Genetic and epigenetic SLC18A2 silencing in prostate cancer is an independent adverse predictor of biochemical recurrence after radical prostatectomy.
OBJECTIVE
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.


METHODS
Expression and single nucleotide polymorphism microarray analyses identified SLC18A2 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 (n=738). Furthermore, SLC18A2 immunoreactivity in radical prostatectomy tumor specimens (n=506) was correlated to clinicopathologic characteristics and recurrence-free survival. The possibility of SLC18A2 silencing by aberrant DNA methylation in prostate cancer cells was investigated by bisulfite sequencing.


RESULTS
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; P<0.001) independent of prostate-specific antigen, Gleason score, tumor stage, and surgical margin status. SLC18A2 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, SLC18A2 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 SLC18A2 expression in three prostate cancer cell lines.


CONCLUSIONS
SLC18A2 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.
Sørensen
Karina Dalsgaard
KD
Molecular Diagnostics Laboratory, Department of Clinical Biochemistry, Institute of Pathology, Aarhus University Hospital, Aarhus, Denmark. karina.dalsgaard.sorensen@ki.au.dk
Wild
Peter Johannes
PJ
Mortezavi
Ashkan
A
Adolf
Katja
K
Tørring
Niels
N
Heebøll
Sara
S
Ulhøi
Benedicte Parm
BP
Ottosen
Peter
P
Sulser
Tullio
T
Hermanns
Thomas
T
Moch
Holger
H
Borre
Michael
M
Ørntoft
Torben Falck
TF
Dyrskjøt
Lars
L
D019175:DNA Methylation; D020868:Gene Silencing; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D015999:Multivariate Analysis; D009364:Neoplasm Recurrence, Local / Q000235:genetics*; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000401:mortality / Q000601:surgery; D046888:Tissue Array Analysis; D050493:Vesicular Monoamine Transport Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology
C493452:SLC18A2 protein, human; D050493:Vesicular Monoamine Transport Proteins