Thyrotropin Causes Dose-dependent Biphasic Regulation of cAMP Production Mediated by Gsand Gi/oProteins
| Autor: | Joanna Klubo-Gwiezdzinska, Christine C Krieger, Bernice Marcus-Samuels, Susanne Neumann, Sarah S. Malik, Marvin C. Gershengorn, Elena Eliseeva, Daesong Jang |
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| Rok vydání: | 2019 |
| Předmět: |
0301 basic medicine
Pharmacology endocrine system medicine.medical_specialty endocrine system diseases G protein Chemistry HEK 293 cells Stimulation Pertussis toxin eye diseases 03 medical and health sciences Dose–response relationship 030104 developmental biology 0302 clinical medicine Endocrinology Downregulation and upregulation Internal medicine medicine Molecular Medicine Protein kinase A Receptor hormones hormone substitutes and hormone antagonists 030217 neurology & neurosurgery |
| Zdroj: | Molecular Pharmacology. 97:2-8 |
| ISSN: | 1521-0111 0026-895X |
| DOI: | 10.1124/mol.119.117382 |
| Popis: | The thyrotropin (TSH) receptor (TSHR) signals via G proteins of all four classes and β-arrestin 1. Stimulation of TSHR leads to increasing cAMP production that has been reported as a monotonic dose-response curve that plateaus at high TSH doses. In HEK 293 cells overexpressing TSHRs (HEK-TSHR cells), we found that TSHR activation exhibits an "inverted U-shaped dose-response curve" with increasing cAMP production at low doses of TSH and decreased cAMP production at high doses (>1 mU/ml). Since protein kinase A inhibition by H-89 and knockdown of β-arrestin 1 or β-arrestin 2 did not affect the decreased cAMP production at high TSH doses, we studied the roles of TSHR downregulation and of Gi/Go proteins. A high TSH dose (100 mU/ml) caused a 33% decrease in cell-surface TSHR. However, because inhibiting TSHR downregulation with combined expression of a dominant negative dynamin 1 and β-arrestin 2 knockdown had no effect, we concluded that downregulation is not involved in the biphasic cAMP response. Pertussis toxin, which inhibits activation of Gi/Go, abolished the biphasic response with no statistically significant difference in cAMP levels at 1 and 100 mU/ml TSH. Concordantly, co-knockdown of Gi/Go proteins increased cAMP levels stimulated by 100 mU/ml TSH from 55% to 73% of the peak level. These data show that biphasic regulation of cAMP production is mediated by Gs and Gi/Go at low and high TSH doses, respectively, which may represent a mechanism to prevent overstimulation in TSHR-expressing cells. SIGNIFICANCE STATEMENT: We demonstrate biphasic regulation of TSH-mediated cAMP production involving coupling of the TSH receptor (TSHR) to Gs at low TSH doses and to Gi/o at high TSH doses. We suggest that this biphasic cAMP response allows the TSHR to mediate responses at lower levels of TSH and that decreased cAMP production at high doses may represent a mechanism to prevent overstimulation of TSHR-expressing cells. This mechanism could prevent chronic stimulation of thyroid gland function. |
| Databáze: | OpenAIRE |
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