Chen B, Hales B F
Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada.
Toxicol Appl Pharmacol. 1994 Oct;128(2):293-301. doi: 10.1006/taap.1994.1209.
Cadmium, a cytotoxic heavy metal, is embryotoxic. Cadmium interferes with the functions of other cations such as zinc and calcium. Cadherins, calcium-dependent cell adhesion molecules, are expressed and spatiotemporally regulated in embryos and their yolk sacs during organogenesis. Cadmium has been shown to disrupt calcium-dependent cell-cell interactions and to alter the distribution of epithelial or E-cadherin in cultured cells. The purpose of this study was to determine whether the embryotoxicity of cadmium is mediated through an effect on E-cadherin. Day 10 rat embryos were cultured for 1 hr without cadmium and then cultured for another 2, 6, or 20 hr in the presence or absence of 2.5 microM CdCl2. Embryos and yolk sacs were collected and analyzed separately. The growth of embryos and yolk sacs after exposure to cadmium for 2 or 6 hr was not different from that of controls. After 20 hr exposure to cadmium, embryos were growth retarded, with morphological scores 10-15% lower than those of controls; more dramatically, their yolk sacs were thickened and decreased in diameter to only half of that of control yolk sacs. Northern blot analysis revealed no significant differences in the relative amounts of E-cadherin mRNA between control and cadmium-treated embryos or their yolk sacs. There was also no alteration in the abundance of E-cadherin protein in cadmium-treated embryos at any of the times examined. There was a gradual decline in the relative amount of E-cadherin protein in control yolk sacs with time in culture; interestingly, cadmium treatment appeared to prevent this decline, resulting in significantly higher concentrations of E-cadherin protein in the cadmium-exposed yolk sacs after 6 hr (1.7-fold) or 20 hr (2.3-fold) of culture. The relative abundance of other structural proteins such as alpha- or beta-tubulin and actin was unchanged. Exposure of embryos for 20 hr to concentrations of cadmium varying from nonembryotoxic to embryotoxic resulted in concentration-dependent increases in E-cadherin protein in the yolk sac; E-cadherin was only increased in the yolk sac of growth-retarded embryos. Thus, an increase in yolk sac E-cadherin protein is associated with the induction of embryotoxicity by cadmium. To determine the ability of cadmium to interact directly with the cadherins, the binding of radioactive 109Cd to embryo and yolk sac proteins was assessed. 109Cd bound to an unidentified 87-kDa protein; binding to this protein was attenuated by 1 mM zinc, but not by 1 mM calcium.(ABSTRACT TRUNCATED AT 400 WORDS)
镉是一种具有细胞毒性的重金属，具有胚胎毒性。镉会干扰锌和钙等其他阳离子的功能。钙黏蛋白是一种依赖钙的细胞黏附分子，在器官发生过程中，胚胎及其卵黄囊中会表达并受到时空调控。研究表明，镉会破坏依赖钙的细胞间相互作用，并改变培养细胞中上皮钙黏蛋白或E-钙黏蛋白的分布。本研究的目的是确定镉的胚胎毒性是否通过对E-钙黏蛋白的影响介导。将第10天的大鼠胚胎在无镉条件下培养1小时，然后在存在或不存在2.5 microM氯化镉的情况下再培养2、6或20小时。分别收集胚胎和卵黄囊并进行分析。暴露于镉2或6小时后，胚胎和卵黄囊的生长与对照组无差异。暴露于镉20小时后，胚胎生长迟缓，形态学评分比对照组低10 - 15%；更显著的是，它们的卵黄囊增厚，直径减小至对照组卵黄囊的一半。Northern印迹分析显示，对照组和镉处理组的胚胎或其卵黄囊中E-钙黏蛋白mRNA的相对含量无显著差异。在任何检测时间，镉处理组胚胎中E-钙黏蛋白的丰度也没有改变。随着培养时间的延长，对照组卵黄囊中E-钙黏蛋白的相对含量逐渐下降；有趣的是，镉处理似乎阻止了这种下降趋势，导致培养6小时（1.7倍）或20小时（2.3倍）后，镉暴露的卵黄囊中E-钙黏蛋白的浓度显著升高。其他结构蛋白如α-或β-微管蛋白和肌动蛋白的相对丰度没有变化。将胚胎暴露于从无胚胎毒性到有胚胎毒性的不同浓度镉20小时，导致卵黄囊中E-钙黏蛋白的浓度依赖性增加；E-钙黏蛋白仅在生长迟缓的胚胎卵黄囊中增加。因此，卵黄囊中E-钙黏蛋白的增加与镉诱导的胚胎毒性有关。为了确定镉与钙黏蛋白直接相互作用的能力，评估了放射性109Cd与胚胎和卵黄囊蛋白的结合情况。109Cd与一种未鉴定的87 kDa蛋白结合；1 mM锌可减弱与该蛋白的结合，但1 mM钙则不能。（摘要截短至400字）
