APOBEC has been reported to be a restriction factor for multiple

APOBEC has been reported to be a restriction factor for multiple DNA-containing viruses [LCZ696 web reviewed by (Moris et al., 2014)]. Hepatitis B virus (HBV) is one of the most studied instances of APOBEC-mediated inhibition of a DNA virus. HBV is a pararetrovirus that is a major cause of liver cirrhosis and cancer (Beggel et al., 2013; Bonvin and Greeve, 2008). Similar to foamy virus, HBV has a reverse transcriptase that copies packaged pregenomic RNA into DNA within the nascent capsid of the producer cells (Jones and Hu, 2013). Unlike retroviruses, the reverse trascriptase is covalently attached to the 5 end of the minus-strand DNA and does not fully complete plus strand synthesis within producer cells. The remaining single-stranded DNA region represents a natural target for APOBEC family enzymes (Beggel et al., 2013). An initial report using Huh7 order POR-8 hepatoma cells suggested that HBV DNA does not exhibit G-to-A hypermutation after transfection of A3G, but that pregenomic RNA was inefficiently packaged (Seppen, 2004; Turelli et al., 2004). A3G appeared associated with viral cores in the cytoplasm, and similar observations were made for A3B, A3C, A3F, and A3G in another hepatoma cell line (Susp e et al., 2005; Turelli et al., 2004). Further investigation revealed that G-to-A hypermutations were observed at low frequencies (< 1 in 10 genomes) using transfection of HBV and A3G in another hepatoma cell line (Rosler et al., 2004). Both G-toA and C-to-T substitutions were observed with A3B, A3F, and A3G, but not A3C, suggesting that both strands of HBV DNA may be susceptible to deamination (Susp e et al., 2005). AID also has been reported to be associated with an HBV ribonucleoprotein complex and to deaminate viral RNA in tissue culture experiments (Liang et al., 2013). Recent experiments have interrogated endogenous APOBEC3 proteins in multiple cell culture models. Treatment of hepatocyte cells with interferon or an antibody to crosslink the lymphotoxin receptor results in induction of A3A and A3B, respectively, and in G-toA hypermutations and clearance of HBV covalently closed circular DNA (cccDNA) replication intermediates (Lucifora et al., 2014). Thus, analysis of cell culture models of HBV infection have indicated roles for multiple APOBEC family proteins in virus restriction.Virology. Author manuscript; available in PMC 2016 May 01.Harris and DudleyPageAnalysis of patients chronically infected with HBV paints a somewhat different picture of APOBEC restriction. A3G levels appear to be low in primary hepatocytes, but can be induced by interferon (Bonvin et al., 2006). In addition, human A3B, A3C, A3G, A3H, and AID mRNAs are upregulated by inflammation, which often accompanies viral infection (Endo et al., 2007; Vartanian et al., 2010). HBV may replicate in non-hepatic cells, although replication in hematopoietic cells appears to be extremely low (Rosler et al., 2004; Untergasser et al., 2006). HBV DNA sequences from the livers of four patients with high levels of viremia were enriched by 3D-PCR (Susp e et al., 2005). Two of these patient samples gave PCR products at a denaturation temperature of 90 , and sequencing of these products revealed that a small number had G-to-A mutations. The context of these mutations was consistent with the preference of A3G (Susp e et al., 2005). In another study, DNA samples were obtained from patients with liver cirrhosis and analyzed by 3D-PCR at 88.7 . Fifteen of 17 DNAs were amplified under this condition, and f.APOBEC has been reported to be a restriction factor for multiple DNA-containing viruses [reviewed by (Moris et al., 2014)]. Hepatitis B virus (HBV) is one of the most studied instances of APOBEC-mediated inhibition of a DNA virus. HBV is a pararetrovirus that is a major cause of liver cirrhosis and cancer (Beggel et al., 2013; Bonvin and Greeve, 2008). Similar to foamy virus, HBV has a reverse transcriptase that copies packaged pregenomic RNA into DNA within the nascent capsid of the producer cells (Jones and Hu, 2013). Unlike retroviruses, the reverse trascriptase is covalently attached to the 5 end of the minus-strand DNA and does not fully complete plus strand synthesis within producer cells. The remaining single-stranded DNA region represents a natural target for APOBEC family enzymes (Beggel et al., 2013). An initial report using Huh7 hepatoma cells suggested that HBV DNA does not exhibit G-to-A hypermutation after transfection of A3G, but that pregenomic RNA was inefficiently packaged (Seppen, 2004; Turelli et al., 2004). A3G appeared associated with viral cores in the cytoplasm, and similar observations were made for A3B, A3C, A3F, and A3G in another hepatoma cell line (Susp e et al., 2005; Turelli et al., 2004). Further investigation revealed that G-to-A hypermutations were observed at low frequencies (< 1 in 10 genomes) using transfection of HBV and A3G in another hepatoma cell line (Rosler et al., 2004). Both G-toA and C-to-T substitutions were observed with A3B, A3F, and A3G, but not A3C, suggesting that both strands of HBV DNA may be susceptible to deamination (Susp e et al., 2005). AID also has been reported to be associated with an HBV ribonucleoprotein complex and to deaminate viral RNA in tissue culture experiments (Liang et al., 2013). Recent experiments have interrogated endogenous APOBEC3 proteins in multiple cell culture models. Treatment of hepatocyte cells with interferon or an antibody to crosslink the lymphotoxin receptor results in induction of A3A and A3B, respectively, and in G-toA hypermutations and clearance of HBV covalently closed circular DNA (cccDNA) replication intermediates (Lucifora et al., 2014). Thus, analysis of cell culture models of HBV infection have indicated roles for multiple APOBEC family proteins in virus restriction.Virology. Author manuscript; available in PMC 2016 May 01.Harris and DudleyPageAnalysis of patients chronically infected with HBV paints a somewhat different picture of APOBEC restriction. A3G levels appear to be low in primary hepatocytes, but can be induced by interferon (Bonvin et al., 2006). In addition, human A3B, A3C, A3G, A3H, and AID mRNAs are upregulated by inflammation, which often accompanies viral infection (Endo et al., 2007; Vartanian et al., 2010). HBV may replicate in non-hepatic cells, although replication in hematopoietic cells appears to be extremely low (Rosler et al., 2004; Untergasser et al., 2006). HBV DNA sequences from the livers of four patients with high levels of viremia were enriched by 3D-PCR (Susp e et al., 2005). Two of these patient samples gave PCR products at a denaturation temperature of 90 , and sequencing of these products revealed that a small number had G-to-A mutations. The context of these mutations was consistent with the preference of A3G (Susp e et al., 2005). In another study, DNA samples were obtained from patients with liver cirrhosis and analyzed by 3D-PCR at 88.7 . Fifteen of 17 DNAs were amplified under this condition, and f.