| Hepatocellular carcinoma (HCC) is among the most common and lethal cancers in humans, especially in Southern China and sub-Saharan Africa. The prognosis for patients with HCC is generally poor, even after surgery or chemotherapy. The 5-year overall survival rate is between 35% and 41% after resection of primary tumors and between 47% and 61% after liver transplantation. Systemic chemotherapy gives a low response rate of only 10% to 20% and has shown no significant benefit with regard to overall survival. Although the development of HCC has been investigated in these years, research in the molecular marker of prognosis in HCC remains obscure.DNA methylation especially promoter methylation which can bind MBD (methyl-CpG-binding domain) and histone acetylation and cause expression silencing through modifying chromatin structure. In recent years, genomic hypomethylation of tumor suppressor genes have been increasingly found in various types of cancers. The human cancer genome was first found to be hypomethylated in 1983 (Feinberg and Vogelstein,1983). Global hypomethylation and the resulting genomic instability are regarded as hallmarks of cancers today.Pericentromeric heterochromatin contains tightly packed repetitive DNA sequence (LINE, SINE, IAP, and Alu elements). In normal cells, heterochromatin is highly methylated and epigenetically silenced to reduce transcriptional noise. In cancers, global demethylation is commonly observed. Methylation of LINE-1 (long interspersed nucleotide elements) helps to maintain genomic stability and integrity. Loss of methylation increases genomic instability and results in a higher chance of mitotic recombination, both of which are frequently observed in tumor development.DNA methylation at the CpG site in the LINE-1 promoter is comsidered a normal mechanism for silencing of its potentially harmful retrotransposing activity in the mammalian genome. Hypomethylation of the LINE-1 promoter thus provokes instability of the genome. Global hypomethylation of LINE-1 is widely reported in different cancer types, including colorectal cancer, urothelial carcinoma, malignant germ cell tumors,ovarian cancer, cervical cancer, neuroendocrine tumors, prostate cancer, and chronic myeloid leukemia. It was, therefore, LINE-1 methylation was proposed as a surrogate marker for cancer-linked genome demethylation.Research on liver cancer in LINE-1 of the few reports of methylation in tissue samples only showed the different methylation frequency of a very limited number of specimens,and the relationship between LINE-1 methylation and Clinicopathologic features has not been discussed. Another serum LINE-1 methylation studies suggest that the serum LINE-1 methylation level of the HCC patients was was significantly lower than that in the patients of cirrhosis and hepatitis, and the the serum LINE-1 methylation level was associated with the survival rate of patients. However, serum contains very small amount of tumor cells, so, the serum LINE-1 methylation level could not fully represent the LINE-1 methylation level in tumor tissue. Therefore, the detection of LINE-1 methylation level in liver cancer tissues should more comprehensively reflect the LINE-1 methylation level in patients. We examined the promoter hypermethylation status of LINE-1 in 95 cases of HCC and 95 cases of paired non-tumors and 10 normal tissues by real-time quantitative Methylation-specific PCR. And then we investigate the relationship between LINE-1 methylation and Clinicopathologic features in hepatocellular carcinoma.(1) Experimental method and resultThe percentage of methylated LINE-1 was calculated using the formula:100×methylated reaction/(unmethylated reaction+methylated reaction).We examined the promoter hypermethylation status of LINE-1 promoter in 95 cases of HCC and 95 cases of paired non-tumors and 10 normal tissues. We find that the average LINE-1 methylation level in the HCC, paired non-tumors and normal tissues were 75.91±23.698% (means±SD),92.48±12.713%(means±SD),95.30±36.83%(means±SD).The LINE-1 methylation level of the HCC tissues was significantly lower than that in the paired non-tumors(p<0.001) and the normal tissues(p<0.001).Our result suggested that, global demethylation is existed in hepatocellular carcinoma like previous report in other kind of tumor.(2)LINE-1 methylation level associated with clinicopathologic features and prognostic in hepatocellular carcinomaTo evaluate the association between LINE-1 hypomethylation levels and clinicopathological features, the patients with HCC were divided into 2 groups based on the mean value (75.91%) of the whole HCC group. Accordingly, there were 38 patients with LINE-1 methylation levels of<75.91% and 57 patients with levels of≥75.91%. LINE-1 methylation levels were significantly associated with the presence of tumor capsule and venous invasion, tumor size, serum HBV DNA level,TNM stage. The LINE-1 methylation level of the tumor size (d>7cm, diameter,cm) samples (65.11%) was significantly lower than that of the tumor size(4 |
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