The MSG1 non-DNA-binding transactivator binds to the p300/CBP coactivators, enhancing their functional link to the Smad transcription factors.

Yahata T, de Caestecker MP, Lechleider RJ, Andriole S, Roberts AB, Isselbacher KJ, Shioda T
J Biol Chem. 2000 275 (12): 8825-34

PMID: 10722728 · DOI:10.1074/jbc.275.12.8825

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.

MeSH Terms (19)

Amino Acid Sequence Animals Binding Sites Carrier Proteins DNA-Binding Proteins HSC70 Heat-Shock Proteins HSP70 Heat-Shock Proteins Humans Models, Genetic Molecular Sequence Data Multigene Family Nuclear Proteins Protein Binding Protein Structure, Tertiary Sequence Homology, Amino Acid Smad4 Protein Trans-Activators Transcription, Genetic Transcription Factors

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