PROTEIN-KINASE-C REGULATES CYTOKINE-INDUCED TISSUE FACTOR TRANSCRIPTION AND PROCOAGULANT ACTIVITY IN HUMAN ENDOTHELIAL-CELLS

Interleukin-1 alpha (lL-1 alpha) and tumor necrosis factor-alpha (TNF- alpha) induce tissue factor in endothelium, which results in activatio n of the coagulation cascade. Despite extensive investigation, in whic h various stimuli that induce tissue factor have been defined, the int racellular processes that control tissue factor expression are not wel l understood. It has been proposed that protein kinase C regulates tis sue factor expression primarily because phorbol myristate acetate, the protein kinase C activator, induces tissue factor expression, In this study we examined whether IL-1 alpha- or TNF-alpha-stimulated tissue factor production is regulated through a protein kinase C-dependent me chanism. Northern blot analysis showed that cytokine-induced tissue fa ctor mRNA was significantly reduced in human umbilical vein endothelia l cells treated with calphostin C, a specific protein kinase C inhibit or. Tissue factor functional activity was decreased in the presence of calphostin C as well. Calphostin C also inhibited phorbol myristate a cetate-induced tissue factor expression. In contrast, calphostin C did not alter cytokine induction of E-selectin or prostacyclin release. B ecause calcium stimulates protein kinase C binding to the membrane and its resulting catalytic activity, human umbilical vein endothelial ce lls were exposed to IL-1 alpha or TNF-alpha in the presence of calcium ionophore A23187, A23187 had little effect alone but significantly au gmented cytokine stimulation of tissue factor mRNA. Okadaic acid, a ph osphatase inhibitor, increased cytokine-induced tissue factor mRNA com pared 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 ce ll tissue factor expression.