HDAC9 Contributes to Serous Ovarian Cancer Progression through Regulating Epithelial–Mesenchymal Transition

Epithelial ovarian cancer has the highest mortality rate of all gynecological malignant tumors. Metastasis is the main cause of poor prognosis in patients with ovarian cancer. Epigenetic and protein post-translational modifications play important roles in tumor metastasis. As a member of class IIa histone deacetylases, histone deacetylase 9 (HDAC9) is involved in many biological processes by deacetylating histone and nonhistone proteins. However, its roles in ovarian cancer remain unclear. In this study, we found that patients with serous ovarian cancer with high expression of HDAC9 had poor prognoses. On the contrary, patients with non-serous ovarian cancer with high expression of HDAC9 had higher survival rates. In serous ovarian cancer, overexpressed HDAC9 may promote cell migration through the forkhead box protein O1 (FOXO1)/transforming growth factor-beta (TGF-β) axis. In non-serous ovarian cancer, overexpressed HDAC9 exerts antitumor effects that might be caused by the suppression of β-catenin signaling. Therefore, HDAC9 may be a potential target for individualized treatment of patients with different histological subtypes of ovarian cancer.