Staurosporine induces apoptosis through both caspase-dependent and caspase-independent mechanisms.

Sensitivity of tumor cells to anticancer therapy depends on the ability of the drug to induce apoptosis. However, multiple signaling pathways control this induction and thus determine this sensitivity. We report here that staurosporine, a well known inducer of apoptosis in a wide range of cell lines, displays distinct ability to trigger apoptosis in two different L1210 sublines (termed L1210/S and L1210/0). Staurosporine treatment resulted in an early cell death (within 3 h) in L1210/S cells, while in L1210/0 cells, death occurred only after 12 h. In both instances, death occurred by apoptosis. A broad spectrum caspase inhibitor, Z-VAD-fmk, blocked early apoptosis in L1210/S cells but did not confer any protection on late apoptosis in L1210/0 cells. Protection by Z-VAD-fmk observed in L1210/S cells was not lasting and unmasked a secondary process of cell death that also exhibited characteristics of apoptosis. Thus, staurosporine induces apoptotic cell death through at least two redundant parallel pathways. These two pathways normally coexist in L1210/S cells. However, the early cell death mechanism depending on caspase activation disguises the late caspase-independent apoptotic process. Staurosporine-induced apoptosis in L1210/0 cells develops only by the caspase-independent mechanism due to a general defect in caspase activation.

Nuclear translocation of a leukocyte elastase Inhibitor/Elastase complex during staurosporine-induced apoptosis: role in the generation of nuclear L-DNase II activity.

Using L1210 murine leukemia cells, we have previously shown that in response to treatment with drugs having different targets, apoptotic cell death occurs through at least two different signaling pathways. Here, we present evidence that nuclear extracts from staurosporine-treated cells elicit DNase II activity that is not detected in nuclear extracts from cisplatin-treated cells. This activity correlates with the accumulation of two nuclear proteins (70 and 30 kDa) which are detected by an anti-L-DNase II antibody. Partial purification of this DNase II activity suggests that the 30-kDa protein could be the nuclease responsible for staurosporine-induced DNA fragmentation. The 70-kDa protein is also recognized by an anti-elastase antibody, suggesting that it carries residues belonging to both L-DNase II and elastase. Since previous findings showed that L-DNase II was generated from the leukocyte inhibitor of elastase, we propose that the 70-kDa protein results from an SDS-stable association between these two proteins and is translocated from the cytoplasm to the nucleus during staurosporine-induced apoptosis.