Identification of ERRα as a specific partner of PGC-1α for the activation of PDK4 gene expression in muscle

Pyruvate dehydrogenase kinase 4 (PDK4) is a key regulatory enzyme involved in switching the energy source from glucose to fatty acids in response to physiological conditions. Transcription of the PDK4 gene is activated by fasting or by the administration of a PPAR alpha ligand in a tissue-specific manner. Here, we show that the two mechanisms are independent, and that ERR alpha is directly involved in PPAR alpha-independent transcriptional activation of the PDK4 gene with PGC-1 alpha as a specific partner. This conclusion is based on the following evidence. First, detailed mutation analyses of the cloned PDK4 gene promoter sequence identified a possible ERR alpha-binding motif as the PGC-1 alpha responsive element. Second, overexpression of ERR alpha by cotransfection enhanced, and the knockout of it by shRNAs diminished, PGC-1 alpha-dependent activation. Third, specific binding of ERR alpha to the identified PGC-1 alpha responsive sequence was confirmed by the electrophoresis mobility shift assay. Finally, cell-type-specific responsiveness to PGC-1 alpha was observed and this could be explained by differences in the expression levels of ERR alpha, however, ectopic expression of ERR alpha in poorly responsive cells did not restore PGC-1 alpha responsiveness, indicating that ERR alpha is necessary, but not sufficient for the response.