title: Interactions with p300 enhance transcriptional activation by the PDZ-domain coactivator Bridge-1.
abstract: Transcriptional coactivators are essential mediators of signal amplification in the regulation of gene expression in response to hormones and extracellular signals. We previously identified Bridge-1 (PSMD9) as a PDZ-domain coregulator that augments insulin gene transcription via interactions with the basic helix-loop-helix transcription factors E12 and E47, and that increases transcriptional activation by the homeodomain transcription factor PDX-1. In these studies, we find that transcriptional activation by Bridge-1 can be regulated via interactions with the histone acetyltransferase and nuclear receptor coactivator p300. In transfection assays, transcriptional activation by Bridge-1 is increased by the inhibition of endogenous histone deacetylase activity with trichostatin A, indicating that the transcriptional activation function of Bridge-1 can be regulated by histone modifications. The exogenous expression of p300 enhances the transcriptional activation by Bridge-1 in a dose-dependent manner. In contrast, the sequestration of p300 by the overexpression of the adenoviral protein E1A, but not by an E1A mutant protein that is unable to interact with p300, suppresses the transcriptional activation by Bridge-1. We demonstrate that p300 and Bridge-1 proteins interact in immunopre-cipitation and glutathione-S-transferase (GST) pull-down assays. Bridge-1 interacts directly with multiple regions within p300 that encompass C/H1 or C/H2 cysteine- and histidine-rich protein interaction domains and the histone acetyltransferase domain. Deletion or point mutagenesis of the Bridge-1 PDZ domain substantially reduces transcriptional activation by Bridge-1 and interrupts interactions with p300. We propose that p300 interactions with Bridge-1 can augment the transcriptional activation of regulatory target genes by Bridge-1.
authors.affiliation: Laboratory of Molecular Endocrinology and Diabetes Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Jee H
authors.initials: JH
authors.lastname: Lee
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Volinic
authors.forename: Constanze
authors.initials: C
authors.lastname: Banz
authors.forename: Kwok-Ming
authors.initials: KM
authors.lastname: Yao
authors.forename: Melissa K
authors.initials: MK
authors.lastname: Thomas
mesh_terms: D017500:Adenovirus E1A Proteins / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D017353:Gene Deletion; D005982:Glutathione Transferase / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids / Q000494:pharmacology; D047468:Immunoprecipitation; D007328:Insulin / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D046988:Proteasome Endopeptidase Complex; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D015003:Yeasts; D050880:p300-CBP Transcription Factors / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D017500:Adenovirus E1A Proteins; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D007328:Insulin; C114476:PSMD9 protein, human; D011506:Proteins; C012589:trichostatin A; D050880:p300-CBP Transcription Factors; D005982:Glutathione Transferase; D046988:Proteasome Endopeptidase Complex