Functional cis-heterodimers of N- and R-cadherins.

Classical cadherins form parallel cis-dimers that emanate from a single cell surface. It is thought that the cis-dimeric form is active in cell-cell adhesion, whereas cadherin monomers are likely to be inactive. Currently, cis-dimers have been shown to exist only between cadherins of the same type. Here, we show the specific formation of cis-heterodimers between N- and R-cadherins. E-cadherin cannot participate in these complexes. Cells coexpressing N- and R-cadherins show homophilic adhesion in which these proteins coassociate at cell-cell interfaces. We performed site- directed mutagenesis studies, the results of which support the strand dimer model for cis-dimerization. Furthermore, we show that when N- and R-cadherins are coexpressed in neurons in vitro, the two cadherins colocalize at certain neural synapses, implying biological relevance for these complexes. The present study provides a novel paradigm for cadherin interaction whereby selective cis-heterodimer formation may generate new functional units to mediate cell-cell adhesion.