UMLS:C0019204 - FACTA Search

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Query: UMLS:C0019204 (hepatocellular carcinoma)
71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The gene coding for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) is expressed in all gluconeogenic tissues, but stimulation of its rate of transcription by cAMP is robust only in liver. Evidence has accumulated which suggests that a liver-enriched transcription factor, likely a member of the CCAAT/enhancer binding protein (C/EBP) family, is required along with other ubiquitously expressed transcription factors to mediate this liver-specific response to cAMP. In this study, we examined the ability of C/EBP to participate in the cAMP-mediated activation of phosphoenolpyruvate carboxykinase (PEPCK) gene transcription in hepatoma cells. Expression of a dominant repressor of C/EBP in hepatoma cells significantly inhibited the protein kinase A-stimulated transcription of the PEPCK promoter, suggesting that a C/EBP family member was required for maximal transcriptional activation by protein kinase A. To provide additional support for this hypothesis, we prepared GAL4 fusion proteins containing C/EBP domains. Both C/EBPalpha and C/EBPbeta GAL4 fusion proteins were capable of stimulating transcription from promoters containing binding sites for the DNA-binding domain of GAL4. However, only the GAL4-C/EBPalpha fusion protein demonstrated the ability to synergize with the other transcription factors bound to the PEPCK promoter which are required to mediate cAMP responsiveness. The DNA-binding domain of C/EBPalpha was not required for this activity in hepatoma cells, although in non-hepatoma cells the basic region leucine zipper domain appeared to inhibit the ability of C/EBPalpha to participate in mediating cAMP responsiveness. These results suggest that the liver-specific nature of the cAMP responsiveness of the PEPCK promoter involves the recruitment of C/EBPalpha to the cAMP response unit.
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PMID:The alpha-isoform of the CCAAT/enhancer-binding protein is required for mediating cAMP responsiveness of the phosphoenolpyruvate carboxykinase promoter in hepatoma cells. 862 91

Recently, Kalvakolanu et al. (Kalvakolanu, D. V. R., Liu, J., Hanson, R. W., Harter, M. L., and Sen, G. C. (1992) J. Biol. Chem. 267, 2530-2536) showed that E1A inhibited the basal and cAMP-stimulated transcription of the gene for phosphoenolpyruvate carboxykinase (PEPCK). This inhibition was mediated by the conserved region 1 (CR1) domain of E1A, which has been shown by other laboratories to bind to the cellular transcriptional adaptor proteins, p300 and cAMP response element binding protein (CREB)-binding protein (CBP). The PEPCK gene promoter contains a functional cAMP-response element, through which CREB and, therefore, CBP modulate transcription, and a consensus p300 DNA binding sequence is also present in a distal protein binding site of the promoter. We hypothesized that E1A might inhibit PEPCK gene transcription by binding to p300 and/or CBP. Surprisingly, we found that E1A consistently stimulated basal transcription from the PEPCK promoter in transfection assays in adenovirus (Ad)-infected HepG2 hepatoma cells or E1A-expressing, stably transfected 3T3 fibroblasts and nuclear run-on assays in Ad-infected H4IIE hepatoma cells. E1A also enhanced the stimulation of PEPCK gene transcription by Bt2cAMP. In transfection assays, wild type Ad5 expressing both 243R and 289R forms of E1A or a mutant virus expressing the 289R form alone stimulated transcription from the PEPCK promoter by approximately 5-fold 20 h postinfection. However, no stimulation was observed in cells infected with a virus expressing either the 243R protein alone or a 289R protein from which conserved region 3 (CR3) was mutated. Mutation or deletion of CR1 of E1A had no significant effect on transcription from the PEPCK promoter. Mutations within conserved region 2 (CR2) of E1A that inhibit the binding of E1A to the retinoblastoma gene product (pRb) further enhanced the stimulation of transcription from the PEPCK promoter by 2 3-fold compared with wild type E1A. These findings suggested that the normal function of pRb is to stimulate PEPCK gene transcription, and that this process is inhibited by the binding of E1A to pRb. This hypothesis was confirmed by overexpressing pRb in HepG2 cells, which stimulated transcription from the PEPCK promoter. Our findings indicate that Ad E1A regulates PEPCK gene transcription through a stimulatory mechanism involving CR3, and by attenuating a stimulatory effect of pRb through CR2.
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PMID:Adenovirus E1A proteins regulate phosphoenolpyruvate carboxykinase gene transcription through multiple mechanisms. 862 93

