Glucose represses connexin36 in insulin-secreting cells.
The gap-junction protein connexin36 (Cx36) contributes to control the functions of insulin-producing cells. In this study, we investigated whether the expression of Cx36 is regulated by glucose in insulin-producing cells. Glucose caused a significant reduction of Cx36 in insulin-secreting cell lines and freshly isolated pancreatic rat islets. This decrease appeared at the mRNA and the protein levels in a dose- and time-dependent manner. 2-Deoxyglucose partially reproduced the effect of glucose, whereas glucosamine, 3-O-methyl-D-glucose and leucine were ineffective. Moreover, KCl-induced depolarization of beta-cells had no effect on Cx36 expression, indicating that glucose metabolism and ATP production are not mandatory for glucose-induced Cx36 downregulation. Forskolin mimicked the repression of Cx36 by glucose. Glucose or forskolin effects on Cx36 expression were not suppressed by the L-type Ca(2+)-channel blocker nifedipine but were fully blunted by the cAMP-dependent protein kinase (PKA) inhibitor H89. A 4 kb fragment of the human Cx36 promoter was identified and sequenced. Reporter-gene activity driven by various Cx36 promoter fragments indicated that Cx36 repression requires the presence of a highly conserved cAMP responsive element (CRE). Electrophoretic-mobility-shift assays revealed that, in the presence of a high glucose concentration, the binding activity of the repressor CRE-modulator 1 (CREM-1) is enhanced. Taken together, these data provide evidence that glucose represses the expression of Cx36 through the cAMP-PKA pathway, which activates a member of the CRE binding protein family.
Allagnat
Florent
F
Department of Internal Medicine, Laboratory of Molecular Biology 19-135S, University Hospital, CHUV-1011 Lausanne, Switzerland.
Martin
David
D
Condorelli
Daniele F
DF
Waeber
Gérard
G
Haefliger
Jacques-Antoine
JA
D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D005576:Colforsin / Q000494:pharmacology; D017630:Connexins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D051786:Cyclic AMP Response Element Modulator / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects*; D005419:Flavonoids / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020218:Response Elements / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics; D013449:Sulfonamides / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D000097004:Gap Junction delta-2 Protein
D005576:Colforsin; D017630:Connexins; D000242:Cyclic AMP; D051786:Cyclic AMP Response Element Modulator; D017868:Cyclic AMP-Dependent Protein Kinases; D004268:DNA-Binding Proteins; D005419:Flavonoids; D005947:Glucose; D007546:Isoquinolines; D020928:Mitogen-Activated Protein Kinases; D009543:Nifedipine; D012333:RNA, Messenger; D013449:Sulfonamides; D013755:Tetradecanoylphorbol Acetate; D000097004:Gap Junction delta-2 Protein; C497412:Crem protein, rat; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one