Copy Number Variation Of APOBEC3B Is Associated With Susceptibility To HBV-related Hepatocellular Carcinoma

Background and Objective:Hepatocellular carcinoma (HCC) is one of the most common malignancies and hepatitis B virus (HBV) and hepatitis C virus (HCV) infection are involved in the development of HCC. However, the infection of both HBV and HCV and their outcomes vary greatly among individuals, suggesting that there exist genetic susceptibility factors. Copy number variation (CNV) is a common form of genetic variations in human genome and has been shown to play an important role in many complex diseases. In this study, we exmamined whether a copy number variation (CNV) in the APOBEC3B (APOBEC3B) gene which encodes a cytidine deaminases enzyme, is associated with susceptibility to HBV-related HCC (BHCC).Methods:Affymetrix GeneChip Human Mapping5.0set was applied to screen genome-wide copy number variations using genomic DNA sample isolated from peripheral blood lymphocytes of patients with BHCC (n=25) and healthy controls (n=25). Real-time quantitative PCR was used to validate the chip results. APOBEC3B CNV, significantly different between HCC patients and controls was analyzed by PCR based method in518patients with BHCC,400patients with chronic hepatitis B (CHB), and501controls without HBV infection. The odds ratios (ORs) and95%confidence intervals (CIs) were estimated by multivariate logistic regression. APOBEC3B RNA expression in nomal liver tissues was determined by real-time RT-PCR. APOBEC3BE255A, a deaminase null mutant, was generated by changing glutamate255to alanine255. The effects of APOBEC3B or APOBEC3BE255A on HBV viral genome replication'and editing (hypermutation) were examined in HepG2cells by differential DNA denaturation PCR, real-time PCR and sequencing.Results:Genotyping results showed that the frequency of APOBEC3B del/del in BHCC patients was12.9%compared with6.4%in controls and7.5%in CHB patients. Subjects with the APOBEC3B del/del genotype had increased risk for developing BHCC (OR=3.16,95%CI=1.98-5.05; P<0.001) or CHB (OR=1.92,95%CI=1.05-3.52; P=0.034) compared with those with the APOBEC3B ins/ins genotype. The APOBEC3B ins/del genotype was also associated with increased risk for BHCC (OR=1.84,95%CI=1.41-2.40; P<0.001) or CHB (OR=1.54,95%CI=1.06-2.24, P=0.025) compared with those with the APOBEC3B ins/ins genotype. Moreover, the variant APOBEC3B genotype (del/del+ins/del) was associated with increased risk for CHB (OR=1.51,95%CI=1.07-2.12; P=0.0184) compared with the APOBEC3B ins/ins genotype. APOBEC3B overexpressed in HepG2significantly reduced HBV RNA levels by50%and caused G>A hypermutation in HBV DNA; however, mutant APOBEC3B E255A had no ability to induce G>A mutation, although it could inhibit HBV RNA production as efficiently as APOBEC3B.Conclusion:These results suggest that APOBEC3B deletion may be a genetic susceptibility factor for HBV infection and BHCC development, probably due to lack of HBV DNA editing and RNA production inhibition.