The Ski-binding protein C184M negatively regulates tumor growth factor-beta signaling by sequestering the Smad proteins in the cytoplasm.
Ski is a transcriptional co-repressor and is involved in the negative regulation of tumor growth factor-beta (TGF-beta) signaling. To understand more fully the role of Ski in TGF-beta signaling, we searched for novel Ski-interacting proteins. The identified C184M protein consists of 189 amino acids and contains the leucine-rich region. An association between Ski and C184M involving the leucine-rich region of C184M and the C-terminal coiled-coil motif of Ski was confirmed by glutathione S-transferase pull-down and immunoprecipitation assays. The C184M protein is located in the cytosol, and the C184M and Ski signals are co-localized in the cytoplasm when C184M was co-expressed with Ski in CV-1 cells. The cytoplasmic C184M-Ski complex inhibited the nuclear translocation of Smad2. Consistent with this, the activity of promoter containing the Smad-binding sites was repressed by C184M, and the TGF-beta-induced growth inhibition of mink lung Mv1Lu cells was attenuated by the ectopic expression of C184M. Thus, C184M inhibits TGF-beta signaling in concert with Ski. In hepatocytes, which express significant levels of C184M, the Ski signals were found only in the cytoplasm, supporting the notion that C184M forms a complex with Ski in the cytosol.
Kokura
Kenji
K
Laboratory of Molecular Genetics, RIKEN Tsukuba Institute, 3-1-1 Koyadai, Ibaraki 305-0074, Japan.
Kim
Hyungtae
H
Shinagawa
Toshie
T
Khan
Md Matiullah
MM
Nomura
Teruaki
T
Ishii
Shunsuke
S
D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000502:physiology*; D056918:Nuclear Receptor Coactivators; D011485:Protein Binding; D021381:Protein Transport; D015398:Signal Transduction / Q000502:physiology*; D051785:Smad Proteins; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D056918:Nuclear Receptor Coactivators; C111791:SNW1 protein, human; C491762:Skiip protein, mouse; D051785:Smad Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta