GROWTH BY NITRIC-OXIDE AND ACTIVATION OF CAMP-DEPENDENT PROTEIN-KINASE BY CGMP

Recent studies indicate that nitric oxide (NO) and guanosine 3',5'-cyc lic monophosphate (cGMP) may inhibit the proliferation of vascular smo oth muscle cells (SMC) in vitro. The purpose of this study was to inve stigate the mechanism of NO- and cGMP-dependent inhibition of cultured rat aortic SMC. The cytokine interleukin-1 beta (IL-1 beta) inhibited serum- and platelet-derived growth factor-stimulated [H-3]thymidine i ncorporation into DNA in subcultured rat aortic SMC. Incubation with I L-1 beta for 24 h markedly increased cGMP levels but not adenosine 3', 5'-cyclic monophosphate (cAMP) levels. However, the IL-1 beta-induced increase in cGMP was correlated with an activation of the cAMP-depende nt protein kinase (cAMP kinase) activity ratio. The activation of the cAMP kinase was prevented by treatments that blocked NO and cGMP produ ction. The NO-generating vasodilator, S-nitroso-N-acetylpenicillamine (SNAP) also inhibited DNA synthesis and elevated cGMP levels. The inhi bition of DNA synthesis by both IL-1 beta and SNAP was observed only w hen cGMP levels were elevated to high levels (10-fold or more). As was the case for IL-1 beta, SNAP increased the activity ratio of cAMP kin ase. Selective inhibition of cAMP kinase using (R)-p-bromoadenosine 3' ,5'-cyclic monophosphorothioate prevented the inhibition of proliferat ion by IL-1 beta. By contrast, the inhibitor of the cGMP-dependent pro tein kinase, (R)-p-bromoguanosine 3',5'-cyclic monophosphorothioate, h ad no effect on IL-1 beta-induced inhibition of cellular proliferation . These studies suggest that cGMP-dependent activation of the cAMP kin ase may be responsible in part at least for the NO-dependent inhibitio n of proliferation of subcultured rat aortic SMC.