Hypoxia Promotes Migration and Induces CXCR4 Expression via HIF-1α Activation in Human Osteosarcoma

Background: Cellular adaptation to a hypoxic microenvironment is essential for tumor progression and is largely mediated by HIF-1 alpha through coordinated regulation of hypoxia-responsive genes. The chemokine SDF-1 alpha and its unique receptor CXCR4 have been implicated in organ-specific metastases of many cancers. In this study, we investigated the response of osteosarcoma cells to hypoxia and the expression of CXCR4 and HIF-1 alpha in human osteosarcoma specimens and explored the roles of CXCR4 and HIF-1 alpha in the cell migration process. Methodology/Principal Findings: We performed immunohistochemistry, immunocytochemistry, quantitative real-time PCR, Western blots and fluorescent reporter assays to evaluate the correlation between CXCR4 and HIF-1 alpha expression in human osteosarcoma specimens or SOSP-9607 cells under normoxic and hypoxic conditions. Transwell assays were used to assess cell migration under different conditions. Exposure of SOSP-9607 cells to hypoxic conditions resulted in significantly increased migration. When SOSP-9607 cells were subjected to hypoxic conditions, the mRNA and protein levels of CXCR4 were significantly increased in a time-dependent manner. Moreover, siHIF-1 alpha significantly decreased the mRNA and protein levels of CXCR4 under hypoxia, whereas pcDNA-HIF-1 alpha significantly increased the mRNA and protein levels of CXCR4 under normoxia. A luciferase reporter gene study showed that siHIF-1 alpha reduced pGL3-CXCR4 luciferase activity. Furthermore, coexpression of HIF-1 alpha and CXCR4 was significantly higher in patients with distant metastasis compared with those without metastasis. Conclusions/Significance: The hypoxia-HIF-1 alpha-CXCR4 pathway plays a crucial role during the migration of human osteosarcoma cells, and targeting this pathway might represent a novel therapeutic strategy for patients suffering from osteosarcoma.