Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The rat Reuber hepatoma cell cell line, H4IIEC3, has been used in gene transfection studies to study the molecular mechanisms of induction of the acyl CoA oxidase gene, the first and rate-limiting enzyme of the peroxisomal fatty acid beta-oxidation spiral. cDNAs encoding the peroxisome proliferator activated receptor and the 9-cis retinoic acid receptor were transfected into the cells, either in the presence or absence of their cognate ligands (Wy-14,643 and 9-cis retinoic acid respectively), in addition to the acyl CoA oxides promoter linked to a chloramphenicol acetyltransferase reporter gene construct. The above experimental approach has confirmed that the 9-cis retinoic acid receptor acts cooperatively with the peroxisome receptor in mediating activation of the acyl CoA oxidase gene. In addition, in vivo experiments have demonstrated that treatment of rats with peroxisome proliferators substantially increase the hepatic levels of the peroxisome receptor mRNA itself. Taken collectively, the above data provides a wealth of molecular and mechanistic information on perioxisome proliferation in the rat and is discussed in terms of the safety assessment of peroxisome proliferators in man.
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PMID:Molecular toxicology of peroxisome proliferators. 786 64

Transcription of the phosphoenolpyruvate carboxykinase gene is stimulated by glucocorticoids, retinoic acid, and cAMP and is dominantly inhibited by insulin and phorbol esters. The glucocorticoid response is mediated by a complex regulatory unit that consists of two glucocorticoid receptor (GR) binding sites (GR1 and GR2) and two adjacent accessory factor elements (AF1 and AF2). Deletion of either the AF1 or the AF2 element results in a 50-75% reduction of the glucocorticoid response. In addition to their accessory role in glucocorticoid action, the AF1 and AF2 elements mediate retinoic acid and insulin/phorbol ester effects, respectively. Site-directed mutagenesis was performed on AF1 and AF2 to precisely locate the sequences responsible for accessory activity in each element. The glucocorticoid accessory activity of the AF1 element maps to the same 12-base pair sequence (TGACCTTTGGCC) involved in the response of the PEPCK gene to retinoic acid. The glucocorticoid accessory activity of the AF2 region maps to the same 10-base pair sequence (TGGTGTTTTG) responsible for mediating the insulin and phorbol ester responses through this element. The AF1 and AF2 elements bind different sets of nuclear proteins, and this binding is not qualitatively or quantitatively affected by treatment of the rat H4IIE hepatoma cells with retinoic acid (AF1) or insulin (AF2). AF2 functions in a heterologous context (a consensus glucocorticoid response element and the thymidine kinase promoter), whereas AF1 functions in this context only if the retinoic acid receptor is overexpressed in the cells. These results show that the AF1 and AF2 elements affect the glucocorticoid response through different protein DNA interactions, and that a small sequence in each serves multiple functions. Together with GR1 and GR2, they form a complex hormone response unit which provides an integrated response of the phosphoenolpyruvate carboxykinase gene to a variety of positive and negative signals.
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PMID:Integration of multiple signals through a complex hormone response unit in the phosphoenolpyruvate carboxykinase gene promoter. 805 68

Retinoic acid (RA) is known to have potent effects on development and differentiation. RA exerts its effects on transcription through two distinct classes of nuclear receptors, the retinoic acid receptor (RAR) and the retinoid X receptor (RXR), that bind to specific RA-responsive elements (RARE) in target genes. alpha-Fetoprotein (AFP), a hepatocyte differentiation, maturation, and carcinogenesis marker, is transcriptionally upregulated by RA in McA-RH8994 hepatoma cells. Using deletion mapping analysis, we have identified a RARE-like sequence that is located between -2406 and -2378 of the transcription initiation site of the rat AFP gene. Sequence analysis demonstrated that this cis-acting element consists of three direct repeats and one inverted repeat of a GGGTCA-like half-site. The putative RARE can specifically bind to both RXR homodimers and RAR/RXR heterodimers as determined by gel mobility shift assays. A DR1 direct repeat was more efficient than a DR5 direct repeat oligonucleotide in competition for binding of the putative RARE to RXR and RAR/RXR. A mutagenesis study indicated that to have a full-strength induction, all the repeats were required. To further analyze the function of this element in vivo, a reporter gene construct of the putative RARE combined with the thymidine kinase promoter was cotransfected with RAR and RXR expression plasmids in CV1 cells. CAT assays demonstrated that overexpression of RXRalpha conferred the best RA response, consistent with our previous observation that 9-cis-RA is more potent than all-trans-RA for inducing the expression of the AFP gene. In addition, the RXR selective ligand LG100153 alone can stimulate the expression of the AFP gene. Our data suggest that an RXR-mediated pathway exists for modulation of AFP gene expression through a specific element.
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PMID:RXR-mediated regulation of the alpha-fetoprotein gene through an upstream element. 894 36

