Thyrotropin (TSH)-induced receptor internalization in nonthyroidal cells transfected with a human TSH-receptor complementary deoxyribonucleic acid.
TSH-induced desensitization was studied in nonthyroidal cells expressing functionally active TSH receptors (TSHR). Chinese hamster ovary (CHO) cells and mouse NIH 3T3 cells were stably transfected with a human TSHR cDNA. Stimulation of the CHO-TSHR and NIH-TSHR cells with 10 mU/ml TSH resulted in a decreased sensitivity to a second TSH stimulation only in the NIH-TSHR cells. A decrease in TSH-induced cAMP was present within 1 h and coincided with a decreased binding of [125I]TSH. The half-maximal effect was observed after a 3- to 4-h stimulation with TSH, and exposure of cells to TSH for 20 h led to a 70-80% inhibition of cAMP formation. After withdrawal of TSH, cells regained full responsiveness to TSH after 6 h. Moreover, the desensitization effect observed in NIH-TSHR cells was not mimicked by forskolin and, therefore, was not mediated by cAMP. Stimulation of the CHO-TSHR cells with TSH did not result in a desensitization toward a second TSH stimulation, nor did it reduce the binding of [125I]TSH. This difference between the two cell lines might be explained by a higher turnover rate of receptors in the CHO cells. Indeed, incubation of cells with [125I]TSH showed a more efficient internalization of ligand in the CHO-TSHR cells compared to the NIH-TSHR cells. In summary, the homologous desensitization observed in TSHR-transfected NIH 3T3 cells appears to be the result of ligand-induced receptor down-regulation.
Heldin
N E
NE
Department of Pathology, University Hospital, Uppsala, Sweden.
Gustavsson
B
B
Hermansson
A
A
Westermark
B
B
D016475:3T3 Cells; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics*; D004705:Endocytosis; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D051379:Mice; D011989:Receptors, Thyrotropin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013539:Simian virus 40 / Q000235:genetics; D013964:Thyroid Neoplasms; D013972:Thyrotropin / Q000378:metabolism / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D011989:Receptors, Thyrotropin; D013972:Thyrotropin; D000242:Cyclic AMP