Two different cell adhesion molecules--cell-CAM 105 and a calcium-dependent protein--occur on the surface of rat...

We have recently identified a 105000 D plasma membrane glycoprotein, denoted cell-CAM 105 (CAM, cell adhesion molecule), that is involved in intercellular adhesion of reaggregating rat hepatocytes (Ocklind & Obrink, J biol chem 257 (1982) 6788 [11]). In this communication we identify another cell surface protein that is also involved in hepatocyte cell-cell adhesion. This protein has an apparent molecular weight (MW) of 70000 and can be released from the surface membrane by chelation of calcium with EGTA. Results are presented indicating that it is identical with a previously discovered protein, CDP-1 (CDP, calcium-dependent protein) (Obrink, Lindström & Svennung, FEBS lett 70 (1976) 28 [28]). Antisera produced against either cell-CAM 105 or CDP-1 inhibit hepatocyte aggregation, but not attachment to collagen. Cell-CAM 105 and CDP-1 are present on the cell surface as separate components, as judged by the fact that both EGTA treatment and trypsin treatment of hepatocytes selectively make the cells insensitive to blocking of aggregation by antibodies against CDP-1 but not by antibodies against cell-CAM 105. However, although much less efficiently, the antibodies against CDP-1 can recognize a 105000 D protein which is also bound by the antibodies against cell-CAM 105, and under certain conditions the antibodies against cell-CAM 105 seem to recognize a 70000 D protein. CDP-1 may thus be derived from cell-CAM 105, or the two proteins might have a common precursor.