ACTIVATION OF P42(MAPK) IN HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS BY INTERLEUKIN-1-ALPHA AND TUMOR-NECROSIS-FACTOR-ALPHA

Work from this and other laboratories has identified a role for protei n tyrosine kinases in interleukin-1 alpha (IL-1 alpha)- and tumor necr osis factor-alpha (TNF-alpha)-induced responses in endothelial cells. In this study, we show that activation of human umbilical vein endothe lial cells (HUVEC) by IL-1 alpha leads to increased tyrosine phosphory lation of several proteins including one with a molecular mass of simi lar to 42 kDa. This protein was identified as p42(mapk) by Western blo t analysis. Tyrosine phosphorylation and catalytic activation of p42(m apk) by IL-1 alpha 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-alpha or to the protein kinase C (PKC)-activating phorbol ester phorbol 12-myristate 13-aceta te (PMA). Pretreatment of HUVEC with IL-1 alpha or TNF-alpha prevented reactivation of p42(mapk) by either cytokine but did not affect subse quent activation in response to PMA. Activation of p42(mapk) by PMA wa s significantly reduced by the PKC inhibitor Ro-31-8220 and completely inhibited by the protein tyrosine kinase inhibitor genistein. Geniste in, but not Ro-31-8220, attenuated IL-1 alpha- and TNF-alpha-induced p 42(mapk) activation. Taken together, the results of this study demonst rate 1) that p42(mapk) is transiently activated in HUVEC by IL-1 alpha and TNF-alpha, 2) that this activation is PKC independent, and 3) tha t a genistein-inhibitable tyrosine kinase may be an upstream regulator of cytokine-induced p42(mapk) activation in human endothelium.