Signaling mechanisms of interferon gamma induced apoptosis in chromaffin cells: involvement of nNOS, iNOS, and NFkappaB.

Previous work of our group stated that exogenously added and endogenous nitric oxide (NO) generated by cytokines induce apoptosis in chromaffin cells. In this work, we investigate the specific regulation of the NO synthase (NOS) isoforms, inducible NOS (iNOS) and neuronal NOS (nNOS), and their particular participation in cell death induced by interferon gamma (IFNgamma). Lipopolysaccharide (LPS) and IFNgamma increase iNOS expression, with no effect on nNOS expression. On the other hand, dexamethasone increases basal nNOS expression but decreases LPS + IFNgamma-induced iNOS expression. IFNgamma-induced cell death was abolished by W-1400, a specific iNOS inhibitor, but only partially by nNOS inhibitors [N-omega-propyl- L-arginine (N-PLA), 3-Bromo-7-nitroindazol (7-NI), L-methyl thiocitrulline and N-methyl L-arginine], indicating the main iNOS participation in chromaffin cell death. IFNgamma and LPS induce nuclear factor kappaB (NFkappaB) translocation to the nucleus, a process implicated in activation of iNOS expression, as inhibition of NFkappaB translocation, by SN50, decreased iNOS expression. In addition, IFNgamma and LPS induce (847)SernNOS phosphorylation, inhibiting nNOS activity. Both processes, nNOS phosphorylation and iNOS expression induced by LPS + IFNgamma, are regulated by Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway, as IFNgamma increases (727)STAT-3 phosphorylation and specific inhibitors of JAK/STAT pathway, such as AG490, inhibited both processes. Taken together, these results support the hypothesis of an inactivating phosphorylation of nNOS by IFNgamma, via JAK/STAT, in bovine chromaffin cells. Low NO concentrations achieved by this event, would activate NFkappaB translocation, increasing iNOS expression and generating, this last, high apoptotic NO concentrations.