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

Abstract

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. Int. J. Cancer 82:256–267, 1999. © 1999 Wiley‐Liss, Inc.

Evaluation of a Panel of Molecular Markers for the Diagnosis of Malignant Serous Effusions

“…Sensitivity, specificity, PPV, and NPV of cytology and of the molecular markers in the whole population (composed of 71malignant and 43 benign effusions) of effusions tumors by Western blot analysis (15,26) and in ovarian cancer tissue by RT-PCR (27). Moreover, MUC1/Y has been detected by flow cytometry on the surface of ovary and breast malignant cells in effusions (19). We showed here that MUC1/Y and MUC1/Z were mostly expressed in malignant effusions of epithelial and nonepithelial origin and poorly expressed in benign effusions.…”

MUC1/X Protein Immunization Enhances cDNA Immunization in Generating Anti-MUC1 α/β Junction Antibodies that Target Malignant Cells

“…Although alternative splicing can generate a variety of MUC1 isoforms (7)(8)(9)(10)(11)(12)(13), the most intensively studied MUC1 protein is a type I transmembrane protein (MUC1/TM) composed of a heavily glycosylated extracellular domain containing a tandem repeat array, a transmembrane domain, and a cytoplasmic domain (9,14,15). MUC1/TM is proteolytically cleaved soon after its synthesis, generating two subunits, a and h, which specifically recognize and bind each other in a strong noncovalent interaction ( Fig.…”

Genetic regulation of MUC1 alternative splicing in human tissues

“…MUC1/Z is the longest transcript, followed by MUC1/Y, which is 54 bases shorter, followed by MUC1/X, which is a further 19 bases shorter, using the nomenclature adopted by Obermair et al (2002). The three transcripts and an additional form called MUC1/Y alt, some of which are likely to be functional (Levitin et al, 2005), have been detected in breast tumours (Baruch et al, 1997Hartman et al, 1999;Obermair et al, 2001), cervical tumours (Obermair et al, 2001) and ovarian tumours (Obermair et al, 2002).…”