UMLS:C0019204 - FACTA Search

Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Target Concepts:

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

The two independently derived hepatoma cell lines (HTC and Fu5-5) have previously been shown to display different sensitivities for the induction of tyrosine aminotransferase (TAT) enzyme activity and mRNA levels by glucocorticoids with the enzyme being half-maximally induced at approximately 7-fold higher concentrations of dexamethasone in HTC cells than in Fu5-5 cells. In the present study we investigated the induction of TAT activity by cAMP in order to see whether the difference is limited to the steroidal induction. Using the stable cAMP derivative (8-(4-chlorophenylthio)-cAMP) as an inducer, we found that a 6-fold higher cAMP concentration was needed in HTC cells to achieve the same extent of enzyme induction as in Fu5-5 cells. The induction of TAT enzyme activity could be accounted for by an increased amount of TAT mRNA. Further experiments involving sequential addition of both inducers in general showed a synergism of steroids and cAMP for TAT induction in HTC cells only at submaximal concentrations of steroid; in Fu5-5 cells, the occurrence of synergism depended on the order of addition of inducers. The maximal response in HTC cells was limited to the value that could be achieved by induction with steroid alone. In Fu5-5 cells, however, the steroid response could be augmented when cAMP was added to cells already maximally induced by steroid. This demonstrates that the effect of a combination of cAMP and steroids depends on their concentration, the sequence of their addition, and the rat hepatoma cell line used. Collectively the data suggest that a common pretranslational event determines the differential sensitivity of TAT induction by glucocorticoids and by cAMP in HTC and Fu5-5 cells. Furthermore a second, or possibly the same, common event also regulates the maximum level of TAT induction that is obtainable under most conditions with glucocorticoids and/or cAMP.
...
PMID:Differential sensitivity of HTC and Fu5-5 cells for induction of tyrosine aminotransferase by 3',5'-cyclic adenosine monophosphate. 290 Oct 31

Treatment of H-4 rat hepatoma cells with 8-bromo-cyclic AMP (8-Br-cAMP) resulted in a transient induction of the gluconeogenic enzyme tyrosine aminotransferase. Synthesis of tyrosine aminotransferase and the level of its corresponding mRNA peaked 2 h after the addition of the cyclic nucleotide and declined thereafter. Tyrosine aminotransferase synthesis and mRNA failed to respond to the readdition of fresh 8-Br-cAMP, a process which we defined as desensitization. Removal of 8-Br-cAMP resulted in a decrease in tyrosine aminotransferase synthesis and mRNA, a process defined as de-induction. The relative transcription rate of the tyrosine aminotransferase gene and the turnover of its mRNA were determined by labeling intact cells with [3H]uridine. 8-Br-cAMP led to an increase in the rate of tyrosine aminotransferase transcription which was sustained for at least 4 h. The transcription rate declined upon de-induction. In addition, 8-Br-cAMP increased the turnover rate of tyrosine aminotransferase mRNA, but only after a 1.5-3 h time lag. This increased degradation rate persisted for at least 1.5 h after the removal of 8-Br-cAMP. These two contrasting and temporally distinct processes could account for the observed changes in tyrosine aminotransferase mRNA levels in response to 8-Br-cAMP treatment and removal.
...
PMID:Increased turnover of the messenger RNA encoding tyrosine aminotransferase can account for the desensitization and de-induction of tyrosine aminotransferase by 8-bromo-cyclic AMP treatment and removal. 290 63

An immunocolloidal gold electron microscopy method is described allowing the ultrastructural localization and quantitation of the regulatory subunits RI and RII and the catalytic subunit C of cAMP-dependent protein kinase. Using a postembedding indirect immunogold labeling procedure that employs specific antisera, the catalytic and regulatory subunits were localized in electron-dense regions of the nucleus and in cytoplasmic areas with a minimum of nonspecific staining. Antigenic domains were localized in regions of the heterochromatin, nucleolus, interchromatin granules, and in the endoplasmic reticulum of different cell types, such as rat hepatocytes, ovarian granulosa cells, and spermatogonia, as well as cultured H4IIE hepatoma cells. Morphometric quantitation of the relative staining density of nuclear antigens indicated a marked modulation of the number of subunits per unit area under various physiologic conditions. For instance, following partial hepatectomy in rats, the staining density of the nuclear RI and C subunits was markedly increased 16 h after surgery. Glucagon treatment of rats increased the staining density of only the nuclear catalytic subunit. Dibutyryl cAMP treatment of H4IIE hepatoma cells led to a marked increase in the nuclear staining density of all three subunits of cAMP-dependent protein kinase. These studies demonstrate that specific antisera against cAMP-dependent protein kinase subunits may be used in combination with immunogold electron microscopy to identify the ultrastructural location of the subunits and to provide a semi-quantitative estimate of their relative cellular density.
...
PMID:Localization of nuclear subunits of cyclic AMP-dependent protein kinase by the immunocolloidal gold method. 299 18

