Endothelial Differentiation Gene Receptors in Pancreatic Islets and INS-1 Cells

Abstract

The endothelial differentiation gene (EDG) receptors are a class of G protein-coupled receptors. EDG-1, -3, -5, -6, and -8 bind the bioactive lipid sphingosine-1-phosphate (SPP) as the primary signaling ligand. EDG-2, -4, and -7 bind the ligand lysophosphatidic acid. EDG-1, -2, -3, -5, -6, and -7, but not -8, mRNAs were expressed in isolated rat pancreatic islets, whereas INS-1 insulinoma cells expressed only EDG-1, -2, -3, and -5 mRNAs. EDG-4 mRNA was expressed in mouse islets. EDG-1 mRNA but not EDG-3 mRNA was rapidly induced relative to 18S rRNA after stimulation of isolated islets with phorbol 12-myristate 13-acetate (PMA) or cholecystokinin-8S for 2 h. The protein kinase C inhibitor GF 109203X blocked the EDG-1 induction by PMA. Similarly, in islets stimulated for 2 h with 17 mmol/l glucose, the relative EDG-1 mRNA levels increased almost twofold compared with levels in control islets at 5.5 mmol/l glucose. In contrast, after 11 mmol/l glucose stimulation for 7 days, the relative levels of rat islet EDG-1 mRNA were significantly reduced to 54% below that of islets cultured at 5.5 mmol/l glucose. There was no change in relative EDG-3 mRNA levels. Stimulation of EDG receptors in islets and INS-1 cells with SPP inhibited glucagon-like peptide 1 (GLP-1)-stimulated cAMP production and insulin secretion in a concentration-dependent manner. Pertussis toxin antagonized the SPP effects on insulin release. Thus, EDG receptors are expressed in pancreatic islet ␤-cells and G i seems to mediate the inhibition by SPP of adenylyl cyclase and cAMP formation and inhibition of the stimulation of insulin secretion by GLP-1. Diabetes

ATP-independent glucose stimulation of sphingosine kinase in rat pancreatic islets

“…Moreover, glucose stimulates DNA biosynthesis and cell proliferation in adult rat islets ( 37 ). Not only long-term but also short-term effects (min or h) of glucose on gene transcription have been reported for islets and INS-1e cells ( 7,13 ). Glucose also had short-term effects on SPHK activity within 1 h and 24 h that are not attributable to new protein synthesis.…”

“…Islet RNA (15-20 islets per extract) was extracted following treatment as described previously ( 7 ). QPCR was carried out using primers to SPHK1a: sense, 5 ′ -AGCATATGGAC-CTCGACTGC-3 ′ ; and antisense, 5 ′ -GCACAGCTTCACACAC-CATC-3 ′ (122 bp), and to SPHK2: sense, 5 ′ -CATCCTCTGGAC-CTGCTCTC-3 ′ ; and antisense, 5 ′ -CACTGCACCCAGTGT-GAATC-3 ′ (150 bp).…”

Human Islet Function Is Not Impaired by the Sphingosine‐1‐Phosphate Receptor Modulator FTY720

“…The current results suggest that FTY720 could have clear advantages over the diabetogenic and/or nephrotoxic drugs that are currently used in islet transplantation, but would be difficult to test clinically because of emerging nonimmune side effects of this agent. The known presence of S1PR receptors on the surface of islets could potentially interfere with insulin secretion, but the current study suggests that there is minimal physiological impact upon islet function and survival over 50 days of study (10). The future development of new S1PR modulators with minor structural changes could have potentially different toxicities, and would certainly require careful further scrutiny to rule out islet-specific toxicities.…”

“…Other compounds in the S1PR modulator class are currently in development. S1PRs are expressed on isolated murine islets and extracellular engagement with its natural ligand sphingosine-1-phosphate (S1P) induces a dose dependent reduction in glucagon-like peptide-1 (GLP-1)-stimulated insulin secretion (10). In addition, S1P acts as an intracellular second messenger (11), and endogenous b-cell sphingosine kinases have been reported in isolated murine islets in vitro (12).…”

Sphingosine Kinase Activity and Sphingosine-1 Phosphate Production in Rat Pancreatic Islets and INS-1 Cells

“…Lysophosphatidic acid preferentially binds to other select EDG receptors (10). This laboratory recently identified EDG receptor mRNAs in rat and mouse pancreatic islets and INS-1 cells (11).…”