APOBEC and iNOS are not the main intracellular effectors of IFN-gamma-mediated inactivation of Hepatitis B virus replication.
OBJECTIVE
Interferon-gamma (IFN-gamma) produced by activated T-cells is the principle mediator of non-cytolytic Hepatitis B virus (HBV) inactivation; however the intracellular pathways responsible are poorly defined. We investigated the role of IFN-gamma-inducible nitric oxide synthase (iNOS) and APOBEC3 (A3) enzyme family in the inhibition of HBV replication by IFN-gamma.


METHODS
Hepatoma-cell lines transfected with HBV DNA were treated with IFN-gamma. Viral replication, iNOS and A3 mRNAs were quantitated by TaqManPCR and the direct nitric oxide (NO) effect on HBV replication was investigated using an NO-donor. A3G antiviral activity was verified by co-transfection with its inhibitor, human immunodeficiency virus (HIV)-associated virion infectivity factor (Vif).


RESULTS
IFN-gamma caused a dose-dependent reduction (>50%) of HBV DNA in the absence of cytotoxicity. Although iNOS mRNA increased 45-fold in IFN-gamma treated cells, NO2- was not detectable in supernatants and the use of an NO-donor did not inhibit HBV replication. A3 enzyme mRNAs varied between cells and were >10-fold higher in lymphocytes than in liver tissue. IFN-gamma up-regulated A3G mRNA by three-fold, associated with significant HBV DNA decrease. However, A3G degradation by Vif did not abolish the antiviral effect of IFN-gamma against HBV.


CONCLUSIONS
IFN-gamma inhibits HBV replication and up-regulates both iNOS and A3G. However, other pathways appear to have a greater role in IFN-gamma-induced HBV inactivation in the liver.
Proto
Sandra
S
Institute of Hepatology, University College London, and MRC Clinical Sciences Centre, Hammersmith Hospital, London WC1E 6HX, UK. s.proto@ucl.ac.uk
Taylor
John A
JA
Chokshi
Shilpa
S
Navaratnam
Naveenan
N
Naoumov
Nikolai V
NV
D000071478:APOBEC Deaminases; D000998:Antiviral Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003564:Cytidine Deaminase; D043525:Cytosine Deaminase / Q000235:genetics / Q000378:metabolism*; D004279:DNA, Viral / Q000378:metabolism; D006515:Hepatitis B virus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D008099:Liver / Q000821:virology; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins; D014779:Virus Replication / Q000187:drug effects
D000998:Antiviral Agents; D004279:DNA, Viral; D011994:Recombinant Proteins; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II; D043525:Cytosine Deaminase; D000071478:APOBEC Deaminases; C502889:APOBEC3 proteins, human; D003564:Cytidine Deaminase