KDM6A Loss Triggers an Epigenetic Switch That Disrupts Urothelial Differentiation and Drives Cell Proliferation in Bladder Cancer

Disruption of KDM6A, a histone lysine demethylase, is one of the most common somatic alternations in bladder cancer. Insights into how KDM6A mutations affect the epigenetic landscape to promote carcinogenesis could help reveal potential new treatment approaches. Here, we demonstrated that KDM6A loss triggers an epigenetic switch that disrupts urothelial differentiation and induces a neoplastic state characterized by increased cell prolifer-ation. In bladder cancer cells with intact KDM6A, FOXA1 inter-acted with KDM6A to activate genes instructing urothelial differ-entiation. KDM6A-deficient cells displayed simultaneous loss of FOXA1 target binding and genome-wide redistribution of the bZIP transcription factor ATF3, which in turn repressed FOXA1-target genes and activated cell-cycle progression genes. Importantly, ATF3 depletion reversed the cell proliferation phenotype induced by KDM6A deficiency. These data establish that KDM6A loss engen-ders an epigenetic state that drives tumor growth in an ATF3-dependent manner, creating a potentially targetable molecular vulnerability. Significance: A gain-of-function epigenetic switch that disrupts differentiation is triggered by inactivating KDM6A mutations in bladder cancer and can serve as a potential target for novel therapies.