Epitope mapping of anti-MUC1 mucin protein core monoclonal antibodies

A panel of 56 murine monoclonal antibodies against the MUC1 mucin was analysed for reactivity against purified MUC1 mucin and synthetic MUC1 mucin protein core-related peptides. In an ELISA assay, with purified normal urinary mucin as the target antigen, 48/56 (86%) of antibodies showed positive reactivity. A smaller proportion of antibodies, 31/56 (55%), reacted with a bovine serum albumin conjugate containing the synthetic peptide, APDTRPAPG. This peptide represents the hydrophilic region of the tandem repeat sequence of the MUC1 mucin core. These 31 anti-mucin core antibodies were then evaluated for reactivity with a set of overlapping heptamers with sequences based upon that of the 20-amino acid tandem repeat of the MUC1 protein core. For this purpose, the 'Pepscan' procedure was employed to detect antibody binding to peptides tethered at their carboxy termini to the polypropylene pins. Synthetic peptides binding to these antibodies were identified for 29 of the samples provided and epitopes or 'minimum binding units' were deduced for these. Most antibodies bound to epitopes of 4 amino acid residues with the sequence RPAP occurring most frequently. The results confirm that the short hydrophilic region PDTRPAP in the MUC1 mucin core is immunodominant in the induction of antibodies to the MUC1 mucin since half of the antibodies submitted reacted with this peptide.