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

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

Single-Cell Cloning of Breast Cancer Cells Secreting Specific Subsets of Extracellular Vesicles

Extracellular vesicles (EVs) mediate communication in health and disease. Conventional assays are limited in profiling EVs secreted from large populations of cells and cannot map EV secretion onto individual cells and their functional profiles. We developed a high-throughput single-cell technique that enabled the mapping of dynamics of EV secretion. By utilizing breast cancer cell lines, we established that EV secretion is heterogeneous at the single-cell level and that non-metastatic cancer cells can secrete specific subsets of EVs. Single-cell RNA sequencing confirmed that pathways related to EV secretion were enriched in the non-metastatic cells compared with metastatic cells. We established isogenic clonal cell lines from non-metastatic cells with differing propensities for CD81+CD63+EV secretion and showed for the first time that specificity in EV secretion is an inheritable property preserved during cell division. Combined in vitro and animal studies with these cell lines suggested that CD81+CD63+EV secretion can impede tumor formation. In human non-metastatic breast tumors, tumors enriched in signatures of CD81+CD63+EV have a better prognosis, higher immune cytolytic activity, and enrichment of pro-inflammatory macrophages compared with tumors with low CD81+CD63+EVs signatures. Our single-cell methodology enables the direct integration of EV secretion with multiple cellular functions and enables new insights into cell/disease biology

Macrophage Ablation Reduces M2-Like Populations and Jeopardizes Tumor Growth in a MAFIA-Based Glioma Model

Monocytes/macrophages are an influential component of the glioma microenvironment. However, understanding their diversity and plasticity constitute one of the most challenging areas of research due to the paucity of models to study these cells' inherent complexity. Herein, we analyzed the role of monocytes/macrophages in glioma growth by using a transgenic model that allows for conditional ablation of this cell population. We modeled glioma using intracranial GL261-bearing CSF-1R–GFP+ macrophage Fas-induced apoptosis (MAFIA) transgenic mice. Conditional macrophage ablation was achieved by exposure to the dimerizer AP20187. Double immunofluorescence was used to characterize M1- and M2-like monocytes/macrophages during tumor growth and after conditional ablation. During glioma growth, the monocyte/macrophage population consisted predominantly of M2 macrophages. Conditional temporal depletion of macrophages reduced the number of GFP+ cells, targeting mainly the repopulation of M2-polarized cells, and altered the appearance of M1-like monocytes/macrophages, which suggested a shift in the M1/M2 macrophage balance. Of interest, compared with control-treated mice, macrophage-depleted mice had a lower tumor mitotic index, microvascular density, and reduced tumor growth. These results demonstrated the possibility of studying in vivo the role and phenotype of macrophages in gliomas and suggested that transitory depletion of CSF-1R+ population influences the reconstitutive phenotypic pool of these cells, ultimately suppressing tumor growth. The MAFIA model provides a much needed advance in defining the role of macrophages in gliomas

Quantification of selected M1/M2 phenotype-associated gene expression in CD11b⁺ cells isolated from naïve and tumor-bearing mice.

<p>Gene expression was analyzed by real-time PCR and the results are presented as fold changes of CD11b⁺ cells isolated from tumor brains versus those from naïve brain tissue. Numbers corresponding to the significantly changed genes (t-test generated p-value<0.05) are marked in bold; NA - not available.</p

Alterations of gene expression in infiltrating microglia/macrophages and intracranial gliomas are modulated by CsA.

<p>A. Gene expression in magnetically sorted CD11b⁺ cells from tumor-bearing and naïve brains was determined by qPCR. Expression of five genes was significantly altered in CD11b⁺ cells: <i>arg-1 (p = 0.000003)</i>; <i>cxcl14 (p = 0.0001)</i>; <i>ifn-β1 (p = 0.0002)</i>; <i>cox-2 (p = 0.000002)</i>; <i>mt1-mmp (p = 0.00002)</i>; n = 5 animals per group; ^*<i>p</i><0.05, ^**<i>p</i><0.01. The middle line represents the median value. Lower ΔC_T are consistent with higher gene expression. B. Quantification of arginase activity in brain tissue extracts from naïve and tumor-bearing mice treated either with PBS or CsA. Results represent the mean ± SEM of 4–5 mice; ^*<i>p</i><0.05, tumor-bearing versus tumor-free hemispheres; ^#<i>p</i><0.05, CsA (10 mg/kg, 8th) versus PBS-treated, tumor-bearing mice. C. MMP-2 activity in proteins extracts from the brains of naïve (N1–5) and tumor-bearing mice (T1–5) determined by gel zymography. Active MMP-2 detected as a prominent band at 62 kDa. D. Quantification of MMP-2 activity using the cleavage of fluorescent DQ-gelatin substrate; means ± SEM of 4–6 mice; ^**<i>p</i><0.01, tumor-bearing versus naïve brain extracts; ^###<i>p</i><0.001, ^#<i>p</i><0.05, CsA- versus PBS-treated tumor-bearing mice.</p

Influx of microglia/macrophages into the tumor is blocked by CsA.

