Stringent rosiglitazone-dependent gene switch in muscle cells without effect on myogenic differentiation.

We have developed a gene switch based on the human transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) and its activation by rosiglitazone. However, ectopic expression of PPARgamma has been demonstrated to convert myogenic cells into adipocyte-like cells and, more generally, may interfere with the physiology of the target tissue. Consequently we modified the DNA-binding specificity of PPARgamma, resulting in a transcription factor that we named PPAR*. We demonstrated by histological and molecular assessment of cell phenotype that the overexpression of PPAR* did not alter the myogenic differentiation program of G8 myoblasts. We showed that PPAR* does not transactivate promoters containing PPARgamma-responsive elements but transactivates promoters containing PPAR*-responsive elements that are at least 80% identical to a 20-bp consensus. We improved the rosiglitazone-dependent gene switch by tuning PPAR* expression with a scaffold/matrix attachment region and by expressing both PPAR* and the reporter gene under the control of PPAR*-responsive elements. Treatment of cultured murine muscle cells (myotubes) with rosiglitazone induced reporter gene expression from assay background up to the level attained by a CMV I/E promoter-enhancer. These results indicate the potential of the PPAR* gene switch for use in gene therapy applications.