On treatment with
7-ketocholesterol (7-keto) or
7beta-hydroxycholesterol (7beta-OH), which are major
oxysterols in
atherosclerotic plaques, the simultaneous identification of oncotic and apoptotic cells suggests that these compounds activate different metabolic pathways leading to various modes of cell death. With U937, MCF-7 (caspase-3 deficient), MCF-7/c3 cells (stably transfected with
caspase-3), we demonstrate that
caspase-3 is essential for
caspase-9, -7, -8 activation, for Bid degradation mediating mitochondrial
cytochrome c release, for cleavage of
poly(ADP-ribose) polymerase and inhibitor of the
caspase-activated deoxyribonuclease, and, at least in part, for internucleosomal DNA fragmentation. The crucial role of
caspase-3 was supported by the use of
z-VAD-fmk and
z-DEVD-fmk, which abolished apoptosis and the associated events. However, inactivation or lack of
caspase-3 did not inhibit 7-keto- and 7beta-OH-induced cell death characterized by staining with
propidium iodide, loss of mitochondrial potential. The mitochondrial release of
apoptosis-inducing factor and
endonuclease G was independent of the
caspase-3 status, which conversely played major roles in the morphological aspects of dead cells. We conclude that
caspase-3 is essential to trigger 7-keto- and 7beta-OH-induced apoptosis, that these
oxysterols simultaneously activate caspase-3-dependent and/or -independent modes of cell death.