Efficient transfer of genes maintaining a correct hormonal control in transfected cells is the prerequisite for gene regulation studies and for gene therapy. Differentiated cells, like adipocytes or hepatocytes, are difficult to transfect. In an attempt to improve gene transfer, we first transiently transfected cultured 3T3-F442A adipocytes with a construct containing the simian virus 40 (SV40) promoter fused to the chloramphenicol acetyltransferase (CAT) gene (pSV2-CAT), using various cationic liposomes. Among these, only lipofectAMINE was five times more efficient than the standard calcium phosphate procedure. To further augment efficiency, we transfected 3T3-F442A adipocytes and FAO hepatoma cells with the lipofectAMINE/pSV2-CAT complex in the presence of replication-deficient recombinant type-5 adenovirus at 200 pfu/cell. CAT activity of transiently transfected cells was increased about 50-fold when compared to the calcium phosphate procedure. To determine whether this methodology would be useful for obtaining stable transfectants and would not interfere with correct gene regulation, we used a construct containing -2100 to +69 bp of the phosphoenolpyruvate carboxykinase gene fused to the CAT gene (pPL1-CAT). This construct was shown previously to be cAMP-responsive after calcium-phosphate-mediated transfection of adipocytes and hepatoma cells. 3T3-F442A or FAO cells in which pPL1-CAT was either transiently or stably transferred by lipofectAMINE and adenovirus responded to isoproterenol or cAMP, respectively, with a 2-3-fold increase in CAT activity. Therefore the association of liposomes and adenovirus is an efficient method for transient or stable transfer of regulated genes in adipocytes and hepatoma cells.
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PMID:Efficient transfer of regulated genes in adipocytes and hepatoma cells by the combination of liposomes and replication-deficient adenovirus. 864 10

Expression of the phenylalanine hydroxylase gene in livers and kidneys of rodents is activated at birth and is induced by glucocorticoids and cyclic AMP in the liver. Regulatory elements in a 10-kb fragment upstream of the mouse gene have been characterized. The promoter lacks TAATA and CCAAT consensus sequences and shows only extremely weak activity in transitory expression assays with phenylalanine hydroxylase-producing hepatoma cells. No key elements for regulation of promoter activity are localized within 2 kb of upstream sequences. However, a liver-specific DNase I-hypersensitive site at kb -3.5 comprises a tissue-specific and hormone-inducible enhancer. This enhancer contains multiple protein binding sites, including sites for ubiquitous factors (NF1 and AP1), the glucocorticoid receptor, and the hepatocyte-enriched transcription factors hepatocyte nuclear factor 1 (HNF1) and C/EBP. Mutation revealed that the last two sites are critical not only for basal activity but also for obtaining a maximal hormone response. Efficient transcription from the highly inducible promoter shows absolute dependence upon the enhancer at kb - 3.5, which in turn requires HNF1 and C/EBP as well as hormones. The regulatory region of the mouse phenylalanine hydroxylase gene differs totally from that of humans, even though the genes of both species are expressed essentially in the liver. Furthermore, the phenylalanine hydroxylase gene of mice shows an expression pattern very similar to those of the rodent tyrosine aminotransferase and phosphoenolpyruvate carboxykinase genes, yet each shows a different organization of its regulatory region.
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PMID:The activity of the highly inducible mouse phenylalanine hydroxylase gene promoter is dependent upon a tissue-specific, hormone-inducible enhancer. 864 24

