Heterophilic and Homophilic Interactions of Junctional Adhesion Molecule-C (JAM-C) Mediate Different Intercellular Adhesive Interactions.

Abstract

Junctional adhesion molecules (JAM) are a new subfamily of the Ig superfamily. We recently identified that the third member of this family, JAM-C, expressed on endothelial, epithelial cells and platelets (i) undergoes a heterophilic interaction with leukocyte β2-integrin Mac-1 (CD11b/CD18) (J Exp Med . 2002; 196:679–91) and (ii) that endothelial JAM-C is predominantly localized within tight junctions and mediates neutrophil transendothelial migration in a Mac-1-dependent manner in vitro and in vivo (J Biol Chem. 2004, 279:55602–8). Here, we characterized JAM-C to undergo a homophilic interaction that participates in tumor cell-endothelial cell interactions. As assessed in a purified system, recombinant soluble JAM-C in fluid phase bound to immobilized JAM-C; moreover, JAM-C-transfected CHO cells adhered to immobilized JAM-C. The homophilic interaction of JAM-C was mediated by the isolated amino-terminal Ig-domain (D1) but not the carboxy-terminal Ig-domain (D2) of the molecule. Dimerization of JAM-A is dependent on the sequence RVE in the aminoterminal Ig-domain. This motif is conserved in JAM-C (R64I65E66) and a single amino acid mutation in this motif (E66R) abolished the homophilic interaction of JAM-C. The lung carcinoma cell line NCI-H522 was found to be positive for JAM-C expression. NCI-H522 cells adhered to immobilized JAM-C, as well as to JAM-C-transfected CHO cells, but not to mock-transfected CHO cells or to CHO cells transfected with the JAM-C mutant (E66R). Adhesion of NCI-H522 cells to JAM-C protein or JAM-C-transfected CHO cells was abolished in the presence of soluble JAM-C or the isolated D1. Furthermore, the adhesion of NCI-H522 cells to endothelial cells was significantly blocked by soluble JAM-C or the isolated D1. Thus, JAM-C undergoes a homophilic interaction via the R64I65E66 motif on the membrane-distal Ig-domain of the molecule. The homophilic interaction of JAM-C can mediate tumor cell-endothelial cell interactions and may thereby be involved in the process of tumor cell metastasis. Together, the heterophilic and homophilic interactions of JAM-C mediate distinct adhesive interactions.