Expression of glucokinase in cultured human muscle cells confers insulin-independent and glucose concentration-dependent increases in glucose disposal and storage

• Published in: Diabetes (New York, N.Y.) Vol. 47; no. 9; pp. 1392 - 1398
• Main Authors: Baqué, S, Montell, E, Guinovart, J J, Newgard, C B, Gómez-Foix, A M
• Format: Journal Article
• Language: English
• Published: Alexandria, VA American Diabetes Association 01-09-1998
• Subjects: Adenoviridae; Animals; Biological and medical sciences; Biological Transport; Cells, Cultured; Deoxyglucose - metabolism; Diabetes. Impaired glucose tolerance; DNA, Complementary; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Etiopathogenesis. Screening. Investigations. Target tissue resistance; Gene Expression; Genetic aspects; Genetic Vectors; Glucokinase - biosynthesis; Glucokinase - genetics; Glucose - metabolism; Glucosephosphates - metabolism; Glycogen - biosynthesis; Glycogen Synthase - biosynthesis; Humans; Insulin - pharmacology; Insulin resistance; Kinetics; Liver - enzymology; Medical sciences; Mice; Mice, Transgenic; Muscle cells; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Phosphorylases - biosynthesis; Rats; Recombinant Proteins - biosynthesis; Endocrinopathy; Human; Pancreatic hormone; Enzyme; Transferases; Glucose; Striated muscle; In vitro; Insulin; Target tissue resistance; Regulation(control); Storage; Enzymatic activity; Glucokinase
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/diabetes.47.9.1392

Expression of glucokinase in cultured human muscle cells confers insulin-independent and glucose concentration-dependent increases
in glucose disposal and storage.
S Baqué ,
E Montell ,
J J Guinovart ,
C B Newgard and
A M Gómez-Foix
Department de Bioquímica i Biologia Molecular, Universitat de Barcelona, Spain.
Abstract
Insulin resistance, as is found in skeletal muscle of individuals with obesity and NIDDM, appears to involve a reduced capacity
of the hormone to stimulate glucose uptake and/or phosphorylation. The glucose phosphorylation step, as catalyzed by hexokinase
II, has been described as rate limiting for glucose disposal in muscle, but overexpression of this enzyme under control of
a muscle-specific promoter in transgenic mice has had limited metabolic impact. In the current study, we investigated in a
cultured muscle model whether expression of glucokinase, which in contrast to hexokinase II is not inhibited by glucose-6-phosphate
(G-6-P), would have a pronounced metabolic impact. We used a recombinant adenovirus containing the cDNA-encoding rat liver
glucokinase (AdCMV-GKL) to increase the glucose phosphorylating activity in cultured human muscle cells by fourfold. G-6-P
levels increased in AdCMV-GKL-treated cells in a glucose concentration-dependent manner over the range of 1-30 mmol/l, whereas
the much smaller increases in G-6-P in control cells were maximal at glucose concentrations <5 mmol/l. Further, cells expressing
glucokinase accumulated 17 times more 2-deoxyglucose-6-phosphate than control cells. In AdCMV-GKL-treated cells, the time-dependent
rise in G-6-P correlated with an increase in the activity ratio of glycogen synthase. AdCMV-GKL-treated cells also exhibited
a 2.5- to 3-fold increase in glycogen content and a four- to fivefold increase in glycolytic flux, proportional to the increase
in glucose phosphorylating capacity. All of these observations were made in the absence of insulin. Thus we concluded that
expression of glucokinase in cultured human muscle cells results in proportional increases in insulin-independent glucose
disposal, and that muscle glucose storage and utilization becomes controlled in a glucose concentration-dependent manner in
AdCMV-GKL-treated cells. These results encourage testing whether delivery of glucokinase to muscle in vivo has an impact on
glycemic control, which could be a method for circumventing the failure of insulin to stimulate glucose uptake and/or phosphorylation
in muscle normally in insulin-resistant subjects.