Glucose enhances insulin promoter activity in MIN6 beta-cells independently of changes in intracellular Ca2+ concentration and insulin secretion.
Recent studies have suggested that glucose may activate insulin gene transcription through increases in intracellular Ca(2+) concentration, possibly acting via the release of stored insulin. We have investigated this question by dynamic photon-counting imaging of insulin- and c-fos-promoter-firefly luciferase reporter construct activity. Normalized to constitutive viral promoter activity, insulin promoter activity in MIN6 beta-cells was increased 1.6-fold after incubation at 30 mM compared with 3 mM glucose, but was unaltered at either glucose concentration by the presence of insulin (100 nM) or the Ca(2+) channel inhibitor, verapamil (100 microM). Increases in intracellular [Ca(2+)] achieved by plasma membrane depolarization with KCl failed to enhance either insulin or c-fos promoter activity in MIN6 cells, but increased c-fos promoter activity 5-fold in AtT20 cells. Together, these results demonstrate that glucose can exert a direct effect on insulin promoter activity in islet beta-cells, via a signalling pathway which does not require increases in intracellular [Ca(2+)] nor insulin release and insulin receptor activation.
Kennedy
H J
HJ
Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, U.K.
Rafiq
I
I
Pouli
A E
AE
Rutter
G A
GA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000737:chemistry / Q000378:metabolism; D017930:Genes, Reporter; D016762:Genes, fos; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000502:physiology*; D008156:Luciferases / Q000235:genetics; D051379:Mice; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D015398:Signal Transduction; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D017362:Cyclic AMP Response Element-Binding Protein; D007328:Insulin; D014700:Verapamil; D008156:Luciferases; D005947:Glucose; D002118:Calcium