TY - JOUR
T1 - Hypermethylation of 18S and 28S ribosomal DNAs predicts progression-free survival in patients with ovarian cancer
AU - Chan, Michael W.Y.
AU - Wei, Susan H.
AU - Wen, Ping
AU - Wang, Zailong
AU - Matei, Daniela E.
AU - Liu, Joseph C.
AU - Liyanarachchi, Sandya
AU - Brown, Robert
AU - Nephew, Kenneth P.
AU - Yan, Pearlly S.
AU - Huang, Tim H.M.
PY - 2005/10/15
Y1 - 2005/10/15
N2 - Purpose: Repetitive ribosomal DNA (rDNA) genes are GC-rich clusters in the human genome. The aim of the study was to determine the methylation status of two rDNA subunits, the 18S and 28S genes, in ovarian tumors and to correlate methylation levels with clinicopathologic features in a cohort of ovarian cancer patients. Experimental Design: 18S and 28S rDNA methylation was examined by quantitative methylation-specific PCR in 74 late-stage ovarian cancers, 9 histologically uninvolved, and 11 normal ovarian surface epithelial samples. In addition, methylation and gene expression levels of 18S and 28S rDNAs in two ovarian cancer cell tines were examined by reverse transcription-PCR before and after treatment with the demethytating drug 5′-aza-2′-deoxycvtidine. Results: The methylation level (amount of methylated rDNA/β-actin) of 18S and 28S rDNAs was significantly higher (P < 0.05) in tumors than in normal ovarian surface epithelial samples. Methylation of 18S and 28S rDNA was highly correlated (R2 = 0.842). Multivariate analysis by Cox regression found that rDNA hypermethylation [hazard ratio (HR), 0.25; P < 0.01], but not age (HR, 1.29; P = 0.291) and stage (HR, 1.09; P = 0.709), was independently associated with longer progression-free survival. In ovarian cancer cell fines, methylation levels of rDNA correlated with gene down-regulation and 5′-aza-2′-deoxycytidine treatment resulted in a moderate increase in 18S and 28S rDNA gene expressions. Conclusion: This is the first report of rDNA hypermethylation in ovarian tumors. Furthermore, rDNA methylation levels were higher in patients with long progression-free survival versus patients with short survival. Thus, rDNA methylation as a prognostic marker in ovarian cancer warrants further investigation.
AB - Purpose: Repetitive ribosomal DNA (rDNA) genes are GC-rich clusters in the human genome. The aim of the study was to determine the methylation status of two rDNA subunits, the 18S and 28S genes, in ovarian tumors and to correlate methylation levels with clinicopathologic features in a cohort of ovarian cancer patients. Experimental Design: 18S and 28S rDNA methylation was examined by quantitative methylation-specific PCR in 74 late-stage ovarian cancers, 9 histologically uninvolved, and 11 normal ovarian surface epithelial samples. In addition, methylation and gene expression levels of 18S and 28S rDNAs in two ovarian cancer cell tines were examined by reverse transcription-PCR before and after treatment with the demethytating drug 5′-aza-2′-deoxycvtidine. Results: The methylation level (amount of methylated rDNA/β-actin) of 18S and 28S rDNAs was significantly higher (P < 0.05) in tumors than in normal ovarian surface epithelial samples. Methylation of 18S and 28S rDNA was highly correlated (R2 = 0.842). Multivariate analysis by Cox regression found that rDNA hypermethylation [hazard ratio (HR), 0.25; P < 0.01], but not age (HR, 1.29; P = 0.291) and stage (HR, 1.09; P = 0.709), was independently associated with longer progression-free survival. In ovarian cancer cell fines, methylation levels of rDNA correlated with gene down-regulation and 5′-aza-2′-deoxycytidine treatment resulted in a moderate increase in 18S and 28S rDNA gene expressions. Conclusion: This is the first report of rDNA hypermethylation in ovarian tumors. Furthermore, rDNA methylation levels were higher in patients with long progression-free survival versus patients with short survival. Thus, rDNA methylation as a prognostic marker in ovarian cancer warrants further investigation.
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U2 - 10.1158/1078-0432.CCR-05-1100
DO - 10.1158/1078-0432.CCR-05-1100
M3 - Article
C2 - 16243810
AN - SCOPUS:27144499187
SN - 1078-0432
VL - 11
SP - 7376
EP - 7383
JO - Clinical Cancer Research
JF - Clinical Cancer Research
IS - 20
ER -