title: TGF-beta-induced phosphorylation of Smad3 regulates its interaction with coactivator p300/CREB-binding protein.
abstract: Smads are intermediate effector proteins that transduce the TGF-beta signal from the plasma membrane to the nucleus, where they participate in transactivation of downstream target genes. We have shown previously that coactivators p300/CREB-binding protein are involved in TGF-beta-mediated transactivation of two Cdk inhibitor genes, p21 and p15. Here we examined the possibility that Smads function to regulate transcription by directly interacting with p300/CREB-binding protein. We show that Smad3 can interact with a C-terminal fragment of p300 in a temporal and phosphorylation-dependent manner. TGF-beta-mediated phosphorylation of Smad3 potentiates the association between Smad3 and p300, likely because of an induced conformational change that removes the autoinhibitory interaction between the N- and C-terminal domains of Smad3. Consistent with a role for p300 in the transcription regulation of multiple genes, overexpression of a Smad3 C-terminal fragment causes a general squelching effect on multiple TGF-beta-responsive reporter constructs. The adenoviral oncoprotein E1A can partially block Smad-dependent transcriptional activation by directly competing for binding to p300. Taken together, these findings define a new role for phosphorylation of Smad3: in addition to facilitating complex formation with Smad4 and promoting nuclear translocation, the phosphorylation-induced conformational change of Smad3 modulates its interaction with coactivators, leading to transcriptional regulation.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: X
authors.initials: X
authors.lastname: Shen
authors.forename: P P
authors.initials: PP
authors.lastname: Hu
authors.forename: N T
authors.initials: NT
authors.lastname: Liberati
authors.forename: M B
authors.initials: MB
authors.lastname: Datto
authors.forename: J P
authors.initials: JP
authors.lastname: Frederick
authors.forename: X F
authors.initials: XF
authors.lastname: Wang
mesh_terms: D017500:Adenovirus E1A Proteins / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D008954:Models, Biological; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D015398:Signal Transduction; D051900:Smad3 Protein; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D017500:Adenovirus E1A Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta