TRAIL (also known as Apo-2L) is a member of the tumor necrosis factor (TNF) ligand family that rapidly induces apoptosis in a variety of transformed cell lines. A fourth member of the emerging TRAIL receptor family, TRAIL-R4, has signaling capacity similar to that of TRAIL-R1 and TRAIL-R2 with respect to NF-kappaB activation, but differs in its inability to induce apoptosis. Like TRAIL-R1 and TRAIL-R2, this receptor shows widespread tissue expression. The human TRAIL-R4 gene has been mapped to chromosome 8p22-21, clustered with three other TRAIL receptors.