Hypertriglyceridemia is a metabolic complication of retinoid therapy. In this study, we analyzed whether retinoids increase the expression of apo C-III, an antagonist of plasma triglyceride catabolism. In men, isotretinoin treatment (80 mg/d; 5 d) resulted in elevated plasma apo C-III, but not apo E concentrations. In human hepatoma HepG2 cells, retinoids increased apo C-III mRNA and protein production. Transient transfection experiments indicated that retinoids increase apo C-III expression at the transcriptional level. This increased apo C-III transcription is mediated by the retinoid X receptor (RXR), since LG1069 (4-[1-(5,6,7,8-tetrahydro-3,5,5,8, 8-pentamethyl-2-naphtalenyl)ethenyl]benzoic acid), a RXR-specific agonist, but not TTNPB ((E)- 4-[2-(5,6,7,8-tetrahydro-5,5,8, 8-tetramethyl-2-naphtalenyl)propenyl]benzoic acid), a retinoic acid receptor (RAR)-specific agonist, induced apo C-III mRNA in HepG2 cells and primary human hepatocytes. Mutagenesis experiments localized the retinoid responsiveness to a cis-element consisting of two imperfect AGGTCA sequences spaced by one oligonucleotide (DR-1), within the previously identified C3P footprint site. Cotransfection assays showed that RXR, but not RAR, activates apo C-III transcription through this element either as a homo- or as a heterodimer with the peroxisome proliferator-activated receptor. Thus, apo C-III is a target gene for retinoids acting via RXR. Increased apo C-III expression may contribute to the hypertriglyceridemia and atherogenic lipoprotein profile observed after retinoid therapy.
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PMID:Retinoids increase human apo C-III expression at the transcriptional level via the retinoid X receptor. Contribution to the hypertriglyceridemic action of retinoids. 969 Oct 99

Pregnane X Receptor (PXR) has been recently shown to regulate the inducible expression of CYP3A genes in response to xenobiotics and steroids. PXR forms a heterodimer with the retinoic acid receptor (RXR) and this complex binds to and transactivates an 18bp region containing two everted repeats TGA(A/C)CT separated by 6 nucleotides (ER6) and located at approximately -150 in the CYP3A4 promoter. In this work we have isolated and sequenced the proximal 5'-flanking region of CYP3A7 from two different human genomic libraries. In contrast to a previously reported sequence (Itoh et al., 1992), we did not observe any mutation in the 3'-half of the CYP3A7 ER6 element. Using electrophoretic mobility shift assays and cotransfection experiments we show that this element is able to bind the PXR:RXR complex and transactivates the expression of a down stream promoter in response to rifampicin, clotrimazole, and RU-486, three compounds known to specifically activate the human PXR. This is consistent with the fact that CYP3A7 mRNA is inducible in several primary cultures of human hepatocytes from different patients, as well as in two hepatocarcinoma cell lines HuH7 and HepG2, in response to these compounds. In contrast to a previous report (Blumberg et al., 1998), based on the sequence published by Itoh et al., we conclude that CYP3A7, like CYP3A4, is inducible in response to xenobiotics and presumably in a large proportion of the population.
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PMID:Evidence for the presence of a functional pregnane X receptor response element in the CYP3A7 promoter gene. 1040 78

