cIAP1 (HIAP2, MIHB) is a member of the family of inhibitor of apoptosis proteins (IAP). IAPs suppress mitochondria- dependent and -independent apoptosis by binding to and inhibiting caspases through their BIR domains. Resistance towards apoptosis is a hallmark of cancer cells, and overexpression of IAPs can contribute to the development of cancer though inhibiting apoptosis. In addition to at least one BIR domain, some IAP members also have a RING-type finger motif at their carboxyl-terminal. The RING finger domain of several IAPs, including cIAP2, have E3 ubiquitin ligase activity and target the degradation of Smac/DIABLO through ubqiuitination. Smac/DIABLO is a death inducer and functions by inhibiting IAP-caspase interactions, thereby promoting apoptosis. Degradation of cell death inducers like Smac/DIABLO is thought to be a conserved mechanism by which IAPs enhance their anti-apoptotic activity, thereby promoting cell survival. The IAPs, including cIAP1, have widespread tissue protein expression, with expression levels and subcellular localization patterns differing depending on the cell lineage.