E3 ubiquitin-protein ligase XIAP (XIAP)

E3 ubiquitin-protein ligase XIAP (X-linked inhibitor of apoptosis protein) is a critical regulator of cell death and a major therapeutic target in oncology (pharmaceutical-technology.com, frontiersin.org). It belongs to the inhibitor of apoptosis (IAP) family and is characterized by three baculoviral IAP repeat (BIR) domains and a C-terminal RING finger domain (mdpi.com, wikipedia.org). The BIR3 domain specifically binds to and inhibits the initiator caspase-9, effectively blocking the intrinsic apoptotic pathway and allowing cancer cells to evade programmed cell death (nih.gov). XIAP also possesses E3 ubiquitin ligase activity via its RING domain, which it uses to regulate inflammatory signaling, copper homeostasis, and the degradation of various substrates (pharmaceutical-technology.com, nih.gov). Small-molecule Smac mimetics have been developed to target the BIR3 domain, mimicking the endogenous protein Smac/DIABLO to displace caspases and restore the cell's ability to undergo apoptosis (mdpi.com, nih.gov). These agents are currently being investigated in clinical trials, primarily for the treatment of solid tumors and hematological malignancies, often showing synergy with conventional chemotherapies (pharmaceutical-technology.com, mdpi.com).

Other names

X-linked inhibitor of apoptosis proteinBaculoviral IAP repeat-containing protein 4Inhibitor of apoptosis protein 3hIAP3API3BIRC4

Smac mimetics (IAP antagonists) bind to the BIR3 domain of XIAP, mimicking the N-terminal AVPI motif of the endogenous antagonist Smac/DIABLO (mdpi.com, nih.gov). This binding displaces and prevents the inhibition of caspase-9, thereby promoting the intrinsic apoptotic pathway (nih.gov, frontiersin.org). Additionally, these drugs often target the BIR3 domains of cIAP1 and cIAP2, leading to their autoubiquitination and proteasomal degradation, which further sensitizes cells to TNF-alpha-mediated apoptosis (nih.gov).