Expression of the serum albumin gene is extinguished in rat hepatoma microcell hybrids that retain mouse chromosome 1. These data define a trans-dominant extinguisher locus, Tse-2, on mouse chromosome 1. To localize the human TSE2 locus, we prepared and characterized rat/human microcell hybrids that contained either human chromosome 1 or chromosome 2, the genetic homologues of mouse chromosome 1. Rat hepatoma microcell hybrids retaining a derivative human chromosome 1 [der 1 t(1;17)(p34.3;q11.2)] expressed their serum albumin genes at levels similar to those of parental hepatoma cells. In contrast, microcell transfer of human chromosome 2 into rat hepatoma recipients produced karyotypically heterogeneous collections of hybrid clones, some of which displayed dramatic albumin extinction phenotypes. For example, albumin mRNA levels in several extinguished microcell hybrids were reduced at least 500-fold, similar to albumin mRNA levels in hepatoma x fibroblast whole-cell hybrids. Expression of several other liver genes, including alpha 1-antitrypsin, aldolase B, alcohol dehydrogenase, and phosphoenolpyruvate carboxykinase, was also affected in some of the microcell hybrids, but expression of these genes was not concordant with expression of albumin. Hybrid segregants were prepared from the albumin-extinguished hybrids, and reexpression of albumin mRNA and protein was observed in sublines that had lost or fragmented human chromosome 2. Finally, expression of mRNAs encoding the liver-enriched trans activators HNF-1, HNF-4, HNF-3 alpha, and HNF-3 beta was not affected in any of the chromosome 2-containing hybrids. These data define and map a genetic locus on human chromosome 2 that extinguishes albumin gene expression in trans, and they suggest that TSE2-mediated extinction is independent of HNF-1, -4, -3 alpha, and -3 beta expression.
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PMID:Extinction of albumin gene expression in a panel of human chromosome 2 microcell hybrids. 883 17

The effect of anisoosmolarity on the abundance of various mRNA species was examined in perfused rat liver and H4IIE rat hepatoma cells. Hyperosmotic exposure (385 mosmol/l) of isolated rat livers increased mRNA levels for tyrosine aminotransferase (TAT) by 246% and those for phosphoenolpyruvate carboxykinase (PEPCK) by 186%, whereas hypoosmotic exposure (225 mosmol/l) decreased their levels to 43% and 42%, respectively. mRNA levels for fructose-1,6-bisphosphatase (FBP), argininosuccinate lyase (ASL), argininosuccinate synthetase (ASS), glutamine synthetase (GS), glutaminase (GA) and glucokinase (GK) were largely unaffected. In H4IIE cells the modulation of TAT and PEPCK mRNA levels by anisoosmotic exposure was similar to that found in perfused rat liver. ASL and glutaminase mRNA levels were influenced in an opposite manner. The effects of anisoosmolarity on PEPCK mRNA levels in H4IIE cells were largely abolished in the presence of the protein kinase inhibitors H-7, H-89 and HA-1004. Other protein kinase inhibitors such as Go-6850, KN-62, Rp-8-CPT-cAMPS, rapamycin, wortmannin, genistein or herbimycin did not prevent the osmosensitivity of PEPCK mRNA levels. Also pertussis and cholera toxin, vanadate and colchicine did not affect the osmosensitivity of PEPCK mRNA levels. The data suggest that anisoosmotic exposure acts on the levels of some but not all mRNA species and that this action may involve changes in protein phosphorylation. They further indicate that the recently identified osmosensitive signal transduction pathway which involves a G-protein and tyrosine kinase dependent activation of mitogen-activated protein kinases is apparently not involved in the osmoregulation of PEPCK mRNA levels.
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PMID:Anisoosmotic regulation of hepatic gene expression. 892 14

We engineered a hepatoma cell line that produces an up-regulation of insulin in response to cAMP, dexamethasone, and retinoic acid, and a down-regulation in response to insulin. We devised a regulatory secretion system by placing proinsulin DNA under the regulatable promoter for phosphoenolpyruvate carboxykinase (PEPCK). To assess the ability to regulate insulin secretion, we used the rat hepatoma cell line, H4IIE. The H4IIE cells secreted immunoreactive insulin (IRI) constantly at a level of 1-3 fmol/10(6) cells/h. IRI increased approximately two-fold upon stimulation with 0.5 mM cAMP and five-fold with the addition of the cAMP-dependent phosphodiesterase inhibitor IBMX, as compared to baseline IRI secretion. IRI increased 18-fold by 1-500 nM dexamethasone together with cAMP and IBMX. Addition of exogenous insulin to the culture medium significantly decreased insulin mRNA expression on Northern blot.
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PMID:Regulatable production of mature insulin from a hepatocyte cell line: insulin production is up-regulated by cAMP and glucocorticoids, and down-regulated by insulin. 898 Jan 15

