Regulation of Gene Expression by Glucose in Pancreatic β-Cells (MIN6) via Insulin Secretion and Activation of Phosphatidylinositol 3′-Kinase

Increases in glucose concentration control the transcription of the preproinsulin (PPI) gene and several other genes in the pancreatic islet β-cell. Although recent data have demonstrated that secreted insulin may regulate the PPI gene (Leibiger, I. B., Leibiger, B., Moede, T., and Berggren, P. O. (1998)Mol. Cell 1, 933–938), the role of insulin in the control of other β-cell genes is unexplored. To study the importance of insulin secretion in the regulation of the PPI and liver-type pyruvate kinase (L-PK) genes by glucose, we have used intranuclear microinjection of promoter-luciferase constructs into MIN6 β-cells and photon-counting imaging. The activity of each promoter was increased either by 30 (versus 3) mM glucose or by 1–20 nM insulin. These effects of insulin were not due to enhanced glucose metabolism since culture with the hormone had no impact on the stimulation of increases in intracellular ATP concentration caused by 30 mM glucose. Furthermore, the islet-specific glucokinase promoter and cellular glucokinase immunoreactivity were unaffected by 30 mM glucose or 20 nM insulin. Inhibition of insulin secretion with the Ca²⁺ channel blocker verapamil, the ATP-sensitive K⁺ channel opener diazoxide, or the α2-adrenergic agonist clonidine blocked the effects of glucose on L-PK gene transcription. Similarly, 30 mMglucose failed to induce the promoter after inhibition of phosphatidylinositol 3′-kinase activity with LY294002 and the expression of dominant negative-acting phosphatidylinositol 3′-kinase (Δp85) or the phosphoinositide 3′-phosphatase PTEN (phosphatase and tensin homologue). LY294002 also diminished the activation of the L-PK gene caused by inhibition of 5′-AMP-activated protein kinase with anti-5′-AMP-activated protein kinase α2 antibodies. Conversely, stimulation of insulin secretion with 13 mM KCl or 10 μM tolbutamide strongly activated the PPI and L-PK promoters. These data indicate that, in MIN6 β-cells, stimulation of insulin secretion is important for the activation by glucose of L-PK as well as the PPI promoter, but does not cause increases in glucokinase gene expression or glucose metabolism.