Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Retinoic acid, the first morphogen described so far in vertebrates, is a vitamin A derivative which exerts striking effects on development and differentiation. The identification of three retinoic acid receptors as members of the nuclear receptor super-family provides an explantation for the molecular action of morphogens on gene expression. Functional analysis of the receptors requires the identification of target genes and of their cis-acting retinoic acid-responsive elements. We have previously shown that the retinoic acid receptor beta gene is transcriptionally up-regulated by retinoic acid and now report the characterization of a functional retinoic acid responsive element in the beta gene that mediates trans-activation by retinoic acid. Using deletion mapping, we have identified a 27-base pair fragment, located 59 base pairs upstream of the transcriptional start, which confers retinoic acid responsiveness on the herpes virus thymidine kinase promoter. This sequence contains a perfect direct repeat of the motif GTTCAC, which is reminiscent of the 5' half-palindrome of the thyroid and oestrogen hormone responsive elements. Specific binding of the beta protein to the retinoic acid responsive element is demonstrated and is independent of the presence of retinoic acid. Both alpha and beta receptors enhance retinoic acid response in CV1 cells, indicating that they can both act through the same DNA sequence.
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PMID:Identification of a retinoic acid responsive element in the retinoic acid receptor beta gene. 215 68

We have previously described the inhibition of glucocorticoid-dependent transcription from the mouse mammary tumor virus long terminal repeat promoter by products of the H-ras and v-mos oncogenes. We have studied the effects of conditional oncogenes on expression of glucocorticoid-dependent indicator genes. Expression of the glucocorticoid-dependent transcription of the tyrosine aminotransferase gene was monitored in FTO-2B rat hepatoma cells during Mr 21,000 protein (p21) H-ras induction. A strong transcriptional repression of the tyrosine aminotransferase gene followed p21 H-ras expression. The sequences in a glucocorticoid-dependent promoter which are responsible for the oncogene-mediated repression could be localized to the glucocorticoid response element; a construct in which a 15-base pair glucocorticoid response element was inserted 5' of the thymidine kinase promoter exhibited the oncogene-mediated repression of transcription. We observed a strong repression of glucocorticoid-dependent promoters and promoter constructs not only in the presence of p21 H-ras and p37 v-mos but also with p60 v-src. p57 v-myc, however, had no effect. Oncogene expression is not a sufficient prerequisite for an initial repression of glucocorticoid hormone-dependent gene transcription, since even in the presence of constitutively high levels of oncogene product a transient stimulation of glucocorticoid-dependent gene expression was found. Protein synthesis inhibition experiments revealed that no hormonally induced cellular protein is needed for the oncogene-mediated repression. It seemed reasonable that this phenomenon might reflect oncogene effects on the glucocorticoid receptor. We, therefore, made measurements of the glucocorticoid receptor protein. In the presence of glucocorticoid hormone the receptor translocated rapidly from the cytoplasm to the nucleus. In normal NIH 3T3 cells, after 24-h treatments the nuclear receptor levels had declined to about 50% of those determined at 2 h and in the presence of p21 H-ras they declined to 15%. The levels of cytoplasmic receptor were not affected by p21 H-ras expression.
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PMID:Oncogene mediated repression of glucocorticoid hormone response elements and glucocorticoid receptor levels. 256 9

We studied potential modulators of antithrombin gene expression. A putative hormone response element (HRE) was identified by sequence similarity analysis of the antithrombin promoter, situated between nucleotides -92 and -54 relative to the transcription start site. This HRE contains three hexa-nucleotide motifs with an AGGTCA consensus, which are potential targets of members of the steroid/thyroid superfamily of nuclear receptors. Stimulation of the hepatoma cell line HepG2 with the receptor ligands L-3,5,3'-tri-iodothyronine, all-trans retinoic acid, or their combination, increased production of antithrombin into the culture medium by 1.3-, 1.6-, and 2.0-fold, respectively. In contrast, the receptor ligand 1,25-dihydroxy-cholecalciferol[1,25-(OH)2VitD3] did not influence antithrombin production. Analysis of promoter chloramphenicol acetyl-transferase (CAT) constructs, showed that the first 86 bp of the antithrombin promoter region are sufficient for basal transcription. The DNA length polymorphism of 32 bp or 108 bp, located upstream of position -276, did not influence anti-thrombin promoter activity. The antithrombin promoter activity dropped to background values when deleting the region -97/-49 of promoter fragment -453/+57. Transactivation of the antithrombin promoter by retinoid X receptor alpha (RXR alpha) (5-7-fold) or thyroid hormone receptor beta (TR beta) (4-5-fold) was only observed when at least -167/+57 bp of the promoter region is present in CAT constructs, and when the appropriate ligand of the nuclear receptor was added. This transactivation was not observed upon deletion of the antithrombin promoter region -97/-49. With three copies of the antithrombin promoter fragment -109/-42 in front of the thymidine kinase minimal promoter, transactivation was only obtained with RXR alpha, and not with TR beta. In conclusion, these results indicate that the ligand-dependent enhancement of antithrombin gene expression is regulated by RXR alpha as well as by TR beta. Transactivation of antithrombin gene expression by RXR alpha and TR beta appears to be dependent upon the presence of promoter region up to nucleotide -167. The HRE segment (-109/-42) only confers RXR alpha responsiveness to a heterologous promoter. Further study is needed to unravel the exact nature of this HRE and its 5'-flanking sequences.
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PMID:Ligand-dependent enhancement of human antithrombin gene expression by retinoid X receptor alpha and thyroid hormone receptor beta. 876 81

