Thyroglobulin Biosynthesis in “Cold” and “Hot” Nodules in The Human Thyroid Gland

Abstract

Studies on "cold" and "hot" nodules from human thyroid gland have been carried out to investigate thyroglobulin biosynthesis and to correlate carbohydrates incorporation and thyroid hormone formation in thyroglobulin. The aim of the investigation was to ascertain the role of carbohydrates of the protein molecule in its migration to the iodinating site of the cell. Thyroid slices from two cases with "cold" and two with "hot" nodules were incubated for 30 to 120 min with [3H]leucine, [3H]carbohydrates (ManNAc, Gal, Man, GlcNAc, GalNAc) and 125I. Soluble and particulate iodoproteins, solubilized by digitonin, were identified by density gradient centrifugation and immunoprecipitation; following hydrolysis carbohydrates and iodothyronines were identified by paper chromatography and chemically determined. While the rate of leucine incorporation into TG increased with time in both "cold" and "hot" nodules, the "cold" nodule, with respect to the "hot" tissue, showed: much lower efficiency incorporating carbohydrates and iodine into TG; lower thyroid/medium ratio of radioiodine; less total soluble protein and soluble TG; more particulate protein and solubilized TG; 1/3 of the carbohydrate and iodine chemical content; only minute amounts of labeled iodothyronines in TG compared to normal levels in "hot" tissue. The formation of thyroid hormone, in enzymatically iodinated TG, and the iodinating activity of the 105,000 X g pellet, incubated with low iodine TG, were similar in both "cold" and "hot" tissues. These results demonstrate that the "cold" nodule is able to synthesize thyroglobulin but the protein is defective in its carbohydrate content. The deficient iodine transport into "cold" tissue and impaired hormonal synthesis are confirmed. The incomplete incorporation of carbohydrates into thyroglobulin in the "cold" nodule could be important for the maturation and migration of the molecule to the iodinating site of the cell

Characterization of microheterogencity of human thyroglobulin from different thyroid disorders

“…This would confirm the findings of Monaco et al (1975a), where a lack in the sialic acid incorpora¬ tion had been postulated in nodular non-toxic goitre. This would confirm the findings of Monaco et al (1975a), where a lack in the sialic acid incorpora¬ tion had been postulated in nodular non-toxic goitre.…”

The role of glycosylation on the biosynthesis, degradation, and secretion of the acth‐β‐lipotropin common precursor and its peptide products

“…Thus contrary to previous proposals [6,7], glycosylation of secretory glycoproteins is not a prerequisite for their secretion.…”

“…Beeley [S] has proposed that the addition of carbohydrates at the p-turns of proteins would result in the masking of the turn conformations, and hence, could be an important feature in protecting the molecule from proteolysis. Glycosylation of secretory proteins has also been suggested to be a prerequisite for secretion, e.g., for thyroglobulin [6,7]. We have therefore examined the role of the carbohydrate on the ACTH-/?LPH hormone precursor with respect to these two issues, using the drug, tunicamycin, an inhibitor of glycosylation.…”

In vitro study on release of thyroid hormone in solitary autonomously functioning thyroid nodules using cell culture method.

“…Some investigators employed iodine organification, thyrotropin (TSH)-induced adenylate cyclase activity, glucose oxidation and thyroglobulin biosynthesis in the thyroid tissues as biochemical parameters for the estimation of synthesis of thyroid hormone in the functioning nodules (Burk and Szabo, 1972;Larsen et al, 1973;Monaco et al, 1975). The present investigation, therefore, was attempted to make clear the secretory modes of thyroid hormone in the solitary AFTN, using the procedures of direct measurement of thyroxine (T4) and triiodothyronine (T3) released into the culture media under basal and TSH-stimulated conditions.…”