CADMIUM-INDUCED RAT EMBRYOTOXICITY IN-VITRO IS ASSOCIATED WITH AN INCREASED ABUNDANCE OF E-CADHERIN PROTEIN IN THE YOLK-SAC

Cadmium, a cytotoxic heavy metal, is embryotoxic. Cadmium interferes w ith the functions of other cations such as zinc and calcium. Cadherins , calcium-dependent cell adhesion molecules, are expressed and spatiot emporally regulated in embryos and their yolk sacs during organogenesi s. Cadmium has been shown to disrupt calcium-dependent cell-cell inter actions and to alter the distribution of epithelial or E-cadherin in c ultured 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 cu ltured for another 2, 6, or 20 hr in the presence or absence of 2.5 mu M 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 contr ol yolk sacs. Northern blot analysis revealed no significant differenc es in the relative amounts of E-cadherin mRNA between control and cadm ium-treated embryos or their yolk sacs. There was also no alteration i n the abundance of E-cadherin protein in cadmium-treated embryos at an y of the times examined. There was a gradual decline in the relative a mount of E-cadherin protein in control yolk sacs with time in culture; interestingly, cadmium treatment appeared to prevent this decline, re sulting in significantly higher concentrations of E-cadherin protein i n the cadmium-exposed yolk sacs after 6 hr (1.7-fold) or 20 hr (2.3-fo ld) of culture. The relative abundance of other structural proteins su ch as alpha- or beta-tubulin and actin was unchanged. Exposure of embr yos for 20 hr to concentrations of cadmium varying from nonembryotoxic to embryotoxic resulted in concentration-dependent increases in E-cad herin protein in the yolk sac; E-cadherin was only increased in the yo lk sac of growth-retarded embryos. Thus, an increase in yolk sac E-cad herin protein is associated with the induction of embryotoxicity by ca dmium. To determine the ability of cadmium to interact directly with t he cadherins, the binding of radioactive Cd-109 to embryo and yolk sac proteins was assessed. Cd-109 bound to an unidentified 87-kDa protein ; binding to this protein was attenuated by 1 mM zinc, but not by 1 mM calcium. No Cd-109 binding was detected in the similar to 120-kDa reg ion, indicating that cadmium did not interact directly with the cadher in molecules. Furthermore, when both 2 mM CaCl2 and 2.5 mu M CdCl2 wer e added to the embryo culture medium, calcium did not prevent the tera togenic effects of cadmium. These data suggest that during the inducti on of embryo malformations by cadmium, the regulation of E-cadherin pr otein in the yolk sac is altered. However, cadmium does not appear to directly interact with E-cadherin. (C) 1994 Academic Press, Inc.