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Investigation into the role of Y-box binding protein-1 (YB-1) in childhood sarcomas EL-Naggar, Amal Mohammad


Objective: To identify the potential roles played by YB-1 in childhood sarcoma progression. Background: Sarcomas are mesenchymal-derived malignant neoplasms that are characterized by early metastatic spread, and poor prognosis. YB-1 is a member of the highly conserved CSD-containing family of proteins known to regulate transcription and translation of a multitude of genes. Importantly, YB-1 promotes an epithelial-to-mesenchymal transition (EMT) in non-invasive breast epithelial cells. In spite of its role in EMT, comprehensive investigations into the role of YB-1 in the progression of childhood sarcomas are currently lacking. Methods: To study the potential role of YB-1 in childhood sarcomatogenesis, we used MNNG and MG63 (osteosarcoma), TC32 and TC71 (Ewing sarcoma), and Rh30 and Rh18 (rhabdomyosarcoma) tumour cell lines, and performed transient and stable YB-1 knockdown (kd) in each cell line. Then, cells were subjected to different assays. Results: Using in vitro cell motility, invasion, and proliferation assays, we found that YB-1 kd significantly reduced migration and invasion of each of these cell lines and this was associated with enhanced proliferative capacity of childhood sarcoma cells. YB-1 kd also profoundly inhibited migration and metastasis of human sarcoma cell lines xenotransplanted into either the yolk sacs of zebrafish embryos or under the kidney capsule of NOD/SCID mice, a model previously utilized for epithelial-derived tumours. We then assessed potential mechanisms, and found that YB-1 directly bound and robustly activated the translation of HIF1α mRNAs, while it had no effect upon HIF1α transcription. YB-1 itself was robustly induced by hypoxia, and blocking this induction blocked HIF1α protein levels. HIF1α kd blocked YB-1 mediated induction of sarcoma cell migration and invasion, and ectopic expression rescued the effects of YB-1 kd under the same parameters in vitro and in vivo. Notably, tumours with YB-1 kd exhibited extensive levels of haemorrhaging and necrosis compared to the control tumours, and this correlated significantly with reduced mean microvessel density and VEGF production. Conclusions: YB-1 promotes childhood sarcoma cell metastasis through translational activation of HIF1α, underscoring the potential impact of YB-1 on sarcoma angiogenesis. Importantly, targeting YB-1 or its downstream effectors represents a promising strategy in the treatment of childhood sarcomas.

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