A Mouse Fas-Associated Protein with Homology to the Human Mort1/FADD Protein Is Essential for Fas-Induced Apoptosis

Abstract

The Fas cell surface receptor belongs to the tumor necrosis factor receptor family and can initiate apoptosis in a variety of cell types. Using the Fas cytoplasmic domain as bait in a yeast two-hybrid screening, we isolated a mouse cDNA encoding a 205-amino-acid protein. Its predicted protein sequence shows 68% identity and 80% similarity with the sequence of recently described human Mort1/FADD. This protein, most likely the mouse homolog of human FADD, associates with Fas in vivo only upon the induction of cell death. A fraction of this protein is highly phosphorylated at serine/threonine residues, with both phosphorylated and unphosphorylated forms being capable of binding to Fas. Stable expression of a truncated form of the Mort1/FADD protein protects cells from Fas-mediated apoptosis by interfering with the wild-type protein-Fas interaction. Thus, mouse Mort1/FADD is an essential downstream component that mediates Fas-induced apoptosis.