[TSH receptors and signal transduction]

The TSH receptors constitute one of the main part of the signal transduction in thyroid cells and are the main biochemical targets in pathological changes. Recent molecular cloning of the TSH receptor and site-directed mutagenesis experiments have provided new evidence. It is well-established that TSH activates the cAMP cascade. Recent evidence however suggests that TSH can also activate the PIP2 cascade, but not anti-TSH receptor antibody. Specific alpha-subunits of the GTP binding protein modulate the stimulation of both pathways. Moreover, the thyroid diseases linked to the mutation of the GTP binding protein are seen. Although the TSH action in thyrocytes, through both pathways, are distinct, they are too complicated to classify clearly. The mechanism of the TSH stimulating pathway and the TSH function in thyrocytes are reviewed.