The effects of APOBEC3 proteins on Hepatitis B virus replication

Hepatitis B virus causes chronic liver infection in 257 million people worldwide. Current treatments against HBV can control, but not cure HBV infection. Therefore, new treatments for chronic HBV infection need to be developed. The APOBEC3 (apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3) proteins are cellular restriction factors, which have been shown to restrict viral replication for a number of viruses (e.g. HIV) and for retrotransposons. The aim of this study is to elucidate the role of APOBEC3 proteins in inhibiting Hepatitis B virus replication. Quantitative polymerase chain reaction (qPCR) was used to evaluate the impact of APOBEC3 family members on the Hepatitis B virus replication in HepG2.2.15 cells. The highest inhibition of intracellular capsid associated HBV DNA, extracellular virion associated HBV DNA was induced by APOBEC3DE, APOBEC3F, and APOBEC3G as compared to the other APOBEC3 proteins. However, APOBEC3DE showed no inhibition of HBV total RNA, whereas the highest inhibition of HBV total RNA was induced by APOBEC3F and APOBEC3G. The sub-cellular localisation of APOBEC3 proteins was determined by immunofluorescence using confocal microscopy. It was found that APOBEC3DE, APOBEC3F, and APOBEC3G localise to the cytoplasm, suggesting a crucial role of these proteins in HBV replication in the cytoplasm. Nevertheless, APOBEC3A and APOBEC3B localise to the nucleus. The expression and co-localisation of APOBEC3 proteins and viral and host proteins (Uracil DNA Glycosylase UNG and ATP-dependent RNA helicase DDX3) in HepG2.2.15 and HEK293T cells are being investigated in order to determine the interaction between these proteins.