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Modulation of the asialoglycoprotein receptor in human hepatoma cells: Effect of glucose

Authors
Journal
Hepatology
0270-9139
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
19
Issue
2
Identifiers
DOI: 10.1016/0270-9139(94)90022-1
Keywords
  • Laboratory Investigation
Disciplines
  • Biology

Abstract

Abstract The hepatic receptor for asialoglycoproteins was found to be modulated by the glucose concentration in the medium of the human hepatoma cell line HepG2. The surface binding of asialoorosomucoid, a well-documented ligand for this receptor, increased from 20 ng/mg of cellular protein to about 40 ng/mg as the glucose concentration was increased from 10 to 50 mg/dl. The up-modulating effect of glucose was mimicked by pyruvate, a product of glucose metabolism, and abolished by both 2-deoxyglucose, an inhibitor of glucose metabolism, and by cycloheximide, an inhibitor of protein synthesis. Scatchard plot analysis indicated a rise in the number of binding sites and a twofold increase in binding affinity. In contrast, the binding of antibody remained unchanged with respect to alterations in glucose concentration, an indication that the actual number of receptors remained constant in face of an increased number of binding sites. Specificity of the glucose effect was shown by the binding of insulin and transferrin to their respective receptors, which was unaffected by the high glucose concentration that increased asialoorosomucoid binding. The repression of receptor binding seen with cells grown in biotin-deprived medium was reversed by increasing the glucose concentration of the medium. In this case, binding was restored to a level sixfold to sevenfold higher than that of the control cells grown in dialyzed serum. The stimulatory effect of glucose was shown to be independent of and significantly greater than that of cyclic GMP, a known regulator of receptor expression of biotin-deficient HepG2 cells. These results suggest that increasing glucose concentrations effect an activation of either silent or nonfunctional receptors or increase the stoichiometry of ligand binding per receptor complex. The data provided here are interpreted as suggesting a potential role of glucose in maintaining hepatic homeostasis through regulation of the asialoglycoprotein receptor.

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