Abstract PO-004: Identification of MLL4 as a novel therapeutic target of pancreatic ductal adenocarcinoma by in vivo genome-wide RNAi screening

Abstract The prognosis of pancreatic ductal adenocarcinoma (PDAC) is extremely poor due to the lack of effective therapeutics. It is urgent to identify novel therapeutic target for PDAC. We performed in vivo genome-wide RNAi screening to identify cancer-associated candidate genes with critical roles in the tumorigenesis of PDAC. We identify mixed-lineage leukaemia 4 (MLL4 also known as KMT2B), which belongs to histone H3 lysine 4 (H3K4) methyltransferase of MLL family, as one of the cancer-associated gene to PDAC tumorigenesis. Here, we firstly report that MLL4 expression was frequently upregulated in PDAC cell lines as well as human PDAC tissue, depicting its potential role in PDAC tumorigenesis. Lysine methylation of different position of Histone is performed by SET (suppressor of variegation) domain of MLL family, aberrant expression of SET domain results in disruption of epigenetic gene regulation and leads to cancer. To characterize the in vitro tumorigenic role of SET domain of MLL4 in the development of PDAC, gain-of-function and loss-of-function approaches of SET domain of MLL4 and MLL4 were performed in PDAC cells, respectively. Ectopic SET expression promotes cell proliferation, colony formation, cell migration as well as invasion, demonstrating its oncogenic role in PDAC cells. Moreover, MLL4-depleted PDAC cells exhibited significantly reduction of tumor growth in nude mice xenograft model. Putative MLL4 activating and repressive targets were identified using gene expression microarray analysis in PDAC cell lines Capan2 and Panc-1. Expression alteration of these genes by regulated by MLL4 contribute to PDAC development and progression. To further delineate whether MLL4 regulates expression of the activating and repressing targets via H3K4 methylation, activity of H3K4 methylation was investigated in PDAC cells with MLL4 knockdown. Suppression of MLL4 reduced the H3K4Me2 and H3K4Me3 occupancies at promoter of MLL4 target genes, suggesting that MLL4 regulates downstream genes expression through H3K4 methylation. Taken together, our findings demonstrate that aberrant overexpression of MLL4 in PDAC cells alters its downstream oncogene and tumor suppressor genes, contributing to PDAC tumorigenesis. Thus, targeting MLL4 may serve as a potential therapeutic modality in the management of PDAC. Citation Format: Frederic K. C. Fung, Yinxin Zhu, Chi Hin Wong, Yangchao Chen. Identification of MLL4 as a novel therapeutic target of pancreatic ductal adenocarcinoma by in vivo genome-wide RNAi screening [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-004.