Upon birth, the liver acquires new functions as a result of the initiation of expression of key enzymes. One example is the initiation of gluconeogenesis which depends on the induced appearance of phosphoenolpyruvate carboxykinase (P-pyruvate-CK) at birth. To characterize other genes that undergo such regulation, a differential screening was performed on a cDNA library from well-differentiated hepatoma cells. The pattern of tissue-specific and developmental-specific expression was determined for seven genes. Three clones, out of which two encode for the known genes alcohol dehydrogenase class I (ADH) and phenylalanine 4-monooxygenase (PAH) and a new gene (clone 116-3), exhibited a pattern of expression similar to that of the P-pyruvate-CK gene, i.e. their expression was liver and kidney specific and induced in the liver upon birth. Determination of the sequence of clone 116-3 revealed that it belonged to the UDP-glucuronosyltransferases type 2 (UGT2) family and thus was named UGT2B-rH4. To examine whether expression of the various genes could be prematurely induced by hormones in the fetal liver, either high levels of cAMP or low levels of insulin were induced in utero. The results demonstrated that cAMP induced a marked expression only of the genes for P-pyruvate-CK and ADH but not of those for PAH or UGT2B-rH4, while insulin deficiency induced premature expression of all four genes. We suggest that a set of genes whose expression is specifically induced in the liver upon birth can be prematurely induced by the hormones in utero.
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PMID:Identification of differentially expressed genes during hepatocytes development and characterization of their prenatal hormonal induction. 902 81

Glucocorticoids inhibit basal and hormone-induced phosphoenolpyruvate carboxykinase (PEPCK) gene transcription in adipocytes whereas beta-adrenergic agonists and fibrates are stimulatory. Here we show that dexamethasone inhibits the induction of PEPCK mRNA by isoprenaline or clofibrate in 3T3-F442A adipocytes. RU 38486 antagonizes dexamethasone effect, suggesting the involvement of the glucocorticoid receptor. In H4IIE hepatoma cells, glucocorticoids enhance PEPCK gene transcription through a complex region which encompasses an element, AF1, with a direct repeat 1-type sequence. Mutations in the AF1 sequence abolish binding of nuclear factors from liver and from 3T3-F442A adipocytes. We transiently transfected 3T3-F442A cells with a wild type or an AF1-mutated PEPCK-CAT construct comprising -2100 to +69 base pairs of the promoter fused to the chloramphenicol acetyltransferase (CAT) gene. With both constructs, CAT activity is decreased by dexamethasone and is increased by isoprenaline or by clofibrate. However, dexamethasone is unable to inhibit clofibrate induction of CAT activity in cells transfected with the AF1-mutated construct whereas it prevents isoprenaline action on both constructs. Hence, although a single hormone can repress stimulations originating from different intracellular routes, sites in the promoter which mediate inhibition of a specific stimulation are distinct.
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PMID:Glucocorticoids use a positive liver element to repress fibrate-induced adipose transcription of the phosphoenolpyruvate carboxykinase gene. 909 12

Glucose-6-phosphatase (G6Pase) catalyzes the final step in the gluconeogenic and glycogenolytic pathways. The transcription of the gene encoding the catalytic subunit of G6Pase is stimulated by glucocorticoids, whereas insulin strongly inhibits both basal G6Pase gene transcription and the stimulatory effect of glucocorticoids. To identify the insulin response sequence (IRS) in the G6Pase promoter through which insulin mediates its action, we have analyzed the effect of insulin on the basal expression of mouse G6Pase-chloramphenicol acetyltransferase (CAT) fusion genes transiently expressed in hepatoma cells. Deletion of the G6Pase promoter sequence between -271 and -199 partially reduces the inhibitory effect of insulin, whereas deletion of additional sequence between -198 and -159 completely abolishes the insulin response. The presence of this multicomponent IRS may explain why insulin potently inhibits basal G6Pase-CAT expression. The G6Pase promoter region between -198 and -159 contains an IRS, since it can confer an inhibitory effect of insulin on the expression of a heterologous fusion gene. This region contains three copies of the T(G/A)TTTTG sequence, which is the core motif of the phosphoenolpyruvate carboxykinase (PEPCK) gene IRS. This suggests that a coordinate increase in both G6Pase and PEPCK gene transcription is likely to contribute to the increased hepatic glucose production characteristic of patients with non-insulin-dependent diabetes mellitus.
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PMID:A multicomponent insulin response sequence mediates a strong repression of mouse glucose-6-phosphatase gene transcription by insulin. 911 20

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