Identification and functional characterization of the peroxisomal proliferator response element in rat GLUT2 promoter

Abstract

We identified the peroxisomal proliferator response element (PPRE) in the +68/+89 region of the rat GLUT2 gene. To identify whether the putative PPRE in the GLUTS gene (GLUT2-PPRE) is functional, GLUTS promoter-luciferase reporter constructs were transfected into CV-1 cells. Promoter activities were increased by coexpression of peroxisomal proliferator-activated receptor (PPAR)-gamma, retinoid X receptor (RXR)-alpha, and treatment of their ligands; troglitazone and g-cis retinoic acid potentiated the transactivational effects, Introduction of mutations in GLUT2-PPBE resulted in loss of transactivational effects of the PPAR-gamma/RXR-alpha heterodimer, Electrophoretic mobility shift assay using nuclear extracts of CV-1 cells, which were transfected with various combinations of PPARs or RXR-alpha expression plasmids, revealed that heterodimers of PPAR-gamma and RXR-alpha preferentially bound to GLUT2-PPRE. In HIT-T15 cells, promoter activity of the mt GLUTS gene was increased by troglitazone and g-cis retinoic acid, and mutations of GLUT2-PPRE resulted in reduction of promoter activity. In addition, we observed increased GLUTS transcription by troglitazone and 9-cis retinoic acid in isolated rat primary islets, These results suggested that the GLUT2-PPRE is functional and plays a significant role in gene expression of GLUTS in pancreatic beta-cells. This is the first report; identifying PPRE in a gene involved in glucose homeostasis, linking the effect; of troglitazone on the regulation of insulin secretion.