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.