Glucose-stimulated and self-limiting insulin production by glucose 6-phosphatase promoter driven insulin expression in hepatoma cells

The liver is an attractive target organ for insulin gene expression in type I diabetes as it contains appropriate cellular mechanisms of regulated gen e expression in response to blood glucose and insulin. We hypothesize that insulin production regulated by both glucose and insulin may be achieved us ing the promoter of the glucose 6-phosphatase gene (G6Pase), the expression of which in the liver is induced by glucose and suppressed by insulin. Rec ombinant adenoviral vectors expressing the reporter gene CAT or insulin und er transcriptional direction of the G6Pase promoter were constructed. Gluco se-stimulated as well as self-limiting insulin production was achieved in v ector-transduced hepatoma cells in which expression of the insulin gene was controlled by the G6Pase promoter. While insulin strongly inhibited the G6 Pase promoter activity under low glucose conditions, its inhibitory capacit y was attenuated when glucose levels were elevated. At the physiologic gluc ose level of 5.5 mM glucose, vector-transduced hepatoma cells produced a se lf-limited level of insulin at approximately 0.2-0.3 ng/ml, which is within the range of fasting levels of insulin in normal animals. These results in dicate that the G6Pase promoter possesses desirable features and may be dev eloped for regulated hepatic insulin gene expression in type 1 diabetes.