Protein kinase C regulates cytokine-induced tissue factor transcription and procoagulant activity in human endothelial cells

Abstract Interleukin-lα (IL-lα) and tumor necrosis factor-α (TNF-α) induce tissue factor in endothelium, which results in activation of the coagulation cascade. Despite extensive investigation, in which various stimuli that induce tissue factor have been defined, the intracellular processes that control tissue factor expression are not well understood. It has been proposed that protein kinase C regulates tissue factor expression primarily because phorbol myristate acetate, the protein kinase C activator, induces tissue factor expression. In this study we examined whether IL-1α- or TNF-α-stimulated tissue factor production is regulated through a protein kinase C-dependent mechanism. Northern blot analysis showed that cytokine-induced tissue factor mRNA was significantly reduced in human umbilical vein endothelial cells treated with calphostin C, a specific protein kinase C inhibitor. Tissue factor functional activity was decreased in the presence of calphostin C as well. Calphostin C also inhibited phorbol myristate acetate-induced tissue factor expression. In contrast, calphostin C did not alter cytokine induction of E-selectin or prostacyclin release. Because calcium stimulates protein kinase C binding to the membrane and its resulting catalytic activity, human umbilical vein endothelial cells were exposed to IL-1α or TNF-α in the presence of calcium ionophore A23187. A23187 had little effect alone but significantly augmented cytokine stimulation of tissue factor mRNA. Okadaic acid, a phosphatase inhibitor, increased cytokine-induced tissue factor mRNA compared with cytokine alone, which suggests that a phosphorylation event is important in tissue factor expression. These results indicate that protein kinase C is involved in cytokine activation of endothelial cell tissue factor expression.