title: Activation of the IκB kinase complex by HTLV-1 Tax requires cytosolic factors involved in Tax-induced polyubiquitination.
abstract: Activation of NF-κB by human T cell leukaemia virus type 1 Tax is thought to be crucial in T-cell transformation and the onset of adult T cell leukaemia. Tax activates NF-κB through activation of the IκB kinase (IKK) complex, similar to cytokine-induced NF-κB activation, which involves active signalling complex formation using polyubiquitin chains as a platform. Although polyubiquitination of Tax was reported to be required for IKK activation, most studies have been performed using intact cells, in which secondary NF-κB activation can be induced by various cytokines that are secreted due to Tax-mediated primary NF-κB activation. Therefore, a cell-free assay system, in which IKK can be activated by adding highly purified recombinant Tax to cytosolic extract, was used to analyse Tax-induced IKK activation. In contrast to the cytosolic extract, the purified IKK complex was not activated by Tax, whereas, it was efficiently activated by MEKK1, that does not require polyubiquitination to activate IKK. Moreover, Tax-induced IKK activation was blocked when the cytosolic extract was mixed with either lysine-free, methylated or K63R ubiquitin. These results obtained through our cell-free assay suggest that K63-linked polyubiquitination is critical, but linear polyubiquitination is dispensable or insufficient for Tax-induced IKK activation.
authors.affiliation: Department of Cancer Biology, Division of Cellular and Molecular Biology, Institute of Medical Science, University of Tokyo, Shirokane-dai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Shibata
authors.forename: Yuetsu
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Jin
authors.initials: J
authors.lastname: Gohda
authors.forename: Jun-ichiro
authors.initials: J
authors.lastname: Inoue
mesh_terms: D016367:Baculoviridae / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D015368:Human T-lymphotropic virus 1 / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D047468:Immunoprecipitation; D019169:Jurkat Cells; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D025941:Protein Interaction Mapping; D011810:Quinoxalines / Q000494:pharmacology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D013450:Sulfones / Q000494:pharmacology; D054875:Ubiquitination
chemical_list: C434003:3-(4-methylphenylsulfonyl)-2-propenenitrile; C471109:4(2'-aminoethyl)amino-1,8-dimethylimidazo(1,2-a)quinoxaline; D016356:Gene Products, tax; D007093:Imidazoles; D009570:Nitriles; D011810:Quinoxalines; D011994:Recombinant Proteins; D013450:Sulfones; C514970:tax protein, Human T-lymphotrophic virus 1; D051550:I-kappa B Kinase; D048728:MAP Kinase Kinase Kinase 1