Staurosporine inhibits protein kinase C and prevents phorbol ester-mediated leukotriene D4 receptor desensitization in RBL-1 cells

Abstract

The aim of the present study was to investigate the effects of staurosporine on phorbol-myristate acetate (PMA)-induced activation of protein kinase C (PKC) and the desensitization of leukotriene D4 (LTD4)-stimulated Ca2+ mobilization in rat basophilic leukemia (RBL-1) cells. Staurosporine, one of the most potent PKC inhibitors known to date, markedly inhibited partially purified PKC from RBL-1 cells with an IC50 of 3 nM. Exposure of RBL-1 cells to PMA resulted in inhibition of LTD4-stimulated Ca2+ mobilization. However, prior treatment of the cells with staurosporine completely prevented PMA-induced desensitization of LTD4-stimulated Ca2+ mobilization. This reversal of Ca2+ desensitization by staurosporine was dose dependent with an IC50 of 0.1 microM. Treatment of RBL-1 cells with PMA resulted in translocation and activation of PKC from the cytosol to the membrane fraction. Pretreatment of RBL-1 cells with staurosporine inhibited the PMA-induced activation of PKC in the membrane fraction. The inhibition of PKC activity by staurosporine was time and dose dependent with an IC50 of 0.9 microM. These results show that PMA-induced heterologous desensitization is mediated by PKC and staurosporine prevented this process by directly inhibiting PKC in intact RBL-1 cells.