Pediatric medulloblastoma (MB) is the most common solid malignant brain neoplasm, with group 3 (G3) MB representing the most aggressive subgroup. Despite MYC amplification representing an independent poor prognostic factor in G3 MB, efforts to target the MYC pathway have met with limited therapeutic success. As such, alternative mediators of G3 MB continue to be sought. The RNA binding protein and neural stem cell determinant Musashi-1 (MSI1) has been implicated in a number of adult stem cells in various organs (e.g., brain, gut, ovaries/testes) with mounting evidence that MSI1 is an essential regulator of cancer stem cells (e.g., brain, gut, lung). Early studies in MB have shown MSI1 to be essential for tumour maintenance, however the direct interactions and specific mechanisms conferring tumours with high MSI1 expression (i.e., G3 MB) are yet to be determined. Here, I show MSI1 is an essential moderator of G3 MB in both a MYC amplified and p53 mutated (MP) mouse model of G3 MB and patient-derived xenograft (PDX) models. MSI1 inhibition resulted in an abrogation of tumour initiation in both models, translating to a significantly prolonged survival. To determine how MSI1 regulates the post-transcriptional landscape of human G3 MB, an unbiased multiplatform approach was undertaken, using enhanced cross-linking and immunoprecipitation (eCLIP), and differential analyses post-MSI1 inhibition at the transcriptome-, proteome-, and translatome-wide scale, revealing MSI1's key role in moderating G3 MB-associated cancer driving genes. In summary, employing innovational multi-platform integrative approach to stem cell cancer biology, I show the neural RNA binding protein MSI1, an essential master stem cell regulator, is hijacked from its normal neural developmental function to orchestrate the aberrant translational landscape of G3 MB. / Thesis / Doctor of Philosophy (PhD) / Brain tumours are the leading cause of childhood cancer death with medulloblastoma (MB) representing the most frequent malignant childhood brain tumour. Analysis of the data retrieved from multiple genetic studies of MB, we have determined that there are 4 genetic subgroups of MB: Wnt, Shh, Group 3 (G3) and Group 4 (G4). The subgroup with the worse prognosis is Group 3, and unique to this subgroup is the overproduction of the MYC gene products (i.e., MYC amplification). In fact, MYC amplification alone is associated with a poor prognosis in these children. As such many researchers and clinicians have been working together to find a way to target MYC. Although many pre-clinical experimental studies have cured MYC-amplified G3 MB using gene-targeting therapy, these results unfortunately have not translated into early clinical trials. Therefore, alternative targets that mediate the aggressiveness of MYC-amplified G3 MB is being sought. As cancer stem cells (CSC) have been implicated in tumour development and maintenance, a gene worthy of investigation in a neurodevelopmental tumour such as MB, is Musashi-1 (MSI1). MSI1 protein has been identified in high levels in many human cancers, been observed to play a crucial role in promoting normal stem cell features, and is also implicated in driving cancer. The protein that the MSI1 gene produces binds to genes and modifies them to either stabilize or destabilize their path to becoming a protein. By manipulating MSI1 in both NSC and MB CSC, I will observe how these cells either display greater or less cancer associated features. Further, with a new technology allowing researchers to identify MSI1 binding sites, we aim to determine how MSI1 modifies cancer causing and normal neural stem cell genes. Moreover, I will be studying both the gene-, pre-protein- and protein-level changes after experimentally manipulating MSI1 gene levels to tease out its’ main cancer associated function. Altogether, we found a core list of genes that MSI1 modulates with functional significance giving us clues for a therapeutic targeting strategy for G3 MB.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/25212 |
| Date | January 2019 |
| Creators | Kameda-Smith, Michelle |
| Contributors | Singh, Sheila K, Biochemistry and Biomedical Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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