FADD is required for multiple signaling events downstream of the receptor Fas

To identify essential components of the Fas-induced apoptotic signaling pat hway, Jurkat T lymphocytes were chemically mutagenized and selected for clo nes that were resistant to Fas-induced apoptosis, We obtained five cell lin es that contain mutations in the adaptor FADD. All five cell lines did not express FADD by immunoblot analysis and were completely resistant to Fas-in duced death. Complementation of the FADD mutant cell lines with wild-type F ADD restored Fas-mediated apoptosis, Fas activation of caspase-2, caspase-3 , caspase-7, and caspase-8 and the proteolytic cleavage of substrates such as BID, protein kinase C delta, and poly(ADP-ribose) polymerase were comple tely defective in the FADD mutant cell lines. In addition, Fas activation o f the stress kinases p38 and c-Jun NH2 kinase and the generation of ceramid e in response to Fas ligation were blocked in the FADD mutant cell lines. T hese data indicate that FADD is essential for multiple signaling events dow nstream of Fas.