title: Specific glucose-induced control of insulin receptor substrate-2 expression is mediated via Ca2+-dependent calcineurin/NFAT signaling in primary pancreatic islet β-cells.
abstract: OBJECTIVE
  Insulin receptor substrate-2 (IRS-2) plays an essential role in pancreatic islet β-cells by promoting growth and survival. IRS-2 turnover is rapid in primary β-cells, but its expression is highly regulated at the transcriptional level, especially by glucose. The aim was to investigate the molecular mechanism on how glucose regulates IRS-2 gene expression in β-cells.
  
  
  METHODS
  Rat islets were exposed to inhibitors or subjected to adenoviral vector-mediated gene manipulations and then to glucose-induced IRS-2 expression analyzed by real-time PCR and immunoblotting. Transcription factor nuclear factor of activated T cells (NFAT) interaction with IRS-2 promoter was analyzed by chromatin immunoprecipitation assay and glucose-induced NFAT translocation by immunohistochemistry.
  
  
  RESULTS
  Glucose-induced IRS-2 expression occurred in pancreatic islet β-cells in vivo but not in liver. Modulating rat islet β-cell Ca(2+) influx with nifedipine or depolarization demonstrated that glucose-induced IRS-2 gene expression was dependent on a rise in intracellular calcium concentration derived from extracellular sources. Calcineurin inhibitors (FK506, cyclosporin A, and a peptide calcineurin inhibitor [CAIN]) abolished glucose-induced IRS-2 mRNA and protein levels, whereas expression of a constitutively active calcineurin increased them. Specific inhibition of NFAT with the peptide inhibitor VIVIT prevented a glucose-induced IRS-2 transcription. NFATc1 translocation to the nucleus in response to glucose and association of NFATc1 to conserved NFAT binding sites in the IRS-2 promoter were demonstrated.
  
  
  CONCLUSIONS
  The mechanism behind glucose-induced transcriptional control of IRS-2 gene expression specific to the islet β-cell is mediated by the Ca(2+)/calcineurin/NFAT pathway. This insight into the IRS-2 regulation could provide novel therapeutic means in type 2 diabetes to maintain an adequate functional mass.
authors.affiliation: Department of Medicine, Section of Endocrinology, Diabetes and Metabolism, Kovler Diabetes Center, University of Chicago, Chicago, Illinois, USA.
authors.forename: Damien
authors.initials: D
authors.lastname: Demozay
authors.forename: Shin
authors.initials: S
authors.lastname: Tsunekawa
authors.forename: Isabelle
authors.initials: I
authors.lastname: Briaud
authors.forename: Ramila
authors.initials: R
authors.lastname: Shah
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Rhodes
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects; D006943:Hyperglycemia / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D050778:NFATC Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009928:Organ Specificity; D011401:Promoter Regions, Genetic / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D046509:Tissue Culture Techniques
chemical_list: D065095:Calcineurin Inhibitors; D002121:Calcium Channel Blockers; D055504:Insulin Receptor Substrate Proteins; C526298:Irs2 protein, mouse; C526299:Irs2 protein, rat; D050778:NFATC Transcription Factors; D012333:RNA, Messenger; D019703:Calcineurin