TIE2-mediated tyrosine phosphorylation of H4 regulates DNA damage response by recruiting ABL1

DNA repair pathways enable cancer cells to survive DNA damage induced after genotoxic therapies. Tyrosine kinase receptors (TKRs) have been reported as regulators of the DNA repair machinery. TIE2 is a TKR overexpressed in human gliomas at levels that correlate with the degree of increasing malignancy. Following ionizing radiation, TIE2 translocates to the nucleus, conferring cells with an enhanced nonhomologous end-joining mechanism of DNA repair that results in a radioresistant phenotype. Nuclear TIE2 binds to key components of DNA repair and phosphorylates H4 at tyrosine 51, which, in turn, is recognized by the proto-oncogene ABL1, indicating a role for nuclear TIE2 as a sensor for genotoxic stress by action as a histone modifier. H4Y51 constitutes the first tyrosine phosphorylation of core histones recognized by ABL1, defining this histone modification as a direct signal to couple genotoxic stress with the DNA repair machinery

Environmental stimuli shape microglial plasticity in glioma

In glioma, microglia and infiltrating macrophages are exposed to factors that force them to produce cytokines and chemokines, contributing to tumor growth and maintaining a pro-tumorigenic, immunosuppressed microenvironment. We demonstrate that housing glioma-bearing mice in enriched environment (EE) reverts the immunosuppressive phenotype of infiltrating myeloid cells, by modulating inflammatory gene expression. Under these conditions, branching and patrolling activity of myeloid cells is increased, and their phagocytic activity is promoted. Modulation of gene expression depends on interferon-(IFN) g produced by natural killer (NK) cells, disappearing in mice depleted of NK cells or lacking IFN-g, and was mimicked by exogenous interleukin-15 (IL-15). Further, we describe a key role for BDNF produced in the brain of mice housed in EE in mediating the expression of IL-15 in CD11b+ cells. These data define novel mechanisms linking environmental cues to the acquisition of a pro-inflammatory, anti-tumor microenvironment in mouse brain

Immune-mediated mechanisms influencing the efficacy of anticancer therapies

Conventional anticancer therapies, such as chemotherapy, radiotherapy, and targeted therapy, are designed to kill cancer cells. However, the efficacy of anticancer therapies is not only determined by their direct effects on cancer cells but also by off-target effects within the host immune system. Cytotoxic treatment regimens elicit several changes in immune-related parameters including the composition, phenotype, and function of immune cells. Here we discuss the impact of innate and adaptive immune cells on the success of anticancer therapy. In this context we examine the opportunities to exploit host immune responses to boost tumor clearing, and highlight the challenges facing the treatment of advanced metastatic disease

Propentofylline Targets TROY, a Novel Microglial Signaling Pathway

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain cancer, with a median survival of less than 2 years after diagnosis with current available therapies. The tumor microenvironment serves a critical role in tumor invasion and progression, with microglia as a critical player. Our laboratory has previously demonstrated that propentofylline, an atypical methylxanthine with central nervous system glial modulating and anti-inflammatory actions, significantly decreases tumor growth in a GBM rodent model by preferentially targeting microglia. In the present study, we used the CNS-1 rat glioma model to elucidate the mechanisms of propentofylline. Here we demonstrate that propentofylline targets TROY, a novel signaling molecule up-regulated in infiltrating microglia, and not macrophages, in response to CNS-1 cells. We identify Pyk2, Rac1 and pJNK as the downstream signaling molecules of TROY through western blot analysis and siRNA transfection. We demonstrate that inhibition of TROY expression in microglia by siRNA transfection significantly inhibits microglial migration towards CNS-1 cells similar to 10 µM propentofylline treatment. These results identify TROY as a novel molecule expressed in microglia, involved in their migration and targeted by propentofylline. Furthermore, these results describe a signaling molecule that is differentially expressed between microglia and macrophages in the tumor microenvironment

Tumour-derived CSF2/granulocyte macrophage colony stimulating factor controls myeloid cell accumulation and progression of gliomas

BACKGROUND: Malignant tumours release factors, which attract myeloid cells and induce their polarisation to pro-invasive, immunosuppressive phenotypes. Brain-resident microglia and peripheral macrophages accumulate in the tumour microenvironment of glioblastoma (GBM) and induce immunosuppression fostering tumour progression. Macrophage colony stimulating factors (CSFs) control the recruitment of myeloid cells during peripheral cancer progression, but it is disputable, which CSFs drive their accumulation in gliomas. METHODS: The expression of CSF2 (encoding granulocyte-macrophage colony stimulating factor) was determined in TCGA datasets and five human glioma cell lines. Effects of stable CSF2 knockdown in glioma cells or neutralising CSF2 or receptor CSF2Rα antibodies on glioma invasion were tested in vitro and in vivo. RESULTS: CSF2 knockdown or blockade of its signalling reduced microglia-dependent glioma invasion in microglia-glioma co-cultures. CSF2-deficient human glioma cells encapsulated in cell-impermeable hollow fibres and transplanted to mouse brains, failed to attract microglia, but stimulated astrocyte recruitment. CSF2-depleted gliomas were smaller, attracted less microglia and macrophages, and provided survival benefit in tumour-bearing mice. Apoptotic microglia/macrophages were detected in CSF2-depleted tumours. CONCLUSIONS: CSF2 is overexpressed in a subset of mesenchymal GBMs in association with high immune gene expression. Tumour-derived CSF2 attracts, supports survival and induces pro-tumorigenic polarisation of microglia and macrophages

