title: UFD2a mediates the proteasomal turnover of p73 without promoting p73 ubiquitination.
abstract: p73 protein level is kept extremely low in mammalian cultured cells and its stability may be regulated by not only the ubiquitin/proteasome-dependent proteolysis but also through other unidentified mechanisms. Here, we found for the first time that p73 is physically as well as functionally associated with the U-box-type E3/E4 ubiquitin ligase UFD2a. The immunoprecipitation experiments demonstrated that this interaction is mediated by the COOH-terminal region of p73alpha containing SAM domain. During the cisplatin-induced apoptosis in SH-SY5Y neuroblastoma cells, p73alpha accumulated at a protein level, whereas the endogenous UFD2a was significantly reduced in response to cisplatin. Ectopic expression of UFD2a decreased the half-life of p73alpha in association with a significant inhibition of the p73alpha-mediated transactivation as well as proapoptotic activity. Downregulation of endogenous UFD2a by antisense strategy resulted in a remarkable accumulation of p73alpha. Unexpectedly, UFD2a-mediated degradation of p73alpha was sensitive to the proteasomal inhibitor, however, UFD2a did not affect the ubiquitination levels of p73alpha. Taken together, our present findings imply that UFD2a might promote the proteasomal turnover of p73 in a ubiquitination-independent manner, and also suggest that UFD2a might play an important role in the regulation of cisplatin-induced apoptosis mediated by p73.
authors.affiliation: Division of Biochemistry, Chiba Cancer Center Research Institute, 666-2 Nitona, Chuoh-ku, Chiba 260- 8717, Japan.
authors.forename: Mitsuchika
authors.initials: M
authors.lastname: Hosoda
authors.forename: Toshinori
authors.initials: T
authors.lastname: Ozaki
authors.forename: Kou
authors.initials: K
authors.lastname: Miyazaki
authors.forename: Syunji
authors.initials: S
authors.lastname: Hayashi
authors.forename: Kazushige
authors.initials: K
authors.lastname: Furuya
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Watanabe
authors.forename: Takahito
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hanamoto
authors.forename: Satoru
authors.initials: S
authors.lastname: Todo
authors.forename: Akira
authors.initials: A
authors.lastname: Nakagawara
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D019556:COS Cells; D002458:Cell Fractionation; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002522:Chlorocebus aethiops; D002945:Cisplatin / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D016147:Genes, Tumor Suppressor; D006207:Half-Life; D006801:Humans; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D013347:Subcellular Fractions / Q000378:metabolism; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; D043743:Ubiquitin-Protein Ligase Complexes; C473697:UBE4B protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; D002945:Cisplatin