No abstract

Zinc (Zn), an endogenous regulator of apoptosis, and has abilities both to induce apoptosis and inhibit the induction of apoptosis via the modulation of caspase activity. Due to the multifunctions of Zn, the intracellular Zn level is strictly regulated by a complex system in physiological and pathological conditions. The commitment of Zn to the regulation of apoptosis is not fully understood. In the present study, we investigated the role of intracellular Zn level in the induction of apoptosis in human leukemia cells (HL‐60 cells) using a Zn ionophore [pyrithione (Py)]. Treatment of HL‐60 cells with Zn for 6 h in the presence of Py (1 µm) exhibited cytotoxicity in a Zn dose‐dependent manner (25–200 µm). Necrotic cells, assayed by trypan blue permeability, increased in number in a Zn dose‐dependent fashion (50–100 µm), but the appearance of apoptotic cells, assayed by formation of a DNA ladder and terminal deoxynucleotidyltransferase‐mediated dUTP‐biotin nick end‐labeling method, peaked at 25 µm, suggesting the dependence of intracellular Zn level on the execution of apoptosis. In fact, treatment with Py resulted in increases in intracellular Zn levels, and N,N,N′,N′‐tetrakis (2‐pyridylmethyl)ethylenediamine, a cell‐permeable Zn chelator, inhibited DNA ladder formation induced by Py/Zn treatment (1 µm Py and 25 µm Zn). Py/Zn treatment activated the caspases, as assessed by the proteolysis of poly(ADP‐ribose) polymerase (PARP), which is a substrate of caspase, and activated p38 mitogen‐activated protein kinase (p38MAPK), which is a transducer of apoptotic stimuli to the apparatus of the apoptosis execution. Z‐Asp‐CH2‐DCB, a broad‐spectrum inhibitor of caspase, attenuated proteolysis of PARP and DNA ladder formation by Py/Zn, indicating that apoptosis induced by Py/Zn is mediated by caspase activation. The p38MAPK‐specific inhibitor SB203580 also inhibited induction of apoptosis by Py/Zn. Although SB203580 suppressed the proteolysis of PARP, Z‐Asp‐CH2‐DCB did not inhibit the phosphorylation of p38MAPK, raising the possibility that apoptosis triggered by Py/Zn might be mediated by the p38MAPK/caspase pathway.

No abstract

Cadmium (Cd) induces apoptosis in vitro and in vivo. However, the mode of action is unclear. Cytochrome C (Cyt c) release from mitochondria into cytoplasm is a key event in apoptosis. In this study, we examined the effects of Cd on the release of Cyt c from mitochondria using human leukemia HL-60 cells and isolated mitochondria. Cd induced apoptosis in HL-60 cells in a dose-dependent manner, in accordance with increases in cytosolic Cyt c. Cd at 25 µM also induced the release of Cyt c from isolated mitochondria. Mitochondrial swelling induced by permeability transition is known to cause outer membrane rupture and Cyt c release from mitochondria. Cd induced a swelling of mitochondria in vitro, as did calcium, a classical inducer of mitochondrial permeability transition. These results suggest that apoptosis induced by Cd appears to be involved in a mitochondria-dependent pathway and in the release of Cyt c from mitochondria by swelling.