Characterization of the oligosaccharide component of α3β1 integrin from human bladder carcinoma cell line T24 and its role in adhesion and migration

Malignant transformation is highly associated with altered expression of cell surface N-linked oligosaccharides. These changes concern integrins, a family of cell surface glycoproteins involved in the attachment and migration of cells on various extracellular matrix proteins. The integrin α3β1 is particularly interesting because of its role in migration and invasion of several types of metastatic tumours. In this study, α3β1 from human bladder T24 carcinoma cells was purified and treated with peptide N-glycosidase F. Then the N-glycans of the α3 and β1 subunits were characterized using matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). In α3β1 integrin the presence of high-mannose, hybrid and predominantly complex type N-oligosaccharides was shown. Unlike to normal epithelium cells, in both subunits of α3β1 integrin from cancer cells, the sialylated tetraantennary complex type glycan Hex7HexNAc6FucSia4 was present. In a direct ligand binding assay, desialylated α3β1 integrin exhibited significantly higher fibronectin-binding capability than untreated integrin, providing evidence that sialic acids play a direct role in ligand-receptor interaction. Moreover, α3β1 integrin was shown to take part in T24 cell migration on fibronectin: anti-α3 antibodies induced ca 30% inhibition of wound closure. Treatment of T24 cells with swainsonine reduced the rate of bladder carcinoma cell migration by 16%, indicating the role of β1,6 branched complex type glycans in this process. Our data show that α3β1 integrin function may be altered by glycosylation, that both subunits contribute to these changes, and that glycosylation may be considered a newly found mechanism in the regulation of integrin function.