A novel protein domain required for apoptosis. Mutational analysis of human Fas antigen

The Fas antigen is a cell surface protein that can mediate apoptosis and that belongs to the tumor necrosis factor receptor family. Murine fibroblast L929 cells or T-cell lymphoma WR19L cells expressing the human Fas antigen were killed within 4-6 h by anti-human Fas antibody in a concentration-dependent manner. Human Fas antigen cDNAs with various mutations in the cytoplasmic region were constructed and expressed in L929 cells. A deletion of 15 amino acids from the C terminus of the Fas antigen enhanced the Fas antibody-induced killing activity, whereas a further deletion abolished its activity. This suggests the presence of an inhibitory as well as a signal-transducing domain in the cytoplasmic region of the Fas antigen. A 68-amino acid portion of the signal-transducing domain significantly conserved in the Fas antigen as well as in the type I tumor necrosis factor receptor was considered to be the novel protein domain required for apoptotic signal transduction.