Molecular Endocrinology, Vol 9, 96-107, Copyright © 1995 by Endocrine Society

ARTICLES

Analysis of structure and expression of the Xenopus thyroid hormone receptor-beta gene to explain its autoinduction

I Machuca, G Esslemont, L Fairclough and JR Tata
Laboratory of Developmental Biochemistry, National Institute for Medical Research, London, United Kingdom.

Transcription of both Xenopus thyroid hormone receptor (TR) genes, xTR alpha and -beta, is strongly up-regulated by their own ligand T3 during natural or T3-induced metamorphosis of tadpoles and in some Xenopus cell lines. To explain this autoinduction, we analyzed the sequence of 1.6 kilobases of xTR beta promoter for putative T3-responsive elements. Two direct repeat +4 AGGTCA hexamer motifs (DR+4), an imperfect distal (-793/-778) and a perfect proximal (-5/11) site, a DR+1 site, and some possible half-sites were located in the 1.6-kilobase promoter. Transfection of Xenopus XTC-2 cells (which express xTR alpha and -beta) and XL-2 cells (which predominantly express TR alpha) with chloramphenicol acetyltransferase reporter constructs of deletion mutants and promoter fragments showed that the distal and proximal DR+4 sites responded to T3, although other flanking sequences may also play a role. The thyroid hormone-responsive element half-site present as DR+1 in the up-stream sequence at -1260/-950, when cloned in front of a heterologous promoter, functions independently. T3 enhanced transcription from the two DR+4-containing fragments when present together by only 2- to 3-fold due to a high basal activity. Overexpression of unliganded xTR alpha and xTR beta in XTC-2 cells repressed basal activity, which was then enhanced 7- to 4-fold by T3, respectively; with XL-2 cells cotransfected with xTR beta, T3 inducibility increased to 16-fold. Electrophoretic mobility shift assays with recombinant Xenopus TR alpha, TR beta, retinoid-X receptor- alpha (RXR alpha) and RXR gamma proteins showed that TR-RXR heterodimers, but not TR or RXR monomers or homodimers, strongly bound the natural and synthetic distal and proximal DR+4 elements in a ligand- independent manner. TR/RXR heterodimers exhibited the highest binding affinity for a 28-mer oligonucleotide probe for the -5/11 proximal DR+4 site, with only slight binding to DR+1 (retinoid-X-responsive element- like) site. The xTR beta promoter binding to XTC-2 cell nuclear extract suggested the in vivo relevance of the findings with recombinant TR/RXR heterodimers. It is concluded that xTR alpha and -beta proteins are capable of regulating the expression of xTR beta gene, which can explain its autoinduction seen during T3-induced metamorphosis.

This article has been cited by other articles:

				P. Bagamasbad, K. L. Howdeshell, L. M. Sachs, B. A. Demeneix, and R. J. Denver A Role for Basic Transcription Element-binding Protein 1 (BTEB1) in the Autoinduction of Thyroid Hormone Receptor J. Biol. Chem., January 25, 2008; 283(4): 2275 - 2285. [Abstract] [Full Text] [PDF]

				A. H. Conrad, Y. Zhang, A. R. Walker, L. A. Olberding, A. Hanzlick, A. J. Zimmer, R. Morffi, and G. W. Conrad Thyroxine Affects Expression of KSPG-Related Genes, the Carbonic Anhydrase II Gene, and KS Sulfation in the Embryonic Chicken Cornea Invest. Ophthalmol. Vis. Sci., January 1, 2006; 47(1): 120 - 132. [Abstract] [Full Text] [PDF]

				W. Mai, M. F. Janier, N. Allioli, L. Quignodon, T. Chuzel, F. Flamant, and J. Samarut Thyroid hormone receptor {alpha} is a molecular switch of cardiac function between fetal and postnatal life PNAS, July 13, 2004; 101(28): 10332 - 10337. [Abstract] [Full Text] [PDF]

