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 GLUT2 gene (GLUT2-PPRE) is functional, GLUT2 promoter-luciferase reporter constructs were transfected into CV-1 cells. Promoter activities were increased by coexpression of peroxisomal proliferator-activated receptor (PPAR)-␥, retinoid X receptor (RXR)-␣, and treatment of their ligands; troglitazone and 9-cis retinoic acid potentiated the transactivational effects. Introduction of mutations in GLUT2-PPRE resulted in loss of transactivational effects of the PPAR-␥/RXR-␣ heterodimer. Electrophoretic mobility shift assay using nuclear extracts of CV-1 cells, which were transfected with various combinations of PPARs or RXR-␣ expression plasmids, revealed that heterodimers of PPAR-␥ and RXR-␣ preferentially bound to GLUT2-PPRE. In HIT-T15 cells, promoter activity of the rat GLUT2 gene was increased by troglitazone and 9-cis retinoic acid, and mutations of GLUT2-PPRE resulted in reduction of promoter activity. In addition, we observed increased GLUT2 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 GLUT2 in pancreatic ␤-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. Diabetes 49:1517-1524, 2000

Identification and characterization of peroxisome proliferator response element in the mouse GLUT2 promoter

“…-196 -184 et al, 2001). On the other hand, PPAR-γ stimulated the promoter activity of genes responsible for glucose sensing apparatus of pancreatic β -cells, suggesting that this ligand could also improve glucosestimulated insulin secretion (Kim et al, 2000;2002b). In the hyperglycemic states of type 2 diabetes, administration of TZDs causes amelioration of blood glucose level, suggesting that the liver glucose sensor can be a direct target of TZDs action.…”

“…The labeled probe (10,000 cpm) was incubated with 5 µg of nuclear extract from rat liver for 30 min on ice. The binding reactions were same as described (Kim et al, 2000). To perform supershift assay, the binding mixtures were incubated for 10 min at room temperature in the presence of 1 µ l of anti-PPARγ (Kim et al, 2002a).…”

“…Thus, the direct role of PPAR-γ ligand on the genes involved in hepatic glucose metabolism cannot be ruled out. Previously, we have characterized the peroxisom proliferator-activator response element (PPRE) in the promoter regions of rat GLUT2 (Kim et al, 2000) and glucokinase (Kim et al, 2002) gene and reported their physiological implications in the insulin secretion in response to changing blood glucose level in the pancreas of type 2 diabetic Zucker diabetic fatty (ZDF) rats. We also showed that liver type glucokinase (L-GK) was directly upregulated by TZDs in its promoter (Kim et al, 2004).…”

Peroxisome Proliferator-activated Receptor γ (PPARγ) and Its Target Genes Are Downstream Effectors of FoxO1 Protein in Islet β-Cells

“…As such, this mouse showed a phenotype of functional ␤-cell failure, with an expression profile that agreed exactly with the proposed signaling pathway in this study. Also, others have reported PPAR␥ regulation of gene expression for GLUT2 (53), glucokinase (54), and GPR40 (55) in ␤-cells, plus key modulatory effects of PPAR␥ in ␤-cell endoplasmic reticulum stress related to a cytokine-induced loss of SERCA2 expression have been shown (56,57). In addition, numerous ␤-cell effects have been attributed to PPAR␥ from thiazolidinedione studies in islets, insulin-containing cell lines, and various animal models, although direct proof that the findings are PPAR␥-mediated is mostly lacking.…”

Novel Anti-Diabetic Formula: Recover Islet ?-Cell dysfunction with the implementation of molecular approach

“…PPAR-γ is known to be expressed in the pancreatic islet [7,8], and PPAR-responsive elements have been identified in the promoters of genes involved in glucosestimulated insulin secretion, including Glut2, Gck, IJASR|VOL 01|ISSUE 02|2015 www.ssjournals.com and Pdx1. [9][10][11][12][13] Information from studies of β-cell lines, humans at risk for type 2 diabetes propose that PPAR-γ agonist function and management guides to protection of β-islet cell mass and rodent models of progressive type 2 diabetes [14][15][16][17]. Whereas the studies noted above suggested a direct or indirect effect of PPAR-γ agonists on the biology of the β-islet, no studies to date have observed the molecular or epigenetic mechanisms whereby β-islet cell function is preserved or enhanced in response to PPAR-γ activation.…”