Summary CHIP is an E3-ubiquitin ligase that contributes to healthy aging and has been characterized as neuroprotective. To elucidate dominant CHIP-dependent changes in protein steady-state levels in a patient-derived human neuronal model, CHIP function was ablated using gene-editing and an unbiased proteomic analysis conducted to compare knock-out and wild-type isogenic induced pluripotent stem cell (iPSC)-derived cortical neurons. Rather than a broad effect on protein homeostasis, loss of CHIP function impacted on a focused cohort of proteins from actin cytoskeleton signaling and membrane integrity networks. In support of the proteomics, CHIP knockout cells had enhanced sensitivity to induced membrane damage. We conclude that the major readout of CHIP function in cortical neurons derived from iPSC of a patient with elevate α-synuclein, Parkinson's disease and dementia, is the modulation of substrates involved in maintaining cellular “health”. Thus, regulation of the actin cytoskeletal and membrane integrity likely contributes to the neuroprotective function(s) of CHIP.

Better understanding of GBM signalling networks in-vivo would help develop more physiologically relevant ex vivo models to support therapeutic discovery. A “functional proteomics” screen was undertaken to measure the specific activity of a set of protein kinases in a two-step cell-free biochemical assay to define dominant kinase activities to identify potentially novel drug targets that may have been overlooked in studies interrogating GBM-derived cell lines. A dominant kinase activity derived from the tumour tissue, but not patient-derived GBM stem-like cell lines, was Bruton tyrosine kinase (BTK). We demonstrate that BTK is expressed in more than one cell type within GBM tissue; SOX2-positive cells, CD163-positive cells, CD68-positive cells, and an unidentified cell population which is SOX2-negative CD163-negative and/or CD68-negative. The data provide a strategy to better mimic GBM tissue ex vivo by reconstituting more physiologically heterogeneous cell co-culture models including BTK-positive/negative cancer and immune cells. These data also have implications for the design and/or interpretation of emerging clinical trials using BTK inhibitors because BTK expression within GBM tissue was linked to longer patient survival.

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Glioblastoma (GBM), one of the most lethal and heterogeneous primary brain tumors, contains cellular hierarchies with both quiescent and self-renewing highly tumorigenic glioblastoma stem cells (GSCs). Cancer stem cells within the context of the brain likely contribute to a lack of progress in patient survival time as they appear to have an innate resistance to both chemotherapeutic drugs and radiotherapy. The aim of this study is to elucidate how constitutive expression of interferons (IFNs) and their downstream signalling pathways maintain GSCs thereby supporting treatment resistance and tumor reoccurrence. To understand the mechanism of action of a subset of IFN regulated genes, originally characterized as a signature for radiation and chemotherapy resistance (IRDS), a panel of patient derived glioma stem cells was generated and manipulated using CRISPR/Cas9 mediated gene-editing. Phenotypic changes in growth, viability and drug resistance were characterised in the edited cells and linked to molecular level events using transcriptomic and proteomic techniques. Using this approach, in conjunction with patient tissue analysis, signalling under basal as well as IFN-activated conditions was studied in the context of GSC status. Immunohistopathology of a glioma tissue micro-array identified an increased expression of IFN induced transmembrane receptors (IFITMs), which co-localised with Nestin, around the blood vessels suggesting that IFITM positive cells were in the stem cell niche. Further analysis showed the presence of both IFITM1 and IFITM3 in GSCs and established that loss of IFITM function impacted on growth rate and cell cycle progression as well as treatment sensitivity. By using wild-type and gene-edited GSC to focus on the relationship between IFITM1 and IFITM3, we have compelling phenotypic and molecular evidence that IFN-induced changes in the localisation of IFITMs impact on the ability of stem cells to ‘escape' normal growth control mechanisms. Taking into consideration the constitutive expression of interferons in the tumor microenvironment, our study provides evidence that IFITMs regulate glioma stem cell self-renewal and are involved in maintaining a quiescent population which can escape chemotherapy. Citation Format: Erisa Nita, Bernard Evers, Marta Nekulova, Gillian Morrison, Kathryn Ball. The role of IFITMs in maintaining glioma stem cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3777.

