Activation of p42mapkin human umbilical vein endothelial cells by interleukin-1α and tumor necrosis factor-α

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 p42mapkby Western blot analysis. Tyrosine phosphorylation and catalytic activation of p42mapkby IL-1α was transient, reaching maximal levels after 30 min and returning to basal levels by 120–300 min. Activation of p42mapkin 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 p42mapkby either cytokine but did not affect subsequent activation in response to PMA. Activation of p42mapkby 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 p42mapkactivation. Taken together, the results of this study demonstrate 1) that p42mapkis 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 p42mapkactivation in human endothelium.