Sialylation of intracellular proteins of thyroid lesions.

Enhanced sialylation represents one of the most frequently occurring alterations of the sugar chain structure in various cancers. However, up to now, sialylation of intracellular proteins of thyroid carcinomas has never been investigated. The aim of this study was comparative analysis of cytoplasmic and nuclear sialoglycoproteins isolated from thyroid benign and malignant tumors as well as non-neoplastic lesions. The sialylation level and types of sialic acid linkages were analysed by lectin blotting and enzyme linked lectino-solid-phase assay (ELLSA) using Sambucus nigra (SNA) and Maakia amurensis (MAA) agglutinins. The presence of alpha2,6 and alpha2,3 linked sialic acid residues was detected in all types of thyroid lesion specimens but there were some differences in the banding and intensity patterns. Analysis of SNA and MAA binding by ELLSA method showed that in the majority of cancer samples the level of sialic acid residues was lower than in non-neoplastic lesions and adenomas. Our present results suggest that decrease in sialylation rather than increase is a characteristic feature of malignant transformation in the thyroid.