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)

Binding of insulin to its receptor triggers multiple cellular responses, including changes in metabolism and in gene expression, resulting from the activation of multiple signalling pathways. Pertussis toxin has been shown to block an insulin-stimulated phospholipase C, resulting in an inhibition of the synthesis of phospholipid second messengers by insulin. In the present study, we investigated the significance of this pathway for the induction of growth-related genes by insulin treatment of H35 hepatoma cells. We found that pertussis toxin dramatically inhibits the induction of c-fos mRNA by insulin. Although c-jun and ornithine decarboxylase induction were also inhibited by pertussis toxin, they were much less sensitive than c-fos. These results indicate an important for lipid second messengers in mitogenic signalling by insulin and further demonstrate distinct roles for this pathway in the induction of c-fos and c-jun.
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PMID:Involvement of a pertussis-toxin sensitive G protein in the induction of gene expression by insulin. 902 11

The P-glycoprotein (Pgp) reversing agent, reserpine, induces MDR1 mRNA and PGP protein in human colon carcinoma cells (Schuetz, E. G., Beck, W. T., and Schuetz, J. D. (1996) Mol. Pharmacol. 49, 311-318) and in H35 rat hepatoma cells. Reserpine's interference with cellular dopamine utilization suggested that dopamine and dopaminergics might be important physiological regulators of PGP expression. Initial studies demonstrated that the H35 cells express the D2 dopamine receptor. Pgp protein and pgp2/mdr1b mRNA was increased (maximum of 10- and 8-fold, respectively) by the potent D2 dopamine receptor agonists bromocriptine, R(-)-propylnorapomorphine hydrochloride, and quinpirole, and Pgp protein induction was blocked by D2 receptor antagonists spiperone and clozapine. D2 receptor agonist induction of pgp2/mdr1b mRNA was paralleled by transcriptional activation of the pgp2/mdr1b promoter but blocked by pretreatment with the D2 dopamine receptor antagonists, spiperone, eticlopride, and clozapine. Co-transfection of a D2 dopamine receptor expression vector enhanced bromocriptine's transcriptional activation of the pgp2/mdr1b promoter. The G-protein, Galphai2, is required for bromocriptine transcriptional activation because the G-protein inhibitor, pertussis toxin, suppressed bromocriptine's activation of pgp2/mdr1b transcription and co-transfection of a dominant negative Galphai2 abrogated bromocriptine activation of pgp2/mdr1b. Gi proteins can transduce signals by activation of mitogen-activated protein kinases (MAPKs), and because Raf-1 is a known activator of MDR1, we tested for Raf-1 involvement. Co-transfection of a dominant negative Raf-1 failed to block bromocriptine induction of pgp2/mdr1b, and bromocriptine treatment caused no phosphorylation of the MAP kinase kinase substrates p42 and p44, demonstrating that the MAP kinase pathway was not involved. These are the first studies demonstrating transcriptional activation of an MDR gene by dopamine receptor agonists and that this activation occurs by a signal transduction pathway requiring the D2 dopamine receptor coupled to a functional G-protein.
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PMID:Bromocriptine transcriptionally activates the multidrug resistance gene (pgp2/mdr1b) by a novel pathway. 911 Oct 66

It is now clearly established that alpha-2 adrenergic receptors can be subdivided in three pharmacological subtypes (alpha-2A, alpha-2B and alpha-2C) encoded by distinct genes (alpha 2C10, alpha 2C2 and alpha 2C4, respectively, in humans). Whereas the study of the regulation of the human alpha-2A adrenergic receptor and of the promoter region of the alpha 2C10 gene has being greatly helped by the availability of the colon carcinoma cell line HT29, the study of the other human receptor subtypes has thus far been limited to homologous desensitization/down-regulation in transfected cells, because of the lack of human cellular models constitutively-expressing alpha-2B or alpha-2C adrenergic receptors. Several human cell lines were thus screened, in an attempt to find such models. Radioligand binding studies with [3H]RX821002 and [3H]MK912, reverse transcription-polymerase chain reactions and RNase mapping experiments with pairs of primers and riboprobes specific for each subtype demonstrated that the hepatoma cell line HepG2 and the neuroblastoma cell line SK-N-MC possess alpha-2 adrenergic receptors of the alpha-2C subtype. However, whereas HepG2 expresses exclusively alpha-2C receptors (55 +/- 7 fmol of [3H]MK912 binding sites/mg of protein), SK-N-MC expresses both alpha-2A and alpha-2C subtypes in fairly similar amounts (20 +/- 8 and 23 +/- 3 fmol of [3H]MK912 binding sites/mg of protein, respectively). The study of the inhibition of 3H-labeled antagonist binding by UK14304 demonstrated that a fraction of the receptor population was coupled to pertussis toxin-sensitive G-proteins, which were identified as Gi2 and Gi3 by immunoblotting. The alpha-2 agonist was, moreover, able to decrease forskolin-stimulated cAMP production by 47% in HepG2 and 23% in SK-N-MC, demonstrating that inhibition of adenylyl cyclase is one of the primary mechanisms of signal transduction in both cell lines. HepG2 and SK-N-MC are the first human cell lines unquestionably shown to natively express alpha-2C adrenergic receptors. The discovery of these two models may be useful for future study of the regulation of alpha 2C4 gene expression in cells of different origins and investigation of the reciprocal regulation of alpha-2A and alpha-2C subtype in single cells.
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PMID:HepG2 and SK-N-MC: two human models to study alpha-2 adrenergic receptors of the alpha-2C subtype. 915 9

