Differential Incorporation of Sulfate into the Chondroitin Chain and Complex Carbohydrate Chains of Human Thyroglobulin: Studies In Normal and Neoplastic Thyroid Tissue*

Abstract

Human thyroglobulin (TG) is one of a growing number of glycoproteins that are known to contain sulfate. Among these TG is unusual because it contains sulfate on both its asparagine-linked complex carbohydrate units and its single chondroitin 6-SO4 unit. We incubated tissue fragments prepared from normal and neoplastic thyroid tissue with [35S]sulfate to study the incorporation of sulfate into these two types of carbohydrate acceptor sites. Incubation conditions (0.1 mM sulfate for 16 h) were selected that maintained linear incorporation of [35S]sulfate and retention of more than 90% of iodinated TG in the tissue. Enzyme susceptibility was used to determine incorporation into the complex carbohydrate units (endoglycosidase-F) and the chondroitin 6-SO4 unit (chondroitin ABC lyase). In a representative experiment, 29.8% of the incorporated sulfate was found in the chondroitin 6-SO4 unit during the first hour of incubation. This increased progressively to 72.5% in the chondroitin unit during the incubation period from 8-16 h. A reciprocal decrease occurred in the proportion of sulfate incorporated into the complex carbohydrate units. TG released into the medium and retained in the tissue had the same ratio of sulfate in the two types of carbohydrate units. Neoplastic thyroid tissue incorporated more [35S]sulfate into TG than normal thyroid tissue from the same patient. Neoplastic and normal tissue differed further in the ratios of sulfate incorporated into the two types of carbohydrate units. We conclude that the incorporation of sulfate into the two types of sulfate-containing carbohydrate units of TG does not occur in a fixed ratio and that this differential incorporation of sulfate does not appear to be related to its release from the tissue.

Thyrotrophin receptors in normal and neoplastic (primary and metastatic) canine thyroid tissue

“…However, no data are available on the glycosylation of TSH receptors in thyroid neoplasms. Decreased glycosylation of thyroglobulin by differentiated thyroid neoplasms has been reported (Monaco, Grimaldi, Dominici & Robbins, 1975;Schneider & Dudlak, 1989).…”

Hormonal regulation of some steps of thyroglobulin synthesis and secretion in bicameral cell culture

“…However, the number of oligosaccharides increased under hormonal stimulation; thus, anionic charges also increased. This point is particularly interesting because pathological Tg has been shown to contain a higher level of sulfate (Schneider and Dudlak, 1989) or phosphate residues (Yamamoto et al, 1985) on the oligosaccharide units. However, the amount of sulfate residues or phosphate residues bound to the peptide chain of Tg may be also increased in defined medium under hormonal stimulation.…”

Thyrotropin regulates tyrosine sulfation of thyroglobulin

“…In human thyroid, some authors have observed an increased incorporation of [ 35 S]sulfate in the oligosaccharide units (complex and chondroitin sulfate) of human thyroglobulin derived from nodules as compared with normal tissue (22,23). Recently, it was reported that gene mutations of a putative sulfate transporter occurred in Pendred syndrome (a congenital sensorineural hearing loss combined with a goiter), suggesting that sulfate metabolism could be linked to hormonogenesis (24).…”

“…Contradictory results from studies of porcine thyroglobulin suggested that a large proportion of the sulfate residues are bound to tyrosine molecules, while the rest are linked to polymannose moieties (15,21). In thyroid pathological states, alterations of thyroglobulin sulfation have been observed: human thyroglobulin from neoplastic thyroid tissue contained more sulfate residues bound to oligosacharide units (22,23).…”