Evolutionary origins of hepatitis A virus in small mammals.

Hepatitis A virus (HAV) is an ancient and ubiquitous human pathogen recovered previously only from primates. The sole species of the genus Hepatovirus, existing in both enveloped and nonenveloped forms, and with a capsid structure intermediate between that of insect viruses and mammalian picornaviruses, HAV is enigmatic in its origins. We conducted a targeted search for hepatoviruses in 15,987 specimens collected from 209 small mammal species globally and discovered highly diversified viruses in bats, rodents, hedgehogs, and shrews, which by pairwise sequence distance comprise 13 novel Hepatovirus species. Near-complete genomes from nine of these species show conservation of unique hepatovirus features, including predicted internal ribosome entry site structure, a truncated VP4 capsid protein lacking N-terminal myristoylation, a carboxyl-terminal pX extension of VP1, VP2 late domains involved in membrane envelopment, and a cis-acting replication element within the 3D(pol) sequence. Antibodies in some bat sera immunoprecipitated and neutralized human HAV, suggesting conservation of critical antigenic determinants. Limited phylogenetic cosegregation among hepatoviruses and their hosts and recombination patterns are indicative of major hepatovirus host shifts in the past. Ancestral state reconstructions suggest a Hepatovirus origin in small insectivorous mammals and a rodent origin of human HAV. Patterns of infection in small mammals mimicked those of human HAV in hepatotropism, fecal shedding, acute nature, and extinction of the virus in a closed host population. The evolutionary conservation of hepatovirus structure and pathogenesis provide novel insight into the origins of HAV and highlight the utility of analyzing animal reservoirs for risk assessment of emerging viruses.

Lysosomes serve as a platform for hepatitis A virus particle maturation and nonlytic release.

Early studies on hepatitis A virus (HAV) in cell culture demonstrated the inclusion of several viral particles in an intracellular lipid-bilayer membrane. However, the origin of these virus-associated membranes and the mechanism for the non-lytic release of HAV into bile are still unknown. Analyzing the association of this virus with cell organelles, we found that newly synthesized HAV particles accumulate in lysosomal organelles and that lysosomal enzymes are involved in the maturation cleavage of the virion. Furthermore, by inhibiting the processes of fusion of lysosomes with the plasma membrane, we found that the nonlytic release of HAV from infected cells occurs via lysosome-related organelles.

Cellular localization and effects of ectopically expressed hepatitis A virus proteins 2B, 2C, 3A and their intermediates 2BC, 3AB and 3ABC.

In the course of hepatitis A virus (HAV) infections, the seven nonstructural proteins and their intermediates are barely detectable. Therefore, little is known about their functions and mechanisms of action. Ectopic expression of the presumably membrane-associated proteins 2B, 2C, 3A and their intermediates 2BC, 3AB and 3ABC allowed the intracellular localization of these proteins and their possible function during the replication cycle of HAV to be investigated. In this study, we used rhesus monkey kidney cells, which are commonly used for cell culture experiments, and human liver cells, which are the natural target cells. We detected specific associations of these proteins with distinct membrane compartments and the cytoskeleton, different morphological alterations of the respective structures, and specific effects on cellular functions. Besides comparable findings in both cell lines used with regard to localization and effects of the proteins examined, we also found distinct differences. The data obtained identify so far undocumented interactions with and effects of the HAV proteins investigated on cellular components, which may reflect unknown aspects of the interaction of HAV with the host cell, for example the modification of the ERGIC (ER-Golgi intermediate compartment) structure, an interaction with lipid droplets and lysosomes, and inhibition of the classical secretory pathway.