Mucins are large o-glycosylated proteins which are present on the surfaces of epithelial cells. These mucins are aberrantly expressed in malignancy, thus serving as useful markers. Since these molecules are extremely immunogenic in rodents, many antibodies to the mucin have been previously characterized and are clinically useful. We have isolated the cDNA coding for the mammary gland or milk mucin, MUC1 (Gendler S, Lancaster C, Taylor-Papadimitriou J. et al. J.Biol.Chem., 1990). This core protein was found to be identical to the mucin produced by the pancreas, although glycosylation varies considerably in content and quantity. The same core protein is also expressed on the apical surfaces of duct cells in die lung, ovary, stomach, salivary gland and kidney - simple secretory epithelial tissues. The MUC1 core protein is an integral membrane protein consisting of distinct domains: an amino terminal region containing a hydrophobic signal sequence, the largest domain consisting of from 30 to 125 well-conserved tandem repeats of twenty amino acids, a hydrophobic membrane spanning domain and a sixty-nine amino acid cytoplasmic tail. The core protein is highly polymorphic in size due to the variable numbers of repeats with molecular weights from about 120,000 to >300,000 Da. The aberrant glycosylation of the core protein that occurs in malignancy exposes T cell epitopes, thus allowing for the possible use of the protein in immunotherapy of some carcinomas. Both syngeneic and transgenic systems have been developed to examine the immune response to PEM based immunogens. To look at function and the role in development more easily, the mouse homologue has been cloned.

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