title: The MSG1 non-DNA-binding transactivator binds to the p300/CBP coactivators, enhancing their functional link to the Smad transcription factors.
abstract: The MSG1 nuclear protein has a strong transcriptional activating activity but does not bind directly to DNA. When cotransfected, MSG1 enhances transcription mediated by the Smad transcription factors in mammalian cells in a manner dependent on ligand-induced Smad hetero-oligomerization. However, the mechanism of this MSG1 effect has been unknown. We now show that MSG1 directly binds to the p300/cAMP-response element-binding protein-binding protein (CBP) transcriptional coactivators, which in turn bind to the Smads, and enhances Smad-mediated transcription in a manner dependent on p300/CBP. The C-terminal transactivating domain of MSG1 is required for binding to p300/CBP and enhancement of Smad-mediated transcription; the viral VP16 transactivating domain could not substitute for it. In the N-terminal region of MSG1, we identified a domain that is necessary and sufficient to direct the specific interaction of MSG1 with Smads. We also found that the Hsc70 heat-shock cognate protein also forms complex with MSG1 in vivo, suppressing both binding of MSG1 to p300/CBP and enhancement of Smad-mediated transcription by MSG1. These results indicate that MSG1 interacts with both the DNA-binding Smad proteins and the p300/CBP coactivators through its N- and C-terminal regions, respectively, and enhances the functional link between Smads and p300/CBP.
authors.affiliation: Laboratory of Tumor Biology, Massachusetts General Hospital Cancer Center, Massachusetts General Hospital-East, Charlestown, Massachusetts 02129, USA.
authors.forename: T
authors.initials: T
authors.lastname: Yahata
authors.forename: M P
authors.initials: MP
authors.lastname: de Caestecker
authors.forename: R J
authors.initials: RJ
authors.lastname: Lechleider
authors.forename: S
authors.initials: S
authors.lastname: Andriole
authors.forename: A B
authors.initials: AB
authors.lastname: Roberts
authors.forename: K J
authors.initials: KJ
authors.lastname: Isselbacher
authors.forename: T
authors.initials: T
authors.lastname: Shioda
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D051901:Smad4 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D051017:Apoptosis Regulatory Proteins; C512688:CITED1 protein, human; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D009687:Nuclear Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators; D014157:Transcription Factors