Browsing by Author "Cutts, Emilie"

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    Investigating the Role of the Mediator Complex in Brain Tumour Stem Cells
    (2021-07-27) Cutts, Emilie; Weiss, Samuel; Luchman, H. Artee; Goodarzi, Aaron; Grewal, Savraj
    The regulation of gene transcription is highly controlled and frequently modified in cancer cells. Glioblastoma (GBM) is a fast-growing, malignant grade IV astrocytoma, with a median patient survival of approximately 15 months. Transcriptional dysregulation contributes to the malignant phenotypes of brain tumour stem cells (BTSCs), which are thought to promote GBM initiation and progression. In response to dynamic tumour microenvironment signals, BTSC plasticity has been shown to facilitate adaptive transcriptional programs to enable cellular proliferation and survival. Therefore, there is a growing interest in elucidating the precise mechanisms of transcriptional regulation which promote BTSC plasticity. The Mediator complex acts as a functional bridge between enhancer-bound transcription factors and the basal transcription machinery at core promoters to activate or repress gene transcription. Regulatory transcription factors, involved in cellular response to environmental cues, have been shown to interact with the Mediator tail module. Therefore, the Mediator complex is thought to integrate environmental signals to facilitate context-dependent gene expression. Recently, we identified a role for the Mediator tail module linked to an epigenetic mechanism of gene regulation important for BTSC growth and differentiation, driven by the histone methyltransferase DOT1L. However, the precise contributions of individual tail subunits for transcriptional regulation in BTSCs warrant further investigation. To determine the extent of context-dependent gene transcription regulated by the Mediator complex tail module, I generated single gene knockouts to individually target all 7 tail subunits in BTSCs. Genetic loss of any of the tail subunits had no effect on the viability, proliferation, or self-renewal potential of BTSCs grown in ideal neural stem cell culture conditions. However, orthotopic xenografts of each Mediator tail subunit knockout cell line in SCID mice, a context which more closely recapitulates the GBM tumour microenvironment, resulted in reduced tumour burden and significantly longer overall mouse survival. I further demonstrate that the Mediator tail module regulates transcriptional pathways related to neurogenesis and inflammation. In support of these findings, I identified a role for the Mediator tail module in facilitating cellular response to inflammatory cues, through the regulation of inducible nitric oxide synthase (iNOS) activity. In this study, I describe novel findings to the field of GBM by demonstrating a requirement for the Mediator complex tail module for gliomagenesis. Furthermore, I identify the Mediator complex as an important molecular player in the dynamic interplay between the GBM tumour microenvironment and BTSC gene transcription.