TRANSCRIPTIONAL ACTIVATION OF THE GLUT1 GENE IN RESPONSE TO OXIDATIVESTRESS IN L6 MYOTUBES

Exposure of L6 myotubes to prolonged low grade oxidative stress result s in increased Glut1 expression at both the protein and mRNA levels, l eading to elevated glucose transport activity, To further understand t he cellular mechanisms responsible for this adaptive response, the Glu t1 transcription rate and mRNA stability were assessed. Nuclear run on assays revealed 2.0- and 2.4 fold increases in Glut1 transcription ra tes in glucose oxidase- and xanthine/xanthine oxidase-pretreated cells , respectively, Glut1 mRNA stability was increased with both treatment s compared with the control (t(1/2) = 7.8 +/- 1.3, 6.0 +/- 2.0, and 2. 4 +/- 0.5 h, respectively), The serum-responsive element and AP-1 (but not the cAMP-responsive element) showed increased binding capacity fo llowing oxidative stress. Both activation of AP-1 binding and elevatio n of Glut1 mRNA were prevented by cycloheximide. The involvement of en hancer 1 of the Glut1 gene was demonstrated using transfected 293 cell s, Induction of Glut1 mRNA in response to oxidative stress differed fr om its activation by chronic insulin exposure as demonstrated by the a bility of rapamycin to inhibit the latter without an effect on the for mer, In conclusion, oxidative stress increases the Glut1 transcription rate by mechanisms that may involve activation of AP-1 binding to enh ancer 1 of the Glut1 gene.