PRAME expression and promoter hypomethylation in epithelial ovarian cancer
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Wa Zhang1,10, Carter J. Barger1, Kevin H. Eng4, David Klinkebiel2, Petra A. Link3, Angela Omilian5, Wiam Bshara5, Kunle Odunsi6,7,8, Adam R. Karpf1,9
1Eppley Institute for Cancer Research, University of Nebraska Medical Center, Omaha, NE, USA
2Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA
3Department of Pharmacology, Roswell Park Cancer Institute, Buffalo, NY, USA
4Department of Biostatistics and Bioinformatics, Roswell Park Cancer Institute, Buffalo, NY, USA
5Department of Pathology, Roswell Park Cancer Institute, Buffalo, NY, USA
6Department of Gynecologic Oncology, Roswell Park Cancer Institute, Buffalo, NY, USA
7Department of Immunology, Roswell Park Cancer Institute, Buffalo, NY, USA
8Center for Immunotherapy, Roswell Park Cancer Institute, Buffalo, NY, USA
9Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE, USA
10Current address: Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA
Adam R. Karpf, email: email@example.com
Keywords: PRAME, cancer testis antigens, epithelial ovarian cancer, high grade serous cancer, DNA methylation
Received: May 02, 2016 Accepted: May 29, 2016 Published: June 13, 2016
PRAME is a cancer-testis antigen (CTA) and potential immuno-therapeutic target, but has not been well-studied in epithelial ovarian cancer (EOC) or its high grade serous (HGSC) subtype. Compared to normal ovary, PRAME expression was significantly increased most EOC, regardless of stage and grade. Interestingly, PRAME mRNA expression was associated with improved survival in the HGSC subtype. The PRAME locus was a frequent target for copy number alterations (CNA) in HGSC but most changes were heterozygous losses, indicating that elevated PRAME expression is not typically due to CNA. In contrast, PRAME promoter DNA hypomethylation was very common in EOC and HGSC and correlated with increased PRAME expression. PRAME expression and promoter hypomethylation both correlated with LINE-1 hypomethylation, a biomarker of global DNA hypomethylation. Pharmacologic or genetic disruption of DNA methyltransferase (DNMT) enzymes activated PRAME expression in EOC cells. Immunohistochemistry (IHC) of PRAME in EOC revealed frequent, but low level, protein expression, and expression was confined to epithelial cells and localized to the cytoplasm. Cytoplasmic PRAME expression was positively associated with PRAME mRNA expression and negatively associated with promoter methylation, but the latter correlation was not statistically significant. PRAME protein expression did not correlate with EOC clinicopathology or survival. In summary, PRAME is frequently expressed in EOC at the mRNA and protein levels, and DNA methylation is a key mechanism regulating its expression. These data support PRAME as an immunotherapy target in EOC, and suggest treatment with DNMT inhibitors as a means to augment PRAME immunotherapy.
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