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

Using the well differentiated rat hepatoma Fao we have studied the regulation of phosphoenolpyruvate carboxykinase (PEPCK) mRNA by insulin and glucose and compared these results to glucose production as estimated by glucose release into the medium. Fao cells possess an active gluconeogenic pathway and, when grown in glucose-free medium, release glucose for over 8 h. Addition of the cAMP analog, 8-(4-chlorophenyl-thio) cAMP (8-CTP-cAMP) or increasing the concentration of dihydroxyacetone and oxaloacetate results in an increase in glucose release which can be suppressed by insulin at concentrations between 1 and 100 nM. These effect of cAMP and insulin are associated with parallel changes in the level of mRNAPEPCK. Insulin treatment reduces mRNAPEPCK levels in these cells by 80%; this effect is transient reaching a maximum at 2-4 h. Addition of glucose to cells grown in glucose-free (G-) medium produces a decrease in mRNAPEPCK which is similar in magnitude and kinetics to that produced by insulin. Conversely, when cells grown in normal medium are placed in G- medium mRNAPEPCK levels triple over a period of 8 h, then return toward the basal value. Cells grown in G- medium or in G- medium plus 10nM insulin for 1 yr exhibit only slightly increased levels of mRNAPEPCK and respond to both 8-CTP-cAMP, and insulin, although the response to 8-CTP-cAMP is slightly blunted. These data indicate that glucose and insulin can play independent roles in regulation of PEPCK gene expression, and that these regulatory effects are usually transient.
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PMID:Acute and chronic regulation of phosphoenolpyruvate carboxykinase mRNA by insulin and glucose. 254 57

The 5' flanking regions of the rat phosphoenolpyruvate carboxykinase gene were used to form chimeric gene constructs with the human growth hormone gene. These constructs were transfected into several renal and one liver cell line and the production of growth hormone (HGH) measured by immunoassay. Cyclic-AMP and glucocorticoid responsiveness of HGH production was observed in all cell lines. In two lines, the rat NRK52E renal epithelial line and the rat H4IIE hepatoma cell line, both capable of expressing PEPCK, lowering extracellular pH increased HGH production several fold. Comparison of hormone and pH effect on cells transfected with a thymidine kinase promoter-HGH chimera indicated that the PEPCK 5' flanking region effects were specific. Thus, part of the pH responsiveness of the PEPCK gene in vivo may be attributed to properties of the 5' flanking regions.
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PMID:The 5'region of the rat phosphoenolpyruvate carboxykinase gene confers pH sensitivity to chimeric genes expressed in renal and liver cell lines capable of expressing PEPCK. 255 24

Tissue-specific extinguisher 1 (Tse-1) is a genetic locus on mouse chromosome 11 that can repress expression of several liver genes in trans. This locus is clearly active in fibroblasts, as hepatoma cells retaining fibroblast chromosome 11 are extinguished for both tyrosine aminotransferase and phosphoenolpyruvate carboxykinase gene expression. To assess the activity of Tse-1 in other tissues, we transferred mouse chromosome 11 from several different cell types into rat hepatoma recipients. Tse-1 was active in nonhepatic cell lines derived from each primary germ layer, but Tse-1 activity was not apparent in hybrids between hepatoma cells and primary mouse hepatocytes. These differences in the genetic activity of murine Tse-1 were apparently heritable in cis.
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PMID:Differential activity of a tissue-specific extinguisher locus in hepatic and nonhepatic cells. 256 81

Somatic cell hybrids formed by fusing hepatoma cells with fibroblasts generally fail to express liver functions, a phenomenon termed extinction. Previous studies demonstrated that extinction of the genes encoding tyrosine aminotransferase, phosphoenolpyruvate carboxykinase, and argininosuccinate synthetase is mediated by a specific genetic locus (TSE1) that maps to mouse chromosome 11 and human chromosome 17. In this report, we show that full repression of these genes requires a genetic factor in addition to TSE1. This conclusion is based on the observation that residual gene activity was apparent in monochromosomal hybrids retaining human TSE1 but not in complex hybrids retaining many fibroblast chromosomes. Furthermore, TSE1-repressed genes were hormone inducible, whereas fully extinguished genes were not. Analysis of hybrid segregants indicated that genetic loci required for the complete repression phenotype were distinct from TSE1.
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PMID:Hormonal regulation of TSE1-repressed genes: evidence for multiple genetic controls in extinction. 257 Oct 76

