The role of the GLUT 4 transporter in regulating rat myoblast glucose transport processes.
Previous studies revealed an inverse relationship between GLUT 1 and GLUT 4 expression in rat myoblasts [L. Xia, Z. Lu, T.C.Y. Lo, J. Biol. Chem., 268 (1993) 23258-23266]. It was not clear whether these were coincidental or causal occurrences. To examine the regulatory roles of the GLUT 4 isoform, rat L6 myoblasts were transfected with full length GLUT 4 cDNAs (2.5 kb) in the sense or antisense orientation. L6 myoblasts transfected with the GLUT 4 sense cDNA (L6/G4S transfectants) possessed much elevated levels of both endogenous GLUT 4 transcripts (1.4 kb and 2.8 kb). Transport and immunofluorescence studies showed that this GLUT 4 sense cDNA was responsible for a functional GLUT 4 transporter. L6 cells transfected with the GLUT 4 antisense cDNA (L6/G4A transfectants) possessed only 6% of the L6 level in day 6 cultures. These antisense transfectants were essentially devoid of any functional GLUT 4 transporter. The activation of transcription of the endogenous GLUT 4 gene in L6/G4S myoblasts suggested auto-regulation of GLUT 4 expression. GLUT 3 expression and activity were not altered in both sense and antisense GLUT 4 transfectants. More interestingly, GLUT 1 expression was reduced in L6/G4S myoblasts, whereas it was elevated in L6/G4A myoblasts. This was the first direct evidence indicating GLUT 4 might play an important role in suppressing GLUT 1 expression.
Broydell
M
M
Department of Biochemistry, University of Western Ontario, London, Ontario, Canada.
Mazzuca
D M
DM
Kudo
P A
PA
Lo
T C
TC
D000818:Animals; D001692:Biological Transport / Q000235:genetics; D002460:Cell Line; D016373:DNA, Antisense / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D014158:Transcription, Genetic; D014162:Transfection
D016373:DNA, Antisense; D018076:DNA, Complementary; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat; D005947:Glucose