Glucose modulation of insulin mRNA levels is dependent on transcription factor PDX-1 and occurs independently of changes in intracellular Ca2+

Glucose regulates insulin production in pancreatic beta-cells in the long t erm by stimulating insulin gene transcription. These effects are partially mediated through the activity of a homeodomain transcription factor, PDX-1, which binds to four sites within the human insulin gene promoter. The avai lability of a human beta-like cell line, NES2Y, which lacks PDX-1 but expre sses the insulin gene, allowed us to determine whether PDX-1 was essential for the stimulatory effect of glucose on insulin mRNA levels. In NES2Y cell s, glucose had no effect on the insulin gene promoter linked to a firefly l uciferase reporter or on endogenous insulin mRNA levels. However, in NES2Y cells stably transfected with PDX-1 (NES-PDX-1), glucose exhibited a marked stimulatory effect on both the insulin promoter (5 +/- 0.2-fold, n = 6) an d insulin mRNA levels (4.8 +/- 0.5-fold, n = 4), NES2Y cells were derived f rom a patient with persistent hyperinsulinemic hypoglycemia of infancy; the cells therefore lacked operational ATP-sensitive potassium channels, which results in the failure to control depolarization-dependent intracellular C a2+ signaling. Despite the loss of control of Ca2+ channel activity, NES-PD X-1 cells maintained normal glucose-responsive insulin gene regulation, The se results demonstrate that glucose modulation of insulin mRNA levels is de pendent on the activity of PDX-1 and that these effects are independent of changes in intracellular Ca2+ concentrations.