Homogeneous catalytic subunit from the cAMP-dependent protein kinase, when derivatized with a fluorophore, was used as a cytochemical probe to locate intracellular sites of the protein kinase regulatory subunit. After conjugation, the fluoresceinated catalytic subunit (F:C), derivatized to a stoichiometry of approximately 1 mol/mol, retained near full activity as judged by specific activity and by titration against either regulatory subunit or Inhibitor Protein of the protein kinase. With this molecular probe the dissociated regulatory subunit was localized by direct cytochemistry in Reuber H-35 hepatoma cells that had been exposed, while intact, for 0-120 min to 10(-4) M 8-Br-cAMP. After stimulation, cultures were fixed and washed and then incubated for 16 h with F:C. Following 8-Br-cAMP stimulation, extensive binding of the probe to both cytoplasmic and nucleolar sites was observed. This binding was diminished but not eliminated when 50 microM cAMP was present during the incubation of the fixed cells with F:C that was eliminated by a 40-fold molar excess of underivatized catalytic subunit but not by heat-denatured catalytic subunit, and was not reduced by a 20-fold molar excess of cGMP-dependent protein kinase, examined plus or minus cGMP. Collectively, the results allow the conclusion that the F:C probe binds free regulatory subunit. The time course of its change with 8-Br-cAMP (measured as the difference between binding in the presence or absence of cAMP during the postfixation treatment) mirrors that previously reported for changes in the catalytic subunit in these cells, also identified cytochemically (Byus, C. V., and Fletcher, W.H. (1982) J. Cell Biol. 93, 727-734). The binding of the F:C probe, detected when cAMP is present during postfixation treatment, may possibly represent binding to free Inhibitor Protein of the cAMP-dependent protein kinase. If so, it was at a level of approximately 20% of the maximal level of detectable regulatory subunit, and it also showed cytosolic and nucleolar localization.
...
PMID:Cytochemical identification of the regulatory subunit of the cAMP-dependent protein kinase by use of fluorescently labeled catalytic subunit. Examination of protein kinase dissociation in hepatoma cells responding to 8-Br-cAMP stimulation. 300 8

Transcription of the gene for cytosolic Phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) from rat liver is increased by cAMP and glucocorticoids and decreased by insulin. A PEPCK-thymidine kinase (TK) chimeric gene was transfected into FTO-2B rat hepatoma cells, which were TK-deficient. Previous studies showed that a cAMP regulatory element is located at the 5' end of the PEPCK gene. In this report, we demonstrate that the 5' end of the gene also contains a glucocorticoid regulatory element, but not one for insulin. Regions of the PEPCK gene that contain these regulatory elements were attached to the Herpes simplex virus TK structural gene containing its own promoter. The hormone regulatory elements within the 5' flanking region of the PEPCK gene conferred cAMP and glucocorticoid responsiveness on the TK gene after transfection into FTO-2B cells. Like viral enhancer elements, these regulatory elements functioned properly when placed in either orientation at various positions 5' or 3' to TK. The presence of the SV40 enhancer element upstream from the PEPCK-TK gene had little effect on the basal level of expression or hormonal regulation of the chimeric gene.
...
PMID:Characterization of the phosphoenolpyruvate carboxykinase (GTP) promoter-regulatory region. I. Multiple hormone regulatory elements and the effects of enhancers. 301 2

Hormonal regulatory elements within the phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) promoter region were mapped using a series of 5' deletions linked to the amino-3'-glycosyl phosphotransferase structural gene. These deletion mutants were stably transfected into the genome of FTO-2B hepatoma cells. A 47-base pair region of the PEPCK promoter was identified which was essential for stimulation by dibutyryl cAMP. A 12-base pair core sequence (CTTACGTCAGAG) within this region shows significant homology with sequences in four other cAMP-regulated genes. There are two glucocorticoid regulatory elements within the promoter, as well as an inhibitory element which depresses the level of basal gene transcription. The deletion of this inhibitory sequence prevents the induction of the chimeric gene by dexamethasone. The existence of the hormone regulatory domains within the PEPCK promoter was confirmed by attaching these elements upstream of the heterologous Herpes simplex virus thymidine kinase structural gene, containing its own promoter.
...
PMID:Characterization of the phosphoenolpyruvate carboxykinase (GTP) promoter-regulatory region. II. Identification of cAMP and glucocorticoid regulatory domains. 301 3

The effect of the tumor promoter phorbol 12-myristate 13-acetate (PMA) on expression of the P-enolpyruvate carboxykinase gene was studied in rat hepatoma H4IIE cells. Like insulin, PMA provokes a concentration and time-dependent decrease of mRNA coding for that enzyme that is due to an inhibition of P-enolpyruvate carboxykinase gene transcription. This effect of PMA is rapid, reversible, specific for phorbol esters known to be active in other systems, and it does not require on-going protein synthesis. PMA overrides the stimulatory effects cAMP and glucocorticoid analogs have on the transcription of this gene. A synthetic diacylglycerol, sn-1,2-dioctanoylglycerol, also inhibits P-enolpyruvate carboxykinase gene transcription. These effects of PMA and synthetic diacylglycerol are specific, since neither affected total mRNA synthesis. We conclude that diacylglycerol and phorbol esters, specific stimulators of protein kinase C, inhibit the transcription of P-enolpyruvate carboxykinase gene in H4IIE cells. The findings support the hypothesis that diacylglycerols generated in the plasma membrane can act as an intracellular signal that regulates specific gene expression.
...
PMID:The effect of phorbol esters and diacylglycerol on expression of the phosphoenolpyruvate carboxykinase (GTP) gene in rat hepatoma H4IIE cells. 302 68

