HtrA3 is regulated by 15-deoxy-Δ12,14-prostaglandin J2 independently of PPARγ in clear cell renal cell carcinomas

Peroxisome proliferator-activated receptor gamma (PPARγ) ligands have been shown to possess anti-proliferative effects in many types of cancer. In clear cell renal cell carcinoma (CCRCC), the targets involved in these effects are not known. In this study, we demonstrated that, in CCRCC cell lines, the endogenous PPARγ ligand 15-deoxy-Δ12,14-prostaglandin J2 (15dPGJ2) induces the expression, both at the mRNA and the protein levels, of the HtrA3 gene. This gene belongs to the High-Temperature Requirement Factor A family of serine proteases that repress signaling by TGF-β family members and inhibit cell migration. Rosiglitazone or ciglitazone, synthetic PPARγ agonists, did not induce HtrA3 expression, and the PPARγ antagonist GW9662 did not prevent 15dPGJ2 induction, suggesting that the up-regulation of HtrA3 by 15dPGJ2 is independent of PPARγ. The MEK/ERK inhibitor PD98059 dramatically repressed HtrA3 induction. Altogether, these data indicate that 15dPGJ2 is able to stimulate the expression of HtrA3 through an indirect mechanism involving the MEK/ERK pathway but independent of PPARγ. Our results provide a better understanding of the mechanisms involved in the regulation of HtrA3, a potential tumor suppressor gene.