Increased expression of G-protein-coupled receptor kinases 3 and 4 in hyperfunctioning thyroid nodules.
G-protein-coupled receptor kinases (GRKs) are implicated in the pathophysiology of human diseases such as arterial hypertension, heart failure and rheumatoid arthritis. While G-protein-coupled receptor kinases 2 and 5 have been shown to be involved in the desensitization of the rat thyrotropin receptor (TSHR), their role in the pathophysiology of hyperfunctioning thyroid nodules (HTNs) is unknown. Therefore, we analyzed the expression pattern of the known GRKs in human thyroid tissue and investigated their function in the pathology of HTNs. The expression of different GRKs in human thyroid and HTNs was measured by Western blotting. The influence of GRK expression on TSHR function was analyzed by coexpression experiments in HEK 293 cells. We demonstrate that in addition to GRKs 2, 5 and 6, GRKs 3 and 4 are also expressed in the human thyroid. GRKs 2, 3, 5 and 6 are able to desensitize the TSHR in vitro. This GRK-induced desensitization is amplified by the additional over-expression of beta-arrestin 1 or 2. We did not find any mutations in the GRKs 2, 3 and 5 from 14 HTNs without TSHR mutations and Gsalpha mutations. The expression of GRKs 3 and 4 was increased in HTNs independently from the existence of TSHR mutations or Gsalpha mutations. In conclusion, the increased expression of GRK 3 in HTNs and the ability of GRK 3 to desensitize the TSHR in vitro, suggest a potential role for GRK 3 as a negative feedback regulator for the constitutively activated cAMP pathway in HTNs.
Voigt
Carsten
C
IIIrd Medical Department, University of Leipzig, Ph.-Rosenthal-Str. 27, D-04103 Leipzig, Germany.
Holzapfel
Hans-Peter
HP
Meyer
Silke
S
Paschke
Ralf
R
D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D054770:G-Protein-Coupled Receptor Kinase 3; D054771:G-Protein-Coupled Receptor Kinase 4; D006801:Humans; D006980:Hyperthyroidism / Q000378:metabolism*; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011989:Receptors, Thyrotropin / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013961:Thyroid Gland / Q000737:chemistry; D016606:Thyroid Nodule / Q000378:metabolism*
D011989:Receptors, Thyrotropin; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C517848:GRK3 protein, human; C517851:Grk3 protein, rat; D054771:G-Protein-Coupled Receptor Kinase 4; C517855:GRK4 protein, human; C517854:Grk4 protein, rat