Pim3 negatively regulates glucose-stimulated insulin secretion.

Pancreatic β-cell response to glucose stimulation is governed by tightly regulated signaling pathways which have not been fully characterized. A screen for novel signaling intermediates identified Pim3 as a glucose-responsive gene in the β cell, and here, we characterize its role in the regulation of β-cell function. Pim3 expression in the β-cell was first observed through microarray analysis on glucose-stimulated murine insulinoma (MIN6) cells where expression was strongly and transiently induced.

Transplantation of PC1/3-Expressing alpha-cells improves glucose handling and cold tolerance in leptin-resistant mice.

Type 2 diabetes (T2D) is characterized by elevated blood glucose levels owing to insufficient secretion and/or activity of the glucose-lowering hormone insulin. Glucagon-like peptide-1 (GLP-1) has received much attention as a new treatment for diabetes because of its multiple blood glucose-lowering effects, including glucose-dependent enhancement of insulin secretion, inhibition of gastric emptying, and promotion of the survival and growth of insulin-producing beta-cells. GLP-1, along with GLP-2 and oxyntomodulin, is produced in the intestinal L-cell via processing of proglucagon by prohormone convertase 1/3 (PC1/3), while in the pancreatic alpha-cell, coexpression of proglucagon and the alternate enzyme PC2 typically results in differential processing of proglucagon to yield glucagon.

A switch from prohormone convertase (PC)-2 to PC1/3 expression in transplanted alpha-cells is accompanied by differential processing of proglucagon and improved glucose homeostasis in mice.

Objective: Glucagon, which raises blood glucose levels by stimulating hepatic glucose production, is produced in alpha-cells via cleavage of proglucagon by prohormone convertase (PC)-2. In the enteroendocrine L-cell, proglucagon is differentially processed by the alternate enzyme PC1/3 to yield glucagon-like peptide (GLP)-1, GLP-2, and oxyntomodulin, which have blood glucose-lowering effects. We hypothesized that alteration of PC expression in alpha-cells might convert the alpha-cell from a hyperglycemia-promoting cell to one that would improve glucose homeostasis.

Technology insight: microarrays--research and clinical applications.

For microarrays, the transition from research to clinical and diagnostic applications is well underway. Microarrays use a range of specific probes that are immobilized in known locations on a support matrix; this technique can measure levels of specific DNA, RNA and proteins, as well as carbohydrates and lipids. It is anticipated that analysis of these levels will lead to identification of biomarkers for the diagnosis, treatment and prognosis of a wide range of diseases.

Shb promotes blood vessel formation in embryoid bodies by augmenting vascular endothelial growth factor receptor-2 and platelet-derived growth factor receptor-beta signaling.

The mechanisms controlling blood vessel formation during early embryonal development have only partly been elucidated. Shb is an adaptor protein previously implicated in the angiogenic response to vascular endothelial growth factor (VEGF). To elucidate a possible role of Shb in embryonic vascular development, wild-type and SH2 domain mutated (R522K) Shb were overexpressed in murine embryonic stem (ES) cells.

Altered proglucagon processing in an alpha-cell line derived from prohormone convertase 2 null mouse islets.

The endoproteolytic processing of proproteins in the secretory pathway depends on the expression of selected members of a family of subtilisin-like endoproteases known as the prohormone convertases (PCs). The main PC family members expressed in mammalian neuroendocrine cells are PC2 and PC1/3. The differential processing of proglucagon in pancreatic alpha-cells and intestinal L cells leads to production of distinct hormonal products with opposing physiological effects from the same precursor.

Contrasting patterns of expression of transcription factors in pancreatic alpha and beta cells.

Pancreatic alpha and beta cells are derived from the same progenitors but play opposing roles in the control of glucose homeostasis. Disturbances in their function are associated with diabetes mellitus. To identify many of the proteins that define their unique pathways of differentiation and functional features, we have analyzed patterns of gene expression in alphaTC1.

Differential gene expression in well-regulated and dysregulated pancreatic beta-cell (MIN6) sublines.

To identify genes involved in regulated insulin secretion, we have established and characterized two sublines derived from the mouse pancreatic beta-cell line MIN6, designated B1 and C3. They have a similar insulin content, but differ in their secretory properties. B1 responded to glucose in a concentration- and cell confluence-dependent manner, whereas C3 did not.

Glucagon replacement via micro-osmotic pump corrects hypoglycemia and alpha-cell hyperplasia in prohormone convertase 2 knockout mice.

Prohormone convertase 2 (PC2) plays an essential role in the processing of proglucagon to mature active glucagon in pancreatic alpha-cells (J Biol Chem 276:27197-27202, 2001). Mice lacking PC2 demonstrate multiple defects, including chronic mild hypoglycemia and dramatic hyperplasia of the pancreatic alpha-cells. To define the contribution of mature glucagon deficiency to the hypoglycemia and alpha-cell hyperplasia, we have attempted to correct the defects by delivery of exogenous glucagon by micro-osmotic pumps.