It is likely that endogenous inhibitors of the apical caspases such as caspase-9 exist to
prevent undesirable activation of caspase cascades. A naturally occurring variant of
caspase-9 named caspase-9S was cloned from human liver. Caspase-9S is missing most of
the large subunit of caspase-9, including the catalytic site, but has the intact prodomain and
small subunit. Caspase-9S did not show apoptotic activity in transfection analysis.
Overexpression of caspase-9S inhibited apoptosis induced by caspase-9, indicating that …