title: Regulation of human growth hormone receptor gene transcription by triiodothyronine (T3).
abstract: In this study the hypothesis that triiodothyronine (T3) and growth hormone (GH) may have some direct or indirect effect on the regulation of GH-receptor/GH-binding protein (GHR/GHBP) gene transcription was tested. Different concentrations of T3 (0, 0.5, 2, 10 nmol/l) and GH (0, 10, 150 ng/ml) were added to human hepatoma (HuH7) cells cultured in serum-free hormonally-defined medium for 0, 1 and 2 h. Thereafter GHR/GHBP mRNA expression was quantitatively assessed by using PCR amplification. GH at a concentration of 10 ng/ml resulted in a significant increase of GHR/GHBP gene expression whereas a supraphysiological concentration of GH (150 ng/ml) caused a significant decrease of GHR/GHBP mRNA levels. The simultaneous addition of 0.5 nmol/l T3 to the variable concentrations of GH did not modify GHR/GHBP mRNA levels whereas the addition of 2 nmol/l up-regulated GHR/GHBP gene expression already after 1 h, an increase which was even more marked when 10 nmol/l of T3 was added. Interestingly, there was a positive correlation between the increase of GHR/GHBP mRNA levels and the T3 concentration used (r: 0.8). In addition, nuclear run-on experiments and GHBP determinations were performed which confirmed the changes in GHR/GHBP mRNA levels. Cycloheximide (10 microg/ml) did not alter transcription rate following GH addition but blocked GHR/GHBP gene transcription in T3 treated cells indicating that up-regulation of GHR/GHBP gene transcription caused by T3 requires new protein synthesis and is, therefore, dependent on indirect mechanisms. In conclusion, we present data showing that T3 on its own has a stimulatory effect on GHR/GHBP gene transcription which is indirect and additive to the GH-induced changes.
authors: Department of Paediatrics, Inselspital, Bern, Switzerland. primus.mullis@insel.ch
authors: P E
authors: PE
authors: Mullis
authors: A
authors: A
authors: Eblé
authors: U
authors: U
authors: Marti
authors: U
authors: U
authors: Bürgi
authors: M C
authors: MC
authors: Postel-Vinay
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D019382:Human Growth Hormone / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D011485:Protein Binding; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000235:genetics*; D011994:Recombinant Proteins / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects*; D014284:Triiodothyronine / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D002352:Carrier Proteins; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D011994:Recombinant Proteins; D014284:Triiodothyronine; D019382:Human Growth Hormone; D003513:Cycloheximide; C051815:somatotropin-binding protein