Relaxation of skeletal muscle requires the re-uptake of Ca2+, which is mediated by the sarcoplasmic reticulum Ca2+-ATPase (SERCA). Thyroid hormone (T3) stimulates the expression of the SERCA1 isoform, which is essential for fast skeletal muscle fiber phenotype. We have cloned and studied the first 962 base pairs of the 5'-flanking region of the rat SERCA1 gene. This sequence was tested for T3-regulated expression in transient transfection experiments using COS7 cells and for binding of thyroid hormone receptor (TR) alpha in mobility shift assays. A construct of the 5'-flanking region and a reporter gene was unresponsive to T3 in the absence of co-transfected thyroid hormone receptor. In the presence of TRalpha, a T3 induction ratio of almost 4.0 was found, and this induction ratio was doubled with co-transfection of an RXR expression plasmid. Analysis of progressive 5'-deletion fragments of the sequence indicated multiple regions involved in T3 responsiveness. Three regions, R1, R2, and R3, were identified that bound TR complexes in mobility shift assays and conferred T3 responsiveness to a heterologous promoter. The most potent of these thyroid hormone response elements, R3, increased the 2-fold background T3 stimulation of the thymidine kinase promoter to nearly 6-fold. Detailed analysis of this element showed that four TR-binding half-sites, comprising two independent thyroid hormone response elements, interact cooperatively to give the maximal T3 response. T3 regulation of SERCA1 expression is mediated by a complex thyroid hormone response element that may serve to provide a greater range of response in interaction with nuclear receptor partners or cell-specific transcription factors.
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PMID:Characterization of the promoter of the rat sarcoplasmic endoplasmic reticulum Ca2+-ATPase 1 gene and analysis of thyroid hormone responsiveness. 894 55

Repression of basal transcription of a 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) responsive 25-hydroxyvitamin D3-24-hydroxylase (CYP24) promoter construct as observed in kidney cells in the absence of ligand and this repression was dependent on a functional vitamin D response element (VDRE). Basal repression was also seen with a construct where a consensus DR-3-type VDRE was fused to the thymidine kinase promoter. Expression of a dominant negative vitamin D receptor (VDR) isoform that strongly bound to the VDRE motif in the CYP24 promoter ablated basal repression. This VDR isoform lacked sequence in the hinge- and ligand-binding domains implicating one or both of these domains in basal repression. It is well known that thyroid hormone and retinoic acid receptors silence basal transcription of target genes in the absence of ligands and this repressor function can be mediated by the nuclear receptor corepressor N-CoR. Two variants of N-CoR have been described, RIP13a and RIP13delta1. N-CoR and the variants contain two receptor interaction domains, ID-I and ID-II, which are identical except region ID-II in RIP13delta1 has an internal deletion. We have used the mammalian two hybrid system to investigate whether VDR, in the absence of ligand 1,25-(OH)2D3, can interact with these domains. The data showed that unliganded VDR does not interact with either ID-I or ID-II from RIP13a and RIP13delta1, but does interact strongly with a composite domain of ID-I and ID-II from RIP13delta1 (but not from RIP13a) and this strong interaction is abrogated in the presence of ligand. This finding implicates RIP13delta1 in VDR-dependent basal repression of the promoter constructs under investigation. However, over-expression of RIP13delta1 in kidney cell lines did not alter basal expression of the CYP24 promoter construct. It is concluded that either the level of endogenous RIP13delta1 in these kidney cells permits maximal repression or that repression occurs by a mechanism that is independent of RIP13delta1. Alternatively, repression may be dependent on RIP13delta1 but requires an additional cofactor that is limiting in these cells.
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PMID:Repression of basal transcription by vitamin D receptor: evidence for interaction of unliganded vitamin D receptor with two receptor interaction domains in RIP13delta1. 968 55

