title: Glucose transporter expression and functional role of hexokinase in insulin biosynthesis in mouse beta TC3 cells.
abstract: It was previously reported that insulin biosynthesis in mouse beta TC3 cells was regulated by glucose (Nagamatsu, S., and D. F. Steiner. Endocrinology 130: 748-754, 1992). In the present study, we examined the effect of glucose on the glucose transporter expression and hexokinase activities and determined the relationship between them and glucose-stimulated insulin biosynthesis in beta TC3 cells. Reverse transcriptase-polymerase chain reaction and Northern blot analysis revealed that beta TC3 cells expressed GLUT-1 and GLUT-3 glucose transporter mRNAs, but not GLUT-2. The levels of GLUT-1 and GLUT-3 mRNAs were not affected by glucose (0 or 11 mM glucose) over a period of 48 h. Immunoprecipitation of metabolically labeled beta TC3 cells with specific antibodies against GLUT-1 or GLUT-3 proteins revealed no effect of glucose on the biosynthesis of glucose transporters. Hexokinase [low Michaelis constant (Km) hexokinase] activity from cells incubated in 11 mM glucose for 48 h increased nearly twofold compared with cells maintained in 0 mM glucose, although the amount of cellular hexokinase protein detected by immunoblot analysis was unchanged between 0 and 11 mM glucose conditions. Glucokinase (high Km hexokinase) activity, in contrast, was not affected by glucose. Preincubation of beta TC3 cells with 2-deoxyglucose to inhibit hexokinase, thereby inhibiting all glycolysis, resulted in the decrease of glucose-stimulated insulin biosynthesis. Thus, in mouse beta TC3 cells that do not express GLUT-2, there is a close relationship between hexokinase activity and glucose-stimulated insulin biosynthesis, but not between the glucose transporter and glucose-stimulated insulin biosynthesis.
authors.affiliation: Department of Biochemistry, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nagamatsu
authors.forename: Y
authors.initials: Y
authors.lastname: Nakamichi
authors.forename: H
authors.initials: H
authors.lastname: Sawa
mesh_terms: D000818:Animals; D002460:Cell Line; D015870:Gene Expression / Q000187:drug effects; D005941:Glucokinase / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D006593:Hexokinase / Q000378:metabolism*; D007328:Insulin / Q000096:biosynthesis*; D007515:Islets of Langerhans / Q000378:metabolism*; D007536:Isomerism; D051379:Mice; D008822:Mice, Transgenic; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D011384:Proinsulin / Q000096:biosynthesis
chemical_list: D007328:Insulin; D009004:Monosaccharide Transport Proteins; D011384:Proinsulin; D006593:Hexokinase; D005941:Glucokinase; D005947:Glucose