Construction and characterization of a chimeric receptor containing the cytoplasmic domain of MUC1 mucin

MUC1 mucin is a transmembrane glycoprotein that is highly expressed in various cancer cell lines and is also present in most: of the glandular epithelial cells including the airway. Although the presence of numerous phosphorylation sites in its cytoplasmic domain suggests its potential role as a receptor, the unavailability of a ligand for MUC1 mucin has limited our understanding of its function. In this paper, we tried to circumvent this problem by constructing a chimeric receptor containing the cytoplasmic domain of MUC1 mucin, which can be phosphorylated on activation. To this end, we constructed a chimeric plasmid vector (pCD8/MUC1) by replacing the extracellular and transmembrane domains of human MUC1 mucin with those of human CD8. Transient transfection of the vector into COS-7 cells resulted in expression of the chimeric receptor on the surface of the COS-7 cells as judged by immunologic assays with various antibodies as well as by fluorescence-activated cell-sorting analysis. Treatment of the transfected COS-7 cells with an anti-CD8 antibody resulted in a significant increase in phosphorylation of tyrosine moieties of the chimeric receptor. This chimeric receptor will serve as a powerful tool in elucidating the signaling mechanism as well as the functional role of MUC1 mucin in the airway.