Tissue-specific extinguisher-1 (TSE1) is a genetic locus on mouse chromosome 11 that can repress expression of several liver genes in trans. The activity of this locus is apparent in rat hepatoma microcell hybrids that retain chromosome 11 from mouse fibroblasts: such hybrids fail to accumulate particular hepatic mRNAs, including those encoding tyrosine aminotransferase (TAT) and phosphoenolpyruvate carboxykinase (PEPCK). In this report, we show that TSE1 from a TAT-, PEPCK- mouse hepatoma cell line expressing a fetal liver phenotype also induced TAT and PEPCK extinction when transferred into rat hepatoma recipients. Thus, TSE1 appears to be active in TAT-, PEPCK- cells of both hepatic and non-hepatic lineages. This suggests that TSE1 may play a role in the developmental regulation of hepatic gene expression in the liver.
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PMID:Genetic activity of a trans-regulatory locus in hepatoma hybrid cells. 257

We used indirect end labeling to identify a series of five hypersensitive (HS) sites in the phosphoenolpyruvate carboxykinase (PEPCK) gene in H4IIE rat hepatoma cells. These sites were found at -4800 base pairs (bp) (site A), at -1300 bp (site B), over a broad domain between -400 and -30 bp (site C), at +4650 bp (site D), and at +6200 bp (site E). Sites A to D were detected only in cells capable of expressing the PEPCK gene, whereas site E was present in all of the cells examined thus far. The HS sites were present in H4IIE cells even when transcriptional activity was reduced to a minimum by treatment with insulin. Stimulation of transcription by a cyclic AMP analog to a 40-fold increase over the insulin-repressed level did not affect the main features of the HS sites. Furthermore, increased transcription did not disrupt the nucleosomal arrangement of the coding region of the gene, nor did it affect the immediate 5' region (site C), which is always nucleosome-free. In HTC cells, a rat hepatoma line that is hormonally responsive but unable to synthesize PEPCK mRNA, the four expression-specific HS sites were totally absent. Our experimental results also showed that, although there is a general correlation between lack of DNA methylation and transcriptional competence of the PEPCK gene, the role, if any, of methylation in the regulation of PEPCK gene activity is likely to be exerted at very specific sites.
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PMID:Hormonal regulation of phosphoenolpyruvate carboxykinase gene expression is mediated through modulation of an already disrupted chromatin structure. 265 89

The multihormonal regulation of phosphoenolpyruvate carboxykinase (PEPCK) was studied using chimeric genes composed of various regions of the PEPCK gene promoter region fused to the coding sequence of the chloramphenicol acetyltransferase (CAT) gene. These constructions, transfected into H4IIE hepatoma cells, are regulated like the endogenous PEPCK gene: dexamethasone and cAMP both stimulate PEPCK-CAT gene expression and their effects are additive; insulin inhibits the individual or combined effects of these stimulatory agents; and insulin inhibits dexamethasone-stimulated PEPCK-CAT fusion gene expression in a concentration-dependent fashion that is half-maximal at 10(-11) M. The induction by dexamethasone and the inhibition by insulin is specific for the DNA sequences that flank the 5' end of the PEPCK gene because similar effects were not observed for a plasmid in which the promoter and enhancer sequences of simian virus 40 (SV40) are fused to CAT. These results imply that the DNA adjacent to the transcription start site of the PEPCK gene contains the cis-acting hormone response elements responsible for the multihormonal regulation of this gene, including the insulin response.
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PMID:Multihormonal regulation of phosphoenolpyruvate carboxykinase-chloramphenicol acetyltransferase fusion genes. Insulin's effects oppose those of cAMP and dexamethasone. 282 6

