Induction of the Intronic Enhancer of the Human Ciliary Neurotrophic Factor Receptor (CNTFRä) Gene by the TR4 Orphan Receptor

Abstract

A conserved hormone response element, CNTFR-DR1 (5-AGGTCAGAGGTCAGG-3), has been identified in the 5th intron of the ␣ component of the ciliary neurotrophic factor receptor (CNTFR␣) gene for the human TR4 orphan receptor (TR4). Electrophoretic mobility shift assay showed a specific binding with high affinity (K d ‫؍‬ 0.066 nM) between TR4 and the CNTFR-DR1. A reporter gene assay using chloramphenicol acetyltransferase demonstrated that the 5th intron of CNTFR␣ has an enhancer activity which could be induced by TR4 in a dose-dependent manner. Furthermore, our in situ hybridization data showed that abundant TR4 transcripts were detected in adult brain, in regions of cortical and hippocampal neurons, as well as in many developing neural structures, including brain, spinal cord, ganglia (sympathetic and sensory), and neuronal epithelia (retinal, otic, olfactory, and gustatory). The striking similarities in the expression patterns of TR4 and CNTFR␣ in the developing and postnatal nervous systems further support the potential role of TR4 in neurogenesis. Collectively, these data suggest that the human CNTFR␣ gene could represent the first identified neural-specific gene induced by TR4.Members of the steroid/thyroid hormone receptor superfamily are transcription factors that can bind to specific DNA sequences called hormone response elements (HRE) 1 and thereby regulate the expression of their target genes (1). This superfamily includes receptors for steroid, thyroid, vitamin D 3 , and retinoids, and a large number of orphan receptors whose cognate ligands are still unknown (1). These members have been grouped into three categories according to their binding preference to HREs, the palindromic half-site AGAACA is preferred for the binding by the androgen, glucocorticoid, mineralocorticoid, and progesterone receptors; the direct repeat with various spacing is preferentially recognized by the estrogen, thyroid, retinoic acid, retinoid X, vitamin D, and many orphan receptors; and the single half-site of AGGTCA preceded by two specific flanking nucleotides is favored by some members which bind as a monomer, such as the steroidogenic factor 1 (2), TR3 orphan receptor (TR3)/NGFI-B/nur77 (3), and the thyroid receptor (4). Some receptors, i.e. thyroid hormone receptor and chicken ovalbumin upstream promoter-transcription factors (COUP-TFs), are shown to be promiscuous for binding to different arrangements of the AGGTCA half-site (4, 5).The human and rat TR4 cDNAs were isolated from testis and hypothalamus by degenerative PCR cloning (6). The TR4 cDNA shows high homology in nucleotide sequence with the TR2 orphan receptor (TR2; another orphan receptor isolated from our laboratory (7)), suggesting that these two orphan receptors constitute an unique subfamily within the steroid receptor superfamily. TR4 mRNA are widely expressed in the adult rat brain (6). Within the supraoptic nucleus, TR4 is one of the most abundant steroid receptors expressed there with the order thyroid hormone receptor Ͼ COUP-TFII Ͼ TR4 ϭ COUP-TFI (8). Des...

Suppression of Hepatitis B Virus Core Promoter by the Nuclear Orphan Receptor TR4

“…Moreover, compared with the marginal suppression of TR2 on CpLuc reporter activity, TR4 has a much stronger suppressive effect on CpLuc reporter activity (data not shown), suggesting that TR4 may play a significant role in this regulation. Also, our data suggest that simple competition for binding to the DR1 site by these two nuclear receptors may not fully account for their distinct regulation of HBV core gene expression, because both nuclear receptors regulate target genes through binding to the DR sites (19,38). The detailed mechanisms underlying the distinct regulation of HBV gene expression by these two closely related orphan receptors remain unclear.…”

“…Earlier studies indicated that TR2 and TR4 could modulate the expression of a set of genes through binding to the same HREs (19,38). Interestingly, Yu et al (14) reported that TR2 could only repress pre-C RNA, but not C RNA expression.…”

“…The distribution of TR4 expression is ubiquitous in many tissues, including the central nervous system, adrenal gland, spleen, thyroid gland, and liver (16,19,23). Also, there are many other nuclear receptors expressed in the liver, such as HNF4␣ (24) and RXR␣/PPAR␣ (25,26).…”

“…Our previous data showed that TR4 recognizes different AGGTCA direct repeat (DR) sequences either inducing or suppressing its target genes. For example, TR4 induces reporters containing the DR1 site of human ciliary neurotrophic factor ␣ receptor promoter and the DR4 site of the ␣-myosin heavy chain promoter (19,20). In contrast, TR4 suppresses RXR␣/retinoic acid receptor (DR1), vitamin D3 receptor (DR3), and RXR␣/PPAR␣ (DR1)-mediated…”

Deficiency in TR4 nuclear receptor abrogates Gadd45a expression and increases cytotoxicity induced by ionizing radiation

“…In vitro data suggest that TR4 functions as a master regulator to modulate many signaling pathways, including induction of the ciliary neurotrophic factor alpha [5, 6], interfering with retinoic acid receptor/retinoid X receptor [7], thyroid receptor [8], androgen receptor [9], and estrogen receptor-mediated pathways [10], and facilitating viral infection and propagation of HPV-16 and SV40 [11]. Mice lacking Tr4 ( TR4KO ) have high rates of early postnatal mortality, show significant growth retardation [12], display reproductive defects in both genders [12, 13], abnormalities in spermatogenesis [14], reduced lipoprotein metabolism [15, 16], and reduced gluconeogenesis [17], as well as defects in cerebella development [18].…”