Intracellular signaling mechanisms of interleukin-1beta in synovial fibroblasts

The possibility that membrane depolarization of synovial fibroblasts caused by interleukin-1beta (IL-1beta) was mediated by protein kinase C (PKC) and Ca2+ influx was studied using inhibitor and activator analysis. The effect of IL-1beta 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-1beta mimicked the depolarization caused by IL-1beta. 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-1beta 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-1beta was therefore established. The role of IL-1beta-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-1beta on protease production (1, 2), suggest that electrophysiological changes are actually part of the pathway for expression of proteases in response to IL-1beta.