title: Monoubiquitination of Tob/BTG family proteins competes with degradation-targeting polyubiquitination.
abstract: Tob belongs to the anti-proliferative Tob/BTG protein family. The expression level of Tob family proteins is strictly regulated both transcriptionally and through post-translational modification. Ubiquitin (Ub)/proteosome-dependent degradation of Tob family proteins is critical in controlling cell cycle progression and DNA damage responses. Various Ub ligases (E3s) are responsible for degradation of Tob protein. Here, we show that Tob family proteins undergo monoubiquitination even in the absence of E3s in vitro. Determination of the ubiquitination site(s) in Tob by mass spectrometric analysis revealed that two lysine residues (Lys48 and Lys63) located in Tob/BTG homology domain are ubiquitinated. A mutant Tob, in which both Lys48 and Lys63 are substituted with alanine, is more strongly polyubiquitinated than wild-type Tob in vivo. These data suggest that monoubiquitination of Tob family proteins confers resistance against polyubiquitination, which targets proteins for degradation. The strategy for regulating the stability of Tob family proteins suggests a novel role for monoubiquitination.
authors.affiliation: Division of Oncology, Institute of Medical Science, University of Tokyo, Shirokanedai, Minato-ku, Japan. toru@ims.u-tokyo.ac.jp
authors.forename: Toru
authors.initials: T
authors.lastname: Suzuki
authors.forename: Minsoo
authors.initials: M
authors.lastname: Kim
authors.forename: Hiroko
authors.initials: H
authors.lastname: Kozuka-Hata
authors.forename: Masato
authors.initials: M
authors.lastname: Watanabe
authors.forename: Masaaki
authors.initials: M
authors.lastname: Oyama
authors.forename: Kouhei
authors.initials: K
authors.lastname: Tsumoto
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D011994:Recombinant Proteins; C098669:TOB1 protein, human; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases