Apoptosis control by death and decoy receptors

The death receptors Fas and tumor necrosis factor receptor 1 (TNFR1) trigge r apoptosis upon engagement by their cognate death ligands. Recently, resea rchers have discovered several novel homologues of Fas and TNFR1: DR 3, 4, 5, and 6 function as death receptors that signal apoptosis, whereas DcR 1, 2, and 3 act as decoys that compete with specific death receptors for ligan d binding. Further, mouse gene knockout studies have enabled researchers to delineate some of the signaling pathways that connect death receptors to t he cell's apoptotic machinery.