Se-methylselenocysteine (Se-MSC) is a potent chemopreventive agent in many test systems and has been shown to inhibit
tumor promotion and induce apoptosis, but its mechanism of action is still not well understood. The present study was designed to assess the mechanism of Se-MSC on the induction of apoptosis in SKOV-3
ovarian cancer cells. Se-MSC displayed strong inhibitory effects on cell proliferation and viability of SKOV-3 cells in dose and time dependent manners and induced apoptosis. Investigation of the mechanism of Se-MSC-induced apoptosis revealed that treatment with Se-MSC produced morphological features of apoptosis and DNA fragmentation. This was associated with
caspase-3 activation and cleavage of
poly(ADP-ribose) polymerase and
phospholipase C-gamma1
proteins. However, SKOV-3 cells treated with Se-MSC did not demonstrate
cytochrome c accumulation in the cytosol during apoptosis induction. Pretreatment of cells with the
caspase inhibitors (
z-VAD-fmk and
DEVD-CHO) prevented Se-MSC-induced apoptosis. These results suggested that Se-MSC induces apoptosis through
cytochrome c-independent
caspase-3 activation in SKOV-3 cells. In late stage of apoptosis, p18kDa fragment of Bax was generated with the down-regulation of the expressions of
survivin,
X-linked inhibitor of apoptosis protein, and human
inhibitor of apoptosis protein 1 following Se-MSC treatment, suggesting that the modulation of Bax and IAP (inhibitors of apoptosis) family
proteins play some role in Se-MSC-mediated apoptosis. Pre-treatments of
z-VAD-fmk and the
calpain inhibitor,
calpeptin inhibited Bax cleavage. These results suggested that Bax cleavage is mediated by
calpain, and
calpain activation may be a
caspase-dependent one. Taken together, the chemopreventive effects of Se-MSC may be related in part to the
caspase-3 activation, the down-regulation of IAP family
proteins, and Bax cleavage mediated by
caspase-dependent
calpain activation.