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Original Article Analysis of Glucocorticoid Response Element and TPA Response Element of Rat Thyrotropin-Releasing Hormine Gene by Site-Directed Mutagenesis.
Sung Woon Kim, Jin Woo Kim, Young Seol Kim, Young Kil Choi, In Myoung Yang, Jung Taek Woo, Woon Won Chung
Endocrinology and Metabolism 1999;14(2):278-292

Published online: January 1, 2001
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BACKGROUND
We previously demonstrated that a GRE/TRE composite sequence, which is located between 200 bp and 220 bp relative to the transcriptional start site of rat TRH gene, is responsible for the dexamethasone (DEX)- and TPA-induced transcriptional activation, and the transcriptional activation by DEX is mediated by interaction between glucocorticoid receptor (GR) and a TRE-binding transcriptional factor such as c-Jun. However, a non-specific binding with the transciption factors can not be excluded as the mutants used in the previous report could not inhibit the binding of GR and c-Jun completely, and it remains unclear which one of the two TRE-like sequences is critical for the interaction of the two transcription factors. METHODS: Luciferase expressing plasmids that contain a part of rat TRH promoter including the composite GRE sequence or its mutants were transfected into HeLa cells by Fugene 6. After the cells were incubated overnight with DEX or/and TPA, the luciferase activity was measured in a chemiluminometer. A gel retardation assay was performed after binding of the labeled composite sequence or its mutants with GR and c-Jun. RESULTS: DEX and TPA increased the transcriptional activity of the wild type composite sequence by 3 folds and 4 folds, respectively, and the combined stimulation increased the activity by 10 folds. The mutants of which all 6 nucleotides of the GRE half site were replaced and removed almost did not bind to GR and eould not enhance the transcriptional activity at all in response to DEX. The GRE-deleted mutant bound to c-Jun with a remarkably lower affinity and showed a lower response to TPA, whereas the GRE-replaced mutant bound to c-Jun with a similar affinity and showed a similar response to TPA compared to those of the wild type. In response to the combined simulation with DEX and TPA, the mutants showed 30-40% of the trancriptional activity of the wild type. Basal transcriptional activity of all the TRE mutants was significantly lower than that of the wild type. While they almost could not bind to c-Jun, their binding affinity to GR was comparable to that of the wild type. Whereas the DEX- and TPA-induced transcriptional activity of 5 TRE mutant was 10% and 15% of that of the wild type, it responded to those agents in a similar pattern as the wild type. The 3 TRE mutant and the mutant of both TRE sites did not respond to DEX and TPA. The GRE-deleted mutant hardly formed the DNA-protein complex as did the wild type, while the GRE -replaced mutant could form the complex in a less amount with nuclear extract of HeLa celL CONCLUSION: These results suggest that GRE/TRE composite sequence of rat TRH gene specifically binds to GR and c-Jun, providing a site for interaction between the two transcription factors, and that both TRE sites play an important role in basal transcription, and that the 3 TRE site is more critical in the interaction between GRE and TRE for DEX-induced transcriptional activation. (J Kor Endocrinol 14:278-292, 1999)

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