Characteristics of the Alternative Phenotype of Microglia/Macrophages and its Modulation in Experimental Gliomas

Microglia (brain resident macrophages) accumulate in malignant gliomas and instead of initiating the anti-tumor response, they switch to a pro-invasive phenotype, support tumor growth, invasion, angiogenesis and immunosuppression by release of cytokines/chemokines and extracellular matrix proteases. Using immunofluorescence and flow cytometry, we demonstrate an early accumulation of activated microglia followed by accumulation of macrophages in experimental murine EGFP-GL261 gliomas. Those cells acquire the alternative phenotype, as evidenced by evaluation of the production of ten pro/anti-inflammatory cytokines and expression profiling of 28 genes in magnetically-sorted CD11b+ cells from tumor tissues. Furthermore, we show that infiltration of implanted gliomas by amoeboid, Iba1-positive cells can be reduced by a systematically injected cyclosporine A (CsA) two or eight days after cell inoculation. The up-regulated levels of IL-10 and GM-CSF, increased expression of genes characteristic for the alternative and pro-invasive phenotype (arg-1, mt1-mmp, cxcl14) in glioma-derived CD11b+ cells as well as enhanced angiogenesis and tumor growth were reduced in CsA-treated mice. Our findings define for the first time kinetics and biochemical characteristics of glioma-infiltrating microglia/macrophages. Inhibition of the alternative activation of tumor-infiltrating macrophages significantly reduced tumor growth. Thus, blockade of microglia/macrophage infiltration and their pro-invasive functions could be a novel therapeutic strategy in malignant gliomas

Myeloid cells expressing VEGF and arginase-1 following uptake of damaged retinal pigment epithelium suggests potential mechanism that drives the onset of choroidal angiogenesis in mice

Whilst data recognise both myeloid cell accumulation during choroidal neovascularisation (CNV) as well as complement activation, none of the data has presented a clear explanation for the angiogenic drive that promotes pathological angiogenesis. One possibility that is a pre-eminent drive is a specific and early conditioning and activation of the myeloid cell infiltrate. Using a laser-induced CNV murine model, we have identified that disruption of retinal pigment epithelium (RPE) and Bruch's membrane resulted in an early recruitment of macrophages derived from monocytes and microglia, prior to angiogenesis and contemporaneous with lesional complement activation. Early recruited CD11b(+) cells expressed a definitive gene signature of selective inflammatory mediators particularly a pronounced Arg-1 expression. Accumulating macrophages from retina and peripheral blood were activated at the site of injury, displaying enhanced VEGF expression, and notably prior to exaggerated VEGF expression from RPE, or earliest stages of angiogenesis. All of these initial events, including distinct VEGF (+) Arg-1(+) myeloid cells, subsided when CNV was established and at the time RPE-VEGF expression was maximal. Depletion of inflammatory CCR2-positive monocytes confirmed origin of infiltrating monocyte Arg-1 expression, as following depletion Arg-1 signal was lost and CNV suppressed. Furthermore, our in vitro data supported a myeloid cell uptake of damaged RPE or its derivatives as a mechanism generating VEGF (+) Arg-1(+) phenotype in vivo. Our results reveal a potential early driver initiating angiogenesis via myeloid-derived VEGF drive following uptake of damaged RPE and deliver an explanation of why CNV develops during any of the stages of macular degeneration and can be explored further for therapeutic gain

Eosinophils in glioblastoma biology

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. The development of this malignant glial lesion involves a multi-faceted process that results in a loss of genetic or epigenetic gene control, un-regulated cell growth, and immune tolerance. Of interest, atopic diseases are characterized by a lack of immune tolerance and are inversely associated with glioma risk. One cell type that is an established effector cell in the pathobiology of atopic disease is the eosinophil. In response to various stimuli, the eosinophil is able to produce cytotoxic granules, neuromediators, and pro-inflammatory cytokines as well as pro-fibrotic and angiogenic factors involved in pathogen clearance and tissue remodeling and repair. These various biological properties reveal that the eosinophil is a key immunoregulatory cell capable of influencing the activity of both innate and adaptive immune responses. Of central importance to this report is the observation that eosinophil migration to the brain occurs in response to traumatic brain injury and following certain immunotherapeutic treatments for GBM. Although eosinophils have been identified in various central nervous system pathologies, and are known to operate in wound/repair and tumorstatic models, the potential roles of eosinophils in GBM development and the tumor immunological response are only beginning to be recognized and are therefore the subject of the present review