SOX4 activates CXCL12 in hepatocellular carcinoma cells to modulate endothelial cell migration and angiogenesis in vivo

The overexpression of SOX4 in various kinds of cancer cells was associated with poor prognosis for patients. The role of SOX4 in angiogenesis and tumor microenvironment modulation was recently documented in breast cancer but remains unclear in hepatocellular carcinoma (HCC). In our study, the clinical relevance of SOX4 overexpression in HCC and its role in the tumor microenvironment were investigated. The overexpression of SOX4 (SOX4^high) in tumor lesions was associated with higher microvessel density (P = 0.012), tumor thrombosis formation (P = 0.012), distant metastasis (P < 0.001), and an independent prognostic factor for disease-free survival in HCC patients (P = 0.048). Endogenous SOX4 knockout in Hep3B cells by the CRISPR/cas9 system reduced the expression of CXCL12, which, in turn, attenuated chemotaxis in human umbilical vein endothelial cells, tube formation in vitro, reduced tumor growth, reticular fiber production, and angiogenesis in vivo in a xenograft mouse model. Treatment with an antagonist targeting CXCR4 (AMD3100), a receptor of CXCL12, inhibited chemotaxis and tube formation in endothelial cells in vitro. The CXCL12 promoter was activated by ectopic expression of a Flag-tagged SOX4 plasmid, endogenous SOX4 knockdown abolished promoter activity of CXCL12 as shown by luciferase assays, and an association with the CXCL12 promoter was identified via chromatin immunoprecipitation in HCC cells. In conclusion, SOX4 modulates the CXCL12 promoter in HCC cells. The secretory CXCL12, in turn, modulates CXCR4 in endothelial cells, reticular fibers to regulate the tumor microenvironment and modulate neovascularization, which might contribute to the distant metastasis of tumors.