Stable overexpression of the glucose-6-phosphatase catalytic subunit attenuates glucose sensitivity of insulin secretion from a mouse pancreatic beta-cell line

Glucose-6-phosphatase (G-6-Pase) hydrolyzes glucose-6-phosphate to glucose, reciprocal with the so-called glucose sensor, glucokinase, in pancreatic b eta cells. To study the role of G-6-Pase in glucose-stimulated insulin secr etion from beta cells, we have introduced rat G-6-Pase catalytic subunit cD NA and have established permanent clones with 3-, 7- and 24-fold G-6-Pase a ctivity of the mouse beta-cell line, MIN6. In these clones, glucose usage a nd ATP production in the presence of 5.5 or 25 mM glucose were reduced, and glucose-stimulated insulin secretion was decreased in proportion to the in creased G-6-Pase activity. In addition, insulin secretory capacity in respo nse to D-fructose and pyruvate was unchanged; however, 25 mM glucose-stimul ated insulin secretion and intracellular calcium response were completely i nhibited. In the done with 24-fold G-6-Pase activity, changes in intracellu lar NAD(P)H autofluorescence in response to 25 mM glucose were reduced, but the changes with 20 mM fructose and 20 mM pyruvate were not altered. Stabl e overexpression of G-6-Pase in beta cells resulted in attenuation of the o verall glucose-stimulated metabolic responses corresponding to the degree o f overexpression. This particular experimental manipulation shows that the possibility exists of modulating glucose-stimulated insulin release by thor oughly altering glucose cycling at the glucokinase/G-6-Pase step.