Zoonotic viruses are an omnipresent threat to global health. Influenza A virus (IAV) transmits between birds, livestock, and humans. Proviral host factors involved in the cross-species interface are well known. Less is known about antiviral mechanisms that suppress IAV zoonoses. We observed CpG dinucleotide depletion in human IAV relative to avian IAV. Notably, human ZAP selectively depletes CpG-enriched viral RNAs with its cofactor KHNYN. ZAP is conserved in tetrapods but we uncovered that avian species lack KHNYN. We found that chicken ZAP does not affect IAV (PR8) or CpG enriched IAV. Human ZAP or KHNYN independently restricted CpG enriched IAV by overexpression in chicken cells or knockout in human cells. Additionally, mammalian ZAP-L and KHNYN also independently restricted an avian retrovirus (ROSV). Curiously, platypus KHNYN, the most divergent from eutherian mammals, was also capable of direct restriction of multiple diverse viruses. We suggest that mammalian KHNYN may be a bona fide restriction factor with cell-autonomous activity. Furthermore, we speculate that through repeated contact between avian viruses and mammalian hosts, protein changes may accompany CpG-biased mutations or reassortment to evade mammalian ZAP and KHNYN.
Significance: Viruses adapt to hosts to replicate successfully. We show that two mammalian proteins, ZAP and KHNYN, restrict CpG-enriched avian viruses. Mammalian KHNYN may be a bona fide restriction factor with cell-autonomous activity. We also identified a platypus KHNYN with potent and broad antiviral activity highlighting a significant need to investigate antiviral mechanisms in novel and understudied species. Ongoing efforts to understand viruses with zoonotic potential will benefit from further identification of species-/class-specific restriction factors and their antiviral preferences. Furthermore, we speculate that evolving viral nucleotide composition indicates zoonotic potential and adaptation to mammals requires dinucleotide and amino acid changes.
Highlights: CpG content is depleted in human and swine IAV relative to avian IAVHuman ZAP-S and KHNYN but not chicken ZAP independently restrict CpG-rich IAV.Mammalian ZAP-L and KHNYN but not chicken ZAP independently restrict ROSV.Platypus KHNYN potently restricts retroviruses, including IAV, HIV-1, MLV, and ROSV.