Activation of p42^mapk in human umbilical vein endothelial cells by interleukin-1α and tumor necrosis factor-α

Abstract

Work from this and other laboratories has identified a role for protein tyrosine kinases in interleukin-1α (IL-1α)- and tumor necrosis factor-α (TNF-α)-induced responses in endothelial cells. In this study, we show that activation of human umbilical vein endothelial cells (HUVEC) by IL-1α leads to increased tyrosine phosphorylation of several proteins including one with a molecular mass of ∼42 kDa. This protein was identified as p42 mapk by Western blot analysis. Tyrosine phosphorylation and catalytic activation of p42 mapk by IL-1α was transient, reaching maximal levels after 30 min and returning to basal levels by 120–300 min. Activation of p42 mapk in HUVEC was also observed in response to TNF-α or to the protein kinase C (PKC)-activating phorbol ester phorbol 12-myristate 13-acetate (PMA). Pretreatment of HUVEC with IL-1α or TNF-α prevented reactivation of p42 mapk by either cytokine but did not affect subsequent activation in response to PMA. Activation of p42 mapk by PMA was significantly reduced by the PKC inhibitor Ro-31-8220 and completely inhibited by the protein tyrosine kinase inhibitor genistein. Genistein, but not Ro-31-8220, attenuated IL-1α- and TNF-α-induced p42 mapk activation. Taken together, the results of this study demonstrate 1) that p42 mapk is transiently activated in HUVEC by IL-1α and TNF-α, 2) that this activation is PKC independent, and 3) that a genistein-inhibitable tyrosine kinase may be an upstream regulator of cytokine-induced p42 mapk activation in human endothelium.