A 338-BP PROXIMAL FRAGMENT OF THE GLUCOSE-TRANSPORTER TYPE-2 (GLUT2) PROMOTER DRIVES REPORTER GENE-EXPRESSION IN THE PANCREATIC-ISLETS OF TRANSGENIC MICE

The high K-m glucose transporter GLUT2 is a membrane protein expressed in tissues involved in maintaining glucose homeostasis, and in cells where glucose-sensing is necessary. In many experimental models of dia betes, GLUT2 gene expression is decreased in pancreatic beta-cells, wh ich could lead to a loss of glucose-induced insulin secretion. In orde r to identify factors involved in pancreatic beta-cell specific expres sion of GLUT2, we have recently cloned the murine GLUT2 promoter and i dentified cis-elements within the 338-bp of the proximal promoter capa ble of binding islet-specific trans-acting factors. Furthermore, in tr ansient transfection studies, this 338-bp fragment could efficiently d rive the expression of the chloramphenicol acetyl transferase (CAT) ge ne in cell lines derived from the endocrine pancreas, but displayed no promoter activity in non-pancreatic cells. In this report, we tested the cell-specific expression of a CAT reporter gene driven by a short (338 bp) and a larger (1311 bp) fragment of the GLUT2 promoter in tran sgenic mice. We generated ten transgenic lines that integrated one of the constructs. CAT mRNA expression in transgenic tissues was assessed using the RNAse protection assay and the quantitative reverse transcr ibed polymerase chain reaction (RT-PCR). Overall CAT mRNA expression f or both constructs was low compared to endogenous GLUT2 mRNA levels bu t the reporter transcript could be detected in all animals in the panc reatic islets and the liver, and in a few transgenic lines in the kidn ey and the small intestine. The CAT protein was also present in Langer hans islets and in the liver for both constructs by immunocytochemistr y. These findings suggest that the proximal 338 bp of the murine GLUT2 promoter contain cis-elements required for the islet-specific express ion of GLUT2.