Activation of extracellular signal-regulated kinase (ERK)1/2 contributes to cytokine-induced apoptosis in purified rat pancreatic beta-cells.

Cytokines may contribute to beta-cell apoptosis in the early stages of type 1 diabetes mellitus. It has been reported recently that interleukin-1 beta (IL-1 beta) induces activation of the mitogen-activated protein kinases (MAPK) p38 and ERK1/2 in neonatal rat islets. Since these kinases may participate in cytokine-induced apoptosis, we evaluated whether cytokines induce activation of MAPKs in FACS-purified primary rat beta-cells, and whether blockers of p38 and/or ERK1/2 prevent beta-cell death. IL-1 beta, but not interferon-gamma (IFN-gamma), caused phosphorylation of the substrates Elk-1, ATF-2 and hsp25, and the phosphorylation of both Elk-1 and hsp25 were decreased by the p38 blocker SB203580 (p38i) and the MAPK/ERK blocker PD 098059 (MEKi). When added together, p38i and MEKi decreased IL-1 beta-induced nitrite production over 24 hours by 60%, but did not affect IL-1 beta-induced manganese superoxide dismutase (MnSOD) mRNA expression. To test the effects of MAPK inhibitors on beta-cell death by necrosis or apoptosis, these cells were exposed for 6 or 9 days to IL-1 beta + IFN-gamma. This treatment induced cell death, mostly by apoptosis. The MEKi, but not the p38i, significantly decreased cytokine-induced apoptosis, thus decreasing the total number of dead cells. This protection was only partial, suggesting that ERK1/2 activation is not the only mechanism by which cytokines induce beta-cell apoptosis. We conclude that IL-1 beta induces activation of both p38 and ERK1/2, and that ERK1/2 contributes to the pro-apoptotic effects of the cytokine in primary beta-cells.