Infection of animal cells by a number of cytolytic viruses leads to increased membrane permeability. Thus, Semliki Forest virus (SFV)
infection of susceptible cells modifies the permeability of the membrane for a number of
cations and metabolites (Muñoz et al. (1985), Virology 146, 203-212). The molecular basis of this modification of the cell membrane has not been investigated in detail. We report that during the
infection of HeLa cells with SFV, or BHK cells with
vesicular stomatitis virus, there is a significant increase in the release of
choline and
arachidonic acid into the culture medium, suggesting that both
phospholipases (PLases) C and A2 become activated during
infection. Both
choline and
phosphorylcholine are released into the medium as expected when PLase C is activated. Cells prelabeled with
arachidonic acid release a significant amount of radioactivity from the third hour postinfection. Most of this radioactivity is present in the medium of SFV-infected cells in the form of
free fatty acid, suggesting that
phospholipid hydrolysis has occurred; no intact
phospholipids are detected in the culture medium. Finally, the action of several inhibitors of PLases, such as
zinc and
cadmium ions,
chloroquine,
chlorpromazine,
amantadine, and
dansylcadaverine were assayed. Our findings indicate that the release of
choline or
arachidonic acid is potently blocked by some of these
lipase inhibitors. Following
infection by SFV HeLa cells become susceptible to the inhibition of
protein synthesis by
hygromycin B due to increased uptake of this
antibiotic. Entry of
hygromycin B was prevented by
zinc ions or
chloroquine, suggesting that the increase in membrane permeability in SFV-infected cells may be mediated in part by
lipase activation.