HEMOPHILIC INTERCELLULAR-ADHESION MEDIATED BY C-CAM IS DUE TO A DOMAIN-1 DOMAIN-1 RECIPROCAL BINDING

The cell adhesion molecule C-CAM belongs to the immunoglobulin superfa mily and is expressed in epithelia, vessel endothelia, and hematopoiet ic cells. Differential splicing gives rise to different isoforms, of w hich the major two are C-CAM1 and C-CAM2, which both have four Ig-like domains in their extracellular portions, but differ in their cytoplas mic domains. Two different allelic variants of C-CAM, named a and b, o ccur in the rat. The adhesive binding mechanism(s) of C-CAM is not kno wn in detail. Evidence for both hemophilic and heterophilic binding ha s been presented, and different species and splice variants of C-CAM h ave shown differences in temperature and cation dependence when expres sed in different cell types. Here, we have analyzed the binding mechan ism of rat C-CAM2a that was expressed in CHO cells. In this system C-C AM2a-mediated adhesion was calcium- and temperature-independent. C-CAM 2a-transfected cells did not adhere to nontransfected cells, demonstra ting that the binding was hemophilic. Cells transfected with C-CAM2a i n which the N-terminal Ig-domain (D1) was deleted did not aggregate, a nd cells with intact C-CAM2a could not bind to these cells. This was i n contrast to cells that were transfected with C-CAM2a in which the fo urth Ig-like domain (D4) had been deleted; they both aggregated and bo und to cells with intact C-CAM2a. Thus, C-CAM2a mediates intercellular adhesion of CHO cells by a hemophilic mechanism, in which the D1 doma in binds reciprocally to a D1 domain on an opposed C-CAM molecule. (C) 1996 Academic Press, Inc.