Glucose-Mediated Repression of Menin Promotes Pancreatic β-Cell Proliferation

Menin, encoded by the Men1 gene, is responsible for beta-cell tumor formation in patients with multiple endocrine neoplasia type 1. Recently, menin has been proven to negatively regulate beta-cell proliferation during pregnancy. However, it is unclear whether menin is involved in pancreatic beta-cell proliferation in response to other physiological replication stimuli, such as glucose. In this study, we found that the menin level was significantly reduced in high glucose-treated INS1 cells and primary rat islets, both with increased proliferation. A similar observation was found in islets isolated from rats subjected to 72-h continuous glucose infusion. The glucose-induced proliferation was inhibited by menin overexpression. Further molecular studies showed that glucose-induced menin suppression was blocked by PI3K/Akt pathway inhibitors. A major PI3K/Akt substrate, Foxo1, was shown to enhance menin transcription levels by binding the promoter region of the Men1 gene. Therefore, we conclude that glucose inhibits menin expression via the PI3K/Akt/Foxo1 path-way and hence promotes pancreatic beta-cell proliferation. Our study suggests that menin might serve as an important intracellular target of glucose to mediate the mitogenic effect that glucose exerts in pancreatic beta-cells. (Endocrinology 153: 602-611, 2012)