SOX4 is associated with poor prognosis in prostate cancer and promotes epithelial-mesenchymal transition in vitro

BACKGROUND: The SOX4 transcription factor is involved in the development and cell fate decision. Although upregulation of SOX4 has been described in human prostate cancer (PCa), the prognostic value of SOX4 and its exact role in PCa progression remain unclear. METHODS: Three tissue microarrays were constructed from 241 Chinese PCa patients who underwent TURP. Immunohistochemistry (IHC) was used to detect the expression of SOX4. Genetic aberrations of epidermal growth factor receptor and HER2 were detected by fluorescence in situ hybridization. The effect of SOX4 on proliferation was evaluated by MTT (methyl thiazolyl tetrazelium), and cell migration and invasion were evaluated by transwell and wound-healing assays. The distribution of cell-cycle phase was analyzed by flow cytometry. Real-time PCR and western blot were used to study transcript and protein levels. RESULTS: Using tissue microarray, we found that SOX4 was overexpressed in 33.0% (76/230) Chinese PCa patients by IHC. SOX4 overexpression was significantly associated with high Gleason scores (P = 0.009) and the presence of distant metastasis (P = 0.023). Additionally, SOX4 overexpression was significantly correlated with high Ki67 labeling index (P = 0.005) and tended to associate with amplification of HER2 (P = 0.052) in our cohort. Notably, SOX4 was correlated with cancer-specific mortality of PCa patients by Kaplan-Meier analysis (P = 0.001). Multivariate Cox regression analysis indicated that SOX4 was an unfavorable independent prognostic factor in Chinese PCas (P = 0.017). SOX4 overexpression enhanced proliferation of Vcap cells and siRNA knockdown of SOX4 significantly decreased Vcap cell migration and invasion, suggesting a role of SOX4 in cancer metastasis. Additionally, flow cytometry DNA analysis revealed that siRNA SOX4 leads to significant accumulation of cells in the S phase and marked decrease of cells in the G2/M phase. Further in vitro study revealed that SOX4 silencing could inhibit TGF-beta (transforming growth factor-beta)-induced epithelial-mesenchymal transition (EMT) in Vcap cells. Overexpression of SOX4 could promote the EMT phenotype in Vcap cells. CONCLUSIONS: Our results define an important role for SOX4 in the progression of PCa by orchestrating EMT and may serve as a prognostic marker for PCa patients.