MECHANISMS AND TARGETING OF NEURODEVELOPMENTAL REGULATOR REST IN MEDULLOBLASTOMA DISSEMINATION

Molecular subgrouping of medulloblastoma (MB) has produced four subgroups: wingless (WNT), sonic hedgehog (SHH), group 3, and group 4. While patients with WNT tumors have the best prognosis, patients with SHH tumors have a more variable prognosis concurrent with metastatic disease. This subset of SHH patients have elevated levels of the neurogenic regulator, RE1 Silencing Transcription factor (REST). To understand the role of REST in MB, we utilized a novel transgenic mouse model wherein REST expression can be conditionally elevated during postnatal development in the cells of origin of SHH MB, cerebellar granule neural progenitors (GNPs). While these mice did not form tumors, an abnormal organization of GNPs in the cerebella of these mice was observed. Molecular investigation of these REST-high GNPs revealed heightened expression of the chemokine receptor, C-X-C-motif receptor 4 (CXCR4). CXCR4 function has established importance in both cerebellar neurodevelopment and MB tumor metastasis. In MB mouse models, increased REST expression resulted in increased CXCR4 expression that was related to increased tumor dissemination and dramatically reduced survival of mice. Analysis of patient samples revealed that REST and CXCR4 levels were concurrently high in patients with metastasis in a subset of SHH (SHH-beta) patients. Examination of human MB cell lines strengthened the observation that REST elevation increased MB cell migration. The final section of my dissertation work has focused on targeting REST activity through inhibition of epigenetic cofactor, lysine specific demethylase 1 (LSD1). To this end, I examined human MB patient samples for LSD1 expression and discovered that while CXCR4 signaling was highly relevant to SHH-beta subgroups, LSD1 was increased in the context of REST most strongly in SHH-alpha and SHH-beta patient groups. In vitro work demonstrated that LSD1 knockdown reduced SHH MB cell line viability in the context of normal and high REST. However, irreversible inhibition of LSD1 had no effect on cell viability but did exert a REST-dependent reduction of migration. Ingenuity pathway analysis of RNA-sequencing data revealed that irreversible inhibition of LSD1 reduced cell migration signaling pathways relevant to MB. In summary, my work has two major findings. First, in the context of REST elevation, CXCR4 expression and signaling increases along with migratory capacity of postnatal GNPs that contribute to perturbed development and medulloblastoma infiltration. Second, REST activity can be targeted against complex member LSD1 and pharmacological targeting of LSD1 with irreversible inhibitors blocks REST-dependent MB cell migration. Collectively, my work has demonstrated that elevated REST expression in the developing brain can perturb neurodevelopment and influences migration signaling pathways to contribute to medulloblastoma dissemination