Biliary glycoprotein, a member of the immunoglobulin supergene family, functions in vitro as a Ca2(+)-dependent intercellular adhesion molecule.

Intercellular adhesion molecules can be classified as Ca2+ dependent or Ca2+ independent. This classification has significant functional implications regarding cellular interactions. The best characterized Ca2(+)-dependent adhesion molecules, such as L-CAM or E-cadherin, belong to the family of closely related cell surface molecules called cadherins. On the other hand, those immunoglobulin supergene family members which function as adhesion molecules, such as neural cell adhesion molecule, have been found to be Ca2+ independent. In agreement with this generalization, we have recently shown that carcinoembryonic antigen (CEA) and nonspecific cross-reacting antigen (NCA), two closely related members of the CEA family, a subset of the immunoglobulin supergene family, function in vitro as Ca2(+)-independent adhesion molecules. In contrast, we show here that transfectants of a third member of the CEA family, biliary glycoprotein (BGP), also aggregate homotypically in suspension but require Ca2+ for aggregation. In addition, like the cadherins and unlike CEA or NCA or other adhesion molecules of the immunoglobulin supergene family, BGP transfectant aggregation requires physiological temperatures. Two forms of BGP, with three and two immunoglobulin C2-set domains, show Ca2(+)- and temperature-dependent adhesion, so that these properties do not reside in the third C2-set domain. The significance of this expression in the range of functional properties of the immunoglobulin supergene family and its CEA subset is discussed.