title: Cell signalling of glucagon-like peptide-1 action in rat skeletal muscle.
abstract: Glucagon-like peptide-1 (GLP-1), an incretin with glucose-dependent insulinotropic and insulin-independent antidiabetic properties, has insulin-like effects on glucose metabolism in extrapancreatic tissues participating in overall glucose homeostasis. These effects are exerted through specific receptors not associated with cAMP, an inositol phosphoglycan being a possible second messenger. In rat hepatocytes, activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB), protein kinase C (PKC) and protein phosphatase 1 (PP-1) has been shown to be involved in the GLP-1-induced stimulation of glycogen synthase. We have investigated the role of enzymes known or suggested to mediate the actions of insulin in the GLP-1-induced increase in glycogen synthase a activity in rat skeletal muscle strips. We first explored the effect of GLP-1, compared with that of insulin, on the activation of PI3K, PKB, p70s6 kinase (p70s6k) and p44/42 mitogen-activated protein kinases (MAPKs) and the action of specific inhibitors of these kinases on the insulin- and GLP-1-induced increment in glycogen synthase a activity. The study showed that GLP-1, like insulin, activated PI3K/PKB, p70s6k and p44/42. Wortmannin (a PI3K inhibitor) reduced the stimulatory action of insulin on glycogen synthase a activity and blocked that of GLP-1, rapamycin (a 70s6k inhibitor) did not affect the action of GLP-1 but abolished that of insulin, PD98059 (MAPK inhibitor) was ineffective on insulin but blocked the action of GLP-1, okadaic acid (a PP-2A inhibitor) and tumour necrosis factor-alpha (a PP-1 inhibitor) were both ineffective on GLP-1 but abolished the action of insulin, and Ro 31-8220 (an inhibitor of some PKC isoforms) reduced the effect of GLP-1 while completely preventing that of insulin. It was concluded that activation of PI3K/PKB and MAPKs is required for the GLP-1-induced increment in glycogen synthase a activity, while PKC, although apparently participating, does not seem to play an essential role; unlike in insulin signaling, p70s6k, PP-1 and PP-2A do not seem to be needed in the action of GLP-1 upon glycogen synthase a activity in rat muscle.
authors.affiliation: Department of Metabolism, Nutrition and Hormones, Fundación Jiménez Díaz, Avda Reyes Católicos 2, 28040-Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Acitores
authors.forename: N
authors.initials: N
authors.lastname: González
authors.forename: V
authors.initials: V
authors.lastname: Sancho
authors.forename: I
authors.initials: I
authors.lastname: Valverde
authors.forename: M L
authors.initials: ML
authors.lastname: Villanueva-Peñacarrillo
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005934:Glucagon / Q000378:metabolism / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D006006:Glycogen Synthase / Q000378:metabolism; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D054645:Protein Phosphatase 1; D011498:Protein Precursors / Q000378:metabolism / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D006006:Glycogen Synthase; D007211:Indoles; D007328:Insulin; D020928:Mitogen-Activated Protein Kinases; D019319:Okadaic Acid; D010446:Peptide Fragments; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D011498:Protein Precursors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D014409:Tumor Necrosis Factor-alpha; D000077191:Wortmannin; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; C064758:Ro 31-8220