LINE-1 Methylation Level and Patient Prognosis in a Database of 208 Hepatocellular Carcinomas
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The level of long interspersed nucleotide element-1 (LINE-1) methylation has become regarded as a surrogate marker of global DNA methylation. Previously, we demonstrated that LINE-1 hypomethylation might contribute to the acquisition of aggressive tumor behavior through genomic gains of oncogenes such as cyclin-dependent kinase 6 (CDK6) in esophageal squamous cell carcinoma. However, the relationship between LINE-1 hypomethylation and clinical outcome in hepatocellular carcinoma (HCC) remains unclear.
LINE-1 methylation level in 208 samples of curatively resected HCCs was measured by pyrosequencing assay, and the prognostic value of LINE-1 methylation level in HCC was examined.
LINE-1 methylation levels in the 208 HCC patients investigated were distributed as follows: mean 64.7; median 64.6; standard deviation (SD) 13.6; range 21.5–99.1; interquartile range 62.9–66.6. Univariate Cox regression analysis revealed a significantly higher cancer recurrence rate in the low-methylation-level group than in the high-methylation-level group (hazard ratio 1.58; 95 % CI 1.05–2.47; p = 0.028). Interestingly, the influence of LINE-1 hypomethylation on patient outcome was modified by hepatitis virus infection (p of interaction = 0.023); LINE-1 hypomethylation was associated with a higher cancer recurrence rate in patients without hepatitis virus infection (log-rank p = 0.0047). CDK6 messenger RNA expression levels were inversely associated with LINE-1 methylation levels (p = 0.0075; R = −0.37).
Genome-wide DNA hypomethylation, as measured by LINE-1 levels, might be associated with poor disease-free survival in HCC patients, suggesting a potential role for LINE-1 methylation level as a biomarker for identifying patients who will experience an unfavorable clinical outcome.
Author contributions: conception and design: Kazuto Harada, Yoshifumi Baba, Toru Beppu, and Hideo Baba; acquisition of data: Kazuto Harada, Yoshifumi Baba, and Toru Beppu; analysis and interpretation of data: Kazuto Harada and Yoshifumi Baba; manuscript writing: Kazuto Harada, Yoshifumi Baba, and Hideo Baba. All authors approved the final manuscript.
Conflict of interest
No conflicts of interest exist.
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