Inhibition of GATA2-dependent transactivation of the TSHβ gene by ligand-bound estrogen receptor α

Abstract

Transcriptional repression of the TSH-specific β subunit (TSHβ) gene has been regarded to be specific to thyroid hormone (tri-iodothyronine, T3) and its receptors (TRs) in physiological conditions. However, TSHβ mRNA levels in the pituitary were reported to decrease in the administration of pharmacologic doses of estrogen (17-β-estradiol, E2) and increase in E2 receptor (ER)-α null mice. Here, we investigated the molecular mechanism of inhibition of the TSHβ gene expression by E2-bound E2-estrogen receptor 1 (E2-ERα). In kidney-derived CV1 cells, transcriptional activity of the TSHβ promoter was stimulated by GATA2 and suppressed by THRBs and ERα in a ligand-dependent fashion. Overexpression of PIT1 diminished the E2-ERα-induced inhibition, suggesting that PIT1 may protect GATA2 from E2-ERα targeting by forming a stable complex with GATA2. Interacting surfaces between ERα and GATA2 were mapped to the DNA-binding domain (DBD) of ERα and the Zn finger domain of GATA2. E2-dependent inhibition requires the ERα amino-terminal domain but not the tertiary structure of the second Zn finger motif in E2-ERα-DBD. In the thyrotroph cell line, TαT1, E2 treatment reduced TSHβ mRNA levels measured by the reverse transcription PCR. In the human study, despite similar free thyroxine levels, the serum TSH level was small but significantly higher in post- than premenopausal women who possessed no anti-thyroid antibodies (1.90 μU/ml±0.13 s.e.m. vs 1.47 μU/ml±0.12 s.e.m., P<0.05). Our findings indicate redundancy between T3-TR and E2-ERα signaling exists in negative regulation of the TSHβ gene.