Pyruvate dehydrogenase E1α phosphorylation is induced by glucose but does not control metabolism-secretion coupling in INS-1E clonal β-cells.
Glucose-induced insulin secretion from pancreatic β-cells depends on mitochondrial activation. In the organelle, glucose-derived pyruvate is metabolised along the oxidative and anaplerotic pathway to generate downstream signals leading to insulin granule exocytosis. Entry into the oxidative pathway is catalysed by pyruvate dehydrogenase (PDH) and controlled in part by phosphorylation of the PDH E1α subunit blocking enzyme activity. We find that glucose but not other nutrient secretagogues induce PDH E1α phosphorylation in INS-1E cells and rat islets. INS-1E cells and primary β-cells express pyruvate dehydrogenase kinase (PDK) 1, 2 and 3, which mediate the observed phosphorylation. In INS-1E cells, suppression of the two main isoforms, PDK1 and PDK3, almost completely prevented PDH E1α phosphorylation. Under basal glucose conditions, phosphorylation was barely detectable and therefore the enzyme almost fully active (90% of maximal). During glucose stimulation, PDH is only partially inhibited (to 78% of maximal). Preventing PDH phosphorylation in situ after suppression of PDK1, 2 and 3 neither enhanced pyruvate oxidation nor insulin secretion. In conclusion, although glucose stimulates E1α phosphorylation and therefore inhibits PDH activity, this control mechanism by itself does not alter metabolism-secretion coupling in INS-1E clonal β-cells.
Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland.
Dmitry
D
Akhmedov
Umberto
U
De Marchi
Claes B
CB
Wollheim
Andreas
A
Wiederkehr
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002999:Clone Cells; D005947:Glucose / Q000494:pharmacology* / Q000633:toxicity; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D030481:Pyruvate Dehydrogenase (Lipoamide) / Q000378:metabolism*; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats
D007328:Insulin; D007527:Isoenzymes; C000631434:Pdk1 protein, rat; C000631438:Pdk3 protein, rat; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D034741:RNA, Small Interfering; D030481:Pyruvate Dehydrogenase (Lipoamide); C065640:pyruvate dehydrogenase E1alpha subunit; D017346:Protein Serine-Threonine Kinases; D005947:Glucose; D002118:Calcium