Hepatocyte Nuclear Factor 4α Contributes to Thyroid Hormone Homeostasis by Cooperatively Regulating the Type 1 Iodothyronine Deiodinase Gene with GATA4 and Krüppel-Like Transcription Factor 9

Abstract

Type 1 iodothyronine deiodinase (Dio1), a selenoenzyme catalyzing the bioactivation of thyroid hormone, is highly expressed in the liver. Dio1 mRNA and enzyme activity levels are markedly reduced in the livers of hepatocyte nuclear factor 4α (HNF4α)-null mice, thus accounting for its liver-specific expression. Consistent with this deficiency, serum T₄ and rT₃ concentrations are elevated in these mice compared with those in HNF4α-floxed control littermates; however, serum T₃ levels are unchanged. Promoter analysis of the mouse Dio1 gene demonstrated that HNF4α plays a key role in the transactivation of the mouse Dio1 gene. Deletion and substitution mutation analyses demonstrated that a proximal HNF4α site (direct repeat 1 [TGGACAAAGGTGC]; HNF4α-RE) is crucial for transactivation of the mouse Dio1 gene by HNF4α. Mouse Dio1 is also stimulated by thyroid hormone signaling, but a direct role for thyroid hormone receptor action has not been reported. We also showed that thyroid hormone-inducible Krüppel-like factor 9 (KLF9) stimulates the mouse Dio1 promoter very efficiently through two CACCC sequences that are located on either side of HNF4α-RE. Furthermore, KLF9 functions together with HNF4α and GATA4 to synergistically activate the mouse Dio1 promoter, suggesting that Dio1 is regulated by thyroid hormone in the mouse through an indirect mechanism requiring prior KLF9 induction. In addition, we showed that physical interactions between the C-terminal zinc finger domain (Cf) of GATA4 and activation function 2 of HNF4α and between the basic domain adjacent to Cf of GATA4 and a C-terminal domain of KLF9 are both required for this synergistic response. Taken together, these results suggest that HNF4α regulates thyroid hormone homeostasis through transcriptional regulation of the mouse Dio1 gene with GATA4 and KLF9.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank Nagaoki Toyoda (Kansai Medical University) for helpful discussion of the Dio1 assay and Shaw-Fang Yet (Harvard Medical School), Jerry Lingrel (University of Cincinnati College of Medicine), Christina Teng (National Institutes of Health), Ichiro Manabe, and Ryozo Nagai (University of Tokyo Graduate School of Medicine) for plasmids.

This study was supported in part by the grants from the Program of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovation (NIBIO), by the NFAT project of the New Energy and Industrial Technology Development Organization (NEDO), and by the Special Coordination Fund for Science and Technology of the Ministry of Education, Culture, Sports, Science, and Technology, the Uehara Memorial Foundation, and the Ono Medical Foundation. J.S. is a recipient of funds from the Special Coordination Fund for Science and Technology of the Ministry of Education, Culture, Sports, Science and Technology.