The peroxisome proliferator-activated receptor alpha (PPARalpha) plays a key role in lipid and lipoprotein metabolism. However, important inter- and intraspecies differences exist in the response to PPARalpha activators. This incited us to screen for PPARalpha variants with different signaling functions. In the present study, using a RT-PCR approach a variant human PPARalpha mRNA species was identified, which lacks the entire exon 6 due to alternative splicing. This deletion leads to the introduction of a premature stop codon, resulting in the formation of a truncated PPARalpha protein (PPARalphatr) lacking part of the hinge region and the entire ligand-binding domain. RNase protection analysis demonstrated that PPARalphatr mRNA is expressed in several human tissues and cells, representing between 20-50% of total PPARalpha mRNA. By contrast, PPARalphatr mRNA could not be detected in rodent tissues. Western blot analysis using PPARalpha-specific antibodies demonstrated the presence of an immunoreactive protein migrating at the size of in vitro produced PPARalphatr protein both in human hepatoma HepG2 cells and in human hepatocytes. Both in the presence or absence of 9-cis-retinoic acid receptor, PPARalphatr did not bind to DNA in gel shift assays. Immunocytochemical analysis of transfected CV-1 cells indicated that, whereas transfected PPARalphawt was mainly nuclear localized, the majority of PPARalphatr resided in the cytoplasm, with presence in the nucleus depending on cell culture conditions. Whereas a chimeric PPARalphatr protein containing a nuclear localization signal cloned at its N-terminal localized into the nucleus and exhibited strong negative activity on PPARalphawt transactivation function, PPARalphatr interfered with PPARalphatr transactivation function only under culture conditions inducing its nuclear localization. Cotransfection of the coactivator CREB-binding protein relieved the transcriptional repression of PPARalphawt by PPARalphatr, suggesting that the dominant negative effect of PPARalphatr might occur through competition for essential coactivators. In addition, PPARalphatr interfered with transcriptional activity of other nuclear receptors such as PPARgamma, hepatic nuclear factor-4, and glucocorticoid receptor-alpha, which share CREB-binding protein/p300 as a coactivator. Thus, we have identified a human PPARalpha splice variant that may negatively interfere with PPARalphawt function. Factors regulating either the ratio of PPARalphawt vs. PPARalphatr mRNA or the nuclear entry of PPARalphatr protein should therefore lead to altered signaling via the PPARalpha and, possibly also, other nuclear receptor pathways.
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PMID:A truncated human peroxisome proliferator-activated receptor alpha splice variant with dominant negative activity. 1047 44

The intracellular fatty acid content of insulin-sensitive target tissues determines in part their insulin sensitivity. Uptake of fatty acids into cells is a controlled process determined in part by a regulated import/export system that is controlled at least by two key groups of proteins, i.e. the fatty acid transport protein (FATP) and acyl-CoA synthetase (ACS), which facilitate, respectively, the transport of fatty acids across the cell membrane and catalyze their esterification to prevent their efflux. Previously it was shown that the expression of the FATP-1 and ACS genes was controlled by insulin and by peroxisome proliferator-activated receptor (PPAR) agonists in liver or in adipose tissue. The aim of this investigation was to determine the effects of retinoic acid derivatives on the expression of FATP-1 and ACS. In several cultured cell lines, it was shown that the expression of both the FATP-1 and ACS mRNAs was specifically induced at the transcriptional level by selective retinoid X receptor (RXR) but not by retinoic acid receptor (RAR) ligands. This effect was most pronounced in hepatoma cell lines. A similar induction of FATP-1 and ACS mRNA levels was also observed in vivo in Zucker diabetic fatty rats treated with the RXR agonist, LGD1069 (4-[1-(3,5,5,8,8-pentamethyl-5,6,7, 8-tetrahydro-2-naphthyl)ethenyl]benzoic acid). Through the use of heterodimer-selective compounds, it was demonstrated that the modulatory effect of these rexinoids on FATP-1 and ACS gene expression was mediated through activation of RXR in the context of the PPAR-RXR heterodimer. The observation that both RXR and PPAR agonists can stimulate the transcription of genes implicated in lipid metabolism, suggest that rexinoids may also act as lipid-modifying agents and support a role of the permissive PPAR-RXR heterodimer in the control of insulin sensitivity.
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PMID:Induction of the fatty acid transport protein 1 and acyl-CoA synthase genes by dimer-selective rexinoids suggests that the peroxisome proliferator-activated receptor-retinoid X receptor heterodimer is their molecular target. 1077 52

