A pancreatic β-cell-specific enhancer in the human PIX-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 beta -cell, To characterize the regulatory elements and potential transcription factors necessary for human PDX-1 gene expression in beta -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 beta- and non-beta -cells a novel beta -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 3 beta (HNF-3 beta) and HNF-1 alpha, Cotransfection experiments suggest that HNF-3 beta, HNF-1 alpha, and SP1 are positive regulators of the herein-described human PDX-I 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.