title: TRIM32 protein sensitizes cells to tumor necrosis factor (TNFα)-induced apoptosis via its RING domain-dependent E3 ligase activity against X-linked inhibitor of apoptosis (XIAP).
abstract: TRIM32, which belongs to the tripartite motif (TRIM) protein family, has the RING finger, B-box, and coiled-coil domain structures common to this protein family, along with an additional NHL domain at the C terminus. TRIM32 reportedly functions as an E3 ligase for actin, a protein inhibitor of activated STAT y (PIASy), dysbindin, and c-Myc, and it has been associated with diseases such as muscular dystrophy and epithelial carcinogenesis. Here, we identify a new substrate of TRIM32 and propose a mechanism through which TRIM32 might regulate apoptosis. Our overexpression and knockdown experiments demonstrate that TRIM32 sensitizes cells to TNFα-induced apoptosis. The RING domain is necessary for this pro-apoptotic function of TRM32 as well as being responsible for its E3 ligase activity. TRIM32 colocalizes and directly interacts with X-linked inhibitor of apoptosis (XIAP), a well known cancer therapeutic target, through its coiled-coil and NHL domains. TRIM32 overexpression enhances XIAP ubiquitination and subsequent proteasome-mediated degradation, whereas TRIM32 knockdown has the opposite effect, indicating that XIAP is a substrate of TRIM32. In vitro reconstitution assay reveals that XIAP is directly ubiquitinated by TRIM32. Our novel results collectively suggest that TRIM32 sensitizes TNFα-induced apoptosis by antagonizing XIAP, an anti-apoptotic downstream effector of TNFα signaling. This function may be associated with TRIM32-mediated tumor suppressive mechanism.
authors.affiliation: Laboratory of Cell Signaling, Aging Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-806, Korea.
authors.forename: Yeung Sook
authors.initials: YS
authors.lastname: Ryu
authors.forename: Younglang
authors.initials: Y
authors.lastname: Lee
authors.forename: Keun Woo
authors.initials: KW
authors.lastname: Lee
authors.forename: Chae Young
authors.initials: CY
authors.lastname: Hwang
authors.forename: Jin-Soo
authors.initials: JS
authors.lastname: Maeng
authors.forename: Jeong-Hoon
authors.initials: JH
authors.lastname: Kim
authors.forename: Yeon-Soo
authors.initials: YS
authors.lastname: Seo
authors.forename: Kwan-Hee
authors.initials: KH
authors.lastname: You
authors.forename: Byeongwoon
authors.initials: B
authors.lastname: Song
authors.forename: Ki-Sun
authors.initials: KS
authors.lastname: Kwon
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D001483:Base Sequence; D015536:Down-Regulation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D054829:RING Finger Domains; D013379:Substrate Specificity; D014157:Transcription Factors / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000070584:Tripartite Motif Proteins; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism*
chemical_list: D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; C094027:TRIM32 protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex