A physical interaction between the cell death protein Fas and the tyrosine kinase p59(fynT)

The Fas antigen (Apol/CD95) is a transmembrane protein belonging to the nerve growth factor receptor family. It is expressed on a variety of cells, including activated T lymphocytes. Ligation of Fas with its natural ligand or with anti-Fas antibodies often results in the apoptotic death of the cell, making Fas an important mediator of down-regulating immune responses. The signal transduction pathways utilized by Fas are currently unknown, although tyrosine kinase activity has recently been strongly implicated. Here, we report that the tyrosine kinase p59(fyn) physically associates with Fas in Fas sensitive cells. In addition, we show that activated T lymphocytes from fyn knockout mice exhibit elevated lifespans and reduced apoptosis in vitro compared to their normal counterparts. Furthermore, activated T lymphocytes from the fyn- deficient mice are less sensitive to killing by both anti-Fas antibody and Fas-ligand cytotoxic T cells. These results suggest that p59(fyn) plays an important role in Fas signal transduction.