TSH induces co-localization of TSH receptor and Na/K-ATPase in human erythrocytes

Thyroid stimulating hormone (TSH) binds to a specific TSH receptor (TSHR) which activates adenylate cyclase and increases cAMP levels in thyroidal cells. Recent studies have reported the presence of TSH receptor in several extra-thyroidal cell types, including erythrocytes. We have previously suggested that TSH is able to influence the erythrocyte Na/K-ATPase ouabain binding properties through a receptor mediated mechanism. The direct interaction of TSH receptor with the Na/K-pump and a functional role of TSHR in erythrocytes was not demonstrated. The interaction of TSH receptor with Na/K-pump and a TSHR functional role are not yet demonstrated in erythrocytes. In this study, we examined the interaction between the two receptors after TSH treatment using immunofluorescence coupled to confocal microscopy and a coimmunoprecipitation technique. The cAMP dependent signalling after TSH treatment was measured to verify TSHR functionality.We found that TSH receptor and Na/K-ATPase are localized on the membranes of both erythrocytes and erythrocyte ghosts; TSH receptor responds to TSH treatment by increasing intracellular cAMP levels from two to tenfold. In ghost membranes TSH treatment enhances up to three fold colocalization of TSHR with Na/K-ATPase and co-immunoprecipitation confirms their direct physical interaction. In conclusion our results are compatible with the existence, in erythrocytes, of a functional TSHR that interacts with Na/K-ATPase after TSH treatment, thus suggesting a novel cell signalling pathway, potentially active in local circulatory control.