Abstract 5172: Forerunner genes contribute to bladder carcinogenesis by altering the basal to luminal urothelial transition program

Background: The idea that microscopically recognizable dysplasia and carcinoma in situ act as precursor conditions for invasive cancer is the prevailing view of how many common epithelial malignancies develop. However, new evidence suggests that these are not the initiating events of carcinogenesis but represent the evolution of pre-existing occult disease, caused by the field effects of carcinogens and/or chronic inflammation, which shows minimal phenotypic deviation from normal tissue. These effects may form large plaques in the mucosa of the affected organ but the mechanisms driving their developments are unknown. Design: We developed a strategy that combines histologic and genetic mapping that permits interrogation of the chronology of genetic changes associated with cancer development on a whole-organ scale. By using this approach, we analyzed the sequence of genetic alterations contiguous to the tumor suppressor RB1 and identified a set of alternative target genes that we term “forerunner” (FR) genes (ITM2B, LPAR6, MLNR, CAB39L, and ARL11) whose silencing was associated with development of clonal plaque-like mucosal field effects initiating bladder carcinogenesis. We focused on two model FR genes, LPAR6 and CAB39L, and validated their involvement in the development of mucosal field effects by in vitro mechanistic studies and in vivo models. Results: We provide evidence that silencing of prototypic FR genes by hypermethylation (LPAR6 and CAB39L) and less frequently by mutations (LPAR6) is associated with the initial expansion of intraurothelial neoplasia and sets the stage for subsequent events of carcinogenesis. We also found that LPAR6 and CAB39L control cell survival and proliferation consistent with the loss of function being contributory to tumorigenesis. We validated their involvement in three large independent cohorts of bladder cancer, which were profiled according to a novel molecular taxonomy and show that they distinctively contribute to the development of luminal (LPAR6) and basal (CAB39L) subtypes. The in vitro studies using cell lines and their ability to form urospheres showed that these genes contribute to carcinogenesis by altering the transition from basal to luminal phenotypes. Consistent with these observations the BBN induced cancers in Lpar6 −/− mice were of luminal type while the cancers induced in Lpar6 +/+ mice were of basal type. Conclusion: Loss of prototypic FR genes contributes to the development of mucosal field effects initiating bladder carcinogenesis by altering the basal to luminal urothelial transition program. Citation Format: Sangkyou Lee, Jolanta Bondaruk, Sooyoung Lee, June G. Lee, Tadeusz Majewski, Woonyoung Choi, Charles Guo, Colin Dinney, Li Zhang, Keith Baggerly, Richard Behringer, David McConkey, Bogdan Czerniak. Forerunner genes contribute to bladder carcinogenesis by altering the basal to luminal urothelial transition program. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5172.