Role of SMARCD3/BAF60C in medulloblastoma

Project Summary/Abstract Medulloblastoma (MB), a fast-growing and heterogeneous brain tumor arising in the cerebellum, has been characterized as four major subgroups: WNT, SHH, Group 3, and Group 4. Among the four subgroups, 30-50% of patients have metastases in the high-risk MBs such as Group 3 and Group 4, particularly Group 3 MB with MYC amplification or overexpression. Tumor metastases and relapse remain the most significant morbidity factors influencing MB patient outcomes. Although surgical resection, radiotherapy, and chemotherapy are effective at eliminating some forms, patients with high-risk MBs cannot be cured with conventional therapies. Furthermore, unknown molecular mechanisms that regulate tumor metastasis represent a major research gap. The overall objective of this application is to delineate the functions of SMARCD3 (also named BAF60C) in neurodevelopment and MB tumorigenesis. We have recently first identified that SMARCD3, a core component of SWI/SNF chromatin-remodeling complexes, is most highly expressed in Group 3 MB and promotes metastatic dissemination by hijacking a neurodevelopmental program of Reelin-Disabled 1 (DAB1)-Src kinase signaling. Based on our published and unpublished data, the central hypothesis of this proposal is that MYC upregulates SMARCD3 expression through enhancer of zeste homologue 2 (EZH2)-mediated chromatin remodeling; elevated SMARCD3 contributes to MYC-induced MB formation through suppression of P53 transcriptional expression and to subsequent metastatic dissemination through DAB1-Src signaling- and Lysyl oxidase (LOX) family-mediated cell migration. Therefore, targeting these signaling pathways provides novel therapeutic strategies for MB patients. The central hypothesis will be tested by pursuing three specific aims: 1) delineate SMARCD3 regulation by MYC-EZH2-mediated chromatin remodeling, 2) determine if SMARCD3 regulates P53 repression contributing to MYC-induced MB formation, and 3) assess the utility of inhibiting SMARCD3- dependent upregulation of DAB1-Src and LOXL1 signaling activation in preclinical MB models. To accomplish these aims, we will use genetic gain/loss-of-function methods, transcriptomic/epigenomic approaches, and pharmacological interventions to delineate the regulatory gene networks (MYC, EZH2, SMARCD3, P53, DAB1, and LOXL1) in early cerebellar development and MB tumorigenesis. We will test each aim hypothesis using different preclinical model systems (in vitro, ex vivo, and in vivo), including patient-derived MB cell lines and orthotopic xenograft mouse modes, MYC-induced de novo MB mouse models, and genetically engineered mouse models. The research proposed in this application is innovative because it is the first work to understand the role of SMARCD3 in brain pathophysiology and to develop a novel antimetastatic strategy for brain cancer therapy. The proposed research is significant because it is expected to provide compelling functional evidence of SMARCD3 in brain development and tumorigenesis. Such knowledge has the potential to offer new rationales for the development of innovative therapies for patients with MB.