The cellular inhibitor of apoptosis protein-1 (cIAP1) is a member of the Inhibitor of Apoptosis family proteins are (IAP) whose members are characterized by a novel domain of about 70 amino acids termed baculoviral IAP repeats (BIRs). The BIR domains of cIAP1 and cIAP2 bind to caspases, the key effector proteases of apoptosis. The IAP protein family which can enhance cell survival are crucial regulators of programmed cell death. Both cIAP1 and cIAP2 are the E3 ubiquitin protein isopeptide ligases for Smac, taking part in promoting cancer survival through functioning as E3 ubiquitin ligases. Removal of cIAP1 by genetic deletion may result in NF-κB signaling activation that induces TNFα production and in killing sensitive tumor cells through enhanced TNF-R1 death-receptor signaling and caspase 8 activation. The substrate-dependent E3 activity of cIAPs is mediated by their RING domains and is dependent on the specific interactions between cIAPs and Smac. cIAP1 and cIAP2 are also reported to be regulators of NF-kB activation upon TNFαtreatment.