Elevated glucose attenuates human insulin gene promoter activity in INS-1 pancreatic β-cells via reduced nuclear factor binding to the A5/core and Z element

Maria F. Pino, Diana Z. Ye, Katrina D. Linning, Christopher D. Green, Barton Wicksteed, Vincent Poitout, L. Karl Olson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

Chronic exposure of pancreatic β-cells to elevated glucose reduces insulin gene promoter activity, and this is associated with diminished binding of two β-cell-enriched transcription factors, Pdx-1 and MafA. In this study using INS-1 β-cells, overexpression of MafA, but not Pdx-1, was able to restore expression of a human insulin reporter gene (-327 to +30 bp) suppressed by elevated glucose. At issue, however, was that MafA also markedly stimulated an insulin reporter gene (-230 to +30 bp) that was only marginally suppressed by glucose, suggesting that glucose-mediated suppression of the insulin promoter involved elements upstream of -230. Using serial truncations and minienhancer constructs of the human insulin promoter, the majority of glucose suppression was localised to regulatory elements between -327 and -261. Nuclear extracts from INS-1 cells exposed to elevated glucose had reduced binding activities to the A5/core (-319 to -307), and to a palindrome (-284 to -267) and an E box (-273 to -257, E3) contained within the Z element. The A5/core binding complex was determined to contain MafA, Pdx-1, and an A2-like binding factor. Two minienhancer constructs containing the A5/core were suppressed by glucose and strongly activated by MafA. Glucose-mediated suppression of the Z minienhancer was not attenuated by overexpression of MafA or Pdx-1. Site-directed mutation of the A5/core, palindrome, and E3 elements attenuated glucose-mediated suppression. These data indicate that glucose suppression of human insulin promoter activity in INS-1 cells involves reduced binding of MafA to the A5/core. Changes in nuclear factor binding to the Z element, which functions as a strong activator element in primary islets and a negative regulatory element in simian virus 40 or T antigen transformed β-cell lines, also participate in glucose suppression of insulin promoter activity.

Original languageEnglish (US)
Pages (from-to)1343-1360
Number of pages18
JournalMolecular Endocrinology
Volume19
Issue number5
DOIs
StatePublished - May 2005

ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology

Fingerprint Dive into the research topics of 'Elevated glucose attenuates human insulin gene promoter activity in INS-1 pancreatic β-cells via reduced nuclear factor binding to the A5/core and Z element'. Together they form a unique fingerprint.

Cite this