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 alpha3beta1 is particularly interesting because of its role in migration and invasion of several types of metastatic tumours. In this study, alpha3beta1 from human bladder T24
carcinoma cells was purified and treated with
peptide N-glycosidase F. Then the N-
glycans of the alpha3 and beta1 subunits were characterized using matrix-assisted
laser desorption ionization mass spectrometry (MALDI MS). In
alpha3beta1 integrin the presence of high-
mannose, hybrid and predominantly complex type N-
oligosaccharides was shown. Unlike to normal epithelium cells, in both subunits of
alpha3beta1 integrin from
cancer cells, the sialylated tetraantennary complex type
glycan Hex7HexNAc6FucSia4 was present. In a direct
ligand binding assay, desialylated
alpha3beta1 integrin exhibited significantly higher
fibronectin-binding capability than untreated
integrin, providing evidence that
sialic acids play a direct role in
ligand-receptor interaction. Moreover,
alpha3beta1 integrin was shown to take part in T24 cell migration on
fibronectin: anti-alpha3
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 beta1,6 branched complex type
glycans in this process. Our data show that
alpha3beta1 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.