Exosome mimicry by a HAVCR1–NPC1 pathway of endosomal fusion mediates hepatitis A virus infection

Abstract

Cell-to-cell communication by exosomes controls normal and pathogenic processes 1 , 2 . Viruses can spread in exosomes and thereby avoid immune recognition 3 . While biogenesis, binding, and uptake of exosomes are well-characterized 4 , 5 , delivery of exosome cargo into the cytoplasm is poorly understood 3 . We report that phosphatidylserine receptor HAVCR1 6 , 7 and cholesterol transporter NPC1 8 participate in cargo delivery from exosomes of hepatitis A virus (HAV)-infected cells (exo-HAV) by clathrin-mediated endocytosis. Using CRISPR/Cas9 knockouts we show that these two lipid receptors, which interact in the late endosome 9 , are necessary for membrane fusion and delivery of RNA from exo-HAVs into the cytoplasm. The HAVCR1/NPC1 pathway, which Ebola virus exploits to infect cells 9 , mediates HAV infection by exo-HAV indicating that viral infection by this exosome mimicry mechanism does not require an envelope glycoprotein. The luminal viral RNA but not endosomal uncoating of HAV particles (vpHAV) contained in the exosome is mainly responsible for exo-HAV infectivity as assessed by methylene blue-inactivation of non-encapsidated RNA. In contrast, infectivity of vpHAV is pH-independent and requires HAVCR1 or other yet unidentified receptor(s) but not NPC1. Our findings show that envelope glycoprotein-independent fusion mechanisms are shared by exosomes and viruses, and call for a reassessment of the role of envelope glycoproteins in infection.

Recent Progress on Exosomes in RNA Virus Infection

“…Feng et al identified exosome-like viral particles, which are characterized by incorporating HAV virions into exosomes with a diameter of 50–110 nm, and termed as quasi-enveloped HAV (eHAV) [ 70 , 71 , 72 ]. It was reported that phosphatidylserine receptor HAVCR1 (CD365) and cholesterol transporter NPC1 involve in the transportation of eHAV through clathrin-mediated endocytosis, which is necessary for the membrane fusion and transport of viral RNA from eHAV into the cytoplasm [ 73 , 74 ]. Moreover, host gangliosides are essential endosomal receptors for uncoating and delivery of the viral RNA genome to the cytoplasm of eHAV and naked HAV [ 72 ].…”

Hepatitis A Virus Incidence Rates and Biomarker Dynamics for Plasma Donors, United States

“…Whether the protracted low-level RNAemia observed during the late phase of infection is relevant from a pathophysiologic perspective is less clear and might depend on the HAV variant circulating. Although naked HAV virions are expected to be neutralized by HAV antibodies, this assumption might not apply to the more recently described quasi-enveloped HAV particles (3) and capsid-free HAV genomes, which are infectious because the RNA plusstrand orientation enables direct use as messenger RNA (24,25). The host cell entry of both of these variants is mediated by exosomes and relies on distinct host cell factors not used in the same way by naked virions (25).…”

Pathogenicity and virulence of hepatitis A virus

“…A third cell-to-cell transmission pathway of HAV has been recently described, based on the delivery of capsid-free RNA genomes which are an abundant cargo of the quasi-enveloped virions [ 53 ]. The quasi-enveloped virions, which are exosomes in nature, carry phosphatidylserine molecules in their membranes, which interact with the extracellular domain of the phosphatidylserine receptor (HAVCR1), previously described as a HAV receptor [ 54 , 55 ], mediating their uptake by clathrin-mediated endocytosis [ 56 ].…”