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

Ann N Y Acad Sci. 2004 Dec;1030:230-42. doi: 10.1196/annals.1329.029.

Abstract

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.

MeSH terms

  • Animals
  • CREB-Binding Protein
  • Calcium / metabolism
  • Cell Line
  • Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Enzyme Activation
  • Enzyme Inhibitors / pharmacology
  • Flavonoids / pharmacology
  • Glucose / toxicity*
  • Ion Transport
  • Islets of Langerhans / drug effects*
  • Islets of Langerhans / enzymology
  • Islets of Langerhans / metabolism
  • Male
  • Mitogen-Activated Protein Kinase 1 / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase 1 / metabolism*
  • Mitogen-Activated Protein Kinase 3 / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase 3 / metabolism*
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Protein Binding
  • Rats
  • Rats, Wistar
  • Trans-Activators / metabolism*

Substances

  • Enzyme Inhibitors
  • Flavonoids
  • Nuclear Proteins
  • Trans-Activators
  • CREB-Binding Protein
  • Crebbp protein, rat
  • Cyclic AMP-Dependent Protein Kinases
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Glucose
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one
  • Calcium