Objective: A new family of guanosine triphosphatase-activating proteins known as regulators of G protein signaling (RGS) has been found to regulate the desensitization of several G protein-coupled ligand-induced processes. The expression of nine RGS mRNAs was found in human thyroid tissue (RGS 2, 3, 5, 6, 9, 10, 12, 14 and 16). At present, little is known as to whether any of the RGS proteins play a role in TSH signaling.
Design and methods: To explore the involvement of RGS proteins in the regulation of TSH receptor (TSHR) signal transduction, mRNA expression levels of the RGS proteins were analyzed after TSH stimulation of human thyroid primary cultures by real-time RT-PCR. Furthermore, the effects of RGS 2 expression on TSHR signaling (cAMP-, inositol-3-phosphate accumulation, TSHR cell surface expression) were studied in COS-7 cells.
Results: Only RGS 2 mRNA was found to be regulated by TSH in thyroid primary cultures. Co-expression of RGS 2 and TSHR in COS-7 cells reduced the TSHR signaling via inositol-3-phosphate but not via cAMP after stimulation with TSH.
Conclusion: TSH-dependent RGS 2 mRNA expression and the suppression of TSH-G(q)alpha signaling by the overexpression of RGS 2 imply that RGS 2 is involved in TSHR-induced G(q) signal transduction.