A mouse carcinoembryonic antigen gene family member is a calcium-dependent cell adhesion molecule

Carcinoembryonic antigen (CEA) is a heavily glycosylated protein used clinically as a tumor marker to detect recurrences of many types of tumors. This glycoprotein belongs to the immunoglobulin superfamily and is the prototype of the large CEA family of proteins. In a concerted effort to determine the function(s) of this family, we have been investigating a similar family of proteins in the mouse. In this paper, we report the characterization of a new mouse family member named mmCGM2; this gene product is highly homologous to the human biliary glycoprotein of the CEA gene family and to a rat hepatocyte ecto-ATPase. In vitro transcription, translation, and glycosylation experiments have revealed that the mmCGM2 cDNA encodes a glycoprotein of 42 kDA with a putative extracellular N-terminal domain and a C2-set type immunoglobulin domain. We have used this cDNA as a probe to detect many different transcripts (1.5-4.6 kilobases) in mouse adult tissues, some of which are specific to particular tissues, while others are expressed ubiquitously. After transfection of a plasmid bearing the mmCGM2 cDNA into mouse fibroblasts known to lack CEA-related gene expression, transfectant cell clones were chosen and used to investigate the adhesion properties conferred onto the cells. Cells expressing the mmCGM2 cDNA in a sense orientation aggregated in a calcium- and temperature-dependent fashion. Together with human biliary glycoprotein, the mmCGM2 gene product is the first member of the immunoglobulin superfamily to exhibit calcium-dependent adhesion. The constant tissue reorganization necessary to the differentiation of precise structures in tissues which express these gene family members (colon, liver, and uterus) implies the necessity of a variety of specific cell-cell contacts which could utilize the cell adhesion properties that we have demonstrated.