Intracellular digestion of reovirus particles requires a low pH and is an essential step in the viral infectious cycle

Abstract

Lysosomotropic drugs such as NH4Cl have been useful for studying the role of low pH in early events in virus infection. NH4Cl blocks the production of infectious progeny virus in mammalian reovirus-infected cells. The inhibitory effect of NH4C1 is mediated by an inhibition of intracellular digestion of reovirus outer capsid proteins. In vitro digestion of viral outer capsid proteins produces infectious partially uncoated particles, called intermediate subviral particles, which are no longer inhibited by the presence of NH4Cl. These results indicate that proteolytic processing of reovirus outer capsid proteins takes place in a low pH compartment of the cell and is an essential step in the viral infectious cycle.

Proteolytic Disassembly Is a Critical Determinant for Reovirus Oncolysis

“…Infection by reovirus requires the disassembly of its outermost capsid in order to penetrate the host and initiate viral gene transcription. [9][10][11] Second, we found that ISVPs efficiently infected "reovirus-resistant" cells. Golden et al also found that the addition of proteases to the media of resistant cells rendered them susceptible to infection.…”

“…to perforate either the endosomal/lysosomal or the plasma membrane and thus to penetrate the cytoplasm. [9][10][11] In order to do this, we labeled reovirus with Cy3-maleimide monofunctional dye and exposed resistant and susceptible cells grown on glass slides to this labeled reovirus. Immunofluorescence was then performed to detect lysosomal associated membrane protein 2, frequently used as a functional marker of lysosomes.…”

“…7,8 This processing gives the subvirion particle the capacity to penetrate the endosome/lysosome or the plasma membrane and thereby gain entry to the cytoplasm where reovirus replication can occur. [9][10][11] Work in animal models suggests that, during natural enteric infections, σ3 is proteolytically degraded extracellularly within the intestinal lumen. 12,13 In cell culture, however, reovirus takes advantage of endosomal and lysosomal proteases for its proteolytic conversion into ISVP.…”

“…12,13 In cell culture, however, reovirus takes advantage of endosomal and lysosomal proteases for its proteolytic conversion into ISVP. 11,14 The necessity of reovirus uncoating for infectivity in vivo and in vitro is further demonstrated by the capacity of protease inhibitors to block enteric infection in mice and restrict reovirus uncoating and infection in cell culture. [13][14][15][16][17][18][19][20][21] Recently, reovirus type-3 Dearing has been investigated as an oncolytic agent against a variety of human cancers (reviewed in ref.…”

Picornavirus inhibitors

“…Most evidence indicates that the majority of naked animal virus particles follow the receptor-mediated endocytosis pathway to infect cells (Marsh and Helenius, 1989). Whether some of these viruses need a low pH step to trigger the crossing of the endosomal membrane, or enter cells by a pH-independent mechanism, remains open to debate (Brown and Burlingham, 1973;Madshus et al, 1984c;Svensson, 1985;Sturzenbecker et al, 1987;Gromeier and Wetz, 1990;Kronenberger et al, 1991;Varga et al, 1991). Two major questions, therefore, remain to be answered with respect to the mechanism of picornavirus entry into cells: Is a given picornavirus species internalized through endosomes in a particular cell type?, or do endosomes need to be acidified for the virus to enter cells?…”