Abstract:
Infection of cultured mammalian cells with African horse sickness virus (AHSV) is known to
induce cell death. To date, the trigger(s) of this response, the apoptotic pathways activated
during AHSV infection and the functional consequences of apoptosis on the virus replication
cycle have yet to be characterized. This study demonstrated that extracellular treatment of BHK-
21 cells with both of the AHSV4 outer capsid proteins, VP2 and VP5, was sufficient to trigger
apoptosis. Whether steps in AHSV4 replication subsequent to viral attachment were required
for AHSV4-induced apoptosis was also investigated. Apoptosis was induced in BHK-21 cells
infected with UV-inactivated AHSV4 and in ribavirin-treated cells infected with AHSV4.
However, both AHSV4- and VP2/VP5-stimulated apoptotic responses were inhibited in the
presence of the endosomal acidification inhibitors ammonium chloride and chloroquine. These
results indicated that uncoating of AHSV4 virions, but not viral transcription or subsequent
steps in viral replication, was required for AHSV4 to induce apoptosis in BHK-21 cells.
Furthermore, this study showed that both the extrinsic (caspase-8) and intrinsic (caspase-9)
apoptotic pathways were induced following AHSV4 infection. The inhibition of caspase activity
in AHSV4-infected cells did not diminish AHSV4 replication, but reduced the release and
dissemination of progeny viral particles. Taken together, the data indicated that uncoating of
AHSV virions was required for apoptosis induction, and that apoptosis enhanced virus spread
and release.
