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 phosphoryla tion of a panel of proteins observed in whole-cell lysates, In the hum an T cell line Jurkat, the activity of a 56-kDa tyrosine kinase was li kewise activated by anti-Pas antibodies. Immunoprecipitation studies o f anti-Pas-stimulated human Jurkat and murine 2B4.11 T cells revealed activation of the Src-family tyrosine kinases Lck and Fyn. Fas recepto r-induced tyrosine phosphorylation of p120 c-cbl proto-oncogene produc t was observed in jurkat T cells. Pharmacological experiments demonstr ated 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 J urkat T cells formed stable complexes with the intracellular domain of the Fas receptor, These data are consistent with the notion that expr ession and activation of members of the Src-family kinases is required for Pas-induced cell death in T lymphocytes and consistent with recen t findings demonstrating decreased Fas-mediated thymocytic death in Fy n-knockout mice.