Artikel
Heterotypic interactions of glioblastoma cells with mesenchymal stem-like cells form microenvironment cues for tumor infiltration
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Veröffentlicht: | 8. Juni 2016 |
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Gliederung
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Objective: Mesenchymal stem-like cells (MSLCs) are detected in many types of cancer including brain tumors, and as such have received considerable attention as components of the tumor microenvironment. However, there is conflicting evidence about whether MSLCs exert anti-tumorigenic effects or contribute to cancer progression, possibly reflecting differences in their origin and tumor type studied. Here, we took advantage of tumor MSLCs (tMSLCs) isolated from primary GBM patients to investigate heterotypic tumor-stromal signaling in the GBM microenvironment. Collectively, our findings uncover the molecular and cellular mechanisms underlying the pathological role of tMSLCs as active contributors to infiltration of GBM cells.
Method: We examined the effect of tMSLCs on malignant phenotypes of GBM cells by co-culture system, in which GBM cells were cultured alone or co-cultured with tMSLCs or with bone marrow mesenchymal stem cells (BM-MSCs). Invasive effects of GBM cells were determined by using transwell and invasion assay in 3-dimentioanl (3D) spheroid culture platform. Human GBM cells were grown in spheroid culture and subjected to embedding in collagen type 1 gels (4 mg/ml). Images were taken using confocal microscopy. To quantify the invasiveness and dynamic behavior of GBM cells, each image was first converted into a binary image and analyzed by image analysis program (ImageJ). The secretion of cytokines that are secreted from MSLCs, being responsible for invasiveness was analyzed in those co-culture systems. The cytokine-dependent intracellular signaling events such as epithelial-mesenchymal transition (EMT) were also evaluated by comparing among the three groups (GBM cells alone vs. GBM cells with tMSLCs vs. GBM cells with BM-MSCs). In orthotopic xenograft mice for the three groups, we also examined the survival of mice, infiltration extent of tumor margin using mmunohistochemical analysis.
Results: Notably, tumor MSLCs (tMSLCs) are isolated from human glioblastoma (GBM) specimens as an independent cohort. Here, we show that tMSLCs secrete C5a, previously known for its role as a complement component, triggering intracellular p38 MAPK signaling in GBM cells and thereby boosting ZEB1-driven mesenchymal transformation, ultimately leading to diffusion of GBM cells into parenchymal brain tissue. Additionally, although tMSLCs are non-tumorigenic, our findings suggest that they originate from GBM cells.
Conclusions: The detection of MSLCs in tumor microenvironment has raised interest in their role; however, many evidence are in conflict, presumably due to differences in their origin and type of tumors studied. Here, we show that GBM patient-derived tMSLCs secrete C5a, previously known for its role as a complement component, triggering intracellular p38 MAPK signaling in GBM cells and thereby boosting their infiltration into parenchymal brain tissue. Though tMSLCs are non-tumorigenic, our findings implicate their GBM cell origin. Our results also demonstrate the unprecedented activity of C5a in GBM progression and add to understanding of how GBM cells acquire infiltrative feature in MSLC-supported tumor microenvironment.