GSE134597
Musashi1 is a master regulator of aberrant translation in Group 3 medulloblastoma
Pediatric medulloblastoma (MB) is the most common solid malignant brain neoplasm, with group 3 (G3) MB representing the most aggressive subgroup associated with a poor prognosis and a remarkable ability to resist upfront multimodal therapy. Despite a low mutational burden of disease and MYC amplification identified as a independent factor associated with poor survivorship, efforts to target the MYC has met with limited therapeutic success. Consequently alternative mediators associated with the aggressive phenotype of G3 MB continues as a common goal within the MB community. Here we show how the neural stem cell determinant Musashi 1 (MSI1) is a central and vital moderator of G3 MB in both a MYC amplified mouse model of G3 MB and patient derived xenografts (PDX). Specifically, we modified the MYC amplified and p53 mutated (MP) mouse model of G3 MB to generate Msi1 conditional knockout mice (Msi1flox/flox), which led to the observation that MSI1 is required for tumor initiation of MP tumors. To identify the translational potential of these findings, we employed shRNA against Msi1 in multiple PDX lines, observing a striking deficit in multiple key stem cell features including self-renewal, proliferation, and failure to progress through the cell cycle. Notably, Msi1 inhibition resulted in a failure of tumor initiation, translating to a significantly prolonged survival, reaffirming the essential role for MSI1 in G3 MB. To determine how MSI1 symphonizes the anarchic post-transcriptional landscape of G3MB, we differentially analyzed the MSI1 binding sites in normal neural stem cells and G3 MB and subsequently compared the MSI1-binding transcriptome, and proteome following Msi1 inhibition. Comparative analysis suggested an integral role for post-transcriptional regulators, such as MSI1 and its binding prey mRNA, as a therapeutic target. Here we propose the neural RNA binding protein MSI1, as a master regulator, hijacked from its normal neural developmental function, orchestrating the aberrant translational landscape of G3 MB. Overall design: shRNA against Msi1 in a patient-derived xenograft line.