Two Modes of Entry of Reovirus Particles into L Cells

Abstract

SUMMARYEvidence is presented supporting the hypothesis that reovirus intermediate subviral particles (ISVP), which show increased infectivity relative to intact virions, can gain entry into host L cells by two alternative pathways. One pathway is by the process of viropexis, involving phagocytic vacuoles. A second entry pathway is via direct penetration of the plasma membrane of the cell, without involvement of a phagocytic vacuole. Using electron microscopy, a kinetic analysis of the uptake process was carried out. Results indicate that at 37 °C ISVP gain entry into host cells primarily by direct entry, although viropexis also occurs, while intact virions gain entry by viropexis almost exclusively. A second line of experimental evidence consistent with the idea that ISVP can 'melt' their way through the plasma membrane is provided by studies on the release of pre-loaded radioactive 51Cr from host cells following infection. 51Cr release data demonstrate that infection with ISVP leads to an immediate increased leakiness of the cell plasma membrane, whereas no such increase takes place following infection with an equivalent number of intact virions. This demonstrates that ISVP can interact with the plasma membrane of the cell in a manner which is qualitatively different from the interaction between intact virions and the plasma membrane.The ability of ISVP to directly penetrate the plasma membrane of the host cell, which intact virions apparently cannot do, could explain the decreased duration of the eclipse phase, as well as the increased infectivity of ISVP, relative to that observed for infection with intact virions.

The oncolytic effect in vivo of reovirus on tumour cells that have survived reovirus cell killing in vitro

“…Indeed, addition of exogenous proteases to the culture medium has been shown to facilitate reovirus infection of a variety of cells, which would not otherwise be susceptible (Golden et al, 2002). Studies have shown that protease-generated ISVPs are capable of directly penetrating the cell membrane and entering the cytoplasm where viral replication can take place (Borsa et al, 1979;Chandran et al, 2002). Such a scenario probably plays out in the human gastrointestinal tract where the presence of intestinal proteases likely promotes reovirus infection.…”

Cathepsin B Is Inhibited in Mutant Cells Selected during Persistent Reovirus Infection

“…Persistent reovirus infections of murine L929 (L) cells select viral and cellular mutations that affect acid-dependent proteolysis of viral outer-capsid proteins during viral entry (5)(6)(7)(8). Following attachment to cell surface receptors sialic acid (9,10) and junctional adhesion molecule 1 (11), reovirus virions are internalized into cells by receptormediated endocytosis (12)(13)(14)(15). Within the endocytic pathway, host proteases catalyze the conversion of virions to infectious subvirion particles (ISVPs) by cleavage of viral outer-capsid proteins (13,(15)(16)(17).…”

Involvement of the vacuolar H+-ATPase in animal virus entry

“…In principle, these viruses could pass directly through the plasma membrane after receptor binding. Some evidence suggests this mode of entry for certain viruses, such as adenoviruses (Brown & Burlingham, 1973), poliovirus (Dunnebacke et al, 1969), rotaviruses (Kaljot et al, 1988) and reovirus subviral particles (Borsa et al, 1979). Alternatively, the virus particles can be internalized by receptor-mediated endocytosis and then cross the endosomal membrane.…”