The pancreatic islet β-cell-enriched transcription factor Pdx-1 regulates Slc30a8 gene transcription through an intronic enhancer

Biochem J. 2011 Jan 1;433(1):95-105. doi: 10.1042/BJ20101488.

Abstract

The SLC30A8 gene encodes the zinc transporter ZnT-8, which provides zinc for insulin-hexamer formation. Genome-wide association studies have shown that a polymorphic variant in SLC30A8 is associated with altered susceptibility to Type 2 diabetes and we recently reported that glucose-stimulated insulin secretion is decreased in islets isolated from Slc30a8-knockout mice. The present study examines the molecular basis for the islet-specific expression of Slc30a8. VISTA analyses identified two conserved regions in Slc30a8 introns 2 and 3, designated enhancers A and B respectively. Transfection experiments demonstrated that enhancer B confers elevated fusion gene expression in both βTC-3 cells and αTC-6 cells. In contrast, enhancer A confers elevated fusion gene expression selectively in βTC-3 and not αTC-6 cells. These data suggest that enhancer A is an islet β-cell-specific enhancer and that the mechanisms controlling Slc30a8 expression in α- and β-cells are overlapping, but distinct. Gel retardation and ChIP (chromatin immunoprecipitation) assays revealed that the islet-enriched transcription factor Pdx-1 binds enhancer A in vitro and in situ respectively. Mutation of two Pdx-1-binding sites in enhancer A markedly reduces fusion gene expression suggesting that this factor contributes to Slc30a8 expression in β-cells, a conclusion consistent with developmental studies showing that restriction of Pdx-1 to pancreatic islet β-cells correlates with the induction of Slc30a8 gene expression and ZnT-8 protein expression in vivo.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Cation Transport Proteins / genetics*
  • Enhancer Elements, Genetic / genetics*
  • Gene Expression Regulation*
  • Homeodomain Proteins / physiology*
  • Introns / genetics
  • Islets of Langerhans / chemistry*
  • Islets of Langerhans / metabolism
  • Mice
  • Tissue Distribution
  • Trans-Activators / physiology*
  • Transcription Factors
  • Transcription, Genetic*
  • Zinc Transporter 8

Substances

  • Cation Transport Proteins
  • Homeodomain Proteins
  • Slc30a8 protein, mouse
  • Trans-Activators
  • Transcription Factors
  • Zinc Transporter 8
  • pancreatic and duodenal homeobox 1 protein