IAP

IAP (Inhibitor of apoptosis) proteins, a family of anti-apoptotic proteins, have an important role in evasion of apoptosis, as they can both block apoptosis-signaling pathways and promote survival. Eight members of this family have been described in humans (BIRC1/NAIP, BIRC2/cIAP1, BIRC3/cIAP2, BIRC4/XIAP, BIRC5/Survivin, BIRC6/Apollon, BIRC7/ML-IAP and BIRC8/ILP2).

IAP genes encode proteins that directly bind and inhibit caspases, and thus play a critical role in deciding cell fate. The IAPs are in turn regulated by endogenous proteins (second mitochondrial activator of caspases and Omi) that are released from the mitochondria during apoptosis. IAP protein family members are frequently overexpressed in cancer and contribute to tumor cell survival, chemo-resistance, disease progression, and poor prognosis. Targeting critical apoptosis regulators, like IAPs, is an attractive therapeutic way undertaken for the development of new classes of therapies for cancer.

Although best known for their ability to regulate caspases, IAPs also influence ubiquitin (Ub)-dependent pathways that modulate innate immune signaling via activation of NF-κB. Several members of the IAP family regulate innate and adaptive immunity through modulation of signal transduction pathways, cytokine production, and cell survival. The regulation of immunity by the IAPs is primarily mediated through the ubiquitin ligase function of cIAP1, cIAP2, and XIAP, the targets of which impact NF-κB and MAPK signalling pathways.