Src and Cas mediate JNK activation but not ERK1/2 and p38 kinases by reactive oxygen species

c-Jun NH2-terminal kinase (JNK) is activated by a number of cellular stimul i such as inflammatory cytokines and environmental stresses. Reactive oxyge n species also cause activation of JNK; however, the signaling cascade that leads to JNK activation remains to be elucidated. Because recent reports s howed that expression of Cas, a putative Src substrate, stimulates JNK acti vation, we hypothesized that the Src kinase family and Cas would be involve d in JNK activation by reactive oxygen species. An essential role for both Src and Cas was demonstrated, First, the specific Src family tyrosine kinas e inhibitor, PP2, inhibited JNK activation by H2O2 in a concentration-depen dent manner but had no effect on extracellular signal-regulated kinases 1 a nd 2 and p38 activation. Second, JNK activation in response to H2O2 was com pletely inhibited in cells derived from transgenic mice deficient in Src bu t not Fyn. Third, expression of a dominant negative mutant of Cas prevented H2O2-mediated JNK activation but had no effect on extracellular signal-reg ulated kinases 1 and 2 and p38 activation. Finally, the importance of Src w as further supported by the inhibition of both H2O2-mediated Cas tyrosine p hosphorylation and Cas.Crk complex formation in Src-/- but not Fyn-/- cells . These results demonstrate an essential role for Src and Cas in H2O2-media ted activation of JNK and suggest a new redox-sensitive pathway for JNK act ivation mediated by Src.