Detection of apoptosis induced by topoisomerase inhibitors and serum deprivation in Syrian hamster embryo cells

The sensitivity of normal diploid Syrian hamster embryo (SHE) cells to apop tosis was tested after treatment with the topoisomerase inhibitors camptoth ecin and etoposide and after serum withdrawal. Programmed cell death (PCD) was identified through morphological, biochemical, and molecular changes an d compared with that of HL60 cell line. The results showed that topoisomera se inhibitors, which mere shown to be potent PCD inducers in the HL60 cell line, induced a weaker apoptotic response in SHE cells than after growth fa ctor deprivation. In addition, serum-free medium, which rapidly induced apo ptosis in SHE cells, did not affect the HL60 cell line. In both cell types, PCD was expressed by condensed chromatin, fragmented nuclei, and DNA ladde ring on electrophoretic gels, an indisputable sign of apoptosis. In apoptot ic HL60 cells, the cleavage of 113-kDa poly-(ADP-ribose)polymerase (PARP) r esulted in the so-called apoptotic 89-kDa fragment and was associated with increased caspase-3 activity. In apoptotic SHE cells, PARP degraded early b ut the degradation profile was not characterized by the appearance of an 89 -kDa fragment. Moreover, no activation of caspase-3 was noted. ZnCl2, which is known to prevent protease activity responsible for apoptosis features, inhibited PARP cleavage and nuclear modifications induced by apoptotic stim uli in both cell types, but with a higher sensitivity in SHE cells. Apoptos is induced by serum deprivation was linked with c-myc negative regulation i n SHE cells, but not with p53 protein accumulation, while topoisomerase inh ibitors led to p53 stabilization without any change in c-myc expression. Se rum-free medium and topoisomerase inhibitors did not modify c-myc expressio n in the HL60 cell line. The overall results demonstrated that apoptosis, w hich is a carefully regulated process of cell death, may proceed through me chanisms varying according to cell type or apoptosis inducer. In addition, markers which are generally considered hallmarks of apoptosis may fail to a ppear in some cell types. (C) 2000 Academic Press.