The purpose of this study was to determine whether changes in ADP-ribosylation affect expression of the gene encoding the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in H4IIE hepatoma cells. Treatment with 3-aminobenzamide, a specific inhibitor of poly(ADP ribose) synthetase, caused an 89% decrease of ADP-ribosylation in isolated nuclei, and resulted in a two- to threefold induction of immunoassayable PEPCK in cultured cells. In contrast, the structurally related compound p-aminobenzoic acid had no significant effect on either process. In vivo labeling of proteins with [35S]methionine, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, showed that the induction of immunoreactive PEPCK by 3-aminobenzamide was due to a selective increase in the synthesis of the protein. The specific induction of PEPCK synthesis by 3-aminobenzamide was accounted for by a twofold increase of mRNAPEPCK which reached its maximal value 4 h after the addition of 3-aminobenzamide and returned to the basal level by 10 h. A possible role of ADP-ribosylation in cAMP or glucocorticoid induction of PEPCK was investigated in experiments in which H4IIE cells were treated with combinations of 3-aminobenzamide and either dexamethasone or a cAMP analog. In each case the effects on PEPCK induction were additive, indicating that glucocorticoids and cAMP induce PEPCK by pathways different from that used by 3-aminobenzamide.
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PMID:3-Aminobenzamide inhibits poly(ADP ribose) synthetase activity and induces phosphoenolpyruvate carboxykinase (GTP) in H4IIE hepatoma cells. 282 39

Nuclei isolated from H4IIE rat hepatoma cells were used in an in vitro run-on assay, with probes directed against various regions of the phosphoenolpyruvate carboxykinase [GTP: oxaloacetate carboxy-lyase (transphosphorylating); EC 4.1.1.32] gene, to analyze whether transcription proceeds uniformly across this gene in response to insulin and cAMP treatment. Fewer polymerase II complexes were associated with the phosphoenolpyruvate carboxykinase gene after insulin treatment, as compared with cAMP-treated cells, but they were distributed uniformly, so insulin does not block transcription at a discrete site, nor does it cause gradual, but progressive, premature termination. The phosphoenolpyruvate carboxykinase primary transcript was synthesized at a rate of about 2500 nucleotides per min in cAMP-treated cells and about 1000 nucleotides per min in insulin-treated cells. Thus insulin retards transcript elongation in comparison with cAMP, but this action does not account for the total effect insulin has on transcription. After insulin treatment, few, if any, nascent transcripts are associated with the first 69 nucleotides of the gene, whereas in cAMP-treated cells the opposite is true. These observations lead us to suggest that both insulin and cAMP exert their primary effects directly at the level of transcription initiation, but in opposite ways.
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PMID:Regulation of phosphoenolpyruvate carboxykinase gene transcription by insulin and cAMP: reciprocal actions on initiation and elongation. 283 22

It is now well established that cAMP induces the transcription rate of the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) and that this induction is dependent on a nucleotide domain located within the promoter-regulatory region of the gene (Short, J. M., Wynshaw-Boris, A., Short, H. P., and Hanson, R. W. (1986) J. Biol. Chem. 261, 9721-9726). We report here that cAMP also stabilizes phosphoenolpyruvate carboxykinase mRNA against degradation. Using two independent experimental approaches, we show that the half-life of the mRNA for phosphoenolpyruvate carboxykinase is extended when FTO-2B rat hepatoma cells are exposed to dibutyryl cyclic AMP (Bt2cAMP). In the first experiment, the rate of decay of phosphoenolpyruvate carboxykinase mRNA was determined in cells incubated in the presence of insulin, which has been shown to block the transcription rate of the gene for the enzyme. Under these conditions, the half-life of phosphoenolpyruvate carboxykinase mRNA was 30 min. However, in cells incubated in the presence of Bt2cAMP, the mRNA decayed with a half-life of 150 min. In the other experiment, mRNA stability was measured under steady state conditions, utilizing a "pulse-chase" approach. The apparent half-life of phosphoenolpyruvate carboxykinase mRNA increased from 40 min to over 250 min in Bt2cAMP-treated cells. No significant change in the stability of total cellular RNA was noted. Other experiments have shown that the transcription rate of the gene for phosphoenolpyruvate carboxykinase peaks within the first 20 min after exposing the cells to Bt2cAMP and then levels off, while the abundance of the mRNA reaches a maximum at about 90 min and remains at this level thereafter. Thus, the long term effect of cAMP on the expression of the gene coding for phosphoenolpyruvate carboxykinase occurs at least in part, through an alteration in the degradation rate of the mRNA for this enzyme.
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PMID:Cyclic AMP stabilizes the mRNA for phosphoenolpyruvate carboxykinase (GTP) against degradation. 283 95


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