Dehydroepiandrosterone sulfotransferase (STD) is a hydroxysteroid sulfo-conjugating enzyme with preferential substrate specificity for C-19 androgenic steroids and C-24 bile acids. STD is primarily expressed in the liver, intestine and adrenal cortex. Earlier studies have shown that androgens inhibit the rat Std promoter function through a negative androgen response region located between -235 and -310 base pair positions (Song, C. S., Jung, M. H., Kim, S. C., Hassan, T., Roy, A. K., and Chatterjee, B. (1998) J. Biol. Chem. 273, 21856-21866). Here we report that the primary bile acid chenodeoxycholic acid (CDCA) also acts as an important regulator of the Std gene promoter. CDCA is a potent inducer of the Std gene, and its inducing effect is mediated through the bile acid-activated farnesoid X receptor (FXR), a recently characterized member of the nuclear receptor superfamily. The ligand-activated FXR acts as a heterodimer with the 9-cis-retinoic acid receptor (RXR) and regulates the Std gene by binding to an upstream region at base pair positions -169 to -193. This specific binding region was initially identified by bile acid responsiveness of the progressively deleted forms of the Std promoter in transfected HepG2 hepatoma and enterocyte-like Caco-2 cells. Subsequently, the precise RXR/FXR binding position was established by protein-DNA interaction using in vitro footprinting and electrophoretic mobility shift analyses. Unlike all other previously characterized FXR target genes, which contain an inverted repeat (IR) of the consensus hexanucleotide half-site (A/G)G(G/T)TCA with a single nucleotide spacer (IR-1), the bile acid response element of the Std promoter does not contain any spacer between the two hexanucleotide repeats (IR-0). A promoter-reporter construct carrying three tandem copies of the IR-0 containing -169/-193 element, linked to a minimal thymidine kinase promoter, can be stimulated more than 70-fold in transfected Caco-2 cells upon CDCA treatment. Autoregulation of the STD gene by its bile acid substrate may provide an important contributing role in the enterohepatic bile acid metabolism and cholesterol homeostasis.
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PMID:Dehydroepiandrosterone sulfotransferase gene induction by bile acid activated farnesoid X receptor. 1153 40

The multidrug resistance-associated protein 2 (MRP2, ABCC2), mediates the efflux of several conjugated compounds across the apical membrane of the hepatocyte into the bile canaliculi. We identified MRP2 in a screen designed to isolate genes that are regulated by the farnesoid X-activated receptor (FXR, NR1H4). MRP2 mRNA levels were induced following treatment of human or rat hepatocytes with either naturally occurring (chenodeoxycholic acid) or synthetic (GW4064) FXR ligands. In addition, we have shown that MRP2 expression is regulated by the pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3). Thus, treatment of rodent hepatocytes with PXR or CAR agonists results in a robust induction of MRP2 mRNA levels. The dexamethasone- and pregnenolone 16alpha-carbonitrile-dependent induction of MRP2 expression was not evident in hepatocytes derived from PXR null mice. In contrast, induction of MRP2 by phenobarbital, an activator of CAR, was comparable in wild-type and PXR null mice. An unusual 26-bp sequence was identified 440 bp upstream of the MRP2 transcription initiation site that contains an everted repeat of the AGTTCA hexad separated by 8 nucleotides (ER-8). PXR, CAR, and FXR bound with high affinity to this element as heterodimers with the retinoid X receptor alpha (RXRalpha, NR2B1). Luciferase reporter gene constructs containing 1 kb of the rat MRP2 promoter were prepared and transiently transfected into HepG2 cells. Luciferase activity was induced in a PXR-, CAR-, or FXR-dependent manner. Furthermore, the isolated ER-8 element was capable of conferring PXR, CAR, and FXR responsiveness on a heterologous thymidine kinase promoter. Mutation of the ER-8 element abolished the nuclear receptor response. These studies demonstrate that MRP2 is regulated by three distinct nuclear receptor signaling pathways that converge on a common response element in the 5'-flanking region of this gene.
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PMID:Regulation of multidrug resistance-associated protein 2 (ABCC2) by the nuclear receptors pregnane X receptor, farnesoid X-activated receptor, and constitutive androstane receptor. 1170 36

