Decreased expression of 14-3-3 sigma is associated with advanced disease in human epithelial ovarian cancer: its correlation with aberrant DNA methylation.
OBJECTIVE
In this study, we examined the promoter methylation status and expression of 14-3-3 sigma and evaluated its clinical significance in epithelial ovarian cancer.


METHODS
Twelve ovarian cancer cell lines; 2 ovarian surface epithelial cell lines; and 8 normal, 8 benign, 12 borderline, and 102 ovarian cancer tissues were examined. Methylation-specific PCR, quantitative reverse transcription-PCR, and immunohistochemistry were used to evaluate methylation status and expression of 14-3-3 sigma gene and protein.


RESULTS
Among the 12 ovarian cancer cell lines, the presence of a methylated band was detected in seven cell lines. Median values of relative 14-3-3 sigma gene expression in cancers with methylation (3.27) were significantly lower than those without methylation (16.4; P < 0.001). Treatment of 5-aza-2'-deoxycitidine resulted in the demethylation of the promoter CpG islands and reexpression. All of the normal, benign, and borderline tissues were positive for 14-3-3 sigma protein, and in ovarian cancer tissues, 73.5% (75 of 102) were positive for 14-3-3 sigma protein and was almost consistent with methylation status. Negative immunoreactivity of 14-3-3 sigma was significantly correlated with high age and serous histology, high-grade, advanced-stage residual tumor of >2 cm, high serum CA125, high Ki-67 labeling index, and positive p53 immunoreactivity. 14-3-3 sigma immunoreactivity was significantly associated with overall survival (P = 0.0058).


CONCLUSIONS
Our findings suggest that 14-3-3 sigma is inactivated mainly by aberrant DNA methylation and that it may play an important role in the pathogenesis of epithelial ovarian cancer.
Akahira
Jun-ichi
J
Department of Obstetrics and Gynecology, Tohoku University Graduate School of Medicine, Sendai, Japan. jakahiro-tohoku@umin.ac.jp
Sugihashi
Youko
Y
Suzuki
Takashi
T
Ito
Kiyoshi
K
Niikura
Hitoshi
H
Moriya
Takuya
T
Nitta
Makoto
M
Okamura
Hitoshi
H
Inoue
Satoshi
S
Sasano
Hironobu
H
Okamura
Kunihiro
K
Yaegashi
Nobuo
N
D048948:14-3-3 Proteins; D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000096:biosynthesis*; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D018076:DNA, Complementary / Q000378:metabolism; D018450:Disease Progression; D004847:Epithelial Cells / Q000378:metabolism*; D005092:Exonucleases / Q000096:biosynthesis*; D005095:Exoribonucleases; D005260:Female; D015723:Gene Library; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000096:biosynthesis*; D010051:Ovarian Neoplasms / Q000378:metabolism* / Q000473:pathology; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
D048948:14-3-3 Proteins; D014408:Biomarkers, Tumor; D018076:DNA, Complementary; D009363:Neoplasm Proteins; D005092:Exonucleases; D005095:Exoribonucleases; C413442:SFN protein, human