SOX6 plays important roles in cell proliferation, differentiation, and cell fate determination. It has been confirmed that SOX6 is a tumor suppressor and downregulated in various cancers, including esophageal squamous cell carcinoma, hepatocellular carcinoma, and chronic myeloid leukemia. Netrin-1 is highly expressed in various human cancers and acts as an anti-apoptotic and proangiogenic factor to drive tumorigenesis. The role of SOX6 and netrin-1 in regulating the growth of ovarian tumor cells still remains unclear. Real-time polymerase chain reaction and western blot were used to determine the SOX6 messenger RNA and protein levels, respectively, in ovarian cancer cells and tumor tissues. Stable transfection of SOX6 was conducted to overexpress SOX6 in PA-1 and SW626 cells. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Invasion of ovarian cancer cells and migration of human umbilical vein endothelial cells were confirmed by Transwell assays. To overexpress netrin-1, ovarian cancer cells with SOX6 restoration was transduced with netrin-1 lentiviral particles. PA-1 xenografts in a nude mice model were used to conduct in vivo evaluation of the role of SOX6 and its relationship with netrin-1 in tumor growth and angiogenesis. In this study, we found significantly reduced SOX6 levels in PA-1, SW626, SK-OV-3, and CaoV-3 ovarian cancer cell lines and human tumor tissues in comparison with normal human ovarian epithelial cells or matched non-tumor tissues. SOX6 overexpression by stable transfection dramatically inhibited proliferation and invasion of PA-1 and SW626 cells. Also, conditioned medium from PA-1 and SW626 cells with SOX6 restoration exhibited reduced ability to induce human umbilical vein endothelial cells migration and tube formation compared with conditioned medium from the cells with transfection control. Furthermore, an inverse relationship between SOX6 and netrin-1 expression was observed in PA-1 and SW626 cells. Overexpression of netrin-1 in ovarian cancer cells with forced SOX6 expression remarkably abrogated the inhibitory effect of SOX6 on proliferation, invasion of the cells, and tumor xenograft growth and vascularity in vivo. Human umbilical vein endothelial cell migration and tube formation were enhanced in the conditioned medium from the ovarian cancer cells transduced with netrin-1 lentivirus particles. Our observations revealed that SOX6 is a tumor suppressor in ovarian cancer cells, and SOX6 exerts an inhibitory effect on the proliferation, invasion, and tumor cell-induced angiogenesis of ovarian cancer cells, whereas nerin-1 plays an opposite role and its expression is inversely correlated with SOX6. Moreover, our findings suggest a new role of SOX6 and netrin-1 for understanding the progression of ovarian cancer and have the potential for the development of new diagnosis and treatment strategies for ovarian cancer.
Productive Cross-Talk with the Microenvironment: A Critical Step in Ovarian Cancer Metastasis