Abstract
ANP32 proteins have been implicated in supporting influenza virus replication, but most of the work to date has focused on the ability of avian Anp32 proteins to overcome restriction of avian influenza polymerases in human cells. Using a CRISPR approach, we show that the human acidic nuclear phosphoproteins (ANPs) ANP32A and ANP32B are functionally redundant but essential host factors for mammalian-adapted influenza A virus (IAV) and influenza B virus (IBV) replication in human cells. When both proteins are absent from human cells, influenza polymerases are unable to replicate the viral genome, and infectious virus cannot propagate. Provision of exogenous ANP32A or ANP32B recovers polymerase activity and virus growth. We demonstrate that this redundancy is absent in the murine Anp32 orthologues; murine Anp32A is incapable of recovering IAV polymerase activity, while murine Anp32B can do so. Intriguingly, IBV polymerase is able to use murine Anp32A. We show, using a domain swap and point mutations, that the leucine-rich repeat (LRR) 5 region comprises an important functional domain for mammalian ANP32 proteins. Our approach has identified a pair of essential host factors for influenza virus replication and can be harnessed to inform future interventions.IMPORTANCE Influenza virus is the etiological agent behind some of the most devastating infectious disease pandemics to date, and influenza outbreaks still pose a major threat to public health. Influenza virus polymerase, the molecule that copies the viral RNA genome, hijacks cellular proteins to support its replication. Current anti-influenza drugs are aimed against viral proteins, including the polymerase, but RNA viruses like influenza tend to become resistant to such drugs very rapidly. An alternative strategy is to design therapeutics that target the host proteins that are necessary for virus propagation. Here, we show that the human proteins ANP32A and ANP32B are essential for influenza A and B virus replication, such that in their absence cells become impervious to the virus. We map the proviral activity of ANP32 proteins to one region in particular, which could inform future intervention.
Highlights
ANP32 proteins have been implicated in supporting influenza virus replication, but most of the work to date has focused on the ability of avian Anp32 proteins to overcome restriction of avian influenza polymerases in human cells
Two independent clones with diallelic disruption of the Anp32A or Anp32B locus were verified by next-generation sequencing (NGS) and Sanger sequencing of individual alleles, and loss of protein expression was confirmed by Western blotting against ANP32A or ANP32B, respectively (Fig. 1b and data not shown)
Here, we show that human ANP32A and ANP32B are functionally redundant in their support for influenza virus polymerase in human cells and that the RNA-dependent RNA polymerase (RdRp) does not carry out RNA replication in the absence of both family members
Summary
ANP32 proteins have been implicated in supporting influenza virus replication, but most of the work to date has focused on the ability of avian Anp proteins to overcome restriction of avian influenza polymerases in human cells. Using a CRISPR approach, we show that the human acidic nuclear phosphoproteins (ANPs) ANP32A and ANP32B are functionally redundant but essential host factors for mammalian-adapted influenza A virus (IAV) and influenza B virus (IBV) replication in human cells. When both proteins are absent from human cells, influenza polymerases are unable to replicate the viral genome, and infectious virus cannot propagate. Each segment is packaged in a double helical loop structure bound by nucleoprotein (NP) along its length, except for the pseudocomplementary 3= and 5= untranslated regions that comprise the promoter [3,4,5] These termini instead associate with an RNA-dependent RNA polymerase (RdRp) encoded by the virus [6]. The difference between avian and mammalian ANP32A proteins has been suggested to account for host range restriction of avian influenza strains in mammalian cells, and much of the work to date has focused on the avian orthologues, those from chickens [23]
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