Transcriptional activation of the GLUT2 gene by the IPF-1/STF-1/IDX-1 homeobox factor.

Abstract

The homeodomain protein PDX-1, referred as IPF-1/STF-1/IDX-1, is a transcriptional factor that plays a critical role in the control of several genes expressed in the pancreatic islet. PDX-1 gene expression has been previously shown to be reduced in cultured beta-cell lines chronically exposed to high glucose concentrations. As the glucose transporter type 2 (GLUT2) gene expression is selectively decreased in the beta-pancreatic cells of experimental models of diabetes, we postulated that the loss of GLUT2 gene expression in the pancreatic islets of diabetic animals may be due to the loss of PDX-1 transacting function on the GLUT2 gene. We, therefore, investigated the potential role of PDX-1 in the transcriptional control of GLUT2. We have identified a repeat of a TAAT motif (5'-TAATA-ATAACA-3') conserved in the sequence of the human and murine GLUT2 promoters. Recombinant PDX-1 binds to this GLUT2TAAT motif in electrophoretic mobility shift experiments. PDX-1 antiserum detects the formation of the complex of PDX-1 with the GLUT2TAAT motif in nuclear extracts from the pancreatic insulin-secreting cell line, beta TC3. The GLUT2TAAT motif was mutated in the murine GLUT2 promoter (-1308/+49 bp) linked to a luciferase reporter gene and transfected into beta TC3 cells. Compared with the transcriptional activity of the wild type promoter, that of the mutated promoter decreases by 41%. Multiple copies of the GLUT2TAAT motif were ligated 5' to a heterologous promoter and transfected into a PDX-1-expressing cell line (beta TC3) and into cell lines lacking the homeobox factor (InR1-G9 and JEG-3). The GLUT2TAAT motif mediates the activation of the heterologous promoter in the PDX-1-expressing cell line but not in InR1-G9 or JEG-3 cell lines. Furthermore, cotransfection in a PDX-1-deficient cell line with the expression vector encoding PDX-1 transactivates specifically the heterologous promoter containing the multimerized GLUT2TAAT motif. These data demonstrate that the murine GLUT2 promoter is controlled by the PDX-1 homeobox factor through the identified GLUT2TAAT motif.

Sirtuin 3 regulates mouse pancreatic beta cell function and is suppressed in pancreatic islets isolated from human type 2 diabetic patients

“…5a-d). Pdx1 and Mafa are crucial for beta cell development and also function as transcription factors for other important genes, including insulin (Ins1) and Slc2a2 (essential for glucose uptake into the beta cell) [30][31][32][33][34]. For all these genes, incubation with Sirt3 siRNA caused a similar level of suppression as incubation with TNFα and IL1β.…”

A feat of metabolic proportions: Pdx1 orchestrates islet development and function in the maintenance of glucose homeostasis

“…These included the genes encoding insulin [68,70,71,126], Glut2 [127,128], glucokinase [129,130], islet amyloid polypeptide (IAPP) [63,75,131,132], Pax4 [133], Nkx6.1 [69,134], MafA [72], liver receptor homolog (Lrh) 1 [135], and Pdx1 itself [37]. In recent years, the direct regulation of many of these genes by Pdx1 has been confirmed using loss-of-function studies in islets and intact animals, and occupancy by Pdx1 of the endogenous genes in islets and β cell lines has been confirmed using the chromatin immunoprecipitation (ChIP) assay [70].…”

Pleiotropic effects of fatty acids on pancreatic β‐cells

“…IDX-1 is a transcription factor expressed in the duodenum and pancreatic beta and delta cells. It is required for embryonic development of the pancreas (Jonsson et al, 1994) and transactivates the GLUT2 (Waeber et al, 1996), glucokinase (Watada et al, 1996), insulin (Petersen et al, 1994), and somatostatin (Leonard et al, 1993) genes expression.…”