MafA, NeuroD1 and HNF1β synergistically activate the Slc2a2 (Glut2) gene in β-cells

Glucose transporter type 2 (GLUT2), encoded by the SLC2A2 gene, is an essential component of glucose-stimulated insulin secretion in pancreatic islet beta-cells. Like that of the gene encoding insulin, expression of the SLC2A2 gene expression is closely linked to 6-cell functionality in rodents, but the mechanism by which beta-cell-specific expression of SLC2A2 is controlled remains unclear. In this report, to identify putative enhancer elements of the mouse Slc2a2 gene, we examined evolutional conservation of the nucleotide sequence of its genomic locus, together with ChIP-seq data of histone modifications and various transcription factors published in previous studies. Using luciferase reporter assays, we found that an evolutionarily conserved region (ECR) located approximately 40 kbp downstream of the transcription start site of Slc2a2 functions as an active enhancer in the MIN6 beta-cell line. We also found that three beta-cell-enriched transcription factors, MafA, NeuroD1 , and HNF1 beta, synergistically activate transcription through this 3' downstream distal enhancer (ECR3') and the proximal promoter region of the gene. Our data also indicate that the simultaneous binding of HNF1 beta to its target sites within the promoter and ECR3' of Slc2a2 is indispensable for transcriptional activation, and that binding of MafA and NeuroD1 to their respective target sites within the ECR3' enhances transcription. Co-immunoprecipitation experiments suggested that MafA, NeuroD1, and HNF1 beta interact with each other. Overall, these results suggest that promoter-enhancer communication through MafA, NeuroD1, and HNF1 beta is critical for Slc2a2 gene expression. These findings provide clues to help elucidate the mechanism of regulation of Slc2a2 gene expression in beta-cells.

Automated summary

The study identified an evolutionarily conserved region located approximately 40 kbp downstream of the transcription start site of the Slc2a2 gene as an active enhancer in the MIN6 beta-cell line. Three beta-cell-enriched transcription factors, MafA, NeuroD1, and HNF1 beta, were found to synergistically activate transcription through this enhancer and the proximal promoter region of the gene. Co-immunoprecipitation experiments suggested that these transcription factors interact with each other and are critical for Slc2a2 gene expression.