Define the oncogenic role of METTL3 in the pathogenesis of chronic lymphocytic leukemia - Project Summary Aggressive chronic lymphocytic leukemia (CLL) remains incurable despite with improved chemotherapy regimens and targeted therapies. Better understanding of the biology underlying aggressive CLL is expected to design novel therapies. We recently discovered that high spliceosome complex protein expression results in aberrant RNA splicing, is associated with aggressive disease and serves as an independent predictive marker for poor prognosis in CLL, highlighting RNA splicing dysregulation underlies aggressive CLL. Through an integrated transcriptome and proteome analysis on normal and primary CLL B cells, we discovered that METTL3, an RNA methyltransferase that deposits N6-methyladenosine (m6A) modification on mRNA, is strongly implicated as a key regulator for RNA splicing in CLL. METTL3 is a highly expressed protein in CLL, associated with poor clinical outcome, and significantly correlated with splicing factor protein expression. Moreover, efficacious small molecule inhibitors of METTL3 have been developed and have shown promising results in hematological malignancy. Treatment with METTL3 inhibitor results in growth defect in CLL cell lines and decreases RNA splicing factor protein expression. Moreover, we have obtained evidence that METTL3 overexpression is oncogenic by rending IL-3 independency in Ba/F3 cell line model. Based on these preliminary data, we hypothesize that METTL3 potentially acts as an oncogene and drives the onset and progression of CLL through the regulation of RNA splicing network, making it a potential target for treating aggressive CLL. To address this hypothesis, we propose to investigate METTL3 is required for both development and maintenance of CLL using murine models (Aim 1). We will dissect the molecular mechanism underlying the targets of RNA splicing network in CLL and understand how they are regulated by METTL3 (Aim 2). Moreover, we will determine whether METTL3 is a viable therapeutic target in treating aggressive CLL and if targeting both METTL3 and RNA splicing regulatory network has a synergistic effect in CLL (Aim 3). Collectively, the results of the experiments proposed in this application will establish METTL3 as an CLL oncogene, elucidate the m6A-modification on target transcripts that modulated by METTL3 to promote and maintain CLL, and evaluate a new therapeutic approach for aggressive CLL.
