A pathogenic picornavirus acquires an envelope by hijacking cellular membranes

Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292, USA.
Nature (Impact Factor: 42.35). 03/2013; 496(7445). DOI: 10.1038/nature12029
Source: PubMed

ABSTRACT Animal viruses are broadly categorized structurally by the presence or absence of an envelope composed of a lipid-bilayer membrane, attributes that profoundly affect stability, transmission and immune recognition. Among those lacking an envelope, the Picornaviridae are a large and diverse family of positive-strand RNA viruses that includes hepatitis A virus (HAV), an ancient human pathogen that remains a common cause of enterically transmitted hepatitis. HAV infects in a stealth-like manner and replicates efficiently in the liver. Virus-specific antibodies appear only after 3-4 weeks of infection, and typically herald its resolution. Although unexplained mechanistically, both anti-HAV antibody and inactivated whole-virus vaccines prevent disease when administered as late as 2 weeks after exposure, when virus replication is well established in the liver. Here we show that HAV released from cells is cloaked in host-derived membranes, thereby protecting the virion from antibody-mediated neutralization. These enveloped viruses ('eHAV') resemble exosomes, small vesicles that are increasingly recognized to be important in intercellular communications. They are fully infectious, sensitive to extraction with chloroform, and circulate in the blood of infected humans. Their biogenesis is dependent on host proteins associated with endosomal-sorting complexes required for transport (ESCRT), namely VPS4B and ALIX. Whereas the hijacking of membranes by HAV facilitates escape from neutralizing antibodies and probably promotes virus spread within the liver, anti-capsid antibodies restrict replication after infection with eHAV, suggesting a possible explanation for prophylaxis after exposure. Membrane hijacking by HAV blurs the classic distinction between 'enveloped' and 'non-enveloped' viruses and has broad implications for mechanisms of viral egress from infected cells as well as host immune responses.

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    • "While enteroviruses have historically been considered non-enveloped (i.e., lacking a hostderived membrane bilayer around their capsids) and thus rely on cell lysis to exit, recent reports of extracellular Coxsackievirus B3 (CVB3) being present in vesicles (Robinson et al., 2014) and PV being able to spread non-lytically among host cells (Bird et al., 2014) have raised important questions regarding the extracellular nature of enteroviral particles and the significance of non-lytic exit in the viral life cycle. Moreover hepatitis A, hepatitis E and blue tongue viral particles, all long considered non-enveloped , have been observed surrounded by membranes (Feng et al., 2013; Takahashi et al., 2008; Owens et al., 2004). A central paradigm in virology is that viruses behave as independent infectious units (Flint et al., 2009). "
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    ABSTRACT: A central paradigm within virology is that each viral particle largely behaves as an independent infectious unit. Here, we demonstrate that clusters of enteroviral particles are packaged within phosphatidylserine (PS) lipid-enriched vesicles that are non-lytically released from cells and provide greater infection efficiency than free single viral particles. We show that vesicular PS lipids are co-factors to the relevant enterovirus receptors in mediating subsequent infectivity and transmission, in particular to primary human macrophages. We demonstrate that clustered packaging of viral particles within vesicles enables multiple viral RNA genomes to be collectively transferred into single cells. This study reveals a novel mode of viral transmission, where enteroviral genomes are transmitted from cell-to-cell en bloc in membrane-bound PS vesicles instead of as single independent genomes. This has implications for facilitating genetic cooperativity among viral quasispecies as well as enhancing viral replication. Copyright © 2015 Elsevier Inc. All rights reserved.
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    • "Combined with our previous results [10] showing that HCV particles are transported from early to late endosomes/MVB, our current studies suggest that the NS5A-containing HCV particles most likely exit the cells via fusion of MVB to the plasma membrane. Exosomes have been demonstrated to facilitate the budding of human immunodeficiency virus (HIV) [54] and hepatitis A virus (HAV) [55]. Exosome have been known to play important roles in intercellular communications. "
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    ABSTRACT: Nonstructural protein 5A (NS5A) of hepatitis C virus (HCV) serves dual functions in viral RNA replication and virus assembly. Here, we demonstrate that HCV replication complex along with NS5A and Core protein was transported to the lipid droplet (LD) through microtubules, and NS5A-Core complexes were then transported from LD through early-to-late endosomes to the plasma membrane via microtubules. Further studies by cofractionation analysis and immunoelectron microscopy of the released particles showed that NS5A-Core complexes, but not NS4B, were present in the low-density fractions, but not in the high-density fractions, of the HCV RNA-containing virions and associated with the internal virion core. Furthermore, exosomal markers CD63 and CD81 were also detected in the low-density fractions, but not in the high-density fractions. Overall, our results suggest that HCV NS5A is associated with the core of the low-density virus particles which exit the cell through a preexisting endosome/exosome pathway and may contribute to HCV natural infection.
    PLoS ONE 06/2014; 9(6):e99022. DOI:10.1371/journal.pone.0099022 · 3.23 Impact Factor
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    • "Other pathogenic microbes have evolved mechanisms to actively benefit from host autophagy. Multiple viruses deploy such subversion strategies, but the molecular mechanisms involved are unclear (Feng et al., 2013; Heaton and Randall, 2010; Klein and Jackson, 2011; Reggiori et al., 2010). The sizes of RNA virus genomes are evolutionarily constrained (Belshaw et al., 2008). "
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    ABSTRACT: Autophagy recycles cellular components and defends cells against intracellular pathogens. While viruses must evade autophagocytic destruction, some viruses can also subvert autophagy for their own benefit. The ability of influenza A virus (IAV) to evade autophagy depends on the Matrix 2 (M2) ion-channel protein. We show that the cytoplasmic tail of IAV M2 interacts directly with the essential autophagy protein LC3 and promotes LC3 relocalization to the unexpected destination of the plasma membrane. LC3 binding is mediated by a highly conserved LC3-interacting region (LIR) in M2. The M2 LIR is required for LC3 redistribution to the plasma membrane in virus-infected cells. Mutations in M2 that abolish LC3 binding interfere with filamentous budding and reduce virion stability. IAV therefore subverts autophagy by mimicking a host short linear protein-protein interaction motif. This strategy may facilitate transmission of infection between organisms by enhancing the stability of viral progeny.
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