Binding of tumor antigen mucin (MUC1) derived peptides to the heat shock protein DnaK

The human epithelial mucin encoded by the gene MUC1 is a tumor-associated a ntigen expressed on breast, pancreatic, colon and ovarian cancer cells reco gnized by cytotoxic T-cells and antibodies. Underglycosylated as well as gl ycosylated mucin-peptide epitopes are promising targets for vaccination aga inst cancel: Heat shock proteins of 70 kDa (HSP70), also highly expressed i n tumor cells, can function as chaperones for peptides and proteins and are involved in antigen processing. The involvement of HSP70 molecules in muci n antigen binding, processing and presentation has not yet been examined. H ere we present first results concerning the relative binding affinities of various mucin- derived peptides to the bacterial 70 kDa heat shock protein DnaK. Interestingly, longer mucin peptides reveal a higher. affinity to Dna K than short peptides. The non-glycosylated mucin-derived peptides of 5-8 a mino acids length were able to compete with a high affinity (unrelated) ref erence peptide at millimolar concentrations. Glycosylation of the investiga ted short peptides lowers their binding affinity to DnaK, depending on the position of the carbohydrate. The binding affinity is not influenced by fre e charges at unprotected ends. The peptide (MUC1)5 consisting of five repea ting units has an affinity enhanced by a factor of three as compared to the peptide with only one repenting unit. Mucin peptide-HSP-complexes could be the basis of developing new kinds of tumor vaccines.