Regulation of 5'-promoter activity of the rat growth hormone and growth hormone-releasing hormone receptor genes in the MtT/S and MtT/E cells.
The MtT/E and MtT/S cells have been established from a mammotrophic pituitary tumor, and postulated to be progenitor and premature growth hormone (GH) cells, respectively. The difference in the regulation of GH and GH-releasing hormone (GHRH) receptor gene transcription in relation to the developmental stage of GH cells were examined in these two cell lines. In MtT/S cells, triiodothyronine (T3), all-trans retinoic acid (RA) and 9-cis retinoic acid (9cRA) stimulated GH promoter activity but dexamethasone (DEX) did not. On the other hand, DEX stimulated GHRH-receptor promoter alone. T3, RA and 9cRA showed little effect alone but each of them augmented the effect of DEX when used together with DEX. In MtT/E cells, DEX, RA and 9cRA showed similar effect as observed in MtT/S cells on both GH and GHRH-receptor promoter activity. However, T3 neither stimulated GH promoter activity nor augmented the DEX-induced GHRH-receptor gene transcription in MtT/E cells. RT-PCR analyses revealed that both cell types expressed TRalpha1, TRbeta1 and TRalpha2, but expression of TRbeta2, a pituitary specific isoform of TR, was only detected in MtT/S cells. However, the deficiency of TRbeta2 for its own sake does not appear to be a reason why T3 action was not observed in MtT/E cells, because co-transfection of expression plasmids for TRbeta2 and RXRalpha failed in conferring on the cells an ability to respond to T3 by increased GH or GHRH-receptor promoter activity. These results suggest that the acquisition of mechanisms responsible for the regulation of GH or GHRH-receptor transcription by T3 may be involved in the process of functional development of GH cells.
Nogami
Haruo
H
Department of Neuroendocrinology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Japan. hnogami@md.tsukuba.ac.jp
Hiraoka
Yoshiki
Y
Inoue
Kinji
K
Aiso
Sadakazu
S
Hisano
Setsuji
S
D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D005786:Gene Expression Regulation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic; D013006:Growth Hormone / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats; D018013:Receptors, Neuropeptide / Q000235:genetics* / Q000378:metabolism; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics* / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000235:genetics* / Q000378:metabolism; D014212:Tretinoin / Q000031:analogs & derivatives / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D011986:Receptors, Somatotropin; D014284:Triiodothyronine; C105492:9,13-retinoic acid; D014212:Tretinoin; D013006:Growth Hormone; C048250:somatotropin releasing hormone receptor