ESRP1 is overexpressed in ovarian cancer and promotes switching from mesenchymal to epithelial phenotype in ovarian cancer cells.

Epithelial splicing regulatory protein 1 (ESRP1) and 2 (ESRP2), epithelial cell-specific regulators of alternative splicing, are downregulated during the epithelial-mesenchymal transition (EMT). These factors have roles in tumor progression and metastasis in some cancers; however, their expression and function in ovarian cancer (OC) remain unclear. We found that ESRP1 and ESRP2 mRNAs were expressed at higher levels in OC cells than in immortalized ovarian surface epithelial (IOSE) cells, and confirmed their overexpression in OC tissues at the protein level. The Cancer Genome Atlas (TCGA) data analysis revealed frequent gene amplification of ESRP1 in OC tissues; however, we detected no significant correlation between ESRP1 gene copy number and gene expression in OC cells. Importantly, expression of ESRP1 and ESRP2 was inversely correlated with DNA methylation in OC cells, and ESRP2 overexpression in OC tissues was significantly associated with DNA hypomethylation. Notably, survival analysis using TCGA data from 541 OC tissues revealed that high ESRP1 expression was significantly associated with shorter 5-year survival of patients. Ectopic ESRP1 expression in mesenchymal OC cells promoted cell proliferation but suppressed cell migration. Furthermore, we found that ESRP1 drives a switch from mesenchymal to epithelial phenotype characterized by reduced cell migration in association with induction of epithelial cell-specific variant of CD44 and ENAH. Taken together, our findings suggest that an epigenetic mechanism is involved in ESRP1 overexpression, and that ESRP1 has a role in OC progression.