cAMP-dependent protein kinase and Ca2+ influx through L-type voltage-gated calcium channels mediate Raf-independent activation of extracellular regulated kinase in response to glucagon-like peptide-1 in pancreatic beta-cells.
Glucagon like peptide-1 (GLP1) is a G(s)-coupled receptor agonist that exerts multiple effects on pancreatic beta-cells, including the stimulation of insulin gene expression and secretion. In this report, we show that treatment of the mouse pancreatic beta-cell line MIN6 with GLP1 leads to the glucose-dependent activation of Erk. These effects are mimicked by forskolin, a direct activator of adenylate cyclase, and blocked by H89, an inhibitor of cAMP-dependent protein kinase. Additionally, we provide evidence that GLP1-stimulated activation of Erk requires an influx of calcium through L-type voltage-gated calcium channels and the activation of calcium/calmodulin-dependent protein kinase II. GLP1-stimulated activation of Erk is blocked by inhibitors of MEK, but GLP1 does not induce the activation of A-Raf, B-Raf, C-Raf, or Ras. Additionally, dominant negative forms of Ras(N17) and Rap1(N17) fail to block GLP1-stimulated activation of Erk. In conclusion, our results indicate that, in the presence of stimulatory concentrations of glucose, GLP1 stimulates the activation of Erk through a mechanism dependent on MEK but independent of both Raf and Ras. This requires 1) the activation of cAMP-dependent protein kinase, 2) an influx of extracellular Ca(2+) through L-type voltage-gated calcium channels, and 3) the activation of CaM kinase II.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1; D017136:Ion Transport; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D021381:Protein Transport; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*
D020746:Calcium Channels, L-Type; D010446:Peptide Fragments; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D019908:Proto-Oncogene Proteins c-raf; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium