title: Glucagon receptor activates extracellular signal-regulated protein kinase 1/2 via cAMP-dependent protein kinase.
abstract: We prepared a stable cell line expressing the glucagon receptor to characterize the effect of G(s)-coupled receptor stimulation on extracellular signal-regulated protein kinase 1/2 (ERK1/2) activity. Glucagon treatment of the cell line caused a dose-dependent increase in cAMP concentration, activation of cAMP-dependent protein kinase (PKA), and transient release of intracellular calcium. Glucagon treatment also caused rapid dose-dependent phosphorylation and activation of mitogen-activated protein kinase kinase/ERK kinase (MEK1/2) and ERK1/2. Inhibition of either PKA or MEK1/2 blocked ERK1/2 activation by glucagon. However, no significant activation of several upstream activators of MEK, including Ras, Rap1, and Raf, was observed in response to glucagon treatment. In addition, chelation of intracellular calcium reduced glucagon-mediated ERK1/2 activation. In transient transfection experiments, glucagon receptor mutants that bound glucagon but failed to increase intracellular cAMP and calcium concentrations showed no glucagon-stimulated ERK1/2 phosphorylation. We conclude that glucagon-induced MEK1/2 and ERK1/2 activation is mediated by PKA and that an increase in intracellular calcium concentration is required for maximal ERK activation.
authors.affiliation: Laboratory of Molecular Biology and Biochemistry, Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10021, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Jiang
authors.forename: A M
authors.initials: AM
authors.lastname: Cypess
authors.forename: E D
authors.initials: ED
authors.lastname: Muse
authors.forename: C R
authors.initials: CR
authors.lastname: Wu
authors.forename: C G
authors.initials: CG
authors.lastname: Unson
authors.forename: R B
authors.initials: RB
authors.lastname: Merrifield
authors.forename: T P
authors.initials: TP
authors.lastname: Sakmar
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D051381:Rats; D018027:Receptors, Glucagon / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D018027:Receptors, Glucagon; D005934:Glucagon; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins; D002118:Calcium