Cooperative effects between protein kinase A and p44/p42 mitogen-activated protein kinase to promote cAMP-responsive element binding protein activation after beta cell stimulation by glucose and its alteration due to glucotoxicity.
Long-term hyperglycemia, a major characteristic of the diabetic state, contributes to the deterioration of the beta cell function, a concept known as beta cell glucotoxicity. We used the MIN6 beta cell line and isolated rat islets to clarify the signaling mechanism(s) used by glucose to activate cAMP-responsive element binding protein (CREB), a transcription factor crucial for beta cell biology, and to evaluate the possible downregulation of this mechanism mediated by long-term hyperglycemia. We report that glucose (10 mM) induces an increase in cytosolic calcium concentration that leads to cAMP-induced protein kinase A (PKA) activation, promoting nuclear translocation of activated ERK1/2. The observation that glucose-induced CREB phosphorylation was totally inhibited by the PKA inhibitor H89 (2 microM) and reduced by 50% with the ERK1/2 inhibitor PD98059 (20 microM) indicates that ERK1/2, located downstream of PKA, cooperates with PKA and is responsible for half of the PKA-mediated CREB phosphorylation elicited by glucose in MIN6 beta cells. We also found that exposure of mu cells for 24 h to high glucose (25 mM) induced a 70% decrease in cellular ERK1/2 and a 50% decrease in CREB content. In high-glucose-treated, ERK1/2- and CREB-downregulated beta cells, there was a loss of glucose (10 mM, 5 min)-stimulated ERK1/2 and CREB phosphorylation that was associated with nuclear apoptotic characteristics. Since we have shown that activation of ERK1/2 is crucial for CREB phosphorylation, loss of the ERK1/2-CREB signaling pathway in beta cells due to long-term hyperglycemia is likely to exacerbate beta cell failure in diabetic states by affecting physiologically relevant gene expression and by inducing apoptosis.
Costes
Safia
S
Unité Institut National de la Santé et de la Recherche Médicale U376, CHU Arnaud-de-Villeneuve, 371 rue du Doyen Gaston Giraud, 34295 Cedex 5 Montpellier, France.
Longuet
Christine
C
Broca
Christophe
C
Faruque
Omar
O
Hani
El Habib
EH
Bataille
Dominique
D
Dalle
Stephane
S
D000818:Animals; D050882:CREB-Binding Protein; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005947:Glucose / Q000633:toxicity*; D017136:Ion Transport; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D015534:Trans-Activators / Q000378:metabolism*
D004791:Enzyme Inhibitors; D005419:Flavonoids; D009687:Nuclear Proteins; D015534:Trans-Activators; D050882:CREB-Binding Protein; C494365:Crebbp protein, rat; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D005947:Glucose; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium