We recently showed that activation of G protein-coupled receptor 119 (GPR119) (also termed glucose dependent insulinotropic receptor) improves glucose homeostasis via direct cAMP-mediated enhancement of glucose-dependent insulin release in pancreatic beta-cells. Here we show that GPR119 also stimulates incretin hormone release and thus may regulate glucose homeostasis by this additional mechanism. GPR119 mRNA was found to be expressed at significant levels in intestinal subregions that produce glucose-dependent insulinotropic peptide and glucagon-like peptide (GLP)-1. Furthermore, in situ hybridization studies indicated that most GLP-1-producing cells coexpress GPR119 mRNA. In GLUTag cells, a well-established model of intestinal L-cell function, the potent GPR119 agonist AR231453 stimulated cAMP accumulation and GLP-1 release. When administered in mice, AR231453 increased active GLP-1 levels within 2 min after oral glucose delivery and substantially enhanced total glucose-dependent insulinotropic peptide levels. Blockade of GLP-1 receptor signaling with exendin(9-39) reduced the ability of AR231453 to improve glucose tolerance in mice. Conversely, combined administration of AR231453 and the DPP-4 inhibitor sitagliptin to wild-type mice significantly amplified both plasma GLP-1 levels and oral glucose tolerance, relative to either agent alone. In mice lacking GPR119, no such enhancement was seen. Thus, GPR119 regulates glucose tolerance by acting on intestinal endocrine cells as well as pancreatic beta-cells. These data also suggest that combined stimulation of incretin hormone release and protection against incretin hormone degradation may be an effective antidiabetic strategy.

Pancreatic ␤-cell dysfunction is a hallmark event in the pathogenesis of type 2 diabetes. Injectable peptide agonists of the glucagon-like peptide 1 (GLP-1) receptor have shown significant promise as antidiabetic agents by virtue of their ability to amplify glucose-dependent insulin release and preserve pancreatic ␤-cell mass. These effects are mediated via stimulation of cAMP through ␤-cell GLP-1 receptors. We report that the G␣ s -coupled receptor GPR119 is largely restricted to insulin-producing ␤-cells of pancreatic islets. Additionally, we show here that GPR119 functions as a glucose-dependent insulinotropic receptor. Unlike receptors for GLP-1 and other peptides that mediate enhanced glucose-dependent insulin release, GPR119 was suitable for the development of potent, orally active, small-molecule agonists. The GPR119-specific agonist AR231453 significantly increased cAMP accumulation and insulin release in both HIT-T15 cells and rodent islets. In both cases, loss of GPR119 rendered AR231453 inactive. AR231453 also enhanced glucose-dependent insulin release in vivo and improved oral glucose tolerance in wild-type mice but not in GPR119-deficient mice. Diabetic KK/A y mice were also highly responsive to AR231453. Orally active GPR119 agonists may offer significant promise as novel antihyperglycemic agents acting in a glucose-dependent fashion. (Endocrinology

Inslien gene transcription is a unique feature of the pancreatic 1 cells and Is increased In response to glucose.The recent cloning of inin promoter factor 1 (IPF1) and somatosatin ascription factor 1 (STF1) unexpectedly revealed that these are mouse and rat homologues of the same protein mediating trctivation through binding of CT boxlike elements in rat insulin 1 and somatostatin promoter/enhancer egions, respectively. By using oligonuceotides Early gene transfection analysis demonstrated the presence oftranscriptional control elements within the 5' flanking region of the rat insulin I gene (3). Although not fully conserved in sequence among rodents and man, the 5' flanking region is functionally conserved, allowing (-cellspecific transcription of the human insulin (HI) gene in transgenic mice (4-6) and in pluripotent rat islet tumors (7). The control of tissue-specific expression involves the interaction of specific DNA-binding factors with the 5' flanking region of the gene. Two types of sequence motifs, the E and the CT boxes, have been shown to be important for transcriptional regulation ofthe HI gene (8). The E box (positions -110 to -104) binds IEF1 which is composed of helix-loophelix proteins such as Panl or Pan2 [the human homologues are E47 and E12, respectively (9)] interacting with an unidentified protein of "'25 kDa (10,11). In contrast to the rat insulin I enhancer, the HI enhancer does not contain a second E box, but the corresponding sequence (-237 to -232) binds the helix-loop-helix protein USF (12). A negative regulatory element has been identified that decreases the transcriptional activity in both insulin-producing and non-insulin-producing cells (13,14).

The endocrine pancreas consists of several differentiated cell types that are distinguished by their selective expression of peptide hormones such as insulin, glucagon, and somatostatin. Although a number of homeobox-type factors have been proposed as key regulators of individual peptide genes in the pancreas, their cellular distribution and relative abundance remain uncharacterized. Also, their overlapping DNA binding specificities have further obscured the regulatory functions these factors perform during development. In this report we characterize a novel homeobox-type somatostatin transactivating factor termed STF-1, which is uniformly expressed in cells of the endocrine pancreas and small intestine. The 283-amino acid STF-1 protein binds to tissue-specific elements within the somatostatin promoter and stimulates somatostatin gene expression both in vivo and in vitro. Remarkably, STF-1 comprises the predominant tissue-specific element-binding activity in nuclear extracts from somatostatin-producing pancreatic islet cells, suggesting that this protein may have a primary role in regulating peptide hormone expression and specifying endocrine cell lineage in the developing gut.

GPR119 agonists mediate a unique nutrient-dependent dual elevation of both insulin and glucagon like peptide 1/glucose-dependent insulinotropic peptide levels in vivo. As a stand-alone therapy or in tandem with approved DPP-IV inhibitors, they could herald a brand new treatment paradigm for type 2 diabetes mellitus. With the passage of the first GPR119 agonist clinical candidates into Phase I trials (Arena/Ortho McNeil APD597; Metabolex MBX-2982; Prosidion/OSI PSN821) and confirmatory reports of clinical proof of concept with respect to glycemic control and incretin release, the spotlight has been set for this new class of therapeutic.