title: Control of cell cycle-dependent degradation of c-Ski proto-oncoprotein by Cdc34.
abstract: It is known that excess amounts of Ski, or any member of its proto-oncoprotein family, causes disruption of the transforming growth factor beta signal transduction pathway, thus causing oncogenic transformation of cells. Previous studies indicate that Ski is a relatively unstable protein whose expression levels can be regulated by ubiquitin-mediated proteolysis. Here, we investigate the mechanism by which the stability of Ski is regulated. We show that the steady-state levels of Ski protein are controlled post-translationally by cell cycle-dependent proteolysis, wherein Ski is degraded during the interphase of the cell cycle but is relatively stable during mitosis. Furthermore, we demonstrate that the ubiquitin-conjugating enzyme Cdc34 mediates cell cycle-dependent Ski degradation both in vitro and in vivo. Overexpression of dominant-negative Cdc34 stabilizes Ski and enhances its ability to antagonize TGF-beta signaling. Our data suggest that regulated proteolysis of Ski is one of the key mechanisms that control the threshold levels of this proto-oncoprotein, and thus prevents epithelial cells from becoming TGF-beta resistant.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado-Boulder, Boulder, CO 80309, USA.
authors.forename: Mara
authors.initials: M
authors.lastname: Macdonald
authors.forename: Yong
authors.initials: Y
authors.lastname: Wan
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Roberts
authors.forename: Tom Hiu
authors.initials: TH
authors.lastname: Cheung
authors.forename: Richard
authors.initials: R
authors.lastname: Erickson
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Knuesel
authors.forename: Xuedong
authors.initials: X
authors.lastname: Liu
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008907:Mink; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D014981:Xenopus
chemical_list: D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C060615:SKIL protein, human; D016212:Transforming Growth Factor beta; C060614:SKI protein, human; C577447:CDC34 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases