Over-expression of β-1,4-galactosyltransferase I, II, and V in human astrocytoma

Purpose: β-1,4-Galactosyltransferase (β-1,4-GalT) I, II, and V are the enzymes responsible for the biosynthesis of N-acetyllactosamine on N-glycans by transferring UDP-galactose to the terminal N-acetylglucosamine (N-GlcNAc) residues with the formation of a β-1,4-linkage. Neoplasms undergo various changes in the carbohydrate of their glycoconjugates, indicating the possible changes in glycosyltransferases themselves. Method: Therefore, we compared the expression of β-1,4-GalTs between astrocytoma and normal brain tissues. Results: Our reverse-transcription polymerase chain reaction (RT-PCR) results showed that β-1,4-GalT I transcript was absent in normal adult brain but detectable in grade II, III, and IV astrocytomas; the level of β-1,4-GalT II transcript was increased in grade II, III, and IV astrocytomas while only a trace amount was found in normal brain; β-1,4-GalT V transcript existed in normal brain and increased in the process of astrocytoma progress, with the highest level in grade IV astrocytoma. By Ricinus communis agglutinin-1 (RCA-1) lectin blot assay, we also found the more extensive galactosylated bands in astrocytomas compared with normal brain. A major 61kD protein was galactosylated in astrocytoma but not in normal brain tissues. Conclusion: These results indicate that the increase of galactosylation in astrocytomas may be caused by the alterations of gene expression of β-1,4-GalT I, II, and V and that the malignant degree of astrocytoma is correlated with the expression of β-1,4-GalT V.