Characterization of the human SLC30A8 promoter and intronic enhancer
Genome-wide association studies have shown that a polymorphic variant inSLC30A8, which encodes zinc transporter-8, is associated with altered susceptibility to type 2 diabetes (T2D). This association is consistent with the observation that glucose-stimulated insulin secretion is decreased in islets isolated fromSlc30a8knockout mice. In this study, immunohistochemical staining was first used to show thatSLC30A8is expressed specifically in pancreatic islets. Fusion gene studies were then used to examine the molecular basis for the islet-specific expression ofSLC30A8. The analysis ofSLC30A8-luciferase expression in βTC-3 cells revealed that the proximal promoter region, located between −6154 and −1, relative to the translation start site, was only active in stable but not transient transfections. VISTA analyses identified three regions in theSLC30A8promoter and a region inSLC30A8intron 2 that are conserved in the mouseSlc30a8gene. Additional fusion gene experiments demonstrated that none of theseSlc30a8promoter regions exhibited enhancer activity when ligated to a heterologous promoter whereas the conserved region inSLC30A8intron 2 conferred elevated reporter gene expression selectively in βTC-3 but not in αTC-6 cells. Finally, the functional effects of a single nucleotide polymorphism (SNP), rs62510556, in this conserved intron 2 enhancer were investigated. Gel retardation studies showed that rs62510556 affects the binding of an unknown transcription factor and fusion gene analyses showed that it modulates enhancer activity. However, genetic analyses suggest that this SNP is not a causal variant that contributes to the association betweenSLC30A8and T2D, at least in Europeans.