Activation of Src-family tyrosine kinases during Fas-induced apoptosis

Stimulation of several human and murine hematopoietically derived cell lines with anti-Fas antibodies induced increased tyrosine phosphorylation of a panel of proteins observed in whole-cell lysates. In the human T cell line Jurkat, the activity of a 56-kDa tyrosine kinase was likewise activated by anti-Fas antibodies. Immunoprecipitation studies of anti-Fas-stimulated human Jurkat and murine 2B4.11 T cells revealed activation of the Src-family tyrosine kinases Lck and Fyn. Fas receptor-induced tyrosine phosphorylation of p120 c-cbl proto-oncogene product was observed in Jurkat T cells. Pharmacological experiments demonstrated that pretreatment of Jurkat cells with tyrphostins inhibited Fas-induced apoptosis; likewise, Lck activity was inhibited by tyrphostins in a dose-dependent fashion. Finally, Lck derived from unstimulated Jurkat T cells formed stable complexes with the intracellular domain of the Fas receptor. These data are consistent with the notion that expression and activation of members of the Src-family kinases is required for Fas-induced cell death in T lymphocytes and consistent with recent findings demonstrating decreased Fas-mediated thymocytic death in Fyn-knockout mice.