N-CADHERIN IN ADULT-RAT CARDIOMYOCYTES IN CULTURE .1. FUNCTIONAL-ROLEOF N-CADHERIN AND IMPAIRMENT OF CELL-CELL CONTACT BY A TRUNCATED N-CADHERIN MUTANT

N-cadherin is a transmembrane Ca2+-dependent glycoprotein that is part of adherens junctions, It functions with the cell adhesion N-terminal extracellular domain as a site of hemophilic cell-cell contacts. The intracellular C-terminal domain provides via a catenin complex the int eraction with the cytoskeleton. Ectopic expression of chicken N-cadher in in adult rat cardiomyocytes (ARC) in culture was obtained after mic roinjection into non-dividing cardiomyocytes; it was demonstrated that the exogenous protein colocalized with the endogenous N-cadherin at t he plasma membrane of the cell and formed contact sites. A dominant ne gative chicken N-cadherin mutant was constructed by a large deletion o f the extracellular domain. This mutant was expressed and inhibited th e function of the endogenous rat N-cadherin probably by competing for the catenin complex binding domain, which is essential for the formati on of a stable cell-cell contact of ARC, The injected cells lost conta ct with neighbouring cells and retracted; the connexons of the gap jun ctions were pulled out as well, This could be avoided by another N-cad herin mutation, which, in addition to the N-terminal truncation, conta ined a deletion of the catenin binding domain, In the case of the trun cated N-cadherin at the N terminus, the sarcomeric structure of the my ofibrils of ARC was also affected. Myofibrils were the most vulnerable cytoskeletal structures affected by the overexpressed dominant negati ve N-cadherin mutation. Similar behaviour was shown when cardiomyocyte s separated following Ca2+ depletion and when new cell-cell contacts w ere formed after Ca2+ replenishment, N-cadherin is thought to be the e ssential component for establishing new cell-cell contacts which event ually led to a new formation of intercalated disc-like structures in t he cardiac cell culture.