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 (By similarity). TNFRSF6 stimulation triggers recruitment to the death-inducing signaling complex (DISC) formed by TNFRSF6, FADD and CASP8 (By similarity). A proteolytic fragment (p43) stays associated with the DISC (By similarity). Interacts with RIPK1 (PubMed:31519887). Highly expressed in heart. At 9.5 and 10.5 dpc, highly expressed in developing heart. Isoform 1 but not isoform 2 is activated by BCR cross-linking in primary B-cells. The caspase domain lacks the active site residues involved in catalysis. Proteolytically processed by CASP8 generating subunits p43 and p12. Belongs to the peptidase C14A family.