Secretion of Endothelial-Leukocyte Adhesion Molecule (ELAM-1) Upon Deletion of Portions of Its Carboxyl Terminus
The carboxyl terminus of endothelial-leukocyte adhesion molecule (ELAM-1) consists of a 22-amino acid, hydrophobic domain followed by a 32-amino acid, hydrophilic domain. In an effort to identify the portions of the carboxyl terminus necessary for efficient subcellular transport and anchoring of ELAM-1 in the endothelial cell membrane, we have altered these domains by site-directed mutagenesis of the molecularly cloned sequence of ELAM-1. Expression of mature ELAM-1 in mammalian cells produced no detectable ELAM-1 in the conditioned media, as determined by pulse-chase labeling with 35S-methionine. Modifications within the carboxyl terminus of ELAM-1 resulted in expression and secretion of the variant forms. Unlike cells expressing full-length ELAM-1, none of the cells expressing secreted mutant forms bound either neutrophils or HL-60 cells (a promyelocytic precursor of neutrophils), indicating that functional ELAM-1 was not associated with the cell. We conclude that the carboxyl terminal region is required for anchoring ELAM-1 into the cell membrane.