The MUC4 gene, which encodes a human epithelial mucin, is expressed in various epithelial tissues, just as well in adult as in poorly differentiated cells in the embryo and fetus. Its N-terminus and central sequences have previously been reported as comprising a 27-residue peptide signal, followed by a large domain varying in length from 3285 to 7285 amino acid residues. The present study establishes the whole coding sequence of MUC4 in which the C-terminus is 1156 amino acid residues long and shares a high degree of similarity with the rat sialomucin complex (SMC). SMC is a heterodimeric glycoprotein complex composed of mucin (ascites sialoglycoprotein 1, ASGP-1) and transmembrane (ASGP-2) subunits. The same organization is found in MUC4, where the presence of a GlyAspProHis proteolytic site may cleave the large precursor into two subunits, MUC4α and MUC4β. Like ASGP-2, which binds the receptor tyrosine kinase p185neu, MUC4β possesses two epidermal growth factor-like domains, a transmembrane sequence and a potential phosphorylated site. MUC4, the human homologue of rat SMC, may be a heterodimeric bifunctional cell-surface glycoprotein of 2.12 µm. These results confer a new biological role for MUC4 as a ligand for ErbB2 in cell signalling.
Complete sequence of the human mucin MUC4: a putative cell membrane-associated mucin
Nicolas MONIAUX, Séverine NOLLET, Nicole PORCHET, Pierre DEGAND, Anne LAINE, Jean-Pierre AUBERT; Complete sequence of the human mucin MUC4: a putative cell membrane-associated mucin. Biochem J 1 March 1999; 338 (2): 325–333. doi: https://doi.org/10.1042/bj3380325
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