An analysis of glycoproteins synthesized by human breast.

Previous studies of glycoprotein structure and synthesis in breast cancer have used cell lines or animal models with limited analysis of primary tissues. Previous histochemical approaches have shown tumour associated alterations, although specific information relating to glycoprotein structure and size was not available. This study analyzed the glycoproteins secreted and/or shed from non-malignant and malignant breast tissue and established human breast cancer cell lines. Major changes associated with malignancy were identified with glycoprotein size and fucosylation. A group of high molecular weight glycoproteins was analyzed further using immunological and biochemical techniques, and shown to be of similar protein core structure. The expression of a fucosylated glycoprotein of 230kD was of particular note since it was detected in 70% of carcinomas, six breast cancer cell lines, but no benign tissues. It was also one of a small number of glycoproteins that appeared susceptible to hormone modulation. Studies with the glycosylation inhibitor tunicamycin suggested that these glycoproteins contain predominantly asparagine linked oligosaccharide chains. A polyclonal antiserum (P5252) was raised to one of the glycoproteins of this group and used to screen a number of normal and malignant human tissues. Competition studies and immunoblotting showed that the antiserum recognized antigens not detected with other antibodies directed against the milk fat globule membrane, breast tumour antigens and fibronectin. Attempts to purify the glycoprotein from primary tumours was unsuccessful which neccessitated the use of breast cancer cell lines. Analysis of plasma membranes, to determine the probable location of the glycoproteins, highlighted the difficulties of working with primary tumour tissue having a high stromal content. Preliminary analysis of membrane preparations from cell lines was also done. This work has shown many differences in the glycoproteins released from benign and malignant human breast, in particular a tumour specific fucosylated glycoprotein of 230kD which is worthy of further study.