The Control of Human Thyroid Cell Function, Proliferation and Differentiation

The study of thyroid regulation at the cellular level is the main interest of our laboratory since many years. The complex picture emerging from these studies leads to conclusions of general relevance. The regulation of the thyroid cell was once a classical example of the concept one hormone — one cell type — one intracellular secondary messenger with its pleiotypic effects. It should now rather be considered as a network of crosslinked regulatory steps where the extracellular and intracellular signal-molecules act on their receptors as bits of information in an electronic circuit, i.e., express on/off regulations with no definite general physiological meaning per se. Such networks differ from one cell type to another and for a given cell type from one species to another. In the case of the thyroid, many apparent discrepancies in the literature are explained if this is taken into account. In this presentation, we wish to draw mainly on the results of our group to illustrate this point with regard to the regulation of function, proliferation and differentiation of the thyroid cell.