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[Recent advance in the thyroid testing with special reference to the gene analysis]
1Department of Clinical Pathology/Laboratory Medicine, Dokkyo University School of Medicine, Tochigi.
Thyroglobulin (Tg) is a large (660 kd) homodimeric glycoprotein molecule, encoded by a gene on chromosome 8, that is secreted uniquely by thyroid follicular cells. The steps of mature dimeric Tg synthesis include folding and assembly of nascent Tg with glycosylation, in the endoplasmic reticulum (ER), and dimerization and carbohydrate modification in the Golgi apparatus, followed by incorporation into exocytotic vesicles for export into the lumen of thyroid follicles, after which thyroid peroxidase catalyses iodination of tyrosyl residues and coupling of some of them within the Tg polypeptides to form thyroid hormones (thyroxine and triiodothyronine). Here, we reviewed recent progress in the study of Tg synthesis mechanisms, especially of the function of some molecular chaperones which possibly participate in the Tg synthesis. Our recent findings indicated that Tg mutations C1263R and C1995S caused a defect in intracellular transport of Tg. The thyroid disease caused by Tg gene mutations was considered as a model of the defect in the intracellular transport of de novo synthesized protein (the ER storage disease [ERSD]). ERSDs seen in organs other than the thyroid gland are also briefly reviewed. Gene abnormalities in the other proteins in the thyroid gland, such as thyroid peroxidase, Na/I symporter, TSH receptor, thyroid transcription factor (TTF) 1, TTF 2, and PAX 8, are also discussed.
Thyroglobulin (Tg) is a large (660 kd) homodimeric glycoprotein molecule, encoded by a gene on chromosome 8, that is secreted uniquely by thyroid follicular cells. The steps of mature dimeric Tg synthesis include folding and assembly of nascent Tg with glycosylation, in the endoplasmic reticulum (ER), and dimerization and carbohydrate modification in the Golgi apparatus, followed by incorporation into exocytotic vesicles for export into the lumen of thyroid follicles, after which thyroid peroxidase catalyses iodination of tyrosyl residues and coupling of some of them within the Tg polypeptides to form thyroid hormones (thyroxine and triiodothyronine). Here, we reviewed recent progress in the study of Tg synthesis mechanisms, especially of the function of some molecular chaperones which possibly participate in the Tg synthesis. Our recent findings indicated that Tg mutations C1263R and C1995S caused a defect in intracellular transport of Tg. The thyroid disease caused by Tg gene mutations was considered as a model of the defect in the intracellular transport of de novo synthesized protein (the ER storage disease [ERSD]). ERSDs seen in organs other than the thyroid gland are also briefly reviewed. Gene abnormalities in the other proteins in the thyroid gland, such as thyroid peroxidase, Na/I symporter, TSH receptor, thyroid transcription factor (TTF) 1, TTF 2, and PAX 8, are also discussed.