Hepatocytes prepared from 18-day-old mouse embryos were grown in serum-free medium and reached confluence after two days in culture. The total amount of the 26 kDa gap junction protein decreased in these cells during the first 24 h in culture and increased again between day 1 and day 3 more than 10-fold. At day 3 a half-life time of 2.5 to 3 h was determined for the 26 kDa protein by [35S]methionine incorporation and immunoprecipitation using affinity-purified anti-26 kDa. Incorporation of [32P]orthophosphate into the 26 kDa protein of cultured hepatocytes was found at serine residues (98%) and tyrosine residues (about 2%). The addition of dibutyryl cyclic adenosine monophosphate (db cAMP) to the culture medium at day 2 had two effects: After 15 min the extent of phosphorylation of the 26 kDa protein increased 2.7-fold whereas the total amount of the 26 kDa protein increased only 1.2-fold. After 3 h of incubation with db cAMP, a 2.5-fold increase of the 26 kDa protein was noticed which was accompanied by a 3.2-fold increase in phosphorylation of serine residues. The effects of db cAMP on phosphorylation of the 26 kDa protein could be augmented or mimicked by the addition of isoproterenol, theophylline or forskolin to the culture medium of hepatocytes. In extracts of rat hepatocarcinoma MH1C1 cells and dog kidney MDCK cells, a phosphorylated 26 kDa protein can be immunoprecipitated using anti-liver 26 kDa. These results demonstrate that the gap junction 26 kDa protein can be posttranslationally modified by cAMP-dependent phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Cyclic adenosine monophosphate stimulates biosynthesis and phosphorylation of the 26 kDa gap junction protein in cultured mouse hepatocytes. 303 32

Several studies have found high cAMP content in hepatomas in vivo, while hepatoma cells in vitro have very low levels. To explore this discrepancy and the regulation of cAMP in hepatomas, we have examined the cell line MH1C1 from Morris hepatoma 7795. These cells in culture contained low intracellular cAMP concentrations (approximately 0.5 pmol/mg protein at confluency), and were unresponsive to glucagon and prostaglandins (PG) E1 and E2. In contrast, solid hepatomas in rats developed from inoculates of MH1C1 had a 40-fold higher basal cAMP concentration and were stimulated by PGE1 and PGE2. Fibroblasts cultured from these tumours also contained high cAMP levels and responded strongly to PGE1. This may suggest that the difference in cAMP regulation between hepatomas in vivo and hepatoma cells in vitro results from the presence of other cells in the solid tumour rather than from selection of low-cAMP cells during the cloning procedure. Low-Km and intermediate-Km cAMP phosphodiesterase activity was high in MH1C1, compared to normal hepatocytes. This might contribute to the low cAMP level. The ability of MH1C1 to form cAMP was not defective, as the level could be increased more than 200-fold by beta-adrenergic activation in the presence of the phosphodiesterase inhibitor methylisobutylxanthine.
...
PMID:The regulation of cyclic AMP levels in cultured MH1C1 rat hepatoma cells and in solid tumours derived from MH1C1 cell inoculates. 303 96

Regulation of carbamoyl-phosphate synthetase I (CPS) synthesis by various hormones was compared in primary cultured hepatocytes from adult rat and in Reuber hepatoma H-35 by pulse labeling of the cells with [35S]methionine. CPS synthesis in hepatocytes was stimulated 8-fold and 5-fold by dexamethasone and glucagon respectively. CPS synthesis in hepatocytes was synergically (about 50-fold) stimulated by a combination of dexamethasone and glucagon. Less synergic stimulation was observed by combining dexamethasone with N6, O2'-dibutyryladenosine 3',5'-monophosphate (dibutyryl-cAMP) or with isoproterenol. The basal level of CPS synthesis in hepatoma cells was higher than that in hepatocytes. CPS synthesis in hepatoma cells was stimulated by dexamethasone and dibutyryl-cAMP but the extent was only 3-fold and 1.8-fold respectively. The synergic effect of combination of dexamethasone and dibutyryl-cAMP was not observed in hepatoma cells. Neither glucagon nor isoproterenol exhibited an appreciable effect on CPS synthesis in hepatoma cells. Insulin and epinephrine suppressed CPS synthesis both in hepatocytes and hepatoma cells. The effect of epinephrine was indicated to be through alpha-adrenergic receptors. The effects of insulin and epinephrine were additive on CPS synthesis both in hepatocytes and hepatoma cells.
...
PMID:Hormonal regulation of carbamoyl-phosphate synthetase I synthesis in primary cultured hepatocytes and Reuber hepatoma H-35. Defective regulation in hepatoma cells. 304 Mar 99

<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>