Thyroglobulin

Source: Wikipedia, the free encyclopedia.
TG
Identifiers
Gene ontology
Molecular function
Cellular component
Biological process
Sources:Amigo / QuickGO
Ensembl
UniProt
RefSeq (mRNA)

NM_003235

NM_009375

RefSeq (protein)

NP_003226

NP_033401

Location (UCSC)Chr 8: 132.87 – 133.13 MbChr 15: 66.54 – 66.72 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse

Thyroglobulin (Tg) is a 660

follicular cells of the thyroid and used entirely within the thyroid gland. Tg is secreted and accumulated at hundreds of grams per litre in the extracellular compartment of the thyroid follicles, accounting for approximately half of the protein content of the thyroid gland.[5] Human TG (hTG) is a homodimer of subunits each containing 2768 amino acids as synthesized (a short signal peptide of 19 amino acids may be removed from the N-terminus in the mature protein).[6]

Thyroglobulin is in all vertebrates the main precursor to

thyroperoxidase in the follicular colloid. It takes two iodinated tyrosines to make a thyroid hormone molecule; therefore, each Tg molecule forms approximately 5 thyroid hormone molecules.[5]

Function

rough endoplasmic reticulum
until proteolytic release of the thyroid hormones.

Thyroglobulin (Tg) acts as a substrate for the synthesis of the

thyroxine (T4) and triiodothyronine (T3), as well as the storage of the inactive forms of thyroid hormone and iodine within the follicular lumen of a thyroid follicle.[7]

Newly synthesized thyroid hormones (T3 and T4) are attached to thyroglobulin and comprise the colloid within the follicle. When stimulated by

thyroid stimulating hormone (TSH), the colloid is endocytosed from the follicular lumen into the surrounding thyroid follicular epithelial cells. The colloid is subsequently cleaved by proteases to release thyroglobulin from its T3 and T4 attachments.[8]

The active forms of thyroid hormone: T3 and T4, are then released into circulation where they are either unbound or attached to plasma proteins, and thyroglobulin is recycled back into the follicular lumen where it can continue to serve as a substrate for thyroid hormone synthesis.[8]

Clinical significance

Half-life and clinical elevation

Metabolism of thyroglobulin occurs in the liver via thyroid gland recycling of the protein. Circulating thyroglobulin has a half-life of 65 hours. Following thyroidectomy, it may take many weeks before thyroglobulin levels become undetectable. Thyroglobulin levels may be tested regularly for a few weeks or months following the removal of the thyroid.[9] After thyroglobulin levels become undetectable (following thyroidectomy), levels can be serially monitored in follow-up of patients with papillary or follicular thyroid carcinoma.[clarification needed]

A subsequent elevation of the thyroglobulin level is an indication of recurrence of papillary or follicular thyroid carcinoma. In other words, a rise in thyroglobulin levels in the blood may be a sign that thyroid cancer cells are growing and/or the cancer is spreading.[9] Hence, thyroglobulin levels in the blood are mainly used as a tumor marker[10][9] for certain kinds of thyroid cancer (particularly papillary or follicular thyroid cancer). Thyroglobulin is not produced by medullary or anaplastic thyroid carcinoma.

Thyroglobulin levels are tested via a simple blood test. Tests are often ordered after thyroid cancer treatment.[9]

Thyroglobulin antibodies

In the clinical laboratory, thyroglobulin testing can be complicated by the presence of anti-thyroglobulin antibodies (ATAs, alternatively referred to as TgAb). Anti-thyroglobulin antibodies are present in 1 in 10 normal individuals, and a greater percentage of patients with thyroid carcinoma. The presence of these antibodies can result in falsely low (or rarely falsely high) levels of reported thyroglobulin, a problem that can be somewhat circumvented by concomitant testing for the presence of ATAs. The ideal strategy for a clinician's interpretation and management of patient care in the event of confounding detection of ATAs is testing to follow serial quantitative measurements (rather than a single laboratory measurement).

ATAs are often found in patients with

euthyroid individuals. ATAs are also found in patients with Hashimoto's encephalopathy, a neuroendocrine disorder related to—but not caused by—Hashimoto's thyroiditis.[11]

Interactions

Thyroglobulin has been shown to

References

  1. ^ a b c GRCh38: Ensembl release 89: ENSG00000042832Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000053469Ensembl, May 2017
  3. ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. ^ .
  6. ^ "Protein" thyroglobulin precursor [Homo sapiens]". National Center for Biotechnology Information, U.S. National Library of Medicine.
  7. ^ "TG thyroglobulin [Homo sapiens (human)] – Gene – NCBI". National Center for Biotechnology Information (NCBI). Retrieved 2019-09-16.
  8. ^
    PMID 25905405
    . Retrieved 2019-09-17.
  9. ^ a b c d "Thyroglobulin: MedlinePlus Lab Test Information". medlineplus.gov. Retrieved 2019-05-06.
  10. ^ "ACS :: Tumor Markers". American Cancer Society. Archived from the original on 2010-05-13. Retrieved 2009-03-28.
  11. S2CID 21610036
    .
  12. .
  13. .

Further reading

External links