High level expression of the anti-retroviral protein APOBEC3G is induced by influenza A virus but does not confer antiviral activity.

Human APOBEC3G is an antiretroviral protein that was described to act via deamination of retroviral cDNA. However, it was suggested that APOBEC proteins might act with antiviral activity by yet other mechanisms and may also possess RNA deamination activity. As a consequence there is an ongoing debate whether APOBEC proteins might also act with antiviral activity on other RNA viruses. Influenza A viruses are single-stranded RNA viruses, capable of inducing a variety of antiviral gene products. In searching for novel antiviral genes against these pathogens, we detected a strong induction of APOBEC3G but not APOBEC3F gene transcription in infected cells. This upregulation appeared to be induced by the accumulation of viral RNA species within the infected cell and occurred in an NF-kappaB dependent, but MAP kinase independent manner. It further turned out that APOBEC expression is part of a general IFNbeta response to infection. However, although strongly induced, APOBEC3G does not negatively affect influenza A virus propagation.