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

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Abstract
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 co‐immunoprecipitation 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 co‐localization 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. Copyright © 2009 John Wiley & Sons, Ltd.

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