Glioblastoma, one of the most lethal and heterogeneous primary brain tumours, contains cellular hierarchies with both quiescent and self-renewing glioblastoma stem cells (GSCs). GSCs contribute to a lack of progress in patient survival as they appear to have an innate resistance to both chemotherapy and radiotherapy. The aim of this study is to elucidate how constitutive expression of interferons (IFNs) and their downstream signalling pathways maintain GSCs thereby supporting treatment resistance and tumour reoccurrence. To understand the mechanism of action of a subset of IFN regulated genes, originally characterized as a signature for radiation and chemotherapy resistance (IRDS), a panel of patient derived GSCs was generated and manipulated using CRISPR/Cas9 gene-editing. Phenotypic changes in growth, viability and drug resistance were characterised and linked to molecular level events using transcriptomic and proteomic techniques. Using this approach, in conjunction with patient tissue analysis, signalling under basal as well as IFN-activated conditions was studied in the context of GSC status. Immunohistopathology of a glioma tissue micro-array identified an increased expression of IFN induced transmembrane receptors (IFITMs), which co-localised with Nestin, around the blood vessels suggesting that IFITM positive cells were in the stem cell niche. Further analysis showed the presence of IFITM1 and IFITM3 in GSCs and established that loss of IFITMs function impacted on growth rate and cell cycle progression as well as treatment sensitivity. By using wild-type and gene-edited GSC to focus on the relationship between IFITM1 and IFITM3, we have compelling phenotypic and molecular evidence that IFN-induced changes in the localisation of IFITMs impact on the ability of stem cells to ‘escape’ normal growth control mechanisms. Taking into consideration the constitutive expression of interferons in the tumour microenvironment, our study provides evidence that IFITMs regulate GSC self-renewal and are involved in maintaining a quiescent population which can escape chemotherapy.

IntroductionConstitutive expression of interferons (IFNs) and their downstream signalling pathways play a critical role in host responses to cell transformation in the tumour microenvironment. Induction of IFNs initiates the transcription of a variety of genes, so called IFN- stimulated genes (ISGs). Although expression of ISGs is classically associated with tumour suppression, a subset defined as the IRDS (Interferon - Related DNA- Damage Resistance Signature), is elevated in response to endogenous IFN, self-DNA and RNA exposure in the tumour microenvironment acquiring radiation and chemotherapy resistance. INF induced transmembrane receptor (IFITM1) is thought to participate in proliferating signalling and oncogenesis. Three out of five IFITM genes (IFITM1,2,3) share high amino-acid homology, however, IFITM1 has a unique C-terminal domain, a 13 amino-acid extension, and a shorter N-terminal amino-acid sequence.Material and methodsTo analyse the impact of IFITM1 loss, or mutation, on signalling and phenotypic events such as growth, viability and drug resistance, knock – out, knock – in and domain mutants were generated using Crispr/Cas9 mediated gene – editing. To identify the effects of radiation in the growth of wild type and mutant IFITM1 cells, proliferation assays were conducted while immunoassays were used to check for activation of the IRDS pathway. The gene edited cell lines were used in Mass Spectrometry proteomic approaches to discover IFITM1 interacting proteins under normal growth conditions as well as in INF treated and/or radiated cells.Results and discussionsIrradiation of glioma stem cells, results in a substantial increase in the expression of IFITM1 and an activation of the IRDS pathway which suggests a potential mechanism by which cancer stem cells escape chemotherapy. Deletion of IFITM1 in SiHa cells results in sensitivity to chemo- and radiation therapy, while loss of both IFITM1 and IFITM3 function generates chemoresistant cancer cells suggesting a potential interaction between IFITM1 and IFITM3.Structure-function analysis has shown that the C-terminal regulatory domain of IFITM1 is required for its ability to promote cell growth and to localise to the membrane.ConclusionWe have identified IFITM1 as an upstream regulator of the IRDS which promotes cancer cell survival and mediates chemoresistance. The C-terminal domain of IFITM1 is important for its proliferative activity in cancer and lay the foundation for future research aiming to determine IFITM1’s potential as a therapeutic target in cancer.