Regulation of the phosphatidylinositol 3-kinase, Akt/protein kinase B, FRAP/mammalian target of rapamycin, and ribosomal S6 kinase 1 signaling pathways by thyroid-stimulating hormone (TSH) and stimulating type TSH receptor antibodies in the thyroid gland.
Thyroid-stimulating hormone (TSH) regulates the growth and differentiation of thyrocytes by activating the TSH receptor (TSHR). This study investigated the roles of the phosphatidylinositol 3-kinase (PI3K), PDK1, FRAP/mammalian target of rapamycin, and ribosomal S6 kinase 1 (S6K1) signaling mechanism by which TSH and the stimulating type TSHR antibodies regulate thyrocyte proliferation and the follicle activities in vitro and in vivo. The TSHR immunoprecipitates exhibited PI3K activity, which was higher in the cells treated with either TSH or 8-bromo-cAMP. TSH and cAMP increased the tyrosine phosphorylation of TSHR and the association between TSHR and the p85alpha regulatory subunit of PI3K. TSH induced a redistribution of PDK1 from the cytoplasm to the plasma membrane in the cells in a PI3K- and protein kinase A-dependent manner. TSH induced the PDK1-dependent phosphorylation of S6K1 but did not induce Akt/protein kinase B phosphorylation. The TSH-induced S6K1 phosphorylation was inhibited by a dominant negative p85alpha regulatory subunit or by the PI3K inhibitors wortmannin and LY294002. Rapamycin inhibited the phosphorylation of S6K1 in the cells treated with either TSH or 8-bromo-cAMP. The stimulating type TSHR antibodies from patients with Graves disease also induced S6K1 activation, whereas the blocking type TSHR antibodies from patients with primary myxedema inhibited TSH- but not the insulin-induced phosphorylation of S6K1. In addition, rapamycin treatment in vivo inhibited the TSH-stimulated thyroid follicle hyperplasia and follicle activity. These findings suggest an interaction between TSHR and PI3K, which is stimulated by TSH and cAMP and might involve the downstream S6K1 but not Akt/protein kinase B. This pathway may play a role in the TSH/stimulating type TSH receptor antibody-mediated thyrocyte proliferation in vitro and in the response to TSH in vivo.
Suh
Jae Mi
JM
Laboratory of Endocrine Cell Biology, Department of Internal Medicine, Chungnam National University School of Medicine, 640 Daesadong Chungku, Taejon 301-040, Korea.
Song
Jung Hun
JH
Kim
Dong Wook
DW
Kim
Ho
H
Chung
Hyo Kyun
HK
Hwang
Jung Hwan
JH
Kim
Jin Man
JM
Hwang
Eun Suk
ES
Chung
Jongkyeong
J
Han
Jeung-Hwan
JH
Cho
Bo Youn
BY
Ro
Heung Kyu
HK
Shong
Minho
M
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002455:Cell Division; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D020033:Protein Isoforms; D011494:Protein Kinases / Q000096:biosynthesis* / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D058570:TOR Serine-Threonine Kinases; D013936:Thymidine / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism; D013972:Thyrotropin / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D000077191:Wortmannin
D015124:8-Bromo Cyclic Adenosine Monophosphate; D000730:Androstadienes; D002867:Chromones; D007074:Immunoglobulin G; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D020033:Protein Isoforms; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D013936:Thymidine; D013972:Thyrotropin; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human; C546845:mTOR protein, rat; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; C069329:RPS6KA1 protein, human; C512963:Rps6ka1 protein, rat