OVEREXPRESSION OF HEXOKINASE-I BUT NOT GLUT1 GLUCOSE-TRANSPORTER ALTERS CONCENTRATION-DEPENDENCE OF GLUCOSE-STIMULATED INSULIN-SECRETION INPANCREATIC BETA-CELL LINE MIN6

The recently established pancreatic beta-cell line MIN6 retains the ab ility to secrete insulin in response to physiological glucose concentr ations. To investigate the role of glucose transport and phosphorylati on in glucose-stimulated insulin secretion by beta-cells, MIN6 cells w ere stably transfected with a rabbit GLUT1 glucose transporter cDNA or a rat hexokinase I cDNA cloned in an expression vector. Overexpressio n of GLUT1 increased 3-O-methylglucose uptake, but did not alter eithe r glucose utilization or glucose-stimulated insulin secretion. In cont rast, clones overexpressing hexokinase I exhibited enhanced glucose-st imulated insulin secretion at glucose concentrations below 10 mM with a concomitant increase in glucose utilization. Maximal insulin secreti on as well as the maximal rate of glucose utilization were not altered in these clones. Insulin secretion stimulated by 2-ketoisocaproate, a non-glucose secretagogue, was not affected by hexokinase I expression . These results strongly suggest that the glucose phosphorylating step , but not glucose transport step, regulates glucose-stimulated insulin secretion by modulating the glycolytic rate in the beta-cell.