Abstract B003: Inactivation mutations of Kmt2c/d license a molecular “field effect” and prime the urothelium for tumorigenesis

Abstract Urothelial carcinoma (UC) is widely recognized to arise from a “field” of precancerous but histologically normal urothelium (HNU). The molecular mechanism that licenses the “field effect” remains elusive. Recent studies revealed prevalent KMT2C and KMT2D loss-of-function (LOF) mutations in HNU and cancer adjacent urothelium, suggesting their potential involvement in UC initiation. Here, we demonstrated that knockout (KO) of Kmt2c and/or Kmt2d in murine urothelial cells induced drastic alterations of cellular states by single cell RNA analysis, but was insufficient to induce robust histological changes. Kmt2c/d loss enhanced organoid formation efficiency, induced epithelial-mesenchymal transition (EMT), and impaired urothelial differentiation, indicating the augmented lineage plasticity after Kmt2c/d KO. Additionally, we identified that Kmt2c/d KO induced a pre-tumorigenic transcriptome with increased enrichments of gene sets associated with inflammation and decreased enrichments of gene sets associated with differentiation. Consequently, loss of Kmt2c/d sensitized urothelial cells to common oncogenic mutations to initiate UC in mouse models. We further observed that KO of Kmt2c/d increased tumorigenic susceptibility in carcinogen-induced UC model. Mechanistically, we observed decreased H3K4me1, H3K27Ac histone marks and decreased enhancer RNA production at the majority of enhancers that correlate with downregulation of urothelial specific lineage gene expression after Kmt2c/d KO. Furthermore, we observed increased Menin deposition on promoters of up-regulated genes. Blockade of Menin-KMT2A complex by small molecule inhibitor partially rescued the EMT and basal differentiation induced by Kmt2c/d KO. Together, our data posit that Kmt2c/d represents a key molecular determinant and their functional loss licenses a molecular “field effect” which primes the urothelium for oncogenic transformation. Citation Format: Naitao Wang, Mohini R. Pachai, Dan Li, Cindy Lee, Sarah Warda, Guojia Xie, Cheng Qian, Wai Pung E. Wong, Juan Yan, Wenhuo Hu, Alison Smith, Kai Ge, Sarat Chandarlapaty, Gopakumar V. Iyer, Jonathan E. Rosenberg, David B. Solit, Hikmat A. AI-Ahmadie, Ping Chi, Yu Chen. Inactivation mutations of Kmt2c/d license a molecular “field effect” and prime the urothelium for tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr B003.