Glucagon gene transcription activation mediated by synergistic interactions of pax-6 and cdx-2 with the p300 co-activator.
In the endocrine pancreas, alpha-cell-specific expression of the glucagon gene is mediated by DNA-binding proteins that interact with the proximal G1 promoter element, which contains several AT-rich domains. The homeodomain transcription factors brain-4, pax-6, and cdx-2 have been shown to bind to these sites and to transactivate glucagon gene expression. In the present study, we investigated the interaction of cdx-2 and pax-6 with p300, a co-activator coupled to the basal transcription machinery. In transient transfection-expression experiments, we found that the transactivating effects of cdx-2 and pax-6 on the glucagon gene were greatly enhanced by the additional expression of p300. This enhancement was due to direct protein-protein interactions of both pax-6 and cdx-2 with the N-terminal C/H1 domain of p300. pax-6 and cdx-2 also directly interacted with one another at the protein level. pax-6, bound to its DNA recognition site in the glucagon G1 promoter element, tethered cdx-2 to the molecular complex of pax-6 and p300. Further, we found that the presence of cdx-2 enhanced the interaction of pax-6 with p300, thus establishing a molecular complex of transcription factors implicated in tissue-specific glucagon gene expression with the basal transcriptional machinery.
Hussain
M A
MA
Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
Habener
J F
JF
D000818:Animals; D000071616:CDX2 Transcription Factor; D002460:Cell Line; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005136:Eye Proteins; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005934:Glucagon / Q000235:genetics*; D018398:Homeodomain Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism*; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D010179:Pancreas / Q000378:metabolism; D011233:Precipitin Tests; D052336:Proglucagon; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011498:Protein Precursors / Q000235:genetics*; D012097:Repressor Proteins; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation
D000071616:CDX2 Transcription Factor; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D011498:Protein Precursors; D012097:Repressor Proteins; D015534:Trans-Activators; D052336:Proglucagon; D005934:Glucagon