Abstract

Thyroid function is tightly regulated by TSH. Although individual follicles are exposed to the same blood supply of TSH and express relatively homogenous levels of the TSH receptor, the function of individual follicles is variable. It was shown that thyroglobulin (Tg), stored in the follicular lumen, is a potent negative feedback regulator of follicular function. Thus, physiological concentrations of Tg significantly suppress thyroid-specific gene expression and antagonize the TSH-mediated stimulation that induces expression of thyroid-specific genes. Tg coordinately regulates both basal and apical iodide transporters in thyroid follicular cells. Recently, it was also reported that Tg could induce thyroid cell growth in the absence of TSH. These results indicate that Tg is an essential autocrine regulator of physiological thyroid follicular function that counteracts the effects of TSH.