MECHANISMS OF CADMIUM TOXICITY IN EPITHELIAL CELLS

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Cadmium (Cd2+) is an important industrial and environmental pollutant that has been shown to cause severe damage to a variety of organs, and to have mutagenic, teratogenic and carcinogenic activities. In spite of its importance as an environmental health problem, relatively little is known about the specific cellular and molecular mechanisms by which Cd2+ produces its many effects. The long-term objective of this project is to identify some of these mechanisms. Reports in the literature suggest that some of the effects of Cd2+ in vivo may result from the disruption of the junctions between cells in various epithelial or endothelial surfaces. To examine this possibility in more detail, studies were undertaken to examine the effects of Cd2+ on cell-cell junctions in the established porcine renal epithelial cell line, LLC-PK1. Results of these studies have shown that Cd2+ has specific damaging effects on the adhering and occluding junctions between LLC-PK1 cells and that these effects may involve the interaction of Cd2+ with E-cadherin, a Ca2+-dependent glycoprotein that plays a key role in epithelial cell-cell adhesion. The work described in this proposal is a direct extension of these previous studies and is aimed at resolving three important issues. The first goal is to identify the mechanisms by which Cd2+ disrupts E-cadherin dependent cell-cell junctions in the LLC-PK1 cell line. The hypothesis to be tested is that Cd2+ can competitively displace Ca2+ from binding sites on E- cadherin and thereby alter the adhesive properties of the molecule. The second goal is to determine whether or not Cd2+ can selectively disrupt calcium-dependent cell-cell junctions in vascular endothelial cells. This is an important issue because the vascular endothelium is one of the primary targets for Cd2+ toxicity in vivo. The third major goal is to determine whether Cd2+ can selectively damage cadherin-dependent cell-cell junctions in vivo, and whether such a mechanism may contribute to overt toxic effects of Cd2+. These issues will be addressed by using a multidisciplinary approach that includes morphologic, biophysical and biochemical techniques. Results of these studies should provide important new insights into the mechanisms by which Cd2+ produces some of its toxic effects and should lay the groundwork for future studies in this area. Furthermore, the results of these studies could have more general implications concerning the mechanisms by which toxic substances damage living cells.