Identification, purification and analysis of a 55 kDa lectin binding glycoprotein present in breast cancer tissue.

The Helix pomatia agglutinin (HPA)-binding glycoproteins from primary breast cancers and their metastases were compared with appropriate normal control tissues on Western blots. From these studies a single glycoprotein of 55 kDa was found to bind HPA in tumours but not in normal control tissues. The glycoprotein was identified by protein sequencing as being homologous to human immunoglobulin heavy chain variable region. Subsequent immunostaining showed it to be immunoglobulin subclass A. IgA1 was purified from both tumour and normal tissue by affinity chromatography. It was demonstrated that IgA1 from tumour tissue bound HPA whereas IgA1 from normal tissue did not. The oligosaccharides were cleaved from the protein backbone and the glycans from the HPA-binding glycoform of IgA1 were compared with those from normal human IgA1. IgA1 from tumour tissue appears to be associated with an HPA-binding glycan which is not present on the normal tissue-derived IgA1.