The thyrotropin receptor is not involved in the activation of p42/p44 mitogen-activated protein kinases by thyrotropin preparations in Chinese hamster ovary cells expressing the human thyrotropin receptor.
We studied whether bovine pituitary thyrotropin (bTSH) or human recombinant thyrotropin (rhTSH) stimulated p42/p44 mitogen-activated protein kinases (MAPKs) in Chinese hamster ovary cells expressing human thyrotropin receptor (CHO-hTSHR cells). We show that p42/p44 MAPK phosphorylation was induced by both TSH preparations at similar levels in CHO-hTSHR cells and in wild-type CHO cells. In contrast, cyclic adenosine monophosphate (cAMP) production was stimulated by TSH only in CHO-hTSHR cells, demonstrating that p42/p44 MAPK stimulation was independent of the TSH receptor. Moreover, similar results were obtained with two other cell lines: the FRTL-5 thyroid cell line and the CCL39 fibroblast cell line. Maximal stimulation of p42/p44 MAPK phosphorylation was observed after a 5- to 10-minute incubation with bTSH and rhTSH preparations. At this time, the phosphorylation of GST-Elk1 was also increased in a time- and concentration-dependent manner by bTSH preparations. The phosphorylation of p42/p44 MAPKs was abolished by PD 98059 and GF 109203X, indicating the involvement of MAPK kinases (MEK 1/2) and protein kinase C. In contrast, the activation of p42/p44 MAPKs was insensitive to H89, to cholera toxin and to pertussis toxin. These data suggest that the protein kinase A pathway was not implicated in p42/p44 MAPK activation by TSH preparations. Moreover, Gs or Gi/Go proteins do not appear to participate in p42/p44 MAPK activation. We also showed that these TSH preparations failed to induce activation of c-Jun NH2 terminal kinase. We therefore conclude that the commercial TSH preparations used in this study contained factor(s) responsible for the specific activation of p42/p44 MAPKs by a TSH receptor-independent mechanism.
Corrèze
C
C
Unité de Recherche, Transduction Hormonale et Régulation Cellulaire, U 486 INSERM, Faculté de Pharmacie, Châtenay-Malabry, France.
Blondeau
J P
JP
Pomerance
M
M
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011989:Receptors, Thyrotropin / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013961:Thyroid Gland / Q000378:metabolism; D013972:Thyrotropin / Q000494:pharmacology*; D014162:Transfection
D011989:Receptors, Thyrotropin; D011994:Recombinant Proteins; D013972:Thyrotropin; D000242:Cyclic AMP; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases