Intracellular signaling mechanisms of interleukin-1β in synovial fibroblasts

Abstract

The possibility that membrane depolarization of synovial fibroblasts caused by interleukin-1β (IL-1β) was mediated by protein kinase C (PKC) and Ca2+influx was studied using inhibitor and activator analysis. The effect of IL-1β was blocked by bisindolylmaleimide I, an inhibitor of PKC, and by the Ca2+ channel blockers nifedipine and verapamil. In other experiments, PKC was activated using phorbol 12-myristate 13-acetate, and Ca2+ influx was increased by means of a Ca2+ ionophore. Simultaneous application of phorbol ester and Ca2+ ionophore in the absence of IL-1β mimicked the depolarization caused by IL-1β. The results were consistent with the hypothesis that, under the conditions studied, activation of PKC and Ca2+ influx are necessary and sufficient processes in the transduction of IL-1β by synovial cells leading to membrane depolarization. The essential role of protein phosphorylation and Ca2+ influx in the early electrophysiological response of synovial fibroblasts to IL-1β was therefore established. The role of IL-1β-induced depolarization in regulating protein expression by the cells remains to be determined, but the results reported here, taken together with observations that protein phosphorylation and Ca2+influx also mediate the effect of IL-1β on protease production (1, 2), suggest that electrophysiological changes are actually part of the pathway for expression of proteases in response to IL-1β.