Elevated Glucose Represses Liver Glucokinase and Induces Its Regulatory Protein to Safeguard Hepatic Phosphate Homeostasis

Author:

Arden Catherine1,Petrie John L.1,Tudhope Susan J.1,Al-Oanzi Ziad12,Claydon Amy J.3,Beynon Robert J.3,Towle Howard C.4,Agius Loranne1

Affiliation:

1. Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, U.K.

2. Department of Laboratory Medicine, Al-Jouf University, Sakaka, Saudi Arabia

3. Protein Function Group, Institute of Integrative Biology, University of Liverpool, Liverpool, U.K.

4. Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota

Abstract

OBJECTIVE The induction of hepatic glucose 6-phosphatase (G6pc) by glucose presents a paradox of glucose-induced glucose intolerance. We tested whether glucose regulation of liver gene expression is geared toward intracellular homeostasis. RESEARCH DESIGN AND METHODS The effect of glucose-induced accumulation of phosphorylated intermediates on expression of glucokinase (Gck) and its regulator Gckr was determined in hepatocytes. Cell ATP and uric acid production were measured as indices of cell phosphate homeostasis. RESULTS Accumulation of phosphorylated intermediates in hepatocytes incubated at elevated glucose induced rapid and inverse changes in Gck (repression) and Gckr (induction) mRNA concomitantly with induction of G6pc, but had slower effects on the Gckr-to-Gck protein ratio. Dynamic metabolic labeling in mice and liver proteome analysis confirmed that Gckr and Gck are low-turnover proteins. Involvement of Max-like protein X in glucose-mediated Gck-repression was confirmed by chromatin immunoprecipitation analysis. Elevation of the Gck-to-Gckr ratio in hepatocytes was associated with glucose-dependent ATP depletion and elevated urate production confirming compromised phosphate homeostasis. CONCLUSIONS The lowering by glucose of the Gck-to-Gckr ratio provides a potential explanation for the impaired hepatic glucose uptake in diabetes. Elevated uric acid production at an elevated Gck-to-Gckr ratio supports a role for glucose regulation of gene expression in hepatic phosphate homeostasis.

Publisher

American Diabetes Association

Subject

Endocrinology, Diabetes and Metabolism,Internal Medicine

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