Differential activation mechanisms of Erk-1/2 and p70(S6K) by glucose in pancreatic beta-cells.
Glucose can activate the mitogen-activated kinases, Erk-1/2, and the ribosomal-S6 kinase, p70(S6K), in beta-cells, contributing to an increase in mitogenesis. However, the signaling mechanism by which glucose induces Erk-1/2 and p70(S6K) phosphorylation activation is undefined. Increased glucose metabolism increases [Ca(2+)](i) and [cAMP], and it was investigated if these secondary signals were linked to glucose-induced Erk-1/2 and p70(S6K) activation in pancreatic beta-cells. Blocking Ca(2+) influx with verapamil, or inhibiting protein kinase A (PKA) with H89, prevented glucose-induced Erk-1/2 phosphorylation. Increasing cAMP levels by GLP-1 potentiated glucose-induced Erk-1/2 phosphorylation via PKA activation. Elevation of [Ca(2+)](i) by glyburide potentiated Erk-1/2 phosphorylation, which was also inhibited by H89, suggesting increased [Ca(2+)](i) preceded PKA for glucose-induced Erk-1/2 activation. Adenoviral-mediated expression of dominant negative Ras in INS-1 cells decreased IGF-1-induced Erk-1/2 phosphorylation but had no effect on that by glucose. Collectively, our study indicates that a glucose-induced rise in [Ca(2+)](i) leads to cAMP-induced activation of PKA that acts downstream of Ras and upstream of the MAP/Erk kinase, MEK, to mediate Erk-1/2 phosphorylation via phosphorylation activation of Raf-1. In contrast, glucose-induced p70(S6K) activation, in the same beta-cells, was mediated by a distinct signaling pathway independent of Ca(2+)/cAMP, most likely via mTOR-kinase acting as an "ATP-sensor."
Briaud
Isabelle
I
Pacific Northwest Research Institute, Seattle, Washington, USA.
Lingohr
Melissa K
MK
Dickson
Lorna M
LM
Wrede
Christian E
CE
Rhodes
Christopher J
CJ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D005947:Glucose / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D006801:Humans; D007515:Islets of Langerhans / Q000201:enzymology*; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D013449:Sulfonamides; D014700:Verapamil / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007546:Isoquinolines; D010446:Peptide Fragments; D013449:Sulfonamides; C055453:glucagon-like peptide 1 (7-36)amide; D004763:Glucagon-Like Peptides; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D014700:Verapamil; D000242:Cyclic AMP; D019908:Proto-Oncogene Proteins c-raf; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D005947:Glucose; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D005905:Glyburide; D002118:Calcium