APOBEC deaminases as cellular antiviral factors: a novel natural host defense mechanism

The APOBEC (acronym for apolipoprotein B editing catalytic polypeptide) family of cytidine deaminases are widely distributed in the biological world and play a central role in diverse enzymatic pathways. Members of this family (APOBEC3G and APOBEC3F) have been recently shown to be able to restrict HIV-1 replication in physiologically relevant target cells (macrophages, lymphocytes), presumably by triggering extensive deamination of the viral RNA/DNA replication intermediates. This natural antiretroviral host defense mechanism is counteracted by the HIV-1 protein Vif, which is able to target APOBECs to degrade. The so-called "Vif/APOBEC3G paradigm" has been confirmed by a growing literature. However, evidence arising from recent studies has expanded this view, showing that the replication of other viruses is also restricted by APOBEC family members and suggesting antiviral mechanism(s) of action unrelated to the catalytic activity of these proteins. Furthermore, evolutionary investigations on primates have shown that APOBEC3 gene expansion might be related to an ancient adaptive selection to prevent endogenous genetic instability, indicating an additional ancient protective role of APOBECs. This article is aimed at broadening the current knowledge about the antiviral activity of the APOBEC members and to highlight the notion that their role(s) might be more general than previously anticipated.