Cyclic-AMP inhibits nitric oxide-induced apoptosis in human osteoblast: The regulation of caspase-3,-6,-9 and the release of cytochrome c in nitric oxide-induced apoptosis by cAMP

Nitric oxide (NO) induces apoptotic cell death and cAMP has a significantly protective effect on NO-induced cytotoxicity in human osteoblasts, MG-63 c ells. Treatment with S-nitroso-N-acetylpenicillamine (SNAP) (0.6 mM) result ed in genomic DNA fragmentation, characteristic of apoptosis, However, conc omitant incubation of the cells with tither DBcAMP or forskolin markedly in hibited SNAP-induced apoptosis in a dose-dependent manner. Furthermore, pre treatment of MG-63 cells with H-89 or KT5720, which is known to inhibit cAM P-dependent protein kinase (PKA), abolished the protective effect of DBcAMP and forskolin on SNAP-induced apoptosis, In this study, we explored the in volvement of caspases in the regulatory mechanism of SNAP-induced apoptosis by cAMP. Our data show that DBcAMP or forskolin blocked SNAP-induced caspa se-3-like cysteine protease activation and that H-89, a PKA inhibitor, reve rsed the cAMP-induced regulatory effect of caspase-3 like protease, Consist ent with the results, cAMP inhibited the proteolytic cleavage of caspase-3, -6, -9 and cytochrome c release to cytoplasm. The inhibition of caspase-3 activation did not block SNAP-induced cytochrome c release to cytoplasm. su ggesting that caspase-3 activation may occur downstream of cytochrome c rel ease, In summary, these findings show that the exposure of MG-63 cells to c AMP analogs renders them more resistant to NO-induced damage and suggests t he presence of regulatory mechanisms of the cell death pathway by cAMP in w hich caspase-3, -6, and -9 and cytochrome c release scn es to mediate NO-in duced apoptosis.