Cellular inhibitor of apoptosis protein 2 (cIAP2) BIR3 domain (cIAP2)

Cellular inhibitor of apoptosis protein 2 (cIAP2), encoded by the BIRC3 gene, is a multi-domain protein that plays a pivotal role in regulating programmed cell death and inflammatory signaling (UniProt Q13489). The BIR3 (Baculovirus IAP Repeat 3) domain is a specific structural motif within cIAP2 that mediates interactions with IAP-binding motif (IBM)-containing proteins, most notably the pro-apoptotic factor SMAC/DIABLO (PubMed: 18057361). Functionally, cIAP2 acts as an E3 ubiquitin ligase, facilitating the ubiquitination of components in the NF-kappaB pathway, which promotes cell survival and suppresses apoptosis. In many cancers, including MALT lymphoma and chronic lymphocytic leukemia, cIAP2 is overexpressed or genetically altered, allowing tumor cells to evade death signals (PubMed: 24469444). Small-molecule SMAC mimetics are designed to bind the BIR3 domain with high affinity, triggering the autoubiquitination and subsequent proteasomal degradation of cIAP2. This degradation sensitizes cancer cells to apoptosis, particularly through the TNF-alpha-mediated extrinsic pathway, making the BIR3 domain a high-priority target in oncology (ClinicalTrials.gov).

Other names

Baculoviral IAP repeat-containing protein 3BIRC3Apoptosis inhibitor 2API2Mammalian IAP homolog bMIHBIAP homolog CIAP-CRNF49

SMAC mimetics target the BIR3 domain of cIAP2 to mimic the binding of the endogenous antagonist SMAC/DIABLO (PubMed: 18057361). Upon binding, these compounds induce a conformational change in the cIAP2 protein that activates its C-terminal RING domain's E3 ubiquitin ligase activity. This leads to rapid K48-linked autoubiquitination and subsequent degradation of cIAP2 by the proteasome (PubMed: 24469444). The depletion of cIAP2 prevents the ubiquitination of RIPK1, leading to the destabilization of the canonical NF-kappaB signaling complex and the formation of a pro-apoptotic complex (Complex II), which activates caspase-8 and triggers cell death.