Abstract 3632: Epigenetic silencing and biomarker potential of miR-224, miR-452 and their host gene GABRE in prostate cancer
Authors: Kristensen Helle , Haldrup Christa , Mortensen Martin M. , Borre Michael , Høyer Søren , Wild Peter J. , Ørntoft Torben F. , Sørensen Karina D. 
Published: August 2012

Abstract
Prostate cancer (PC) is the most frequently diagnosed cancer and the second most frequent cause of cancer related death among men in the Western world. Currently used methods for PC diagnosis and prognosis are suboptimal and novel molecular biomarkers are urgently needed. This study investigates the expression and biomarker potential of miR-224, miR-452 and their host gene gamma-aminobutyric acid (GABA) A receptor family epsilon subunit (GABRE) in PC by transcriptional profiling and DNA methylation analyses of the GABRE promoter associated CpG island. Transcriptional expression of GABRE was determined by microarray analysis of two independent clinical sample sets, including a total of 25 nonmalignant and 50 prostate cancer tissue samples. Expression of the mature form of miR-224 and miR-452 was measured in a separate set of 27 nonmalignant and 80 PC tissue samples. The transcriptional analyses revealed that miR-224, miR-452 and GABRE transcript levels were significantly reduced in PC tissue compared to nonmalignant prostate tissue samples (p&lt;0.001). Bisulfite sequencing of 11 nonmalignant and 21 PC tissue samples showed frequent promoter hypermethylation of GABRE in PC compared to nonmalignant prostate tissue (p&lt;0.001), suggesting epigenetic silencing of the genomic GABRE locus in PC. This was validated by quantitative methylation-specific PCR (MethyLight) in an independent clinical sample set consisting of 35 nonmalignant and 249 PC tissue samples: GABRE promoter methylation accurately distinguished nonmalignant from PC tissue samples (p&lt;0.001) with a sensitivity of 95.2% and a specificity of 94.2%, thus potentially allowing the detection of PC through GABRE methylation analysis. Additionally, by univariate analysis, high GABRE methylation was significantly associated with early PSA recurrence after radical prostatectomy in two independent radical prostatectomy PC patient cohorts, including 129 and 190 patients, respectively (p=0.022 and p=0.034). Furthermore, in a multivariate model, GABRE methylation added significant independent value to established prognostic factors in both patient cohorts (p=0.048 and p=0.032). In conclusion, our results showed that PC is associated with significant downregulation of miR-224, miR-452 and GABRE expression. Furthermore, we identified GABRE as a new promising methylation marker candidate for PC detection and prognosis. We are currently investigating the biomarker potential of GABRE protein expression by immunohistochemical analysis of two PC tissue microarrays including ∼400 PC patients. Moreover, initial functional studies in the PC cell lines PC3 and DU145 suggest roles for miR-224 and miR-452 in proliferation and invasion. Results from these additional studies will be presented at the meeting.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3632. doi:1538-7445.AM2012-3632