Figure 3.

PGC-1 specifically transactivates the GLUT4 promoter via a MEF2 element. (A) PGC-1 increases transcriptional activity of the GLUT4 promoter. C₂C₁₂ myoblast cells were transfected in a 24-well format with 150 ng GLUT4 2.4-kb promoter-luciferase plasmid, 50 ng CMV βgal plasmid, and 700 ng of CMV-driven expression vectors either for p300, p/CAF, or full-length PGC-1. The cells were transfected for 3 h and 10% FBS/DMEM was replaced overnight. The transfected cells were induced to differentiate for at least 24 h before lysis. Luciferase activity was normalized by β-galactosidase activity. (B) PGC-1 coactivates GLUT4 promoter activity via the MEF2 enhancer element. The MEF2 recognition sequence (-473 to -464) of the 2.4-kb GLUT4 promoter was mutated from CTAAAAATAG to CTAAGGCTAG by site-directed mutagenesis. C₂C₁₂ myoblast cells were transfected as described above. (C and D) PGC-1 preferentially coactivates MEF2C. 293 cells were transfected in a 24-well format with 150 ng 3× MEF2 recognition sequence-luciferase plasmid, 50 ng CMV β-gal plasmid, 700 ng of CMV-driven expression vectors either for p/CAF or PGC-1, and either pRC-CMV MEF2A, MEF2C, or MEF2D. Cells were grown for 36 h posttransfection, before lysis.