Alterations in the expression and activity of guanine nucleotide regulatory proteins (G proteins) have been linked to the growth of several human tumors. We hypothesized that the expression and activity of G proteins are altered in human hepatocellular carcinoma (HCC). The expression of Gi and Gs proteins was determined in six human tumors and six normal controls (adjacent nonneoplastic liver) by Western blotting using specific antisera raised against the alpha subunit of G proteins Gi1, Gi1-2, Gi3, and Gs. Differences in G-protein expression were quantified by densitometry and expressed as percentage change from normal controls. The expression of Gi alpha1 was significantly increased in 80% of tumors (Gi alpha1, 284% +/- 77%; P < .05 percent of normal tissue), whereas Gi alpha1-2 and Gi alpha3 expression was increased in 67% of tumors (Gi alpha1-2, 218% +/- 21%; Gi alpha3, 154% +/- 6%; P < .05 percent of normal tissue). The functional activity of Gi alpha proteins as determined by pertussis toxin-catalyzed adenosine diphosphate (ADP)-ribosylation was also significantly increased in these tumors. In contrast, Gs alpha-protein expression was significantly reduced in all tumors examined (74% +/- 8% of normal tissue, P < .05). The functional activity of Gs alpha, as determined by adenylyl cyclase (AC) activity, was significantly decreased in tumor as compared to normal liver under both basal and agonist stimulated (guanosine triphosphate gamma S and forskolin) conditions. In summary, these data show for the first time a significant alteration in G-protein expression and functional activity in human HCC tissue. These alterations indicate a down-regulation of the AC-linked enzyme effector system in HCC that may be of critical importance to the formation and progression of human hepatocellular carcinoma.
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PMID:Alterations in guanine nucleotide regulatory protein expression and activity in human hepatocellular carcinoma. 936 61

Guanine nucleotide regulatory proteins (G-proteins) play an important role in the onset and progression of malignancy. We hypothesized that alterations in inhibitory G-protein (Gi) expression and/or function may contribute to cellular invasion and formation of hepatocellular carcinoma (HCC). H4IIE hepatoma cells were inoculated directly into the liver parenchyma of ACI strain rats, and membranes were prepared from HCC livers and adjacent nonneoplastic livers 12 days following the initial inoculation. Expression of inhibitory Gialpha proteins was determined by Western blot analysis and changes in the functional activity of these proteins confirmed by pertussis toxin catalyzed ADP ribosylation and adenylyl cyclase activity. Inhibitory Gialpha1, Gialpha1/2, and Gialpha3 protein expression was significantly elevated in HCC when compared to adjacent nonneoplastic liver and sham-operated hepatic tissue. Pertussis toxin catalyzed ADP ribosylation of Gialpha substrates was significantly enhanced in HCC concomitant with increased basal and stimulated adenylyl cyclase activity following uncoupling of Gi-proteins with manganese ions. The role of Gi-proteins in cellular proliferation was confirmed using cultured H4IIE cells and normal hepatocytes. In quiescent H4IIE cells, mastoparan (Gialpha activator) increased [3H] thymidine incorporation and cell growth in a dose-dependent manner, whereas both pertussis toxin (a Gi-protein inhibitor) and 8-bromo-cAMP inhibited mitogenesis. In contrast, in isolated cultured hepatocytes, mastoparan inhibited [3H] thymidine incorporation, while pertussis toxin and 8-bromo-cAMP were mitogenic. We conclude that HCC is associated with marked changes in Gialpha-protein expression in vivo and in vitro, direct activation of which leads to increased mitogenesis in H4IIE cells in vitro.
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PMID:Altered expression of inhibitory guanine nucleotide regulatory proteins (Gi-proteins) in experimental hepatocellular carcinoma. 957 74

