UPK2 and urothelial hyperplasia: The urothelium-specific expression of mutant Ha-ras, which is driven by the urothelium-specific uroplakin II (UPKII) promoter, results in the sequential development of simple urothelial hyperplasia, papillary hyperplasia, nodular hyperplasia, and low-grade papillary urothelial cell carcinoma within 6 months of age in our UPII-mutant Ha-ras transgenic mouse model [6].