Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cholesterol 7-alpha-hydroxylase (CYP7A1) catalyzes a rate-limiting step in bile acid synthesis in liver, and its gene transcription is under complex regulation by multiple nuclear receptors in response to bile acids, cholesterol derivatives, and hormones. The liver receptor homolog-1 (LRH-1), a member of the fushi tarazu factor 1 subfamily of nuclear receptors, has emerged as an essential regulator for the expression of cyp7a1. In this report, we demonstrate Prox1, a prospero-related homeobox transcription factor, identified through a yeast two-hybrid screening, can directly interact with human LRH-1 (hLRH-1) and suppresses hLRH-1-mediated transcriptional activation of human cyp7a1 gene. Biochemical analysis demonstrates that Prox1 interacts with both the ligand binding domain (LBD) and the DNA binding domain (DBD) of hLRH-1. An LRKLL motif in Prox1 is important for the interaction with the LBD but not the DBD of hLRH-1. In hLRH-1 LBD, helices 2 and 10 are essential for Prox1 recruitment. The suppression by Prox1 on the transcriptional activity of hLRH-1 can be mediated through its interaction with the LBD or the DBD of hLRH-1. Gel shift assays reveal that Prox1 impairs the binding of hLRH-1 to the promoter of human cyp7a1 gene.
Mol Endocrinol 2004 Oct
PMID:Prospero-related homeobox (Prox1) is a corepressor of human liver receptor homolog-1 and suppresses the transcription of the cholesterol 7-alpha-hydroxylase gene. 1520 72

The orphan receptor SHP interacts with many nuclear receptors and inhibits their transcriptional activities. SHP is central to feedback repression of cholesterol 7alpha hydroxylase gene (CYP7A1) expression by bile acids, which is critical for maintaining cholesterol homeostasis. Using CYP7A1 as a model system, we studied the molecular mechanisms of SHP repression at the level of native chromatin. Chromatin immunoprecipitation studies showed that mSin3A and a Swi/Snf complex containing Brm as a central ATPase were recruited to the promoter. This recruitment was associated with chromatin remodeling after bile acid treatment that was blunted by inhibition of the endogenous Swi/Snf function by dominant-negative ATPase mutants. Biochemical studies indicated that SHP was associated with the mSin3A-Swi/Snf complex by direct interaction with Brm and mSin3A through its repression domain. Expression of Brm, but not an ATPase mutant, inhibited CYP7A1 promoter activity and further enhanced SHP-mediated repression. Bile acid-induced recruitment of mSin3A/Brm, chromatin remodeling, and concomitant repression of endogenous CYP7A1 expression were impaired when SHP expression was inhibited by SHP small interfering RNA. Our results suggest that SHP mediates recruitment of mSin3A-Swi/Snf to the CYP7A1 promoter, resulting in chromatin remodeling and gene repression, which may also be a mechanism for the repression by SHP of genes activated by many nuclear receptors. Our study establishes the first link between a Swi/Snf complex and regulation of cholesterol metabolism.
Mol Cell Biol 2004 Sep
PMID:Role of an mSin3A-Swi/Snf chromatin remodeling complex in the feedback repression of bile acid biosynthesis by SHP. 1531 77

Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor and acts as a coregulator of various nuclear receptors. Herein, we examined a novel cross talk between SHP and a forkhead transcription factor HNF3 (hepatocyte nuclear factor 3/Foxa. Transient transfection assay demonstrated that SHP inhibited the transcriptional activity of all three isoforms of HNF3, HNF3alpha, beta, and gamma. In vivo and in vitro protein interaction studies showed that SHP physically interacted with HNF3. Adenovirus-mediated overexpression of SHP significantly decreased the mRNA levels of glucose-6-phosphase (G6Pase), cholesterol 7-alpha-hydroxylase (CYP7A1), and phosphoenolpyruvate carboxykinase (PEPCK) in HepG2 cells and rat primary hepatocytes. Moreover, the mRNA level of G6Pase was notably increased by down-regulation of SHP with small interfering RNA. Interestingly, HNF3 transactivity was still repressed by SHPDelta128-139 that fails to repress nuclear receptors. Mapping of interaction domain revealed that SHP interacted with forkhead DNA binding domain of HNF3alpha. Gel mobility shift and chromatin immunoprecipitation assays demonstrated that SHP inhibits DNA binding of HNF3. These results suggest that SHP is involved in the regulation of G6Pase, CYP7A1, and PEPCK gene expression via novel mechanism of inhibition of HNF3 activity and expand the role of SHP as a coregulator of other family of transcription factors in addition to nuclear receptors.
Mol Endocrinol 2004 Dec
PMID:Orphan nuclear receptor small heterodimer partner represses hepatocyte nuclear factor 3/Foxa transactivation via inhibition of its DNA binding. 1535 35