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

We review the therapeutic and preventive applications of a retinoid analog (vitamin A and its derivatives) for human cancers. Chemoprevention of cancer is an intervention in the carcinogenic process by chemical agents that block or reverse the malignant transformation of cells. Retinoids are prime candidates for cancer chemoprevention since cancer is characterized by abnormal growth with a lack of differentiation, which could be modified by retinoids. Retinoids exert their biological functions through nuclear receptors, retinoic acid receptor (RAR) and retinoid X receptor (RXR). A number of experimental and clinical studies have been performed in the past two decades with retinoids showing that they inhibit or reverse the carcinogenic process in some organs, including hematological malignancy as well as premalignant and malignant lesions in the oral cavity, head and neck, breast, skin and liver. We particularly focus upon the therapeutic application of all-trans RA (atRA) to acute promyelocytic leukemia (APL) and on the preventive approach to hepatocellular carcinoma (HCC) by a synthetic retinoid analog, acyclic retinoid. In both malignancies, malfunction of retinoid nuclear receptors is closely related to their carcinogenic process. In APL, a chromosomal translocation produces a chimeric protein between RAR alpha and a protein called promyelocyte leukemia protein (PML). PML-RAR alpha works as a dominant negative receptor in the leukemic cells, interfering with the normal function of RAR alpha and/or PML, which in turn results in the arrest of cell maturation at the stage of promyelocytes. Oral administration of atRA induces differentiation of promyelocytic leukemic cells to mature neutrophils, and leads to a high rates (over 90%) of complete remission. AtRA therapy has become standard in the treatment of APL. In the case of HCC, post-translational modification of RXR by phosphorylation impairs its function, which leads to uncontrolled cell growth. Acyclic retinoid suppresses the phosphorylation of RXR alpha, restores its function in the presence of its endogenous ligand, 9-cis RA, and thereby induces apoptosis of the cancer cells. Acyclic retinoid given orally successfully suppresses the development of second primary tumors in cirrhotic patients who undergo curative removal of preceding HCC. Eradication of (pre)malignant clones ('clonal deletion') from the liver is suggested as a mechanism of the chemopreventive effect. Further development of more effective retinoids as well as their use in combination with other classes of anticancer agents including immunopreventive drugs like interferons may provide strategies for cancer prevention.
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PMID:Retinoids in cancer chemoprevention. 1513 35

Activation of phosphoenolpyruvate carboxykinase (PEPCK) gene transcription in response to all-trans-retinoic acid (RA) or a glucocorticoid such as dexamethasone (Dex) requires a distinct arrangement of DNA-response elements and their cognate transcription activators on the gene promoter. Two of the accessory factor-binding elements involved in the Dex response (gAF1 and gAF3) coincide with the DNA-response elements involved in the RA response. We demonstrate here that the combination of Dex/RA has a synergistic effect on endogenous PEPCK gene expression in rat hepatocytes and H4IIE hepatoma cells. Reporter gene studies show that the gAF3 element and one of the two glucocorticoid receptor-binding elements (GR1) are most important for this effect. Chromatin immunoprecipitation assays revealed that when H4IIE cells were treated with Dex/RA, ligand-activated retinoic acid receptors (retinoic acid receptor/retinoid X receptor) and glucocorticoid receptors are recruited to this gene promoter, as are the transcription coregulators p300, CREB-binding protein, p/CIP, and SRC-1. Notably, the recruitment of p300 and RNA polymerase II to the PEPCK promoter is increased by the combined Dex/RA treatment compared with Dex or RA treatment alone. The functional importance of p300 in the Dex/RA response is illustrated by the observation that selective reduction of this coactivator, but not that of CREB-binding protein, abolishes the synergistic effect in H4IIE cells.
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PMID:The synergistic effect of dexamethasone and all-trans-retinoic acid on hepatic phosphoenolpyruvate carboxykinase gene expression involves the coactivator p300. 1516 31


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