Contrasting actions of staurosporine, a protein kinase C inhibitor, on human neutrophils and primary mouse epidermal cells.

Staurosporine, a recently described microbial alkaloid, is uniquely potent as an inhibitor of protein kinase C in vitro, being active at nM concentrations rather than the microM concentrations typical of other inhibitor classes. Like these other inhibitors, however, staurosporine exhibits only limited selectivity among different protein kinases. We report here that, in intact human neutrophils, nM concentrations of staurosporine blocked the action of the phorbol ester tumor promoters. In mouse primary epidermal cells, on the other hand, staurosporine failed to block the effects of phorbol 12,13-dibutyrate on epidermal growth factor binding and on induction of ornithine decarboxylase and epidermal transglutaminase. Unexpectedly, staurosporine induced morphological changes in keratinocytes to a dendritic shape resembling that induced by the phorbol esters. It also induced epidermal transglutaminase and cornified envelope production, markers of the differentiative pathway in the epidermal cells. We conclude that the effectiveness of staurosporine as a protein kinase C inhibitor in intact cells may depend markedly on the cell system. Other actions of staurosporine may predominate, and, in keratinocytes, its activity is suggestive of a tumor promoter rather than of an inhibitor of tumor promotion.