Ski acts as a co-repressor with Smad2 and Smad3 to regulate the response to type beta transforming growth factor.
The c-ski protooncogene encodes a transcription factor that binds DNA only in association with other proteins. To identify co-binding proteins, we performed a yeast two-hybrid screen. The results of the screen and subsequent co-immunoprecipitation studies identified Smad2 and Smad3, two transcriptional activators that mediate the type beta transforming growth factor (TGF-beta) response, as Ski-interacting proteins. In Ski-transformed cells, all of the Ski protein was found in Smad3-containing complexes that accumulated in the nucleus in the absence of added TGF-beta. DNA binding assays showed that Ski, Smad2, Smad3, and Smad4 form a complex with the Smad/Ski binding element GTCTAGAC (SBE). Ski repressed TGF-beta-induced expression of 3TP-Lux, the natural plasminogen activator inhibitor 1 promoter and of reporter genes driven by the SBE and the related CAGA element. In addition, Ski repressed a TGF-beta-inducible promoter containing AP-1 (TRE) elements activated by a combination of Smads, Fos, and/or Jun proteins. Ski also repressed synergistic activation of promoters by combinations of Smad proteins but failed to repress in the absence of Smad4. Thus, Ski acts in opposition to TGF-beta-induced transcriptional activation by functioning as a Smad-dependent co-repressor. The biological relevance of this transcriptional repression was established by showing that overexpression of Ski abolished TGF-beta-mediated growth inhibition in a prostate-derived epithelial cell line.
Xu
W
W
Huffington Center on Aging and Departments of Molecular and Cellular Biology and Dermatology, Baylor College of Medicine and Veterans Affairs Medical Center, Houston, TX 77030, USA.
Angelis
K
K
Danielpour
D
D
Haddad
M M
MM
Bischof
O
O
Campisi
J
J
Stavnezer
E
E
Medrano
E E
EE
D002467:Cell Nucleus / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D046911:Macromolecular Substances; D008545:Melanoma / Q000473:pathology; D009363:Neoplasm Proteins / Q000502:physiology*; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012097:Repressor Proteins / Q000502:physiology*; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D020798:Two-Hybrid System Techniques
D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; C060614:SKI protein, human; D008156:Luciferases