It was shown previously that hNIS mRNA expression is stimulated by retinoic acid (RA) in human follicular thyroid carcinoma cell lines FTC-133 and FTC-238, and patients with thyroid carcinomas lacking iodide uptake respond to RA treatment with increased radioiodide transport. Here, in transient transfection experiments using FTC-238 cells, hNIS promoter/luciferase reporter constructs showed an up to 2.5-fold increase in transcriptional activity after incubation with 1 microM RA. Stimulation by 10 nM T3 was up to 2.4-fold. Deletion or block mutation of a putative nuclear receptor recognition site, 'DR10', abolished RA and T3 responses. Four copies of the DR10 cloned 5' to the thymidine kinase promoter gave a 2.6-fold and a 1.4-fold increase in transcriptional activity after RA and T3 stimulation, respectively. In electrophoretic mobility shifts, a wildtype DR10 oligonucleotide, but not block mutants of either DR10 halfsite, interacted with nuclear receptors. Thus, RA redifferentiation of advanced thyroid carcinomas may reinduce iodide uptake by stimulating hNIS expression and thereby make tumours accessible for radioiodide therapy again.
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PMID:The promoter of the human sodium/iodide-symporter gene responds to retinoic acid. 1203 73

The vitamin D receptor (VDR) is known to mediate the biological actions of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] through its ability to regulate cellular programs of gene expression. Although RXR appears to participate as a heterodimeric partner with the VDR, absolute evidence for its role remains equivocal in vivo. To test this role and to investigate the requirement for comodulator interaction, we identified VDR- and retinoid X receptor (RXR)-interacting LXXLL peptides and examined whether these molecules could block vitamin D and 9-cis retinoic acid (9-cis RA) response. We used a mammalian cell two-hybrid system to screen a series of nuclear receptor (NR)-reactive LXXLL peptides previously identified through phage display screening for hormone-dependent reactivity with either VDR or RXR. Three categories of peptides were identified: those reactive with both VDR and RXR, those selective for RXR, and those unreactive to either receptor. Peptide fusion proteins were then examined in MC3T3-E1 cells for their ability to block induction of the osteocalcin (OC) promoter by 1,25(OH)2D3 or stimulation of a retinoic acid response element-thymidine kinase (RARE-TK) reporter by 9-cis-RA. Peptides that interacted with both VDR and RXR blocked 1,25(OH)2D3-dependent transcription by up to 75%. Control LXXLL sequences derived from Src-1 and Grip also suppressed 1,25(OH)2D3-induced transactivation; peptides that interacted with RXR blocked 9-cis-RA-induced transcription. Interestingly, two RXR-interacting peptides were also found to block 1,25(OH)2D3 response effectively. These studies support the idea that comodulator recruitment is essential for VDR- and RXR-mediated gene expression and that RXR is required for 1,25(OH)2D3-induced OC gene transcription. This approach may represent a novel means of assessing the contribution of RXR in various endogenous biological responses to 1,25(OH)2D3.
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PMID:Inhibition of 1,25-dihydroxyvitamin D3-dependent transcription by synthetic LXXLL peptide antagonists that target the activation domains of the vitamin D and retinoid X receptors. 1246 13

Dehydroepiandrosterone sulfotransferase (SULT2A1) is a cytosolic enzyme that mediates sulfo-conjugation of endogenous hydroxysteroids (dehydroepiandrosterone, testosterone, bile acids), and diverse xenobiotic compounds. Upon sulfonation, SULT2A1 substrates become polar and water-soluble and thus suitable for rapid excretion. SULT2A1 is abundantly expressed in the liver and intestine. Recent evidence has shown that the ligand-activated vitamin D receptor (VDR) can transcriptionally induce the xenobiotic-metabolizing cytochrome P450 enzymes. Herein, we report that VDR also targets SULT2A1 for transcriptional activation. Vitamin D stimulated endogenous SULT2A1 expression and induced transfected human, mouse, and rat SULT2A1 promoters in liver and intestinal cells upon cotransfection with VDR. An inverted repeat DNA element (IR0), located within -191 to -168 positions of mouse and rat Sult2A1, mediates VDR induction of Sult2A1. DNase1 footprinting, competition EMSA, and antibody supershift assay showed that the IR0 is a binding site for the RXR-alpha/VDR heterodimer. Point mutations within the IR0 prevented RXR/VDR binding and abolished VDR-mediated Sult2A1 induction. The IR0 element conferred VDR responsiveness on a thymidine kinase promoter. Thus, VDR-mediated nuclear signaling may be important in the phase II metabolism involving Sult2A1. The rodent Sult2A1 gene is also induced by the farnesoid X receptor (FXR) and pregnane X receptor (PXR) through the same IR0. In competition transfections, FXR or PXR inhibited VDR induction of the IR0. Competitive functional interactions among VDR, PXR, and FXR suggest that the intracellular hormonal and metabolic milieu may determine the extent to which a specific nuclear receptor pathway would influence steroid/xenobiotic metabolism using dehydroepiandrosterone sulfotransferase.
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PMID:Dehydroepiandrosterone sulfotransferase is a target for transcriptional induction by the vitamin D receptor. 1497 51


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