Peroxisome proliferator-activated receptor γ regulates E-cadherin expression and inhibits growth and invasion of prostate cancer

Peroxisome prolliferator-activated receptor gamma (PPAR gamma) might not be permissive to ligand activation in prostate cancer cells. Association of PPART with repressing factors or posttranslational modifications in PPAR,y protein could explain the lack of effect of PPAR-gamma ligands in a recent randomized clinical trial. Using cells and prostate cancer xenograft mouse models, we demonstrate in this study that a combination treatment using the PPAR-gamma agonist pioglitazone and the histone deacetylase inhibitor valproic acid is more efficient at inhibiting prostate tumor growth than each individual therapy. We show that the combination treatment impairs the bone-invasive potential of prostate cancer cells in mice. In addition, we demonstrate that expression of E-cadherin, a protein involved in the control of cell migration and invasion, is highly up-regulated in the presence of valproic acid and pioglitazone. We show that E-cadherin expression responds only to the combination treatment and not to single PPAR-gamma agonists, defining a new class of PPAR gamma target genes. These results open up new therapeutic perspectives in the treatment of prostate cancer.