<p>A. Representative confocal images of Iba1 staining in intact brain tissue, tumor-bearing brain slices from mice treated with PBS or CsA. Scale bar = 20 µm. B–C. Quantification of microglia and blood-derived macrophages in naïve, tumor-bearing and CsA-treated mice (4 per group). Each bar represents the mean ± SEM. ^***<i>p</i><0.001, ^**<i>p</i><0.01 tumor-bearing versus naïve mice; ^##<i>p</i><0.01, CsA-treated versus PBS-treated tumor-bearing mice.</p

Accumulation and activation of microglia/macrophages in experimental glioma.

<p>A. Representative confocal images of brain sections 15 days after implantation of pEGFP-N1 GL261 cells into the striatum of C57BL/6 mice. Note the infiltration and morphological transformation of glioma-infiltrating Iba1⁺ cells. Scale bar: left image – 1000 µm, right image – 20 µm. B. Contralateral and ipsilateral hemisphere from tumor-bearing brain 15 days after injection of pEGFP-N1 GL261 cells. Images showed merged Iba1 and EGFP fluorescence. Scale bar = 750 µm. C. Microglia/macrophages were separated using a magnetic-bead-conjugated anti-CD11b antibody and stained with CD45 PerCP-Cy5.5 and CD11b PE prior to FACS acquisition. Propidium iodide staining was performed to eliminate necrotic/apoptotic cells (Gate R3, R4) and viable cells were gated (Gate R1; <b>B1</b>, Gate R2; <b>B2</b>). D. Efficiency of CD11b-positive cells separation in the negative fraction (CD11b-negative cells) from each sample was controlled. E. Representative dot plots for microglia (Gate R4, CD11b⁺/CD45^low) and macrophages (Gate R5, CD11b⁺/CD45^high) from tumor-bearing hemispheres. F. Kinetics of microglia/macrophage influx into tumor tissue. CD11b⁺ cells separated from the brains of naïve, sham operated and tumor-bearing mice at day 3, 8 or 15 after implantation (n = 4/group) were sorted according to CD45 expression. Each bar represents the mean ± SEM; ^***<i>p</i><0.001, ^*<i>p</i><0.05 tumor-bearing mice at 8th day versus naïve mice; ^##<i>p</i><0.01 tumor-bearing mice at day 15 versus day 8.</p

Cytokine profile in glioma-bearing brains.

<p>A. The levels of ten pro/anti-inflammatory cytokines were determined by flow cytometry in protein extracts isolated from hemispheres of naïve, LPS-injected and tumor-bearing mice. The results show the means ± SEM (n = 5 per group); ^#<i>p</i><0.05 significant change between LPS-treated v. naïve mice; ^*<i>p</i><0.05 significant difference between tumor-bearing v. naïve mice. B. Elevated levels of IL-10 and GM-CSF detected in tumors are reduced by CsA treatment. Each dot represents an individual animal; a horizontal line represents a mean of each group; ^*<i>p</i><0.05; ^**<i>p</i><0.01. C. Expression of IL-10 in glioma-infiltrating microglia and macrophages. Left panel: expression of IL-10 on sorted CD11b⁺ cells (50,000 cells) determined by flow cytometry with the anti-IL-10 antibody conjugated to Alexa Fluor647. Representative histograms of IL-10 detection in microglia (light grey) and macrophages (dark grey) cells from naïve (a) and tumor-bearing (b) brains. Right panel: quantification of microglia/macrophages expressing IL-10 in naïve and tumor-bearing brains (means ± SEM, 3 animals per group); significant increase of IL-10-positive microglia (** <i>p</i><0.01) and macrophages (^###<i>p</i><0.001) in tumor-bearing brains. D. Quantification of <i>gm-csf</i> and <i>m-csf</i> expression in GL261 glioma cells and non-transformed astrocytes (means ± SD from 3 experiments). E. Quantitative evaluation of <i>gm-csf</i> mRNA expression in GL261 glioma cells exposed to 0.1 and 1 µM CsA for 24 hours (means ± SD from two experiments with three or four replicates per condition) compared to untreated control cells. Statistical analysis was done by Student <i>t</i> test, ** <i>p</i><0.01.</p