A Pancreatic β-Cell-specific Enhancer in the Human PDX-1 Gene Is Regulated by Hepatocyte Nuclear Factor 3β (HNF-3β), HNF-1α, and SPs Transcription Factors

The PDX-1 transcription factor plays a key role in pancreas development. Although expressed in all cells at the early stages, in the adult it is mainly restricted to the β-cell. To characterize the regulatory elements and potential transcription factors necessary for human PDX-1 gene expression in β-cells, we constructed a series of 5′ and 3′ deletion fragments of the 5′-flanking region of the gene, fused to the luciferase reporter gene. In this report, we identify by transient transfections in β- and non-β-cells a novel β-cell-specific distal enhancer element located between -3.7 and -3.45 kilobases. DNase I footprinting analysis revealed two protected regions, one binding the transcription factors SP1 and SP3 and the other hepatocyte nuclear factor 3β (HNF-3β) and HNF-1α. Cotransfection experiments suggest that HNF-3β, HNF-1α, and SP1 are positive regulators of the herein-described human PDX-1 enhancer element. Furthermore, mutations within each motif abolished the binding of the corresponding factor(s) and dramatically impaired the enhancer activity, therefore suggesting cooperativity between these factors.