XIAP Recombinant Protein

This gene encodes a protein that belongs to a family of apoptotic suppressor proteins. Members of this family share a conserved motif termed, baculovirus IAP repeat, which is necessary for their anti-apoptotic function. This protein functions through binding to tumor necrosis factor receptor-associated factors TRAF1 and TRAF2 and inhibits apoptosis induced by menadione, a potent inducer of free radicals, and interleukin 1-beta converting enzyme. This protein also inhibits at least two members of the caspase family of cell-death proteases, caspase-3 and caspase-7. Mutations in this gene are the cause of X-linked lymphoproliferative syndrome. Alternate splicing results in multiple transcript variants. Pseudogenes of this gene are found on chromosomes 2 and 11.[provided by RefSeq, Feb 2011]

Function: Multi-functional protein which regulates not only caspases and apoptosis, but also modulates inflammatory signaling and immunity, copper homeostasis, mitogenic kinase signaling, cell proliferation, as well as cell invasion and metastasis. Acts as a direct caspase inhibitor. Directly bind to the active site pocket of CASP3 and CASP7 and obstructs substrate entry. Inactivates CASP9 by keeping it in a monomeric, inactive state. Acts as an E3 ubiquitin-protein ligase regulating NF-kappa-B signaling and the target proteins for its E3 ubiquitin-protein ligase activity include: RIPK1, CASP3, CASP7, CASP8, CASP9, MAP3K2/MEKK2, DIABLO/SMAC, AIFM1, CCS and BIRC5/survivin. Ubiquitinion of CCS leads to enhancement of its chaperone activity toward its physiologic target, SOD1, rather than proteasomal degradation. Ubiquitinion of MAP3K2/MEKK2 and AIFM1 does not lead to proteasomal degradation. Plays a role in copper homeostasis by ubiquitinationg COMMD1 and promoting its proteasomal degradation. Can also function as E3 ubiquitin-protein ligase of the NEDD8 conjugation pathway, targeting effector caspases for neddylation and inactivation. Regulates the BMP signaling pathway and the SMAD and MAP3K7/TAK1 dependent pathways leading to NF-kappa-B and JNK activation. Acts as an important regulator of innate immune signaling via regulation of Nodlike receptors (NLRs). Protects cells from spontaneous formation of the ripoptosome, a large multi-protein complex that has the capability to kill cancer cells in a caspase-dependent and caspase-independent manner. Suppresses ripoptosome formation by ubiquitinating RIPK1 and CASP8. Acts as a positive regulator of Wnt signaling and ubiquitinates TLE1, TLE2, TLE3, TLE4 and AES. Ubiquitination of TLE3 results in inhibition of its interaction with TCF7L2/TCF4 thereby allowing efficient recruitment and binding of the transcriptional coactivator beta-catenin to TCF7L2/TCF4 that is required to initiate a Wnt-specific transcriptional program. Ref.7 Ref.8 Ref.10 Ref.12 Ref.14 Ref.20 Ref.22 Ref.26 Ref.27 Ref.30 Ref.36 Ref.44

Subunit structure: Monomer, and homodimer. Interacts with DIABLO/SMAC and with PRSS25; these interactions inhibit apoptotic suppressor activity. Interacts with TAB1/MAP3K7IP1 and AIFM1. Interaction with SMAC hinders binding of TAB1/MAP3K7IP1 and AIFM1. Interacts with TCF25 and COMMD1. Interacts with SEPT4 isoform 6, but not with other SEPT4 isoforms. Interacts with RIP1, RIP2, RIP3, RIP4, CCS and USP19. Interacts (via BIR 2 domain and BIR 3 domain) with HAX1 (via C-terminus) and this interaction blocks ubiquitination of XIAP/BIRC4. Interacts with the monomeric form of BIRC5/survivin. Interacts with TLE3 and TCF7L2/TCF4. Ref.12 Ref.13 Ref.18 Ref.20 Ref.22 Ref.23 Ref.27 Ref.32 Ref.33 Ref.34 Ref.36 Ref.43

Subcellular location: Cytoplasm. Nucleus. Note: TLE3 promotes its nuclear localization. Ref.15 Ref.36

Tissue specificity: Ubiquitous, except peripheral blood leukocytes.

Domain: The first BIR domain is involved in interaction with TAB1/MAP3K7IP1 and is important for dimerization. The second BIR domain is sufficient to inhibit CASP3 and CASP7, while the third BIR is involved in CASP9 inhibition. The interactions with DIABLO/SMAC and PRSS25 are mediated by the second and third BIR domains.

Post-translational modification: S-Nitrosylation down-regulates its E3 ubiquitin-protein ligase activity.Autoubiquitinated and degraded by the proteasome in apoptotic cells.Phosphorylation by PKB/AKT protects XIAP against ubiquitination and protects the protein against proteasomal degradation.

Involvement in disease: Lymphoproliferative syndrome, X-linked, 2 (XLP2) [MIM:300635]: A rare immunodeficiency characterized by extreme susceptibility to infection with Epstein-Barr virus (EBV). Symptoms include severe or fatal mononucleosis, acquired hypogammaglobulinemia, pancytopenia and malignant lymphoma.Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.16

Sequence similarities: Belongs to the IAP family.Contains 3 BIR repeats.Contains 1 RING-type zinc finger.