M. Naito et al., INDUCTION OF IN-VITRO NUCLEAR APOPTOSIS ACTIVITY COINCIDES WITH THE PRODUCTION OF 50 KDA CYTOSOLIC PROTEIN, Cell death and differentiation, 4(7), 1997, pp. 617-622
Human monocytic leukemia U937 cells undergo apoptosis when cells are t
reated with the anticancer drug etoposide. To study the mechanism of d
rug-induced apoptosis, we used an in vitro apoptosis system with cytos
ol from etoposide-treated U937 cells. The cytosol from apoptotic U937
cells showed activity to induce morphologic changes and oligonucleosom
al DNA fragmentation in isolated nuclei in vitro; both are typical fea
tures of apoptosis. We generated monoclonal antibodies to the proteins
in the etoposide-treated U937 cytosol. We found that a 50 kDa protein
, recognized by SN-1 monoclonal antibody, appeared in the cytosol of U
937 cells, in accordance with its cell-free apoptosis activity. Z-Asp,
an inhibitor of interleukin-1 beta converting enzyme (ICE) family pro
teases, inhibited the appearance of the 50 kDa protein and the emergen
ce of the cell-free apoptosis activity in the etoposide-treated U937 c
ytosol. These results indicate that the 50 kDa protein is produced by
the activation of ICE family protease during apoptosis and suggest som
e roles of the protein in the development of apoptosis.