Methylation and messenger RNA expression of p15INK4b but not p16INK4a are independent risk factors for ovarian cancer.
OBJECTIVE
The purpose of this research was to compare methylation status and mRNA expression of p15INK4b and p16INK4a in serous epithelial ovarian cancer tissues and normal ovarian tissues.


METHODS
We analyzed the DNA methylation status and mRNA expression of p15INK4b and p16INK4a in 52 ovarian cancer specimens and 40 normal ovarian specimens by using methylation-specific PCR and real-time reverse transcription-PCR, respectively.


RESULTS
Although the p15INK4b and p16INK4a mRNA expression levels were highly correlated with each other (P < 0.001), the methylation status did not seem to be linked with levels of mRNA expression, as no association between the two events was found for either gene. Promoter hypermethylation of p15(INK4b) was more common in ovarian cancer (30.8% for the 52 cases) than in normal ovaries (5% for the 40 controls without ovarian cancer; P = 0.005) but not methylation of p16INK4a (25% for cancer versus 37.5% for normal; P = 0.288). The relative mRNA expression levels of p15INK4b were significantly lower in ovarian cancer (12.9%) than in normal ovaries (41.7%; P = 0.008) but not those of p16INK4a (27% for cases versus 32.8% for controls; P = 0.754). Only high methylation rate and low mRNA expression of p15INK4b were independent risk factors for ovarian cancer (adjusted odds ratio, 5.67; 95% confidence interval, 0.85-37.9 for high methylation rate and odds ratio, 8.98; 95% confidence interval, 1.58-50.9 for low mRNA expression, respectively).


CONCLUSIONS
Our results suggest that epigenetic alterations in p15INK4b but not p16INK4a have an important role in ovarian carcinogenesis and that mechanisms other than methylation may exist to reduce gene expression of p15INK4b in ovarian cancer.
Department of Epidemiology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Zhensheng
Z
Liu
Li-E
LE
Wang
Luo
L
Wang
Karen H
KH
Lu
Gordon B
GB
Mills
Melissa L
ML
Bondy
Qingyi
Q
Wei
D000368:Aged; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics*; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D010051:Ovarian Neoplasms / Q000208:ethnology / Q000235:genetics / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012307:Risk Factors
D019941:Cyclin-Dependent Kinase Inhibitor p16; D004273:DNA, Neoplasm; D012333:RNA, Messenger