BETA2 Activates Transcription From the Upstream Glucokinase Gene Promoter in Islet β-Cells and Gut Endocrine Cells

Abstract

Glucokinase (GK) gene transcription initiates in the islet (β-cell), gut, and brain from promoter sequences residing ∼35 kbp upstream from those used in liver. Expression of βGK is controlled in β-cells by cell-enriched (i.e. pancreatic duodenal homeobox 1 [PDX-1]) and ubiquitously (i.e., Pal) distributed factors that bind to and activate from conserved sequence motifs within the upstream promoter region (termed βGK). Here, we show that a conserved E-box element also contributes to control in the islet and gut. βGK promoter-driven reporter gene activity was diminished by mutating the specific sequences involved in E-box-mediated basic helix-loop-helix factor activator binding in islet β-cells and enteroendocrine cells. Gel shift assays demonstrated that the βGK and insulin gene E-box elements formed the same cell-enriched (BETA2:E47) and generally distributed (upstream stimulatory factor [USF]) protein-DNA complexes. βGK E-box-driven activity was stimulated in cotransfection assays performed in baby hamster kidney (BHK) cells with BETA2 and E47, but not USF. Chromatin immunoprecipitation assays performed with BETA2 antisera showed that BETA2 occupies the upstream promoter region of the endogenous βGK gene in β-cells. We propose that BETA2 (also termed NeuroD1) regulates βGK promoter activity.