title: Molecular interaction between HAX-1 and XIAP inhibits apoptosis.
abstract: Caspase-3 is an important executor caspase that plays an essential role in apoptosis. Recently, HS1-associated protein X1 (HAX-1) was found to be a substrate of caspase-3. Although HAX-1 has serve multifunctional roles in cellular functions such as cell survival and calcium homeostasis, the detailed functional mechanism of HAX-1 remains still unclear. In this study, we performed proteomic experiments to identify the HAX-1 interactome. Through immunoprecipitation and 2D gel electrophoresis, we identified X-linked inhibitor of apoptosis protein (XIAP) as a novel HAX-1-interacting protein. By performing the GST pull-down assay, we defined the interaction domains in HAX-1 and XIAP, showing that HAX-1 binds to the BIR2 and BIR3 domains of XIAP whereas XIAP binds to the C-terminal domain of HAX-1. In addition, surface plasma resonance experiments showed that both BIR2 and BIR3 domains of XIAP bind to HAX-1 with affinity similar to that of full-length XIAP, indicating that either domain is necessary and sufficient for tight binding to HAX-1. Taken together with the observation that HAX-1 suppresses the polyubiquitination of XIAP, the cell viability assay results suggest that the formation of the HAX-1-XIAP complex inhibits apoptosis by enhancing the stability of XIAP against proteosomal degradation.
authors.affiliation: Medical Proteomics Research Center, KRIBB, Daejeon 305-806, Republic of Korea.
authors.forename: Young Ji
authors.initials: YJ
authors.lastname: Kang
authors.forename: Mi
authors.initials: M
authors.lastname: Jang
authors.forename: Yun Kyung
authors.initials: YK
authors.lastname: Park
authors.forename: Sunghyun
authors.initials: S
authors.lastname: Kang
authors.forename: Kwang-Hee
authors.initials: KH
authors.lastname: Bae
authors.forename: Sayeon
authors.initials: S
authors.lastname: Cho
authors.forename: Chong-Kil
authors.initials: CK
authors.lastname: Lee
authors.forename: Byoung Chul
authors.initials: BC
authors.lastname: Park
authors.forename: Seung-Wook
authors.initials: SW
authors.lastname: Chi
authors.forename: Sung Goo
authors.initials: SG
authors.lastname: Park
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D040901:Proteomics; D054875:Ubiquitination; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C104759:HAX1 protein, human; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D053148:Caspase 3