活性氧和钙离子参与镉诱导的酵母细胞死亡过程调节

以酵母为实验材料,研究了镉(以CdCl2形式添加)对细胞的毒性作用机制.结果显示,浓度为0.25~5 mmol·L-1的镉可降低酵母细胞活性,诱导细胞死亡;随着镉浓度的提高和处理时间的延长,细胞死亡率增高.凋亡抑制剂Z-Asp-CH2-DCB与镉共同作用后,细胞死亡率明显低于镉单独处理组.经镉处理后,酵母细胞内的活性氧(ROS)水平显著升高;外源抗氧化剂抗坏血酸和过氧化氢酶能降低镉引发的细胞死亡,特异性Ca2+螯合剂EGTA或Ca2+通道特异性抑制剂LaCl3亦可明显降低镉诱发的细胞死亡率.研究表明,镉诱发的酵母细胞死亡过程存在依赖于caspase途径的细胞凋亡途径;镉诱发的死亡与镉处理组胞内ROS和Ca2+水平升高有关,ROS可能通过增加胞内Ca2+水平,继而激活相关下游信号导致细胞死亡.

Involvement of ROS and calcium in cadmium-induced yeast cell death

Cadmium(Cd) is a toxic transition metal with great occupational and environmental concern. Soluble cadmium salts accumulate and result in toxicity to various organs including liver, kidneys, brain, lungs and heart. A variety of adverse health effects, such as bone fracture, renal dysfunction, hypertension and cancer, can happen after the constant exposure of cadmium. However, the exact cellular mechanisms of cadmium toxicity are not yet well understood. In this study, cytotoxic effects of cadmium on Saccharomyces cerevisiae were investigated with or without some antagonists. For cadmium treatments, yeast cells of EGY48 strain harvested from the early log phase were incubated in 0.9% NaCl containing varying amounts of cadmium chloride(Cd) for 3 to 24 h. For other combination treatments, selected antagonists including broad caspase inhibitor Z-Asp-2,6-dichlorbenzoyloxymethylketone (Z-Asp-CH₂-DCB), ascorbic acid (AsA) and catalase(CAT), calcium inhibitor ethylene glycol bis-(2-aminoethyl)-tetraacetic acid (EGTA) and LaCl₃ were respectively added to cadmium solutions at 0.05 to 5 mmol·L^-1, using 2',7'-dichlorofluorescein diacetate (DCFH-DA) to indicate intracellular ROS level and methylene blue staining method to measure the cell viability. The results showed that cadmium exposure decreased cell viability in a dose-and time-dependent manner. Exposure to 0.25 mmol·L^-1 Cd for 6 h or exposure to 0.5 mmol·L^-1 and higher concentrations of Cd for 3 h significantly induced cell death. Cadmium exposure induced significant cell death and also an obvious increase of intracellular ROS levels. Caspase inhibitor Z-Asp-CH₂-DCB can significantly block Cd-induced cell death. Moreover, when AsA or CAT was used to block intracellular ROS increase, Cd-induced cell death decreased significantly. Also, EGTA and LaCl₃ can block Cd-induced cell death. These results clearly demonstrated that Cd-induced cell death is associated with an increase of the intracellular ROS and Ca²⁺ levels. Our results suggest that Cd-induced cell death in S.cerevisiae could be one kind of programmed cell death mediated by ROS generation and activation of cytosolic Ca²⁺ signaling.