Engineering glycan-binding proteins for the detection, analysis and treatment of cancer cells

Abstract

Aberrant glycosylation in cancer cells can often lead to an increase in the exposure of unusual glycan structures. The presence of these structures can be exploited by engineering glycan-binding proteins as novel tools for the characterisation of glycoproteins bearing cancer-associated glycan structures. The carbohydraterecognition domain (CRD) of a rat serum mannose-binding protein (MBP) has been modified to mimic the glycan-specificity of a galactose-binding C-type lectin. Galactosebinding MBP (GalMBP) binds selectively to cancer-associated glycan structures on an array of glycans, including Lewis-type structures and T antigen. GalMBP binding to breast cancer cell lines has been demonstrated and GalMBP ligands on these cell lines have been purified on affinity columns of immobilised GalMBP. Analysis and purification of GalMBP ligands from MCF7 cell membranes led to the identification of a restricted population of high molecular weight glycoproteins. Proteomic and glycomic analysis of these glycoproteins by mass spectrometry showed that they are forms of CD98hc that bear glycans displaying heavily fucosylated termini, including Lewisx and Lewisy structures. Glycoproteomic analysis of a panel of commonly studied breast cancer cell lines reveals wide variations in the levels of Lewisx and the T antigen as well as the proteins that they are carried on. Proteins identified in multiple cell lines by GalMBP, including the mucin MUC-1 bearing T antigen and CD98hc, may represent common cancer-cell surface targets for GalMBP. The use of GalMBP as a proteomic tool for characterisation of glycoproteins bearing Lewisx has also been demonstrated on a panel of Hodgkin’s Reed-Sternberg cell lines. Identification of common protein carriers of Lewisx among different cell lines including CD98hc and ICAM-1 provides information about the likely role of these structures in the pathology of Hodgkin's Lymphomas and supports the previous finding that CD98hc is a novel protein carrier of Lewisx structures.