The farnesoid X receptor (FXR) is a nuclear receptor that functions as an endogenous sensor for bile acids (BAs). FXR is bound to and activated by bile acid, and chenodeoxycholic acid (CDCA) is the natural most active ligand. Upon activation, FXR heterodimerizes with the 9-cis retinoic X receptor (RXR) and regulates genes involved in cholesterol and BA homeostasis. 6-Ethyl CDCA (6-ECDCA) is a synthetic BA that binds FXR and induces gene transcription by recruiting coactivators, such as steroid receptor coactivator-1, with histone acetyltransferase activity. In addition to acetylation, histone methylation is critically involved in regulating eukaryotic gene expression. In the present study, we demonstrated that 6-ECDCA activates FXR to interacts with Protein Arginine Methyl-Transferase type I (PRMT1), which induces up-regulation of bile salt export pump (BSEP) and the small heterodimer partner (SHP) mRNA expression and causes a down-regulation of P450 cholesterol 7alpha-hydroxylase and Na(+) taurocholate cotransport peptide genes. Chromatin immunoprecipitation assay suggests that 6-ECDCA induces both the recruitment of PRMT1 and the H4 methylation to the promoter of BSEP and SHP genes. We also provide evidence that a methyltransferase inhibitor blocks the activation of FXR-responsive genes. Our results indicate that histone methylation, similar to acetylation, regulates transcriptional activation of genes involved in cholesterol and BAs homeostasis.
Mol Pharmacol 2005 Aug
PMID:The methyl transferase PRMT1 functions as co-activator of farnesoid X receptor (FXR)/9-cis retinoid X receptor and regulates transcription of FXR responsive genes. 1591 93

Thyroid hormone receptors (TRs) are ligand-regulated transcription factors that bind to thyroid hormone response elements of target genes. Upon ligand binding, they recruit coactivator complexes that increase histone acetylation and recruit RNA polymerase II (Pol II) to activate transcription. Recent studies suggest that nuclear receptors and coactivators may have temporal recruitment patterns on hormone response elements, yet little is known about the nature of the patterns at multiple endogenous target genes. We thus performed chromatin immunoprecipitation assays to investigate coactivator recruitment and histone acetylation patterns on the thyroid hormone response elements of four endogenous target genes (GH, sarcoplasmic endoplasmic reticulum calcium-adenosine triphosphatase, phosphoenolpyruvate carboxykinase, and cholesterol 7alpha-hydroxylase) in a rat pituitary cell line that expresses TRs. We found that TRbeta, several associated coactivators (steroid receptor coactivator-1, glucocorticoid receptor interacting protein-1, and TR-associated protein 220), and RNA Pol II were rapidly recruited to thyroid hormone response elements as early as 15 min after T3 addition. When the four target genes were compared, we observed differences in the types and temporal patterns of recruited coactivators and histone acetylation. Interestingly, the temporal pattern of RNA Pol II was similar for three genes studied. Our findings suggest that thyroid hormone-regulated target genes may have distinct patterns of coactivator recruitment and histone acetylation that may enable highly specific regulation.
Mol Endocrinol 2006 Mar
PMID:Thyroid hormone-regulated target genes have distinct patterns of coactivator recruitment and histone acetylation. 1625 15

The relationship between dietary composition/cholesterol-lowering therapy and final plasma lipid levels is to some extent genetically determined. It is clear that these responses are under polygenic control, with multiple variants in many genes participating in the total effect (and with each gene contributing a relatively small effect). Using different experimental approaches, several candidate genes have been analyzed to date.Interesting and consistent results have been published recently regarding the A-204C promoter variant in the cholesterol 7alpha-hydroxylase (CYP7A1) gene. CYP7A1 is a rate-limiting enzyme in bile acid synthesis and therefore plays an important role in maintaining cholesterol homeostasis. CYP7A1-204CC homozygotes have the greatest decrease in total cholesterol level in response to dietary changes in different types of dietary intervention studies. In contrast, one study has reported that the effect of statins in lowering low-density lipoprotein (LDL)-cholesterol levels was slightly greater in -204AA homozygotes. The CYP7A1 A-204C variant accounts for a significant proportion of the genetic predisposition of the response of plasma cholesterol levels.
Mol Diagn Ther 2006
PMID:Role of cholesterol 7alpha-hydroxylase (CYP7A1) in nutrigenetics and pharmacogenetics of cholesterol lowering. 1666 7

Cytochrome P450 (P450) is a superfamily of individual monooxygenase enzymes that metabolize structurally diverse xenochemicals, including many clinically useful drugs and foreign chemicals widespread in the environment. P450 substrates that can be used to selectively monitor individual P450 enzymes or P450 subfamilies have been identified through studies using P450 enzyme-selective inhibitory antibodies and chemical inhibitors in conjunction with experiments utilizing individual cDNA-expressed P450 enzymes. This chapter describes P450 form-selective substrates that can be used to monitor the activities of human P450 enzymes CYP1A, CYP1B1, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A, CYP4A11, and CYP7A1. Cautions that need to be exercised when using these substrates to probe for individual P450 activities in human liver and other tissues are discussed.
Methods Mol Biol 2006
PMID:Catalytic assays for human cytochrome P450: an introduction. 1671 75

