CD44 Splice Variant v8-10 as a Marker of Serous Ovarian Cancer Prognosis

CD44 is a transmembrane hyaluronic acid receptor gene that encodes over 100 different tissue-specific protein isoforms. The most ubiquitous, CD44 standard, has been used as a cancer stem cell marker in ovarian and other cancers. Expression of the epithelial CD44 variant containing exons v8-10 (CD44v8-10) has been associated with more chemoresistant and metastatic tumors in gastrointestinal and breast cancers, but its role in ovarian cancer is unknown; we therefore investigated its use as a prognostic marker in this disease. The gene expression profiles of 254 tumor samples from The Cancer Genome Atlas RNAseqV2 were analyzed for the presence of CD44 isoforms. A trend for longer survival was observed in patients with high expression of CD44 isoforms that include exons v8-10. Immunohistochemical (IHC) analysis of tumors for presence of CD44v8-10 was performed on an independent cohort of 210 patients with high-grade serous ovarian cancer using a tumor tissue microarray. Patient stratification based on software analysis of staining revealed a statistically significant increase in survival in patients with the highest levels of transmembrane protein expression (top 10 or 20%) compared to those with the lowest expression (bottom 10 and 20%) (p = 0.0181, p = 0.0262 respectively). Expression of CD44v8-10 in primary ovarian cancer cell lines was correlated with a predominantly epithelial phenotype characterized by high expression of epithelial markers and low expression of mesenchymal markers by qPCR, Western blot, and IHC. Conversely, detection of proteolytically cleaved and soluble extracellular domain of CD44v8-10 in patient ascites samples was correlated with significantly worse prognosis (p<0.05). Therefore, presence of transmembrane CD44v8-10 on the surface of primary tumor cells may be a marker of a highly epithelial tumor with better prognosis while enzymatic cleavage of CD44v8-10, as detected by presence of the soluble extracellular domain in ascites fluid, may be indicative of a more metastatic disease and worse prognosis.