M. Broydell et al., THE ROLE OF THE GLUT-4 TRANSPORTER IN REGULATING RAT MYOBLAST GLUCOSE-TRANSPORT PRECESSES, Biochimica et biophysica acta. Biomembranes, 1371(2), 1998, pp. 295-308
Previous studies revealed an inverse relationship between GLLTT 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 lengt
h GLUT 4 cDNAs (2.5 kb) in the sense or antisense orientation. L6 myob
lasts transfected with the GLUT 4 sense cDNA (L6/G4S transfectants) po
ssessed 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 transp
orter. L6 cells transfected with the GLUT 4 antisense cDNA (L6/G4A tra
nsfectants) possessed only 6% of the L6 level in day 6 cultures. These
antisense transfectants were essentially devoid of any functional GLU
T 4 transporter. The activation of transcription of the endogenous GLU
T 4 gene in L6/G4S myoblasts suggested auto-regulation of GLUT 4 expre
ssion. GLUT 3 expression and activity were not altered in both sense a
nd antisense GLUT 4 transfectants. More interestingly, GLUT 1 expressi
on 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 I expression. (C) 1998 Else
vier Science B.V. All rights reserved.