title: Ro52-mediated monoubiquitination of IKK{beta} down-regulates NF-{kappa}B signalling.
abstract: Upon activation, NF-kappaB translocates into the nucleus and initiates biological events. This NF-kappaB signalling is mainly regulated by the protein kinase IKKbeta. Early in this signalling pathway, IKKbeta is phosphorylated for activation by several factors, such as pro-inflammatory cytokines and the Tax oncoprotein of HTLV-1. In cells infected by HTLV-1, IKKbeta is persistently phosphorylated and conjugated with monoubiquitin due to Tax expression. Although this Tax-induced monoubiquitination appears to be an important regulation system for IKKbeta, how the monoubiquitination occurs is unknown and its role in NF-kappaB signalling is still unclear. Here, we show that an E3-ubiquitin ligase Ro52 interacts weakly with wild-type IKKbeta but strongly with a phosphomimetic mutant IKKbeta to conjugate monoubiquitin in cooperation with an E2-ubiquitin-conjugating enzyme UbcH5B. These results suggest that the Tax-induced phosphorylation of IKKbeta causes an interaction with Ro52 for the subsequent monoubiquitination. NF-kappaB reporter assays have shown that the IKKbeta activity is suppressed by wild-type Ro52, but not by its inactive mutant. In addition, monoubiquitin fusion of IKKbeta reduced its activity for NF-kappaB signalling. We also found that Ro52 dramatically reduces the level of Tax. These results suggest that Ro52 down-regulates Tax-induced NF-kappaB signalling by monoubiquitinating IKKbeta and by reducing the level of Tax.
authors.affiliation: Department of Cardiology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Keiji
authors.initials: K
authors.lastname: Wada
authors.forename: Motoko
authors.initials: M
authors.lastname: Niida
authors.forename: Makoto
authors.initials: M
authors.lastname: Tanaka
authors.forename: Tetsu
authors.initials: T
authors.lastname: Kamitani
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D015536:Down-Regulation; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D054875:Ubiquitination; D000099207:SS-A Antigen
chemical_list: D051550:I-kappa B Kinase; D016328:NF-kappa B; D012261:Ribonucleoproteins; D000099207:SS-A Antigen
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