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The highest rates of primary liver cancer are found in East and South-East Asia. Hepatocellular carcinoma (HCC) is the primary histological type of hepatic carcinoma, accounting for 85 - 90% of the total burden of liver cancer all over the world (1, 2). The occurrence and death rate of HCC are almost the same as its high lethality rate (2). The onset of HCC has a multi-factorial and multi-stage course, involving both hereditary and environmental factors. The long-term carcinogenic effects give rise to genetic changes, which can lead to tumor formation (3). It is necessary to search for hereditary factors, which could help us detect the population at highest risk and better regulate the screening procedures. Besides, the recognition of risk factors could lead to better diagnoses and planning of novel prevention measures for high-risk individuals (4).
As an anti-oncogene, the Ras association domain family 1A gene (RASSF1A) has been reported to play a vital role in the maintenance of genomic instability; it controls a sequence of vital cellular functions in the integration of signaling pathways (5-9). The loss of expression by promoter methylation of RASSF1A is one of the most common early events in HCC that plays an important role in tumorigenesis and metastasis of HCC (10, 11). The most widespread form of human genetic variation is single nucleotide polymorphism (SNP), which may contribute to tumor sensitivity. To date, many studies have demonstrated that SNPs of RASSF1A are associated with the risk of many types of cancers, including breast cancer (12-15), lung cancer (16, 17), esophageal cancer (16, 18), head and neck cancer (16), colorectal cancer (16), renal cell carcinoma (19), HCC (20), gastric cancer (18), and prostate cancer (21). It has been proven that guanine (G)/thymine (T) SNP at the first position of codon 133 in exon 3 of RASSF1A (dbSNP ID: rs2073498), leads to the replacement of an Ala residue (GCT) through the Ser residue (TCT) in the ataxia telangiectasia mutated (ATM) phosphorylated position, and can impact the function of RASSF1A (22, 23). However, the results of these studies have been controversial (12-20). This is because the frequency of the Ser allele of RASSF1A Ala133Ser polymorphism varies in different geographic areas and ethnic populations (24).
The Qidong county of Nantong city is one of the regions with the highest incidence of HCC in China (25). In the recent years, several studies have investigated the correlation between genetic polymorphisms, methylation and HCC. Nevertheless, the effects of RASSF1A Ala133Ser polymorphism and methylation on HCC have not been well identified in Nantong.
Determining the molecular spectroscopy of HCC is essential as it could help us recognize molecular biomarkers for the screening of at-risk individuals and achieve early detection.
A hospital-based case control research including 260 HCC cases and 235 controls was carried out to investigate the impact of RASSF1A Ala133Ser polymorphism and promoter methylation on HCC, and its prognostic and functional implications in subjects from a high incidence area in Nantong.
In this study, we investigated whether the RASSF1A Ala133Ser polymorphism could have an impact on the susceptibility to HCC. To the best of our knowledge, this is the first epidemiological study to reveal the association between RASSF1A Ala133Ser polymorphism and HCC risk in China. Our results suggest that the Ser allele of RASSF1A significantly increases the risk of HCC. The RASSF1A Ala133Ser polymorphism is located in a putative ATM phosphorylation site consensus sequence (7, 28). The cell cycle checkpoint responses at G1, S and G2 are all remarkably abnormal in ATM deficient cells (29). The Ser residue at the ATM site can be phosphorylated upon ionizing radiation and it can then induce cell death and suppress colony formation (30). Due to the involvement of ATM in DNA damage control, patients with HCC carrying RASSF1A Ala133Ser polymorphisms may be resistant to radiation-based chemotherapy (31). Therefore, it is reasonable to assume that subjects carrying the Ser allele of the RASSF1A Ala133Ser polymorphism may be susceptible to HCC. Knowledge about the mechanisms involved in HCC carcinogenesis may help identify targets for chemoprevention or therapeutic strategies.
The connection between RASSF1A Ala133Ser polymorphism and the risk of various cancers has been investigated by several studies (24). In this study, the frequency of genotypes containing the Ser allele of RASSF1A Ala133Ser polymorphism is similar to the other Asian cancer types, yet lower than in Caucasian cancer types. The difference in results may be explained by the following points. First, different types of cancer may have different mechanisms of carcinogenesis. Second, the discrepancy could also be interpreted partially by the influence of the gene-environment interaction in a multistep process of carcinogenesis. Third, studies recruiting controls form hospital populations are more likely to acquire significant results in allele comparison, heterozygous and dominant genetic models. Fourth, different cancer risks were also found in the studies using different genotyping methods. In this study, we also investigated promoter methylation of RASSF1A in HCC. Our results suggest that RASSF1A methylation may be an early event in HCC carcinogenesis. Further studies are required to characterize RASSF1A methylation in HCC precancerous lesions.
In order to confirm whether RASSF1A methylation and its Ala133Ser polymorphism are risk-factors predicting shorter survival after surgery, we also analyzed the influence of methylation and Ala133Ser polymorphism on patient survival. The Kaplan-Meier analysis indicated that the life span of patients with RASSF1A methylation was shorter in comparison to that of patients lacking this genetic feature. Besides, for the first time, we found that HCC patients with the Ser allele of RASSF1A Ala133Ser polymorphism had significantly poorer overall survival in Nantong. Univariate and further multivariate analyses demonstrated that hepatocirrhosis, BCLC stage, Edmondson division, RASSF1A methylation and RASSF1A Ala133Ser polymorphism independently predicted the unfavorable overall survival of patients with HCC.
In conclusion, this was the first study to reveal that the RASSF1A Ala133Ser polymorphism might confer genetic susceptibility to HCC in the Chinese population. The Ser allele of RASSF1A Ala133Ser and RASSF1A promoter methylation could significantly increase the risk of HCC development. Of course, further work is necessary to illustrate the mechanism of RASSF1A in the development of HCC. The RASSF1A gene will be developed ultimately as one of the molecular biomarkers for high-risk subject screening and early detection of HCC in the future.
