Identification of glucocorticoid response element of the rat TRH gene.
OBJECTIVE
It was suggested that glucocorticoid exerts cell-specific effects on thyrotropin-releasing hormone (TRH) gene expression at the transcriptional level. Although there is no typical palindromic glucocorticoid response element (GRE) on the rat TRH gene promoter, a perfect GRE half-site is found between -205 bp and -211 bp. We investigated whether the segment between -242 bp and -200 bp of the rat TRH gene promoter is responsible for glucocorticoid response.


METHODS
For the 5' deletion study of the TRH gene, four different plasmid constructs, pTRH(- 554/84), pTRH(-242/84), pTRH(-200/6), pTRH(-113/84) were used for transient transfection study. The plasmid pMAMneo-LUC was used as a positive control and pRSV-GR expression vector, as a co-transfection study. Transfection was performed by the modified calcium precipitation method with 2 micrograms of each lasmid on the HeLa cells.


RESULTS
Dexamethasone (DEX) stimulated the transcriptional activity of pTRH(-554/84)-LUC and pTRH(-242/84)-LUC by approximately 3.2 fold at 10(-8) M and 5.4 fold at 10(-8) M. On the contrary, deletion of the region between -242 to -200 bp reduced the basal transcriptional activity by 90% and also completely abolished the DEX-induced transcriptional activation of the luciferase gene. The DEX-induced transcriptional activation of pTRH(-242/84)-LUC was in dose-dependent manner. While the co-transfection of glucocorticoid receptor expression vector (pRSV-GR) did not increase the basal transcriptional activity of pMAMneo-LUC, it increased the basal transcription of pTRH(-242/84)-LUC by 1.8 fold. The pRSV-GR co-transfection and DEX treatment further increased the transcription of pTRH(-242/84)-LUC by 2-4 fold at the concentration of 10(-8) M.


CONCLUSIONS
These findings suggest that a cis-acting element(s) which is important for the basal transcriptional activation and glucocorticoid response of the rat TRH gene is located between -242 bp and -200 bp. The gene has a weak GRE glucocorticoid response and seems to be mediated by an interaction between glucocorticoid receptor and other transcriptional factor (s).
Lee
G C
GC
Department of Internal Medicine, College of Medicine, KyungHee University, Seoul, Korea.
Yang
I M
IM
Kim
B J
BJ
Woo
J T
JT
Kim
S W
SW
Kim
J W
JW
Kim
Y S
YS
Choi
Y K
YK
D000818:Animals; D001483:Base Sequence; D003907:Dexamethasone / Q000494:pharmacology*; D016762:Genes, fos; D006367:HeLa Cells; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects
D013973:Thyrotropin-Releasing Hormone; D003907:Dexamethasone