Glucose regulated production of human insulin in rat hepatocytes

Insulin gene therapy requires that insulin secretion be coupled to metabolic requirements. To this end, we have developed an insulin transgene whose transcription is stimulated by glucose and inhibited by insulin. Glucose- and insulin-sensitive promoters were constructed by inserting glucose-responsive elements (GIREs) from the rat L-pyruvate kinase (L-PK) gene into the insulin-sensitive, liver-specific, rat insulin-like growth factor binding protein-1 (IGFBP-1) promoter. Glucose (5 to 25 mM) stimulated and insulin (10(-10) to 10(-7) M) inhibited luciferase expression driven by these promoters in primary cultured rat hepatocytes. The capacity of transfected hepatocytes to secrete mature, biologically active insulin was demonstrated using a human proinsulin cDNA (2xfur), modified to allow protein processing by endogenous endopeptidase activity. Medium conditioned by insulin-producing hepatocytes contained greater than 300 mu U/ml immunoreactive insulin, while denaturing SDS-PAGE of an anti-insulin immunoprecipitate revealed bands with the mobilities of insulin A, and B chains. Biological activity of hepatocyte-produced insulin was demonstrated in a transfection assay, in which medium conditioned by insulin-producing hepatocytes exerted an effect similar to 10(-7) M insulin. We then combined the glucose- and insulin-sensitive promoter with the modified human proinsulin cDNA to create a metabolically sensitive insulin transgene ((GIRE)(3)BP-1 2xfur). In both H4IIE hepatoma cells stably transfected with this construct, and normal mt hepatocytes (GIRE)(3)BP-1 2xfur-mediated insulin secretion increased in response to stimulation by glucose. Moreover a capacity to decrease insulin production in response to diminishing glucose exposure was also demonstrated We conclude that the transcriptional regulation of insulin production using these glucose- and insulin-sensitive constructs meets the requirements for application in a rodent model of insulin gene therapy.