[Tumor-stroma interactions: their role in the control of tumor cell invasion and metastasis]

Potential Molecular Mechanisms of AURKB in the Oncogenesis and Progression of Osteosarcoma Cells: A Label-Free Quantitative Proteomics Analysis

Our previous study indicated that knockdown of Aurora-B inhibit the proliferation of osteosarcoma cells. But the function and molecular mechanisms of Aurora-B in osteosarcoma cells growth and metastasis remains unclear. The aim of this study was to investigate the molecular mechanisms of Aurora-B in the progression of osteosarcoma. Osteosarcoma cells (U2-OS and 143B) were treated with specific Lentivirus-Vectors (up or downregulation Aurora-B). The ability of cells proliferation, migration, and invasion was measured using Cell-Counting Kit-8, wound healing and transwell invasion assays. Furthermore, based on label-free quantitative proteomic analysis of potential molecular mechanisms of Aurora-B in human 143B cells. A total of 25 downregulated and 76 upregulated differentially expressed proteins were screened in terms of the change in their expression abundance. We performed functional annotation and functional enrichment analyses. Gene ontology enrichment, KEGG analysis, and protein-protein interaction networks were constructed and analyzed. We found that the PTK2 may play an important role in the progression of osteosarcoma cells. Finally, Western blot revealed that expression of PTK2, AKT, PI3K, and nuclear factor-kappaB increased after over expression of Aurora-B. Overall, these data highlight that Aurora-B may promote the malignant phenotype of osteosarcoma cells by activating the PTK2/PI3K/AKt/nuclear factor-KappaB pathway.

Myeloid-derived suppressor cells in malignant melanoma

Melanoma is known for its rapid progression, metastasis to distant organs and therapeutic resistance. Despite high melanoma immunogenicity, the results of immunotherapeutic clinical studies are mostly unsatisfactory. One explanation is the development of strong immunosuppression mediated by highly immunosuppressive regulatory leukocytes, in particular, myeloid-derived suppressor cells (MDSCs). These cells were found to be enriched and activated in the melanoma microenvironment, inducing a profound impairment of anti-tumor immune responses and leading to the tumor progression. Therefore, understanding the mechanisms of MDSC generation, migration to the tumor site and activation as well as their targeting is important for the development of novel strategies for effective melanoma immunotherapy. We suggest that such therapeutic approaches should involve the inhibition of MDSC-mediated immunosuppressive melanoma microenvironment combined with other immunologic treatments.

Fibroblast-to-myofibroblast switch is mediated by NAD(P)H oxidase generated reactive oxygen species

Tumour–stroma interaction is a prerequisite for tumour progression in skin cancer. Hereby, a critical step in stromal function is the transition of tumour-associated fibroblasts to MFs (myofibroblasts) by growth factors, for example TGFβ (transforming growth factor beta(). In this study, the question was addressed of whether fibroblast-associated NAD(P)H oxidase (NADH/NADPH oxidase), known to be activated by TGFβ1, is involved in the fibroblast-to-MF switch. The up-regulation of αSMA (alpha smooth muscle actin), a biomarker for MFs, is mediated by a TGFβ1-dependent increase in the intracellular level of ROS (reactive oxygen species). This report demonstrates two novel aspects of the TGFβ1 signalling cascade, namely the generation of ROS due to a biphasic NAD(P)H oxidase activity and a ROS-dependent downstream activation of p38 leading to a transition of dermal fibroblasts to MFs that can be inhibited by the selective NAD(P)H oxidase inhibitor apocynin. These data suggest that inhibition of NAD(P)H oxidase activity prevents the fibroblast-to-MF switch and may be important for chemoprevention in context of a ‘stromal therapy’ which was described earlier.

Oncogenic KIT-containing exosomes increase gastrointestinal stromal tumor cell invasion

During tumor development, constant interplay occurs between tumor cells and surrounding stromal cells. We report evidence that gastrointestinal stromal tumor (GIST) cells invade the interstitial stroma through the release of the oncogenic protein tyrosine kinase (KIT)-containing exosomes, which triggers the phenotypic conversion of progenitor smooth muscle cells to tumor-promoting cells. These recipient cells display morphologic changes and acquire tumor-associated phenotypes, including enhanced adhesion to extracellular matrix proteins, activation of intracellular pathways downstream of KIT, expression of Interstitial Cell of Cajal-like markers, and release of various matrix metalloproteinases (MMPs), particularly MMP1. This report shows stimulation of MMP1 production by stromal cells via uptake of tumor-derived exosomes, which leads to tumor cell invasion. Exosomes derived from GIST patients but not healthy donors show enhanced MMP1 secretion by smooth muscle cells and tumor cell invasion, whereas selective blocking of exosome-mediated MMP1 secretion decreases tumor invasiveness. Our study indicates that exosome release and subsequent MMP1 induction creates a positive feedback mechanism established between tumor and stromal cells that drives GIST development and offers unique insights for potential therapeutic strategies to block GIST progression and metastatic spread.

Bone morphogenetic proteins induce expression of metalloproteinases in melanoma cells and fibroblasts

Bone morphogenetic proteins are secreted growth factors which belong to the TGFbeta super family. In recent studies, we showed that the expression of BMP-4 and -7 is induced in melanoma cells in comparison to normal melanocytes. Functional analyses revealed that BMPs are inevitable factors for migration and invasion processes of melanoma cells; however, the role of BMPs in degradation and remodelling of the extracellular matrix remained unknown. We discovered that melanoma cell clones with reduced BMP activity, generated by stable transfection with an antisense BMP-4 construct or with the BMP inhibitor chordin, showed reduced expression of MMP-1, -2, -3 and -9. Moreover, BMPs displayed paracrine effects on stromal fibroblasts. Treatment of fibroblasts with BMP-2 or -4 led to increased MMP-1, -2, -3 and -13 expression. These data show that BMPs play an important role in dissemination of tumour cells from the primary tumour, either by enhancing the matrix degrading capacity of melanoma cells themselves or by stimulating tumour surrounding fibroblasts to induce expression of matrix metalloproteinases.

Reduced tumour cell proliferation and delayed development of high-grade mammary carcinomas in cathepsin B-deficient mice

Expression levels of the papain-like cysteine protease cathepsin B (Ctsb) have been positively correlated with mammary tumour progression and metastasis; however, its roles in the hallmark processes of malignant growth remain poorly defined. Using Ctsb-deficient mice we investigated tumour cell differentiation, proliferation and apoptosis in the Tg(MMTV-PyMT) mouse mammary cancer model. Absence of Ctsb significantly impaired development of high-grade invasive ductal carcinomas and reduced the metastatic burden in the lungs. Mice lacking Ctsb exhibited reduced cell proliferation in mammary carcinomas and their lung metastases. Notably, intravenous injection of primarily isolated, Ctsb-expressing tumour cells into congenic Ctsb-deficient mice revealed impaired cell proliferation in the resulting experimental lung metastases, providing evidence for the involvement of Ctsb in paracrine regulation of cancer cell proliferation. No Ctsb genotype-dependent difference in tumour cell death was observed in vivo or by treatment of isolated PyMT cancer cells with tumour necrosis factor-alpha. However, cancer cells lacking Ctsb exhibited significantly higher resistance to apoptosis induction by the lysosomotropic agent Leu-Leu-OMe. Thus, our results indicate an in vivo role for Ctsb in promoting cellular anaplasia in mammary cancers and proliferation in lung metastases.