Musashi1 contributes to glioblastoma development via regulation of a network of DNA replication, cell cycle, and division genes
RNA binding proteins (RBPs) function as master regulators of gene expression. Alterations in their expression levels and function are often observed in tumors with numerous oncogenic RBPs identified in recent years.  Musashi1 (Msi1) is an RBP and stem cell marker gene that controls the balance between self-renewal and proliferation. High Msi1 levels have been observed in multiple tumor types including glioblastoma and are often associated with poor patient outcomes. Msi1 knockdown is known to affect numerous cancer phenotypes and to prevent growth of different tumor types. To dissect Msi1's main contributions to glioblastoma development, we conducted a comprehensive genomic analysis. We identified a network of cell cycle/division and DNA replication genes and established these processes as its core functions. Msi1 controls this gene network via two mechanisms: direct interaction and indirect regulation mediated by the transcription factors E2F2 and E2F8. We corroborated Msi1's impact on these processes and determined that glioblastoma lines with Msi1 KO display increased sensitivity to cell cycle and DNA replication inhibitors. As Msi1 inhibitors have been identified, a drug combination strategy (Msi1 + cell cycle/DNA replication inhibitors) could be a viable route to treat glioblastoma. Overall design: U251 and U343 control and MSI1 KO cells were plated in 96 wells at a density of 8x104. Cells were synchronized by serum starvation for 24 hours. Following synchronization, cells were exposed to 20 nM of Paclitaxel for 24 hours. Cells were fixed in 4% PFA and stained with Alpha-Tubulin and DAPI. The experiment was performed in triplicates and 1,000 cells were counted per replicate. Differences were assessed with a student's t-test. p < 0.01.