Characterization of thyrotropin receptor antibody-induced signaling cascades.
The TSH receptor (TSHR) is constitutively active and is further enhanced by TSH ligand binding or by stimulating TSHR antibodies (TSHR-Abs) as seen in Graves' disease. TSH is known to activate the thyroid epithelial cell via both Galphas-cAMP/protein kinase A/ERK and Galphaq-Akt/protein kinase C coupled signaling networks. The recent development of monoclonal antibodies to the TSHR has enabled us to investigate the hypothesis that different TSHR-Abs may have unique signaling imprints that differ from TSH ligand itself. We have, therefore, performed sequential studies, using rat thyrocytes (FRTL-5, passages 5-20) as targets, to examine the signaling pathways activated by a series of monoclonal TSHR-Abs in comparison with TSH itself. Activation of key signaling molecules was estimated by specific immunoblots and/or enzyme immunoassays. Continuing constitutive TSHR activity in thyroid cells, deprived of TSH and serum for 48 h, was demonstrated by pathway-specific chemical inhibition. Under our experimental conditions, TSH ligand and TSHR-stimulating antibodies activated both Galphas and Galphaq effectors. Importantly, some TSHR-blocking and TSHR-neutral antibodies were also able to generate signals, influencing primarily the Galphaq effectors and induced cell proliferation. Most strikingly, antibodies that used the Galphaq cascades used c-Raf-ERK-p90RSK as a unique signaling cascade not activated by TSH. Our study demonstrated that individual TSHR-Abs had unique molecular signatures which resulted in sequential preferences. Because downstream thyroid cell signaling by the TSHR is both ligand dependent and independent, this may explain why TSHR-Abs are able to have variable influences on thyroid cell biology.
Morshed
Syed A
SA
Thyroid Research Unit, Mount Sinai School of Medicine, James J. Peters Veterans Affairs Medical Center, New York, New York 10468, USA. syed.morshed@mssm.edu
Latif
Rauf
R
Davies
Terry F
TF
D000818:Animals; D000906:Antibodies / Q000502:physiology*; D016466:CHO Cells; D002455:Cell Division; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000502:physiology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D007145:Immunoglobulin kappa-Chains / Q000276:immunology; D007146:Immunoglobulin lambda-Chains / Q000276:immunology; D051379:Mice; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011989:Receptors, Thyrotropin / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology / Q000502:physiology*; D013972:Thyrotropin / Q000502:physiology
D000906:Antibodies; D007074:Immunoglobulin G; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains; D011989:Receptors, Thyrotropin; D013972:Thyrotropin; D000242:Cyclic AMP; D011493:Protein Kinase C