MUC1 isoform specific monoclonal antibody 6E6/2 detects preferential expression of the novel MUC1/Y protein in breast and ovarian cancer

Mor Li Hartman, Amos Baruch, Ilan Ron, Yair Aderet, Merav Yoeli, Orit Sagi-Assif, Shuli Greenstein, Yona Stadler, Mordechai Weiss, Ella Harness, Margalit Yaakubovits, Iafa Keydar, Nechama I. Smorodinsky, Daniel H. Wreschner*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The products of the MUC1 gene are known to be highly expressed in human breast cancer cells. The best characterized MUC1 protein is a polymorphic, type 1 transmembrane molecule containing a large extracellular domain composed primarily of a variable number of 20 amino acid tandem repeats. We have recently identified a novel protein product of the MUC1 gene, the MUC1/Y protein, that is also a transmembrane protein but is devoid of the tandem repeat array and its immediate flanking sequences. To analyze its expression in tumor cells we generated monoclonal antibodies directed against the MUC1/Y extracellular domain (anti-MUC1/Yex MAbs). Epitope mapping identified the MAb, 6E6, which recognized the MUC1/Y isoform with exquisite specificity- the repeat-array-containing MUC1 isoform could not compete out this immunoreactivity. A 30mer peptide which is unique for MUC1/Y and corresponds to the 'join' region generated by the MUC1/Y specific splice, abrogated all 6E6 MAb immunoreactivity towards MUC1/Y. Immunoprecipitation of the MUC1/Y protein with 6E6 MAbs revealed that, in contrast with the proteolytic cleavage of the tandem-repeat-array-containing MUC1 isoform, MUC1/Y is not cleaved. Flow cytometry analyses using the 6E6 MAbs demonstrated that the MUC1/Y isoform is expressed on the cell surface of both MCF-7 breast cancer cells and malignant epithelial cells present in effusions obtained from breast and ovarian cancer patients. Our results unequivocally establish that the MUC1/Y protein is expressed on the surface of breast cancer cells and cells of other epithelial malignancies. The anti-MUC1/Y MAbs described here can target MUC1/Y expressing tumor cells in vivo and are likely to be important reagents both for epithelial tumor diagnosis and immunotherapy.

Original languageEnglish
Pages (from-to)256-267
Number of pages12
JournalInternational Journal of Cancer
Issue number2
StatePublished - 1999


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