Rl. Debiasi et al., Reovirus-induced apoptosis is preceded by increased cellular calpain activity and is blocked by calpain inhibitors, J VIROLOGY, 73(1), 1999, pp. 695-701
The cellular pathways of apoptosis have not been fully characterized; howev
er, calpain, a cytosolic calcium-activated cysteine protease, has been impl
icated in several forms of programmed cell death. Reoviruses induce apoptos
is both in vitro and in vivo and serve as a model for studying virus-induce
d cell death. We investigated the potential role of calpain in reovirus-ind
uced apoptosis in vitro by measuring calpain activity as well as evaluating
the effects of calpain inhibitors, L929 cells were infected with reovirus
type 3 Abney (T3A), and calpain activity, measured as cleavage of the fluor
ogenic calpain substrate Suc-Leu-Leu-Val-Tyr-AMC, was monitored. There was
a 1.6-fold increase in calpain activity in T3A-infected cells compared to m
ock-infected cells; this increase was completely inhibited by preincubation
with calpain inhibitor I (N-acetyl-leucyl-leucyl-norleucinal [aLLN]), an a
ctive site inhibitor. Both aLLN and PD150606, a specific calpain inhibitor
that interacts with the calcium-binding site, inhibited reovirus-induced ap
optosis in L929 cells by 54 to 93%. Apoptosis induced by UV-inactivated reo
virus was also reduced 65 to 69% by aLLN, indicating that inhibition of apo
ptosis by calpain inhibitors is independent of effects on viral replication
. We conclude that calpain activation is a component of the regulatory casc
ade in reovirus-induced apoptosis.