Abstract
BackgroundCellular adaptation to a hypoxic microenvironment is essential for tumor progression and is largely mediated by HIF-1α through coordinated regulation of hypoxia-responsive genes. The chemokine SDF-1α 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-1α in human osteosarcoma specimens and explored the roles of CXCR4 and HIF-1α in the cell migration process.Methodology/Principal FindingsWe performed immunohistochemistry, immunocytochemistry, quantitative real-time PCR, Western blots and fluorescent reporter assays to evaluate the correlation between CXCR4 and HIF-1α 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-1α significantly decreased the mRNA and protein levels of CXCR4 under hypoxia, whereas pcDNA-HIF-1α significantly increased the mRNA and protein levels of CXCR4 under normoxia. A luciferase reporter gene study showed that siHIF-1α reduced pGL3-CXCR4 luciferase activity. Furthermore, coexpression of HIF-1α and CXCR4 was significantly higher in patients with distant metastasis compared with those without metastasis.Conclusions/SignificanceThe hypoxia-HIF-1α-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.
Highlights
Osteosarcoma (OS) is a highly malignant, aggressive tumor of the bone, with a peak incidence in the second and third decades of life
To examine the effect of hypoxia on osteosarcoma cell metastatic ability, SOSP-9607 cells were transfected with siHIF1a, NC-small interfering RNAs (siRNAs), siCXCR4 and NC-siCXCR4, and treated with normoxia or hypoxia for 48 h, added into the top chamber of a polycarbonate membrane insert
The exposure of SOSP-9607 cells to hypoxic conditions significantly increased migration compared with normoxic conditions, whereas transfection of SOSP-9607 cells with siHIF-1a or siCXCR4 reduced the migration in hypoxic conditions compared with cells transfected with NC-siRNA or NC-siCXCR4 (Figure 1, A and B, * P,0.05, ** P,0.05)
Summary
Osteosarcoma (OS) is a highly malignant, aggressive tumor of the bone, with a peak incidence in the second and third decades of life. It accounts for approximately 45% of all bone sarcomas [1]. Cellular adaptation to a hypoxic microenvironment is essential for tumor progression and is largely mediated by HIF-1a through coordinated regulation of hypoxia-responsive genes. We investigated the response of osteosarcoma cells to hypoxia and the expression of CXCR4 and HIF-1a in human osteosarcoma specimens and explored the roles of CXCR4 and HIF-1a in the cell migration process
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