Glucagon acts through its own receptors in the presence of functional glucagon-like peptide-1 receptors on hamster insulinoma.
The observations that glucagon binds to glucagon-like peptide-1 (tGLP-1) receptors have raised the question of whether glucagon receptors mediate the insulinotropic effect of glucagon. We have investigated the presence and selective activation of glucagon and tGLP-1 receptors on tumor-derived cells. Northern blot analysis detected either glucagon or tGLP-1 receptor messenger RNA in hamster (HIT) and mouse (beta TC3) beta-cell lines, respectively, whereas both receptor messenger RNA were revealed in Syrian hamster insulinoma. Their expression in insulinoma plasma membranes was confirmed by specific covalent labeling with either [125I]glucagon or [125I]tGLP-1. Both glucagon and tGLP-1 receptors showed a single class of high affinity binding sites with respective Kd values of 1.11 +/- 0.11 and 0.82 +/- 0.11 nM. [125I]tGLP binding was dose dependently inhibited with a hierarchy of exendin-4 > tGLP-1 > exendin-(9-39) > oxyntomodulin > glucagon. [125I]Glucagon binding was only inhibited by glucagon and oxyntomodulin. Both glucagon and tGLP-1 increased cAMP formation in insulinoma plasma membranes in a dose-dependent manner, with ED50 values of 170.0 +/- 25.0 and 3.1 +/- 0.4 pM, respectively. Exendin-(9-39), a tGLP-1 receptor antagonist, inhibited tGLP-1-induced, but not glucagon-induced, cAMP formation. Our data demonstrate on hamster insulinoma the presence of high affinity glucagon and tGLP-1 receptors selectively coupled to adenylyl cyclase. The observed low affinity of tGLP-1 receptors for glucagon sustains the idea that each hormone has a direct insulinotropic effect.
Marie
J C
JC
Unité de Recherches sur les Peptides Neurodigestifs et le Diabète, Institut National de la Santé et de la Recherche Médicale, Paris, France.
Boissard
C
C
Skoglund
G
G
Rosselin
G
G
Breant
B
B
D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003432:Cross-Linking Reagents / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology / Q000502:physiology*; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D004763:Glucagon-Like Peptides; D007340:Insulinoma / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000378:metabolism* / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D018027:Receptors, Glucagon / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*
D000067956:Adenylyl Cyclase Inhibitors; D003432:Cross-Linking Reagents; C000593834:Glp1r protein, mouse; D000067757:Glucagon-Like Peptide-1 Receptor; D010446:Peptide Fragments; D010455:Peptides; D012333:RNA, Messenger; D018027:Receptors, Glucagon; C083773:exendin (9-39); D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000262:Adenylyl Cyclases; C051322:glucagon-like peptide 1 (7-37)