SSX2 regulates focal adhesion but does not drive the epithelial to mesenchymal transition in prostate cancer

// Jordan E. Bloom 1 and Douglas G. McNeel 1,2 1 Department of Medicine, University of Wisconsin, Madison, WI, USA 2 University of Wisconsin Carbone Cancer Center, University of Wisconsin, Madison, WI, USA Correspondence to: Douglas G. McNeel, email: // Keywords : SSX, prostate cancer, CTA, focal adhesion, EMT Received : May 17, 2016 Accepted : May 26, 2016 Published : June 02, 2016 Abstract Prostate cancer is the most commonly diagnosed malignancy for men in the United States. Metastatic prostate cancer, the lethal form of the disease, has a life expectancy of approximately five years. Identification of factors associated with this transition to metastatic disease is crucial for future therapies. One such factor is the SSX gene family, a family of cancer/testis antigens (CTA) transcription factors which have been shown to be aberrantly expressed in other cancers and associated with the epithelial to mesenchymal transition (EMT). We have previously shown that SSX expression in prostate cancers was restricted to metastatic tissue and not primary tumors. In this study, we have identified SSX2 as the predominant SSX family member expressed in prostate cancer, and found its expression in the peripheral blood of 19 of 54 (35%) prostate cancer patients, with expression restricted to circulating tumor cells, and in 7 of 15 (47%) metastatic cDNA samples. Further, we examined SSX2 function in prostate cancer through knockdown and overexpression in prostate cancer cell lines. While overexpression had little effect on morphology or gene transcript changes, knockdown of SSX2 resulted in an epithelial morphology, increased cell proliferation, increased expression of genes involved in focal adhesion, decreased anchorage independent growth, increased invasion, and increased tumorigenicity in vivo . We conclude from these findings that SSX2 expression in prostate cancer is not a driver of EMT, but is involved in processes associated with EMT including loss of focal adhesion that may be related to tumor cell dissemination.