Hypochlorous acid stimulation of the mitogen-activated protein kinase pathway enhances cell survival

We investigated the activation of three subfamilies of mitogen-activated pr otein kinases (MAP kinase), the extracellular regulated kinase (ERK1/2), p3 8, and c-Jun N-terminal kinase (JNK), by the myeloperoxidase-derived oxidan t HOCl, in human umbilical vein endothelial cells (HUVEC) and human skin fi broblasts. Treatment of fibroblasts with 10-30 muM HOCl induced a dose-depe ndent increase in the tyrosine phosphorylation of several proteins. ERK1/2 was activated by exposure to sublethal concentrations of reagent HOCl or by HOCl generated by myeloperoxidase as shown by immune complex kinase assays . Maximum activation was seen at 20 muM and peak activation occurred within 10 min. Western blot analysis demonstrated activation of p38 with 30 muM H OCl, occurring at 15-30 min. No activation of JNK was detected in the conce ntration range investigated. These results show that HOCl is able to activa te MAP kinases. Effective doses were considerably lower than with H2O2 and the lack of JNK activation contrasts with the activation frequently seen wi th H2O2. Exposure to HOCl caused a loss of viability in HUVEC that was mark edly enhanced when ERK1/2 activation was inhibited by U0126. This suggests that the activation of ERK promotes cell survival in response to the oxidat ive challenge. (C) 2001 Academic Press.