Altered terminal glycosylation of thyroglobulin in papillary thyroid carcinoma

Samples of thyroglobulin (Tg) were isolated from specimens of differentiated thyroid carcinoma of the papillary type and from normal adjacent glandular tissue, and the content of sialic acid was estimated. Also the in vitro incorporation of 14C-sialic acid, in the form of both CMP (cytidine 5'-monophospho-)--activated and non-activated N-acetyl-neuraminic acid, into Tg of malignant and morphologically normal thyroid. The sialic acid content of Tg preparations from papillary thyroid carcinomas varied considerably (0.27-0.92 mg/100 mg Tg). In six cancerous Tg samples the content of sialic acid was markedly lower than that in Tg from the corresponding apparently normal thyroid tissue (0.71:1.11 mg per 100 mg Tg). In addition, in comparison with the control, the incorporation of non-activated 14C-sialic acid into Tg of malignant thyroid tissue was considerably lower (-41%). However, the incorporation of CMP-activated 14C-sialic acid into cancerous Tg was greater than into Tg of morphologically unchanged tissue of the same gland (+29%). The reduced content and incorporation rate of sialic acid into Tg of differentiated thyroid carcinoma is probably the consequence of disturbances in terminal glycosylation of the Tg molecule in malignantly transformed thyroid tissue. The enhanced incorporation of CMP-sialic acid into cancerous Tg suggests that Tg sialylation in carcinoma is probably altered in the sialic acid activation phase.