Constitutive β-catenin activation induces male-specific tumorigenesis in the bladder urothelium

The incidence for bladder urothelial carcinoma, a common malignancy of the urinary tract, is about three times higher in men than in women. Although this gender difference has been primarily attributed to differential exposures, it is likely that underlying biologic causes contribute to the gender inequality. In this study, we report a transgenic mouse bladder tumor model upon induction of constitutively activated β-catenin signaling in the adult urothelium. We showed that the histopathology of the tumors observed in our model closely resembled that of the human low-grade urothelial carcinoma. In addition, we provided evidence supporting the KRT5-positive;KRT7-negative (KRT5⁺; KRT7^-) basal cells as the putative cells-oforigin for β-catenin-induced luminal tumor. Intriguingly, the tumorigenesis in this model showed a marked difference between opposite sexes; 40% of males developed macroscopically detectable luminal tumors in 12 weeks, whereas only 3% of females developed tumors. We investigated the mechanisms underlying this sexual dimorphism in pathogenesis and showed that nuclear translocation of the androgen receptor (AR) in the urothelial cells is a critical mechanism contributing to tumor development in male mice. Finally, we carried out global gene profiling experiments and defined the molecular signature for the β-catenin-induced tumorigenesis in males. Altogether, we have established a model for investigating sexual dimorphism in urothelial carcinoma development, and implicated synergy between β-catenin signaling and androgen/AR signaling in carcinogenesis of the basal urothelial cells.