Molecular regulation of thyroid gland function.
OBJECTIVE
For de-novo thyroid hormone synthesis ex vivo, thyroid follicular cells require a serum-free medium supplying nutrients, iodide, thyroid-stimulating hormone and insulin-like growth factor I (IGF-I) (or insulin). Under these conditions, T3 and T4 are secreted but so are other factors such as growth factors, plasminogen activators, their inhibitors known as serpins, and so on. What is the function of these factors? Do thyroid cells respond to them or are these paracrine/endocrine factors? The purpose of this review is to highlight the current developments in the identification and role of the signalling pathways that regulate thyroid growth and function and the putative role of endogenous thyroid proteases in regulating this.


RESULTS
The roles of the mitogen-activated protein kinases and phosphoinositol 3 kinases and integrins in mediating growth and function in thyroid cancer cells and the roles of plasminogen activators, their receptors and the downstream signalling pathways they modulate have been developed. Discoveries of novel proteases, expressed in thyroid cancers, may be useful in diagnosis.


CONCLUSIONS
The signalling pathways regulating thyroid activity are examined and the roles of follicular cell products in maintaining thyroid homeostasis evaluated. The possibility that thyroid cell products other than T3 and T4 may circulate and have extrathyroidal effects is proposed.
Eggo
Margaret C
MC
School of Clinical and Experimental Medicine, The University of Birmingham, Birmingham, UK. m.c.eggo@bham.ac.uk
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D004917:Erythromycin / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D016023:Integrins / Q000378:metabolism; D007454:Iodides / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010960:Plasminogen Activators / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D013961:Thyroid Gland / Q000201:enzymology* / Q000254:growth & development*; D013964:Thyroid Neoplasms / Q000201:enzymology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D007328:Insulin; D016023:Integrins; D007454:Iodides; D042461:Vascular Endothelial Growth Factor A; D004917:Erythromycin; D007334:Insulin-Like Growth Factor I; C057513:erythromycin propionate-N-acetylcysteinate; D058539:Phosphatidylinositol 3-Kinase; D020928:Mitogen-Activated Protein Kinases; D010447:Peptide Hydrolases; D010960:Plasminogen Activators; D000111:Acetylcysteine