PM-05 * ARHGAP36 AS A NOVEL DRIVER IN HIGH-RISK HUMAN MEDULLOBLASTOMA

Medulloblastoma (MB) is the most frequent childhood malignancy of the CNS. Current trials aim to identify effective treatments with reduced side effects, but lack of knowledge regarding drivers prevents development of more precise therapies. MB is divided into four subgroups based on gene expression, histology and developmental origin: SHH, WNT, Group 3 and Group 4. Our lab identified a novel driver of MB using Sleeping Beauty (SB) insertional mutagenesis. Rho GTPase Activating Protein 36 (Arhgap36) was the top candidate to emerge from this screen, with activating insertions in 14/22 MB harvest (Larson et al., submitted). Preliminary studies with qRT-PCR, tissue microarray and immunohistochemistry showed ARHGAP36 overexpression in Group 3/4 human MB. We are employing multiple genetic techniques to elucidate the role of Arhgap36 in MB tumorigenesis. We have overexpressed ARHGAP36 in a non-tumor forming immortalized mouse cerebellar cell line (C17.2) and several human MB cell lines (Daoy, Med8A, Ons76 and two primary lines). We will also knockout ARHGAP36 expression in these lines using stable integration of the CRISPR/Cas system. We will use these lines to monitor changes in proliferation, migration, anchorage independent growth, and tumor formation in response to alterations in ARHGAP36 expression. Lastly, the novelty of ARHGAP36 warrants a non-biased approach, so we will analyze cell-wide signaling changes in cells with low, medium and high levels of ARHGAP36 expression using RNA sequencing and MicroWesterns. Arhgap36 overexpression is strongly associated with MB, and our findings indicate that it may play a driving role in Group 3 and Group 4 MB tumorigenesis. Furthermore, Arhgap36 may represent a novel target for therapeutic efforts aimed at treating patients with MB.