C-CAM (cell-CAM 105) is an adhesive cell surface glycoprotein with homophilic binding properties.
C-CAM (Cell-CAM 105) is a cell surface glycoprotein that is involved in cell-cell adhesion of rat hepatocytes in vitro. To elucidate the adhesion mechanism the binding properties of purified C-CAM were investigated. Using proteins immobilized on nitrocellulose it was found that radiolabeled C-CAM bound to C-CAM but not to a variety of other proteins. Partitioning in Triton X-114 showed that C-CAM has hydrophobic properties. In accordance with this, C-CAM was effectively incorporated into phosphatidylcholine liposomes by dialysis from octylglucoside-containing solutions. The C-CAM-containing liposomes bound specifically to isolated hepatocytes. This binding was blocked by Fab fragments of anti-C-CAM antibodies. Furthermore, preincubation of hepatocytes with anti-C-CAM antibodies followed by washing of the cells blocked binding of C-CAM-containing liposomes. At increasing C-CAM contents in the reconstituted liposomes a marked self-aggregation of the liposomes occurred. This aggregation was blocked by Fab fragments of anti-C-CAM antibodies and by alkaline pH. After neutralization a rapid reaggregation occurred. Neither C-CAM binding to C-CAM immobilized on nitrocellulose nor C-CAM-liposome aggregation required calcium ions. Liposomes reconstituted with C-CAM-depleted membrane glycoproteins did not self-aggregate or bind to hepatocytes. Thus, it is concluded that C-CAM can bind specifically to C-CAM in a homophilic binding reaction that does not require calcium. Accordingly, C-CAM has the potential of directly mediating cell-cell adhesion via C-CAM-C-CAM binding between adjacent cells.
Tingström
A
A
Department of Medical and Physiological Chemistry, University of Uppsala, Sweden.
Blikstad
I
I
Aurivillius
M
M
Obrink
B
B
D000251:Adenosine Triphosphatases; D000818:Animals; D015703:Antigens, CD; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D003101:Collodion; D066298:In Vitro Techniques; D008081:Liposomes; D008099:Liver / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains
D015703:Antigens, CD; C069847:CD66 antigens; D015815:Cell Adhesion Molecules; D008081:Liposomes; D003101:Collodion; D000251:Adenosine Triphosphatases