In a well-designed approach to study the effect of JNK signaling on autosomal dominant polycystic kidney disease (ADPKD), Smith et al. first showed polycistin-2 (Pkd2) deletion activates JNK2 signaling, as well as c-Jun phosphorylation levels [125]. This evidence concerns the gene MAPK9 and autosomal dominant polycystic kidney disease.