Apoptosis regulator protein which may function as a crucial link between cell survival and cell death pathways in mammalian cells. Acts as an inhibitor of TNFRSF6 mediated apoptosis. A proteolytic fragment (p43) is likely retained in the death-inducing signaling complex (DISC) thereby blocking further recruitment and processing of caspase-8 at the complex. Full length and shorter isoforms have been shown either to induce apoptosis or to reduce TNFRSF-triggered apoptosis. Lacks enzymatic (caspase) activity. TNFRSF6 stimulation triggers recruitment to the death- inducing signaling complex (DISC) formed by TNFRSF6, FADD and caspase-8. A proteolytic fragment (p43) stays associated with the DISC. Also interacts with caspase-10, caspase-3, TRAF1, TRAF2 and Bcl-X(L) (in vitro). Interacts with HBV protein X. Repressed by IL2/interleukin-2 after TCR stimulation, during progression to the S phase of the cell cycle. Widely expressed. Higher expression in skeletal muscle, pancreas, heart, kidney, placenta, and peripheral blood leukocytes. Also detected in diverse cell lines. Isoform 8 is predominantly expressed in testis and skeletal muscle. Belongs to the peptidase C14A family. 14 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.