Suppression of ERβ signaling via ERβ knockout or antagonist protects against bladder cancer development

Epidemiological studies showed that women have a lower bladder cancer (BCa) incidence, yet higher muscle-invasive rates than men, suggesting that estrogen and the estrogen receptors, estrogen receptor alpha (ER) and estrogen receptor beta (ER), may play critical roles in BCa progression. Using in vitro cell lines and an in vivo carcinogen N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced mouse BCa model, we found that ER plays a positive role in promoting BCa progression. Knockdown of ER with ER-shRNA in ER-positive human BCa J82, 647v and T24 cell lines led to suppressed cell growth and invasion. Mice lacking ER have less cancer incidence with reduced expression of the proliferation marker Ki67 in BBN-induced BCa. Consistently, our results show that non-malignant urothelial cells with ER knockdown are more resistant to carcinogen-induced malignant transformation. Mechanism dissection found that targeting ER suppressed the expression of minichromosome maintenance complex component 5 (MCM5), a DNA replication licensing factor that is involved in tumor cell growth. Restoring MCM5 expression can partially reverse ER knockdown-mediated growth reduction. Supportively, treating cells with the ER-specific antagonist, 4-[2-Phenyl-5,7-bis(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP), reduced BCa cell growth and invasion, as well as MCM5 expression. Furthermore, we provide the first evidence that BCa burden and mortality can be controlled by PHTPP treatment in the carcinogen-induced BCa model. Together, these results demonstrate that ER could play positive roles in promoting BCa progression via MCM5 regulation. Targeting ER through ER-shRNA, PHTPP or via downstream targets, such as MCM5, could serve as potential therapeutic approaches to battle BCa.