Role of p38 mitogen-activated protein kinase (p38 MAPK) in cytokine-induced rat islet cell apoptosis.

The signaling pathways mediating nitric oxide production and apoptosis in pancreatic beta-cells are not fully understood. We investigated cytokine-induced protein phosphorylation events in insulin-producing cells and evaluated their role in inducible nitric oxide synthase (iNOS) induction and cell death. Interleukin-1beta (IL-1beta), but not interferon-gamma (IFN-gamma), induced phosphorylation of p38 mitogen-activated protein kinase, c-Jun NH2-terminal kinase, and mitogen- and stress-activated protein kinase 1 (MSK1) in rat insulin-producing RINm5F cells. This was paralleled by an increased phosphorylation of the transcription factors activating transcription factor-2 (ATF-2) and cAMP-responsive element-binding protein (CREB). The p38 inhibitor SB203580 prevented cytokine-induced phosphorylation of CREB and MSK1, but not of ATF-2. IFN-gamma induced the phosphorylation of signal transducer and activator of transcription 1. The combination of IL-1beta and IFN-gamma increased both apoptosis and necrosis in rat islet cells. SB203580, but not the extracellular signal-regulated kinase inhibitor PD98059, partially prevented cytokine-induced apoptosis, an effect that was not associated with reduced nitrite production or lowered iNOS expression. In conclusion, cytokine-induced p38 activation participates in beta-cell apoptosis, possibly by a nitric oxide-independent mechanism or by enhancing the sensitivity to nitric oxide.