EXPRESSION OF OBCAM-RELATED CDNA CLONES IN COS-1 CELLS - EVIDENCE FORA PHOSPHATIDYLINOSITOL LINKAGE TO THE CELL-MEMBRANE

Previously, our laboratory purified and isolated the cDNA for OBCAM (o pioid binding cell adhesion molecule) from bovine brain, as well as tw o 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 studie s in our own laboratory suggest that OBCAM is important in the regulat ion 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 ce lls with SG13 and DUZ-1 cDNAs, the OBCAM-homologous proteins were expr essed on the surface of the Cos 1 cells. These proteins were released from the membrane of the Cos 1 cells upon digestion with phosphatidyli nositol-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.