Data from Genetic and Epigenetic <i>SLC18A2</i> Silencing in Prostate Cancer Is an Independent Adverse Predictor of Biochemical Recurrence after Radical Prostatectomy

Abstract

<div>Abstract<p><b>Purpose:</b> This study investigates SLC18A2 (vesicular monoamine transporter 2) expression in prostate adenocarcinoma and examines its potential as a predictive marker for prostate cancer patient outcome after radical prostatectomy.</p><p><b>Experimental Design:</b> Expression and single nucleotide polymorphism microarray analyses identified <i>SLC18A2</i> as both down-regulated and subject to common loss-of-heterozygosity in prostate cancer. Down-regulated SLC18A2 expression was validated on tissue microarrays containing benign and malignant prostate specimens from an independent patient group (<i>n</i> = 738). Furthermore, SLC18A2 immunoreactivity in radical prostatectomy tumor specimens (<i>n</i> = 506) was correlated to clinicopathologic characteristics and recurrence-free survival. The possibility of <i>SLC18A2</i> silencing by aberrant DNA methylation in prostate cancer cells was investigated by bisulfite sequencing.</p><p><b>Results:</b> Tissue microarray analysis revealed markedly lower cytoplasmic SLC18A2 staining in cancer compared with nonmalignant prostate tissue samples, confirming RNA expression profiling results. Furthermore, multivariate analysis identified cytoplasmic SLC18A2 immunoreactivity as a novel predictor of biochemical recurrence following prostatectomy (hazard ratio, 0.485; 95% confidence interval, 0.333-0.709; <i>P</i> < 0.001) independent of prostate-specific antigen, Gleason score, tumor stage, and surgical margin status. <i>SLC18A2</i> showed loss-of-heterozygosity in 23% of the tumors and was densely hypermethylated in 15 of 17 (88%) prostate cancer samples plus 6 of 6 prostate cancer cell lines. In contrast, <i>SLC18A2</i> was unmethylated in 4 of 4 adjacent nonmalignant prostate and 3 of 5 benign prostatic hyperplasia tissue samples, whereas 2 of 5 benign prostatic hyperplasia samples had monoallelic hypermethylation. Methylation and histone deacetylase inhibitory agents rescued <i>SLC18A2</i> expression in three prostate cancer cell lines.</p><p><b>Conclusions:</b><i>SLC18A2</i> silencing by DNA hypermethylation and/or allelic loss is a frequent event in prostate cancer and a novel independent predictor of biochemical recurrence after prostatectomy.</p></div>