Mobilization of intracellular Ca2+ is a critical cellular response to lysophosphatidic acid (LPA) in many cell types. Recent identification of endothelial differentiation gene (Edg) 2 and Edg4 as subtypes of G protein-coupled receptors for LPA allowed examination of the Ca2+ mobilization mediated specifically by each subtype. To reduce endogenous background levels while enhancing recombinant receptor-specific signals, the aequorin luminescence method was used to quantify cytoplasmic Ca2+ levels. In TAg-Jurkat T cells transiently co-transfected with apoaequorin and human Edg2 or Edg4 cDNA, LPA dose-dependently increased light emission triggered by increased Ca2+ bound to aequorin. N-Palmitoyl-L-serine-phosphoric acid and N-palmitoyl-L-tyrosine-phosphoric acid, which had been previously shown to be antagonists for Xenopus laevis LPA receptors, did not antagonize the Ca2+-mobilizing effects of Edg2 and Edg4. Surprisingly, they acted as agonists or partial agonists for Edg2 and Edg4. The Ca2+ mobilization by Edg2 and Edg4 was further characterized in stable transfectants of rat HTC4 hepatoma cells. By using the fura-2 fluorescence method, a difference in the kinetics of Ca2+ flux with Edg2 and Edg4 was observed. With Edg2, but not Edg4, the initial increase in the Ca2+ concentration was followed by a sustained influx of extracellular Ca2+. The coincident production of inositol phosphates and the inhibition of Ca2+ mobilization by the phospholipase C inhibitor U73122 strongly suggested that Edg2 and Edg4 mobilize Ca2+ through inositol trisphosphate generated by phospholipase C activation. Pertussis toxin almost completely blocked LPA-induced Ca2+ mobilization by Edg2 but only partially blocked that by Edg4, which suggests that Edg2 transduces Ca2+ mobilization largely through pertussis toxin-sensitive Gi proteins, whereas Edg4 requires both Gi and Gq.
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PMID:Recombinant human G protein-coupled lysophosphatidic acid receptors mediate intracellular calcium mobilization. 980 23

Hepatocellular carcinoma (HCC) is associated with increased expression and function of inhibitory guanine nucleotide regulatory proteins (Gi-proteins). This study addresses the effects of chronic ethanol exposure on the expression and function of adenylyl cyclase (AC)-linked G-proteins (Gs and Gi) and growth in experimental HCC. G-protein expression and function was determined by immunoblot in the hepatic tumorigenic H4IIE cell line and isolated cultured hepatocytes in the absence or presence of ethanol (5-100 mmol/L). Chronic exposure (24 hours) to ethanol dose-dependently increased Gialpha1/2 expression in the H4IIE cell line, but not in cultured hepatocytes. Gsalpha-protein expression remained unchanged in both H4IIE cells and cultured hepatocytes following ethanol treatment. In addition, ethanol directly activated a Gi-protein, because pertussis toxin (PTx)-catalyzed, adenosine diphosphate (ADP)-dependent ribosylation of Gialpha substrates decreased following ethanol treatment. The increased functional activity of Gialpha1/2-protein expression was confirmed by demonstrating that ethanol dose-dependently inhibited basal and stimulated AC activity in H4IIE cells, while not significantly altering basal AC activity in isolated cultured hepatocytes. Furthermore, while ethanol had no significant effect on basal mitogenesis in H4IIE cells or hepatocytes, increased mitogenesis caused by direct Gialpha-protein stimulation (mastoparan M7; 10-5,000 nmol/L) was further enhanced in the presence of ethanol, an effect that was completely blocked following Gi-protein inhibition (PTx; 100 ng/mL). In contrast, activation of Gi-proteins using M7 failed to alter cellular mitogenesis in isolated cultured hepatocytes, whether in the absence or presence of ethanol. Finally, analysis of mitogen-activated protein kinase (MAPK) activity demonstrated that chronic ethanol treatment further enhanced Gi-protein-stimulated MAPK activity in hepatic tumorigenic cells. In conclusion, these data demonstrate that ethanol enhances cellular mitogenesis in experimental HCC as a result of, at least in part, a Gi-MAPK-dependent pathway. Furthermore, this effect may be caused by ethanol's direct up-regulation of the expression and activity of Gi-proteins in HCC.
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PMID:Enhanced Gi-protein-mediated mitogenesis following chronic ethanol exposure in a rat model of experimental hepatocellular carcinoma. 991 17

