Abstract B80: POTE gene expression, epigenetic regulation, and oncogenic functions in human epithelial ovarian cancer
Authors: Sharma Ashok , Zhang Wa , James Smitha , Kufel Christina , Klinkebiel David , Odunsi Kunle , Karpf Adam R. 
Published: August 2014

Background: Prostate-, Ovary-, Testis-, and Placenta-Expressed Gene (POTE) is a recently discovered gene family consisting of 12 autosomal and pericentromeric-located cancer germline/cancer-testis antigen genes. POTE genes have been reported to be expressed in many solid tumor malignancies, and recent data suggest that POTE proteins may be viable targets for cancer immunotherapy. DNA methylation changes are common in epithelial ovarian cancer (EOC), and these changes include DNA hypomethylation at specific repetitive elements (RE), including the interspersed retrotransposon LINE1, and at pericentromeric repeats.

Objective: The purpose of this study was to determine the expression of POTE genes in EOC, to assess whether DNA methylation changes and/or other epigenetic mechanisms regulate POTE expression in EOC, and to define the potential functional contribution(s) of POTE expression to this disease.

Methods: Affymetrix microarrays and RT-qPCR were used to determine POTE gene expression in human normal ovary (NO) and EOC tumors. The DNA methylation status of POTE genes and neighboring pericentromeric regions were determined using sodium bisulfite clonal sequencing and quantitative bisulfite pyrosequencing. The impact of epigenetic drug treatment on POTE gene expression in EOC cell lines was determined. POTE gene knockdown in EOC cell lines was accomplished using RNA interference, and POTED was overexpressed in EOC cell lines and immortalized ovarian surface epithelial (IOSE) cells. Cell proliferation, apoptosis, cell migration, and cell invasion were determined following POTE knockdown or overexpression in cell lines.

Results: Widespread activation of POTE gene expression occurred in EOC, as compared to NO. POTE gene expression levels were significantly higher in EOC tumors showing LINE1 hypomethylation, as compared to EOC tumors showing normal LINE1 methylation, linking global DNA methylation status to POTE gene expression. Hypomethylation of pericentromeric DNA, as determined using NBL2 pyrosequencing, was also linked to POTE expression and hypomethylation. POTE mRNA and protein expression was induced by treatment with DNA methyltransferase (DNMT) and histone deacetylase (HDAC) inhibitors. POTE gene knockdown in EOC cell lines had a small impact on cell proliferation and apoptosis, but resulted in significantly reduced cell migration and cell invasion. POTED overexpression experiments are currently in progress.

Conclusions: POTE genes are widely expressed in EOC, and expression is significantly increased in tumors displaying global DNA hypomethylation. Additional evidence for epigenetic regulation of POTE genes is their induction following treatment with epigenetic modulatory drugs. POTE gene expression in cancer may closely relate to the epigenetic status of pericentromeric DNA. Importantly, POTE proteins appear to functionally contribute to EOC, by promoting cell migration and invasion. Based on these data, further analysis of POTE gene regulation and function in EOC, and development of POTE targeted therapeutic approaches, is warranted.

Citation Format: Ashok Sharma, Wa Zhang, Smitha James, Christina Kufel, David Klinkebiel, Kunle Odunsi, Adam R. Karpf. POTE gene expression, epigenetic regulation, and oncogenic functions in human epithelial ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B80.