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Microglia induces Gas1 expression in human brain tumor-initiating cells to reduce tumorigenecity.

ABSTRACT: We reported previously that microglia decreased the growth of human brain tumor-initiating cells (BTICs). Through microarray analyses of BTICs exposed in vitro to microglia, we found the induction of several genes ascribed to have roles in cell cycle arrest, reduced cell proliferation and differentiation. Herein, we tested the hypothesis that one of these genes, growth arrest specific 1 (Gas1), is a novel growth reduction factor that is induced in BTICs by microglia. We found that microglia increased the expression of Gas1 transcript and protein in glioblastoma patient-derived BTIC lines. Using neurosphere assay we show that RNAi-induced reduction of Gas1 expression in BTICs blunted the microglia-mediated BTIC growth reduction. The role of Gas1 in mediating BTIC growth arrest was further validated using orthotopic brain xenografts in mice. When microglia-induced Gas1-expressing BTIC cells (mGas1-BTICs) were implanted intra-cranially in mice, tumor growth was markedly decreased; this was mirrored in the remarkable increase in survival of mGas1-BT025 and mGas1-BT048 implanted mice, compared to mice implanted with non-microglia-exposed BTIC cells. In conclusion, this study has identified Gas1 as a novel factor and mechanism through which microglia arrest the growth of BTICs for anti-tumor property.

SUBMITTER: Sarkar S

PROVIDER: S-EPMC6191418 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Microglia induces Gas1 expression in human brain tumor-initiating cells to reduce tumorigenecity.

Sarkar Susobhan S Poon Candice C CC Mirzaei Reza R Rawji Khalil S KS Hader Walter W Bose Pinaki P Kelly John J Dunn Jeffrey F JF Yong V Wee VW

Scientific reports 20181016 1

We reported previously that microglia decreased the growth of human brain tumor-initiating cells (BTICs). Through microarray analyses of BTICs exposed in vitro to microglia, we found the induction of several genes ascribed to have roles in cell cycle arrest, reduced cell proliferation and differentiation. Herein, we tested the hypothesis that one of these genes, growth arrest specific 1 (Gas1), is a novel growth reduction factor that is induced in BTICs by microglia. We found that microglia incr ...[more]

PMID: 30327548

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Project description:Glioblastomas (GBM) are poorly differentiated astrocytic tumors arising in the Central Nervous System (CNS), which despite aggressive treatments are still characterized by a fatal outcome. Several studies have shown the existence of a subpopulation of cells within glioma tumors displaying cancer stem cells properties. As the term “tumor initiating cells” (TICs) is frequentely used to describe cells as these with cancer stem cells capacity. Because TICs promotes the tumor chemo- and radio-resistance and angiogenesis it is conceivable that finding a mean to kill these cells would lead to a better therapy for GBM. The NOTCH gene has an important role during the CNS development, in the maintenance of dividing cells in promoting neural lineage entry of Embryonic Stem Cells and the differentiation of astroglia from the rat adult hippocampus-derived multipotent progenitors. The activation of the NOTCH signaling requires the proteolytic processing of this type I integral membrane protein by a two step process catalyzed first by a metalloprotease and then by the gamma-secretase. An increased activation of the NOTCH signaling has been implicated in several tumors types. Recently some studies showed that this pathway induces the survival/proliferation in GBM and glioma cells, and the expression of stem cell properties in glioma cells. Accordingly to these findings, the inhibition of this pathway leads to depletion of stem-like cells and blocks the engraftment in embryonal brain tumors. Furthermore, enhanced NOTCH signaling may lead to one of the tumor resistance mechanisms deployed by GBM. Targeting the NOTCH pathway specifically in GBM TICs appears therefore as a rational approach for exploring novel and hopefully more effective therapeutic strategies for the management of this malignancy. Several molecular tools are available for targeting the Notch pathway such as specific siRNAs, shRNAs or drugs such as gamma-secretase inhibitors. Among these tools, the latter are small peptides/molecules able to inhibit the gamma-secretase by distinct mechanisms. In this study we used two drugs known as gamma-secretase inhibitors, to investigate by gene expression profiling, their ability to interfere specifically with the proliferative properties of GBM TICs previously obtained in our laboratory. Our data show that one of these two drugs, LLNle, is effective in killing these cells in vitro by activating protein catabolic process mediated by the proteasome, suggesting that preclinical studies should definitely be carried on to evaluate whether LLNle is able to significantly improve the survival in hybrid human GBM-animal models. Gamma-secretase inhibitors have been proposed as drugs able to kill cancer cells by targeting the NOTCH pathway. In this study we employed two of such inhibitors, namely the z-Leu-leu-Nle-CHO (LLNle) and N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), to verify whether they were effective in vitro in the killing of human GBM tumor initiating cells (TICs). We first established that of the two drugs only LLNle reduces the viability of GBM TICs obtained from three different patients in the low micromolar range. Cells were treated with 7.5 μM LLNle or DAPT or vehicle alone (DMSO 0.1%) and kept in a humidified 5% CO2 atmosphere at 37°C for the indicated time period (24 or 48 hours). To establish which cellular processes are activated in GBM TICs by LLNle we generated and analyzed the gene expression profile after treatment with this compound and with DAPT and DMSO (vehicle). Our data show that LLNle induces upregulation of genes coding for proteasome subunits and subsequently mitotic arrest in these cells by repressing genes required for DNA synthesis and mitotic progression and by activation of genes acting as mitotic inhibitors. Our data are consistent with proteasome inhibition by LLNle, subsequent upregulation of proteasome activity and subsequent unleash of the apoptotic process in GBM TICs.

Dataset Information

Microglia induces Gas1 expression in human brain tumor-initiating cells to reduce tumorigenecity.

Publications

Microglia induces Gas1 expression in human brain tumor-initiating cells to reduce tumorigenecity.

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