Regulation of glucagon-like peptide-1 synthesis and secretion in the GLUTag enteroendocrine cell line.
Glucagon-like peptide-1 (GLP-1) released from the intestine is a potent stimulator of glucose-dependent insulin secretion. To elucidate the factors regulating GLP-1 secretion, we have studied the enteroendocrine GLUTag cell line. GLP-1 secretion was stimulated in a dose-dependent fashion by activation of protein kinase A or C with forskolin or phorbol 12,13-dibutyrate, respectively (by 2.3 +/- 0.5-fold at 100 microM and 4.3 +/- 0.6-fold at 0.3 microM, respectively; P < 0.01-0.001). Of the regulatory peptides tested, only glucose-dependent insulinotropic peptide stimulated the release of GLP-1 (by 2.3 +/- 0.2-fold at 0.1 microM; P < 0.001); glucagon was without effect, and paradoxically, the inhibitory neuropeptide somatostatin-14 increased secretion slightly (by 1.6 +/- 0.3-fold at 0.01 microM; P < 0.05). In tests of several neurotransmitters, only the cholinergic agonists carbachol and bethanechol stimulated peptide secretion in a dose-dependent fashion (by 2.3 +/- 0.5- and 1.7 +/- 0.3-fold at 1000 microM; P < 0.05-0.001); the beta-adrenergic agonist isoproterenol and the chloride channel inhibitor gamma-aminobutyric acid did not affect release of GLP-1. Long chain monounsaturated fatty acids (18:1), but not saturated fatty acids (16:0), also stimulated the release of GLP-1 (by 1.7 +/- 0.1-fold at 150 microM; P < 0.001). Consistent with the presence of a cAMP response element in the proglucagon gene, activation of the protein kinase A-dependent pathway with forskolin increased proglucagon messenger RNA transcript levels by 2-fold (P < 0.05); glucose-dependent insulinotropic peptide and phorbol 12,13-dibutyrate were without effect. Therefore, by comparison with results obtained using primary L cell cultures or in vivo models, GLUTag cells appear to respond appropriately to the regulatory mechanisms controlling intestinal GLP-1 secretion.
Brubaker
P L
PL
Department of Physiology, Toronto Hospital, and Banting and Best Diabetes Center, University of Toronto, Ontario, Canada. p.brubaker@utoronto.ca
Schloos
J
J
Drucker
D J
DJ
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D019858:Enteroendocrine Cells / Q000378:metabolism*; D005749:Gastric Inhibitory Polypeptide / Q000494:pharmacology; D005934:Glucagon / Q000096:biosynthesis* / Q000378:metabolism; D052216:Glucagon-Like Peptide 1; D051379:Mice; D010446:Peptide Fragments / Q000096:biosynthesis* / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D011498:Protein Precursors / Q000096:biosynthesis* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D010446:Peptide Fragments; D011498:Protein Precursors; D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1; D002217:Carbachol; D005934:Glucagon; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate