title: Negative regulation of SCFSkp2 ubiquitin ligase by TGF-beta signaling.
abstract: TGF-beta is a multifunctional growth factor whose best-known function is to inhibit cell growth and suppress tumor formation. TGF-beta causes cells to accumulate in mid-to-late G1 phase by blocking the transition from G1 to S. It has been shown that TGF-beta inhibits Cdk2-cyclin E kinase activity by promoting the binding of cell cycle inhibitor p27Kip1 to the kinase complexes. Here, we show that TGF-beta treatment leads to stabilization of p27Kip1 during G1 to S transition. We found that TGF-beta negatively regulates components of the SCF complex, which degrades the p27Kip1 during the G1 to S transition, through two distinct mechanisms. Using a pulse-chase analysis, we demonstrated that the stability of Skp2 decreases in the presence of TGF-beta. Destabilization of Skp2 by ubiquitin-mediated proteolysis was also demonstrated that in an in vitro degradation system, using cell extracts prepared from TGF-beta-treated cultured cells. In addition, TGF-beta treatment decreases the levels of Cks1 mRNA. The deficiency of Cks1 in TGF-beta-treated cells likely contributes to the stabilization of p27Kip1 and destabilization of Skp2, because in the absence of Cks1, SCFSkp2 cannot ubiquitinate p27Kip1; instead, self-ubiquitination of Skp2 occurs. Thus, stabilization of the cell cycle inhibitor p27Kip1 and cell growth inhibition in response to TGF-beta occur in part through limiting the threshold of the SCFSkp2 ubiquitin ligase by transcriptional and post-transcriptional mechanisms.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado-Boulder, Boulder, CO 80309, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Dana
authors.initials: D
authors.lastname: Ungermannova
authors.forename: Jianpin
authors.initials: J
authors.lastname: Jin
authors.forename: J Wade
authors.initials: JW
authors.lastname: Harper
authors.forename: Xuedong
authors.initials: X
authors.lastname: Liu
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D016193:G1 Phase; D015971:Gene Expression Regulation, Enzymologic; D016147:Genes, Tumor Suppressor; D005982:Glutathione Transferase / Q000378:metabolism; D008025:Ligases / Q000378:metabolism*; D008168:Lung; D008907:Mink; D008954:Models, Biological; D011494:Protein Kinases / Q000187:drug effects; D011994:Recombinant Proteins / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D016196:S Phase; D044786:S-Phase Kinase-Associated Proteins / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism
chemical_list: C093090:CKS1B protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D011994:Recombinant Proteins; D044786:S-Phase Kinase-Associated Proteins; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; D050760:Cyclin-Dependent Kinase Inhibitor p27; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D005982:Glutathione Transferase; D011494:Protein Kinases; D042846:CDC2-CDC28 Kinases; D018844:Cyclin-Dependent Kinases; D008025:Ligases