MT1G hypermethylation is associated with higher tumor stage in prostate cancer.
OBJECTIVE
Zinc is involved in several physiologic processes, including cell growth and proliferation. Although in normal prostate tissue zinc levels are high, there is a marked decrease in prostate cancer. Metallothioneins control the bioavailability of zinc and one isoform, MT1G, was reported down-regulated in prostate cancer. Here, we investigated whether promoter methylation might cause MT1G silencing in prostate cancer.


METHODS
The MT1G promoter was assessed by quantitative methylation-specific PCR on prospectively collected tissue samples from 121 patients with prostate cancer, 39 paired high-grade prostatic intraepithelial neoplasias (HGPIN), 29 patients with benign prostatic hyperplasia, 13 normal prostate tissue samples from cystoprostatectomy specimens, and prostate cancer cell lines. The methylation levels were calculated and were correlated with clinical and pathologic variables. Reverse transcription-PCR was done in cell lines to assess MT1G mRNA expression before and after demethylating treatment.


RESULTS
MT1G promoter hypermethylation was found in 29 of 121 prostate cancer, 5 of 39 HGPIN, 3 of 29 benign prostatic hyperplasia, and 0 of 13 normal prostate tissue samples. No significant differences in methylation frequencies or levels were found (P = 0.057, for both). Methylation levels were found to correlate with tumor stage but not with Gleason grade. MT1G hypermethylation was more frequent in prostate cancer that spread beyond the prostate capsule. All prostate cancer cell lines tested showed MT1G promoter methylation, but no differences in expression were apparent after demethylation.


CONCLUSIONS
Our findings suggest that MT1G promoter methylation is associated with tumor aggressiveness in prostate cancer and it might be a marker of locally advanced disease.
Henrique
Rui
R
Department of Genetics, Portuguese Oncology Institute, Porto, Rua Dr. Antonio Bernardino Almeida, 4200-072 Porto, Portugal.
Jerónimo
Carmen
C
Hoque
Mohammad O
MO
Nomoto
Shuji
S
Carvalho
André L
AL
Costa
Vera L
VL
Oliveira
Jorge
J
Teixeira
Manuel R
MR
Lopes
Carlos
C
Sidransky
David
D
D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology; D000368:Aged; D000704:Analysis of Variance; D014408:Biomarkers, Tumor / Q000097:blood; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019175:DNA Methylation; D018450:Disease Progression; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008297:Male; D008668:Metallothionein / Q000235:genetics* / Q000378:metabolism; D008875:Middle Aged; D009367:Neoplasm Staging; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D019048:Prostatic Intraepithelial Neoplasia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D012313:RNA; D015032:Zinc / Q000378:metabolism
D014408:Biomarkers, Tumor; D012313:RNA; D008668:Metallothionein; D015032:Zinc