title: The RING domain of cIAP1 mediates the degradation of RING-bearing inhibitor of apoptosis proteins by distinct pathways.
abstract: The Inhibitor of Apoptosis proteins (IAPs) are key repressors of apoptosis. Several IAP proteins contain a RING domain that functions as an E3 ubiquitin ligase involved in the ubiquitin-proteasome pathway. Here we investigated the interplay of ubiquitin-proteasome pathway and RING-mediated IAP turnover. We found that the CARD-RING domain of cIAP1 (cIAP1-CR) is capable of down-regulating protein levels of RING-bearing IAPs such as cIAP1, cIAP2, XIAP, and Livin, while sparing NAIP and Survivin, which do not possess a RING domain. To determine whether polyubiquitination was required, we tested the ability of cIAP1-CR to degrade IAPs under conditions that impair ubiquitination modifications. Remarkably, although the ablation of E1 ubiquitin-activating enzyme prevented cIAP1-CR-mediated down-regulation of cIAP1 and cIAP2, there was no impact on degradation of XIAP and Livin. XIAP mutants that were not ubiquitinated in vivo were readily down-regulated by cIAP1-CR. Moreover, XIAP degradation in response to cisplatin and doxorubicin was largely prevented in cIAP1-silenced cells, despite cIAP2 up-regulation. The knockdown of cIAP1 and cIAP2 partially blunted Fas ligand-mediated down-regulation of XIAP and protected cells from cell death. Together, these results show that the E3 ligase RING domain of cIAP1 targets RING-bearing IAPs for proteasomal degradation by ubiquitin-dependent and -independent pathways.
authors.affiliation: Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada.
authors.forename: Herman H
authors.initials: HH
authors.lastname: Cheung
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Plenchette
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Kern
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Mahoney
authors.forename: Robert G
authors.initials: RG
authors.lastname: Korneluk
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis; D015536:Down-Regulation; D053222:Fas Ligand Protein / Q000378:metabolism; D005799:Genes, Dominant; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism* / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology*; D008954:Models, Biological; D016296:Mutagenesis; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D053222:Fas Ligand Protein; C108257:ITGB1BP1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D016328:NF-kappa B; D034741:RNA, Small Interfering; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex