Figure 3.

Profiles of TRs and transcriptional activity of the TRH gene after a long incubation with T₃. ChIP assays were performed with cells expressing the WT TR using antibodies against TRβ and Pol II phosphorylated at serine-5 (P-Pol II). A, ChIP assays showed that prolonged treatment with 100 nm T₃ caused a significant reduction in the amount of TR on the TRH promoter. B, The amount of P-Pol II on the TRH promoter was reduced at 15 and 60 min after the addition of T₃ but had gradually recovered by 120 min and 24 h. Each level was compared with the basal level (0 min). C, Real-time PCR for Luc mRNA was performed using GH4C1 cells stably expressing the TRH promoter reporter gene and the WT TR. Addition of 100 nm T₃ decreased Luc mRNA expression at 15 min, and that level was maintained until 60 min. A further reduction was observed at 120 min and at 24 h. Each level was compared with the basal level (0 min). The data are presented as the mean ± se for three independent experiments. Asterisks indicate a significant difference vs. 0 min: *, P < 0.05; **, P < 0.01.