A normal-phase, isocratic high-performance liquid chromatography assay is described for cholesterol 7alpha-hydroxylation catalyzed by CYP7A1, which corresponds to the first and rate-limiting step in the conversion of cholesterol into bile acids. This method is based on the conversion of the primary cytochrome P450 metabolite, 7alpha-hydroxycholesterol, into 7alpha-hydroxy-4-cholesten-3-one in a reaction catalyzed by exogenous cholesterol oxidase, followed by chromatographic separation with monitoring at 254 nm. This technique is applicable to enzymatic studies for determination of cholesterol 7alpha-hydroxylation activity catalyzed by cDNA-expressed CYP7A1 and animal or human liver microsomes.
Methods Mol Biol 2006
PMID:An isocratic high-performance liquid chromatography assay for CYP7A1-catalyzed cholesterol 7alpha-hydroxylation. 1671 86

A cDNA microarray analysis was conducted to examine hepatic gene expression profiles in pregnant and lactating F344 rats compared to a virgin control group using an Affymetrix GeneChip system. Of the approximately 16000 gene transcripts interrogated, more than 1000 were significantly modified in their expression when detected either in late pregnancy (19 days of gestation, GD 19, 513 genes upregulated and 579 downregulated) or on the day of delivery (postpartum 0 day, PPD 0, 497 upregulated and 733 downregulated). Particular interest was paid to the gene expression of drug-metabolizing enzymes (DMEs) and nuclear receptors (NRs). Though the expression of a few genes, those for CYP7A1, CYP51 and Sultx3, increased, the expression of a number of genes encoding DMEs (Phase I and Phase II) and NRs decreased during pregnancy and lactation. Changes in the expression of 9 genes encoding DMEs and NRs were confirmed by quantitative real-time PCR. For all 9 genes tested, overall, the results of the microarray and real-time PCR analyses were in agreement. This is the first application of a microarray analysis to the expression profiling of genes encoding DMEs and NRs in the liver of pregnant and lactating rats. When combined with other studies, the present study may provide a basis for investigating the mechanism of toxicity of environmental or other nonphysiologic chemicals to the fetus and mother and drug safety during pregnancy and lactation.
Exp Mol Pathol 2007 Dec
PMID:Gene expression profiles of drug-metabolizing enzymes (DMEs) in rat liver during pregnancy and lactation. 1682 15

The nuclear receptors liver X receptor (LXR) LXRalpha and LXRbeta are differentially expressed ligand-activated transcription factors that induce genes controlling cholesterol homeostasis and lipogenesis. Synthetic ligands for both receptor subtypes activate ATP binding cassette transporter A1 (ABCA1)-mediated cholesterol metabolism, increase reverse cholesterol transport, and provide atheroprotection in mice. However, these ligands may also increase hepatic triglyceride (TG) synthesis via a sterol response element binding protein 1c (SREBP-1c)-dependent mechanism through a process reportedly regulated by LXRalpha. We studied pan-LXRalpha/beta agonists in LXRalpha knockout mice to assess the contribution of LXRbeta to the regulation of selected target genes. In vitro dose-response studies with macrophages from LXRalpha-/- and beta-/- mice confirm an equivalent role for LXRalpha and LXRbeta in the regulation of ABCA1 and SREBP-1c gene expression. Cholesterol-efflux studies verify that LXRbeta can drive apoA1-dependent cholesterol mobilization from macrophages. The in vivo role of LXRbeta in liver was further evaluated by treating LXRalpha-/- mice with a pan-LXRalpha/beta agonist. High-density lipoprotein (HDL) cholesterol increased without significant changes in plasma TG or very low density lipoprotein. Analysis of hepatic gene expression consistently revealed less activation of ABCA1 and SREBP-1c genes in the liver of LXRalpha null animals than in treated wild-type controls. In addition, hepatic CYP7A1 and several genes involved in fatty acid/TG biosynthesis were not induced. In peripheral tissues from these LXRalpha-null mice, LXRbeta activation increases ABCA1 and SREBP-1c gene expression in a parallel manner. However, putative elevation of SREBP-1c activity in these tissues did not cause hypertriglyceridemia. In summary, selective LXRbeta activation is expected to stimulate ABCA1 gene expression in macrophages, contribute to favorable HDL increases, but circumvent hepatic LXRalpha-dominated lipogenesis.
Mol Pharmacol 2006 Oct
PMID:Liver X receptor (LXR)-beta regulation in LXRalpha-deficient mice: implications for therapeutic targeting. 1682 83


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