Insulin gene transcription is mediated by interactions between the p300 coactivator and PDX-1, BETA2, and E47.
Pancreatic beta-cell-type-specific expression of the insulin gene requires both ubiquitous and cell-enriched activators, which are organized within the enhancer region into a network of protein-protein and protein-DNA interactions to promote transcriptional synergy. Protein-protein-mediated communication between DNA-bound activators and the RNA polymerase II transcriptional machinery is inhibited by the adenovirus E1A protein as a result of E1A's binding to the p300 coactivator. E1A disrupts signaling between the non-DNA-binding p300 protein and the basic helix-loop-helix DNA-binding factors of insulin's E-element activator (i.e., the islet-enriched BETA2 and generally distributed E47 proteins), as well as a distinct but unidentified enhancer factor. In the present report, we show that E1A binding to p300 prevents activation by insulin's beta-cell-enriched PDX-1 activator. p300 interacts directly with the N-terminal region of the PDX-1 homeodomain protein, which contains conserved amino acid sequences essential for activation. The unique combination of PDX-1, BETA2, E47, and p300 was shown to promote synergistic activation from a transfected insulin enhancer-driven reporter construct in non-beta cells, a process inhibited by E1A. In addition, E1A inhibited the level of PDX-1 and BETA2 complex formation in beta cells. These results indicate that E1A inhibits insulin gene transcription by preventing communication between the p300 coactivator and key DNA-bound activators, like PDX-1 and BETA2:E47.
Qiu
Yi
Y
Department of Molecular Physiology, Vanderbilt University Medical Center, Nashville, Tennessee 37215, USA.
Guo
Min
M
Huang
Suming
S
Stein
Roland
R
D017500:Adenovirus E1A Proteins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050881:E1A-Associated p300 Protein; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D006367:HeLa Cells; D018398:Homeodomain Proteins; D006801:Humans; D007328:Insulin / Q000235:genetics*; D007515:Islets of Langerhans / Q000378:metabolism; D046911:Macromolecular Substances; D017921:Mastadenovirus / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism*; D051381:Rats; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000378:metabolism*; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection
D017500:Adenovirus E1A Proteins; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D050881:E1A-Associated p300 Protein; D018398:Homeodomain Proteins; D007328:Insulin; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D051820:TCF Transcription Factors; D015534:Trans-Activators; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; C093970:NEUROD1 protein, human; C544912:TCF7L1 protein, human; C553060:Tcf7l1 protein, rat; C084010:pancreatic and duodenal homeobox 1 protein; C494362:Ep300 protein, rat