Insulin action is initiated by binding to its cognate receptor, which then triggers multiple cellular responses by activating different signaling pathways. There is evidence that insulin receptor signaling may involve G protein activation in different target cells. We have studied the activation of G proteins in rat hepatoma (HTC) cells. We found that insulin stimulated binding of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-35S) to plasma membrane proteins of HTC cells, in a dose-dependent manner. This effect was completely blocked by pertussis toxin treatment of the membranes, suggesting the involvement of G proteins of the G alpha i/G alpha o family. The expression of these G alpha proteins was checked by Western blotting. Next, we used blocking antibodies to sort out the specific G alpha protein activated by insulin stimulation. Anti-G alpha il,2 antibodies completely prevented insulin-stimulated GTP binding, whereas anti-G alpha o,i3 did not modify this effect of insulin on GTP binding. Moreover, we found physical association of the insulin receptor with G alpha il,2 by copurification studies. These results further support the involvement of a pertussis toxin-sensitive G protein in insulin receptor signaling and provides some evidence of specific association and activation of G alpha il,2 protein by insulin. These findings suggest that G alpha il,2 proteins might be involved in insulin action.
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PMID:Insulin activates G alpha il,2 protein in rat hepatoma (HTC) cell membranes. 1006 61

Melatonin is an important inhibitor of cancer growth promotion while the essential polyunsaturated fatty acid, linoleic acid is an important promoter of cancer progression. Following its rapid uptake by tumor tissue, linoleic acid is oxidized via a lipoxygenase to the growth-signaling molecule, 13-hydroxyoctadecadienoic acid (13-HODE) which stimulates epidermal growth factor (EGF)-dependent mitogenesis. The uptake of plasma linoleic acid and its metabolism to 13-HODE by rat hepatoma 7288CTC, which expresses both fatty acid transport protein and melatonin receptors, is inhibited by melatonin in a circadian-dependent manner. This inhibitory effect of melatonin is reversible with either pertussis toxin, forskolin or cAMP. While melatonin inhibits tumor linoleic acid uptake, metabolism and growth, pinealectomy or constant light exposure stimulates these processes. Thus, melatonin and linoleic acid represent two important environmental signals that interact in a unique manner to regulate tumor progression and ultimately the host-cancer balance.
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PMID:New actions of melatonin on tumor metabolism and growth. 1008 62

Sphingosine 1-phosphate (S1P) increases intracellular Ca2+ concentration in many cell types, but the signaling mechanism remains uncertain. The recent identification of three closely related seven-transmembrane domain receptors for S1P, termed Edg1, H218, and Edg3, support the extracellular ligand role of S1P and allowed examination of Ca2+ responses mediated specifically by each receptor subtype. To substantiate each subtype in S1P-induced Ca2+ responses and to study the transductional mechanisms, we applied the aequorin luminescence method and the fura-2 fluorescence method in two transfected mammalian cell systems. We showed that H218 and Edg3 were capable of mediating S1P-induced mobilization of intracellular Ca2+ when transiently transfected in human TAg-Jurkat T cells. Ca2+ responses mediated by Edg1 in TAg-Jurkat cells required coexpression of the Gqi5 chimeric G protein that links Gi-coupled receptors to Gq. When H218 and Edg3 were stably expressed in rat HTC4 hepatoma cells, S1P induced Ca2+ responses with nanomolar EC50 values. Edg3, but not H218, elicited a sustained influx of extracellular Ca2+. The coincident formation of inositol phosphates and the complete inhibition of Ca2+ responses by the phospholipase C inhibitor U73122 indicated that H218 and Edg3 mobilized Ca2+ through activation of phospholipase C. Partial inhibition of Ca2+ responses and inositol phosphates formation by pertussis toxin implied that H218 and Edg3 transduce phospholipase C activation and Ca2+ responses only partially through Gi proteins. Although these results did not dismiss that S1P may function as an intracellular second messenger in other settings, they definitively proved that S1P can mobilize Ca2+ as an extracellular ligand for G protein-coupled receptors.
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PMID:Transduction of intracellular calcium signals through G protein-mediated activation of phospholipase C by recombinant sphingosine 1-phosphate receptors. 1022 May 56


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