				J. D. Furlow, H. Y. Yang, M. Hsu, W. Lim, D. J. Ermio, G. Chiellini, and T. S. Scanlan Induction of Larval Tissue Resorption in Xenopus laevis Tadpoles by the Thyroid Hormone Receptor Agonist GC-1 J. Biol. Chem., June 18, 2004; 279(25): 26555 - 26562. [Abstract] [Full Text] [PDF]

				A. Tomita, D. R. Buchholz, and Y.-B. Shi Recruitment of N-CoR/SMRT-TBLR1 Corepressor Complex by Unliganded Thyroid Hormone Receptor for Gene Repression during Frog Development Mol. Cell. Biol., April 15, 2004; 24(8): 3337 - 3346. [Abstract] [Full Text] [PDF]

				L. M. Sachs, P. L. Jones, E. Havis, N. Rouse, B. A. Demeneix, and Y.-B. Shi Nuclear Receptor Corepressor Recruitment by Unliganded Thyroid Hormone Receptor in Gene Repression during Xenopus laevis Development Mol. Cell. Biol., December 15, 2002; 22(24): 8527 - 8538. [Abstract] [Full Text] [PDF]

				W. Lim, N.-H. Nguyen, H. Y. Yang, T. S. Scanlan, and J. D. Furlow A Thyroid Hormone Antagonist That Inhibits Thyroid Hormone Action in Vivo J. Biol. Chem., September 13, 2002; 277(38): 35664 - 35670. [Abstract] [Full Text] [PDF]

				J. D. Furlow and A. Kanamori The Transcription Factor Basic Transcription Element-Binding Protein 1 Is a Direct Thyroid Hormone Response Gene in the Frog Xenopus laevis Endocrinology, September 1, 2002; 143(9): 3295 - 3305. [Abstract] [Full Text] [PDF]

				C. F. Bunn, J. A. Neidig, K. E. Freidinger, T. A. Stankiewicz, B. S. Weaver, J. McGrew, and L. A. Allison Nucleocytoplasmic Shuttling of the Thyroid Hormone Receptor {{alpha}} Mol. Endocrinol., April 1, 2001; 15(4): 512 - 533. [Abstract] [Full Text]

				L. M. Sachs and Y.-B. Shi Targeted chromatin binding and histone acetylation in vivo by thyroid hormone receptor during amphibian development PNAS, November 8, 2000; (2000) 260141297. [Abstract] [Full Text]

				J. Wong, V. C.-T. Liang, L. M. Sachs, and Y.-B. Shi Transcription from the Thyroid Hormone-dependent Promoter of the Xenopus laevis Thyroid Hormone Receptor beta A Gene Requires a Novel Upstream Element and the Initiator, but Not a TATA Box J. Biol. Chem., June 5, 1998; 273(23): 14186 - 14193. [Abstract] [Full Text] [PDF]

				G. M. Wahlström and B. Vennström Requirements for Repression of Retinoid X Receptor by the Oncoprotein P75gag-v-erbA and the Thyroid Hormone Receptors Mol. Endocrinol., May 1, 1998; 12(5): 645 - 653. [Abstract] [Full Text]

				J Wong, Y B Shi, and A P Wolffe A role for nucleosome assembly in both silencing and activation of the Xenopus TR beta A gene by the thyroid hormone receptor. Genes & Dev., November 1, 1995; 9(21): 2696 - 2711. [Abstract] [PDF]

				J. Wong and Y.-B. Shi Coordinated Regulation of and Transcriptional Activation by Xenopus Thyroid Hormone and Retinoid X Receptors J. Biol. Chem., August 4, 1995; 270(31): 18479 - 18483. [Abstract] [Full Text] [PDF]

				F. D. Urnov and A. P. Wolffe An Array of Positioned Nucleosomes Potentiates Thyroid Hormone Receptor Action in Vivo J. Biol. Chem., June 1, 2001; 276(23): 19753 - 19761. [Abstract] [Full Text] [PDF]

				L. M. Sachs and Y.-B. Shi Targeted chromatin binding and histone acetylation in vivo by thyroid hormone receptor during amphibian development PNAS, November 21, 2000; 97(24): 13138 - 13143. [Abstract] [Full Text] [PDF]