Short communication

Diabetologia

, Volume 42, Issue 12, pp 1417-1424

First online:

Induction of glycation suppresses glucokinase gene expression in HIT-T15 cells

  • Y. KajimotoAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , T. MatsuokaAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , H. KanetoAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , H. WatadaAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , Y. FujitaniAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , M. KishimotoAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , K. SakamotoAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , M. MatsuhisaAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • , R. KawamoriAffiliated withDepartment of Medicine, Metabolism and Endocrinology, Juntendo University School of Medicine, Tokyo, Japan
    • , Y. YamasakiAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
    • , M. HoriAffiliated withDepartment of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Osaka, Japan

Abstract

Aims/hypothesis. Chronic hyperglycaemia in patients with Type II (non-insulin-dependent) diabetes mellitus often leads to a decline in glucose-responsive insulin secretion from pancreatic beta cells, a phenomenon called glucose toxicity. Upon hyperglycaemia, glycation reaction occurs in the beta cells and induces oxidative stress. To understand the molecular basis of the beta-cell glucose toxicity, we investigated the possible effects of glycation on the expression and enzymatic activity of glucokinase, which plays a crucial part in glucose-responsive insulin secretion.¶Methods. Glycation and reactive oxygen species were induced in HIT-T15 cells by treatment with d-ribose and effects on glucokinase gene transcription, glucokinase protein amount, glucose phosphorylation activity, and DNA-binding activities of putative glucokinase gene transcription factors were evaluated.¶Results. When glycation was induced in HIT-T15 cells, the activity of the human glucokinase gene beta-cell-type promoter was suppressed substantially (83 % reduction at 60 mmol/l d-ribose). Also, similar reductions in mRNA and protein amounts of glucokinase and in the Vmax of its enzymatic activity were observed. In agreement with the reduction in the promoter activity, the two major transcription factors of the glucokinase gene, the Pal-binding factor and PDX-1, reduced their binding to their target sequences in the glucokinase gene promoter in glycation-induced HIT cells. Because these effects of d-ribose were counteracted by aminoguanidine or N-acetylcysteine, reactive oxygen species, generated by the glycation reaction, appears to be involved in the phenomena.¶Conclusion/interpretation. The induction of the glycation reaction, which is known to occur in pancreatic beta cells in chronic hyperglycaemia, suppresses the glucokinase gene transcription and its enzymatic activity. Thus, hyperglycaemia-dependent inhibition of glucokinase activity could in part explain beta-cell glucose toxicity. [Diabetologia (1999) 42: 1417–1424]

Keywords Gene expression regulation, transcription factors, glycosylation, homeodomain protein, oxidative stress.