Ras homolog enriched in striatum inhibits the functional activity of wild type thyrotropin, follicle-stimulating hormone, luteinizing hormone receptors and activating thyrotropin receptor mutations by altering their expression in COS-7 cells.

Ras homolog enriched in striatum (Rhes) is a member of the Ras family of small GTPases detected in the thyroid. Rhes inhibits signal transduction from Galphas protein. In this study we investigated whether Rhes can interfere with stimulation of cAMP/protein kinase A pathway of TSH, FSH and LH receptors (TSHr, FSHr, LHr) and of activated TSHr mutants. Receptors were transiently transfected in COS-7 cells with or without Rhes; cAMP was evaluated in basal conditions and after hormone stimulation. Constitutive and bovine TSH (bTSH)-stimulated activity of wild type (wt) and mutated TSHr was inhibited after Rhes co-transfection. Rhes decreased cAMP after FSH and hCG beta-subunit (betahCG) stimulation in cells expressing the cognate receptors. In binding experiments Rhes, as another membrane protein, sodium/iodide symporter (NIS), reduced membrane expression of wt TSHr (wtTSHr). In conclusion, Rhes can interfere with the functional activity of wt and mutated TSHr and with the respective hormone-stimulated cAMP production of FSHr and LHr. This interference is not specific and due to the co-expression of two membrane proteins.

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