RGD Reference Report - Bridge-1, a novel PDZ-domain coactivator of E2A-mediated regulation of insulin gene transcription. - Rat Genome Database
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Bridge-1, a novel PDZ-domain coactivator of E2A-mediated regulation of insulin gene transcription.

Authors: Thomas, MK  Yao, KM  Tenser, MS  Wong, GG  Habener, JF 
Citation: Thomas MK, etal., Mol Cell Biol 1999 Dec;19(12):8492-504.
RGD ID: 633869
Pubmed: (View Article at PubMed) PMID:10567574

Proteins in the E2A family of basic helix-loop-helix transcription factors are important in a wide spectrum of physiologic processes as diverse as neurogenesis, myogenesis, lymphopoeisis, and sex determination. In the pancreatic beta cell, E2A proteins, in combination with tissue-specific transcription factors, regulate expression of the insulin gene and other genes critical for beta-cell function. By yeast two-hybrid screening of a cDNA library prepared from rat insulinoma (INS-1) cells, we identified a novel protein, Bridge-1, that interacts with E2A proteins and functions as a coactivator of gene transcription mediated by E12 and E47. Bridge-1 contains a PDZ-like domain, a domain known to be involved in protein-protein interactions. Bridge-1 is highly expressed in pancreatic islets and islet cell lines and the expression pattern is primarily nuclear. The interaction of Bridge-1 with E2A proteins is further demonstrated by coimmunoprecipitation of in vitro-translated Bridge-1 with E12 or E47 and by mammalian two-hybrid studies. The PDZ-like domain of Bridge-1 is required for interaction with the carboxy terminus of E12. In both yeast and mammalian two-hybrid interaction studies, Bridge-1 mutants lacking an intact PDZ-like domain interact poorly with E12. An E12 mutant (E12DeltaC) lacking the carboxy-terminal nine amino acids shows impaired interaction with Bridge-1. Bridge-1 has direct transactivational activity, since a Gal4 DNA-binding domain-Bridge-1 fusion protein transactivates a Gal4CAT reporter. Bridge-1 also functions as a coactivator by enhancing E12- or E47-mediated activation of a rat insulin I gene minienhancer promoter-reporter construct in transient-transfection experiments. Substitution of the mutant E12DeltaC for E12 reduces the coactivation of the rat insulin I minienhancer by Bridge-1. Inactivation of endogenous Bridge-1 in insulinoma (INS-1) cells by expression of a Bridge-1 antisense RNA diminishes rat insulin I promoter activity. Bridge-1, by utilizing its PDZ-like domain to interact with E12, may provide a new mechanism for the coactivation and regulation of transcription of the insulin gene.

Annotation

Gene Ontology Annotations    

Cellular Component
nucleus  (IDA)

Molecular Function

Objects Annotated

Genes (Rattus norvegicus)
Psmd9  (proteasome 26S subunit, non-ATPase 9)
Tcf3  (transcription factor 3)


Additional Information