Expression of OBCAM-related cDNA clones in Cos 1 cells: evidence for a phosphatidylinositol linkage to the cell membrane.

Previously, our laboratory purified and isolated the cDNA for OBCAM (opioid binding cell adhesion molecule) from bovine brain, as well as highly homologous rat brain cDNA clones, SG13 and DUZ-1. Structural similarities with members of the immunoglobulin superfamily suggest a possible role for OBCAM in cell adhesion and recognition, while studies in our own laboratory suggest that OBCAM is important in the regulation of opioid binding and signal transduction. However, OBCAM lacks a putative transmembrane domain, and its possible mode of linkage to the cellular membrane has not been studied. Upon transfection of Cos 1 cells with SG13 and DUZ-1 cDNAs, the OBCAM-homologous proteins were expressed on the surface of the Cos 1 cells. These proteins were released from the membrane of the Cos 1 cells upon digestion with phosphatidylinositol-specific phospholipase C (PI-PLC), demonstrating that they are linked to the membrane via a phosphatidylinositol (PI) linkage. These results are consistent with a role for OBCAM in cell recognition and adhesion, as well as in cellular signaling.