Li M, Kondo T, Zhao Q L, Li F J, Tanabe K, Arai Y, Zhou Z C, Kasuya M
Department of Public Health, the Department of Radiological Sciences, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama, 930-0194, Japan.
J Biol Chem. 2000 Dec 15;275(50):39702-9. doi: 10.1074/jbc.M007369200.
Apoptosis induced by cadmium has been shown in many tissues in vivo and in cultured cells in vitro. However, its molecular mechanism is not fully understood. When the human histiocytic lymphoma cell line U937 was treated with cadmium for 12 h, evidence of apoptotic features, including change in nuclear morphology, DNA fragmentation, formation of DNA ladder in agarose gel electrophoresis, and phosphatidylserine externalization, were obtained. Moreover, loss of the mitochondrial membrane potential (Deltapsi(m)) was observed in the cadmium-treated cells and was inhibited by a broad caspase inhibitor (Z-VAD-FMK). Caspase inhibitors suppressed the DNA fragmentation in the order of Z-VAD-FMK > caspase-8 inhibitor > caspase-3 inhibitor. Expression of Bcl-x(L) and Bid decreased significantly in the cadmium-treated cells, although no apparent change in Bcl-2 and Bax expression was found. Tetrakis-(2-pyridylmethyl) ethylendiamine, a cell-permeable heavy metal chelator, partially reversed the increase of fluorescence of Fura-2 in the cadmium-treated cells. In addition, verapamil (70 microm), a voltage-dependent Ca(2+) channel blocker, inhibited the DNA fragmentation induced by cadmium less than 100 microm and decreased the fluorescence of Fura-2. Cadmium up-regulated the expression of type 1 inositol 1,4,5-trisphosphate receptor (IP(3)R) but not type 2 or type 3 IP(3)R. Calpain inhibitors I and II partially prevented DNA fragmentation. No effects of Z-VAD-FMK on the expression of type 1 IP(3)R or of calpain inhibitors on the loss of Deltapsi(m) were observed. These results suggest that cadmium possibly induced apoptosis in U937 cells through two independent pathways, the Ca(2+)-calpain-dependent pathway and the caspase-mitochondria-dependent pathway.
镉诱导的细胞凋亡已在许多体内组织和体外培养细胞中得到证实。然而，其分子机制尚未完全阐明。当人组织细胞淋巴瘤细胞系U937用镉处理12小时后，出现了凋亡特征的证据，包括核形态改变、DNA片段化、琼脂糖凝胶电泳中DNA梯带的形成以及磷脂酰丝氨酸外翻。此外，在镉处理的细胞中观察到线粒体膜电位（Δψm）的丧失，并且被一种广谱半胱天冬酶抑制剂（Z-VAD-FMK）所抑制。半胱天冬酶抑制剂按Z-VAD-FMK > 半胱天冬酶-8抑制剂 > 半胱天冬酶-3抑制剂的顺序抑制DNA片段化。在镉处理的细胞中，Bcl-x(L)和Bid的表达显著降低，尽管未发现Bcl-2和Bax表达有明显变化。四（2-吡啶甲基）乙二胺，一种可渗透细胞的重金属螯合剂，部分逆转了镉处理细胞中Fura-2荧光的增加。此外，维拉帕米（70 μmol），一种电压依赖性Ca(2+)通道阻滞剂，抑制镉诱导的DNA片段化的程度小于100 μmol，并降低了Fura-2的荧光。镉上调了1型肌醇1,4,5-三磷酸受体（IP(3)R）的表达，但未上调2型或3型IP(3)R的表达。钙蛋白酶抑制剂I和II部分阻止了DNA片段化。未观察到Z-VAD-FMK对1型IP(3)R表达的影响或钙蛋白酶抑制剂对Δψm丧失的影响。这些结果表明，镉可能通过两条独立的途径诱导U937细胞凋亡，即Ca(2+)-钙蛋白酶依赖性途径和半胱天冬酶-线粒体依赖性途径。
