AJP - Cell Physiology, Vol 269, Issue 2 C480-C486, Copyright © 1995 by American Physiological Society
Glucose transporter expression and functional role of hexokinase in insulin biosynthesis in mouse beta TC3 cells
S. Nagamatsu, Y. Nakamichi and H. Sawa
Department of Biochemistry, Kyorin University School of Medicine, Tokyo, Japan.
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.
