Transgenic Expression of Insulin-Response Element Binding Protein-1 in β-Cells Reproduces Type 2 Diabetes

Recent evidence supports the idea that insulin signaling through the insulin receptor substrate/phosphatidyl-inositol 3-kinase/Akt pathway is involved in the maintenance of β-cell mass and function. We previously identified the insulin-response element binding protein-1 (IRE-BP1) as an effector of insulin-induced Akt signaling in the liver, and showed that the 50-kDa carboxyl fragment confers the transcriptional activity of this factor. In this investigation we found that IRE-BP1 is expressed in the α, β, and δ-cells of the islets of Langerhans, and is localized to the cytoplasm in β-cells in normal rats, but is reduced and redistributed to the islet cell nuclei in obese Zucker rats. To test whether IRE-BP1 modulates β-cell function and insulin secretion, we used the rat insulin II promoter to drive expression of the carboxyl fragment in β-cells. Transgenic expression of IRE-BP1 in FVB mice increases nuclear IRE-BP1 expression, and produces a phenotype similar to that of type 2 diabetes, with hyperinsulinemia, hyperglycemia, and increased body weight. IRE-BP1 increased islet type I IGF receptor expression, potentially contributing to the development of islet hypertrophy. Our findings suggest that increased gene transcription mediated through IRE-BP1 may contribute to β-cell dysfunction in insulin resistance, and allow for the hypothesis that IRE-BP1 plays a role in the pathophysiology of type 2 diabetes. IRE-BP1-mediated gene transcription in β-cells may contribute to development of islet cell dysfunction and hyperglycemia in type 2 diabetes.