Glibenclamide activates translation in rat pancreatic beta cells through calcium-dependent mTOR, PKA and MEK signalling pathways.
OBJECTIVE
Prolonged exposure of rat beta cells to the insulin secretagogue glibenclamide has been found to induce a sustained increase in basal insulin synthesis. This effect was calcium-dependent and localised in cells that had been degranulated by the drug. Since it was blocked by the translation inhibitor cycloheximide, we examined whether sustained exposure to glibenclamide activates translational factors by calcium-dependent signalling pathways.


METHODS
Purified rat beta cells were cultured with and without glibenclamide in the presence or absence of inhibitors of calcium-dependent signalling pathways before measurement of basal and stimulated protein and insulin synthesis, and assessment of abundance of (phosphorylated) translation factors.


RESULTS
A 24 h exposure to glibenclamide induced activation of four translation factors, i.e. phosphorylation of eukaryotic initiation factor (eIF) 4e binding protein 1 and ribosomal protein S6 (rpS6), and dephosphorylation of eIF-2alpha and eukaryotic elongation factor 2. The rise in phospho-rpS6 intensity was localised to a subpopulation of beta cells with low insulin content. This activation of translational factors and the associated elevation of insulin synthesis were completely blocked by the calcium channel blocker verapamil and partially blocked by the mammalian target of rapamycin (mTOR) inhibitor rapamycin, the protein kinase A (PKA) inhibitor Rp-8-Br-cAMPs and the mitogen-activated protein kinase/ extracellular signal-regulated kinase kinase (MEK) inhibitor U0126; a combination of inhibitors exhibited additive effects.


CONCLUSIONS
Prolonged exposure to glibenclamide activates protein translation in pancreatic beta cells through the calcium-regulated mTOR, PKA and MEK signalling pathways. The observed intercellular differences in translation activation are proposed as underlying mechanism for functional heterogeneity in the pancreatic beta cell population.
Wang
Q
Q
Diabetes Research Center, Brussels Free University, Laarbeeklaan 103, 1090, Brussels, Belgium.
Heimberg
H
H
Pipeleers
D
D
Ling
Z
Z
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005905:Glyburide / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007166:Immunosuppressive Agents / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D020123:Sirolimus / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; C519510:Crtc1 protein, rat; D007004:Hypoglycemic Agents; D007166:Immunosuppressive Agents; D014157:Transcription Factors; D014700:Verapamil; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D005905:Glyburide; D002118:Calcium; D020123:Sirolimus