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 phosphorylation of insulin-like growth factor binding protein-I (IGFBP-1) alters its binding affinity for insulin-like growth factor I (IGF-I) and thus regulates the bioavailability of IGF-I for binding to the IGF-I receptor. The kinase(s) responsible for the phosphorylation of IGFBP-1 has not been identified. This study was designed to characterize the IGFBP-1 kinase activity in HepG2 human hepatoma cells, a cell line that secretes IGFBP-1 primarily as phosphorylated isoforms. IGFBP-1 kinase activity was partially purified from detergent extracts of the cells by phosphocellulose chromatography and gel filtration. Two kinases of approximate M(r) 150,000 (peak I kinase) and M(r) 50,000 (peak II kinase) were identified. Each kinase phosphorylated IGFBP-1 at serine residues that were phosphorylated by intact HepG2 cells. The kinases were distinct based on their differential sensitivity to inhibition by heparin (IC50 = 2.5 and 16.5 micrograms/ml, peak I and II kinase, respectively) and inhibition by the isoquinoline sulfonamide CKI-7 (IC50 = 50 microM and 100 microM, peak I and II kinase, respectively). In addition, a tenfold molar excess of nonradioactive GTP relative to [gamma-32P]ATP lowered the incorporation of 32P into IGFBP-1 by 80% when the reaction was catalyzed by the peak I kinase, whereas GTP had no effect on the reaction catalyzed by the peak II kinase. In the presence of polylysine, IGFBP-1 was radiolabeled by the partially purified kinase activity when [gamma-32P]GTP served as the phosphate donor indicating the presence of casein kinase II activity. Furthermore, IGFBP-1 was phosphorylated by purified casein kinase I and casein kinase II at sites phosphorylated by the peak I and II kinases. Our data suggest that at least two kinases could be responsible for the phosphorylation of IGFBP-1 in intact HepG2 cells and that the kinases are related to the casein kinase family of protein kinases.
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PMID:Characterization of insulin-like growth factor binding protein-1 kinases from human hepatoma cells. 886 14

Previously, we demonstrated that a single histamine H2 receptor can couple to both the adenosine 3',5'-cyclic monophosphate and inositol 1,4,5-trisphosphate/intracellular Ca2+ signaling pathways in a stimulatory manner. We undertook the present studies to fur her characterize the postreceptor events involved in H2 receptor dual signaling. Histamine H2 receptor-mediated signal transduction was examined in isolated cell membranes prepared from purified canine parietal cells and HEPA cells (rat hepatoma cell line) stably transfected to express the canine H2 histamine receptor cDNA. Histamine dose-dependently stimulated both adenylate cyclase [AC; mean effective concentration (EC50) = 2 x 10(-7) M] and phospholipase C (PLC; EC50 = 3.1 +/- 0.5 x 10(-7) M) activity in an H2-specific and GTP-dependent manner. Cholera toxin pretreatment abolished the stimulatory effect of histamine on PLC activity in isolated membranes without altering binding of the H2 receptor antagonist tiotidine. Anti-Gs alpha dose-dependently inhibited histamine-stimulated AC activity while leaving the effect of this secretagogue on PLC activity unaltered. Although anti-Gq alpha inhibited vasopressin-stimulated PLC activity in HEPA cells and carbachol-stimulated PLC in parietal cells, this antibody did not alter the action of histamine on PLC in the same membrane preparations. Antibody against the NH2 and COOH terminals of the common beta-subunit of heterotrimeric G proteins did not inhibit histamine-stimulated PLC activity. Our studies demonstrate for the the first time that activation of the H2 receptor leads to stimulation of both AC and PLC via separate GTP-dependent mechanisms.
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PMID:Histamine H2 receptor activates adenylate cyclase and PLC via separate GTP-dependent pathways. 889 80

The retinoblastoma (RB) tumor suppressor is a nuclear phosphoprotein important for cell growth control and able to bind specifically to viral oncoproteins such as the SV40 large tumor antigen (T-ag). Human RB possesses a bipartite nuclear localization sequence (NLS) consisting of two clusters of basic amino acids within amino acids 860-877, also present in mouse and Xenopus homologs, which resembles that of nucleoplasmin. The T-ag NLS represents a different type of NLS, consisting of only one stretch of basic amino acids. To compare the nuclear import kinetics conferred by the bipartite NLS of RB to those conferred by the T-ag NLS, we used beta-galactosidase fusion proteins containing the NLSs of either RB or T-ag. The RB NLS was able to target beta-galactosidase to the nucleus both in vivo (in microinjected cells of the HTC rat hepatoma line) and in vitro (in mechanically perforated HTC cells). Mutational substitution of the proximal basic residues of the NLS abolished nuclear targeting activity, confirming its bipartite character. Nuclear accumulation of the RB fusion protein was half-maximal within about 8 min in vivo, maximal levels being between 3-4-fold those in the cytoplasm, which was less than 50% of the maximal levels attained by the T-ag fusion protein, while the initial rate of nuclear import of the RB protein was also less than half that of T-ag. Nuclear import conferred by both NLSs in vitro was dependent on cytosol and ATP and inhibited by the nonhydrolyzable GTP analog GTPgammaS. Using an ELISA-based binding assay, we determined that the RB bipartite NLS had severely reduced affinity, compared with the T-ag NLS, for the high affinity heterodimeric NLS-binding protein complex importin 58/97, this difference presumably representing the basis of the reduced maximal nuclear accumulation and import rate in vivo. The results support the hypothesis that the affinity of NLS recognition by NLS-binding proteins is critical in determining the kinetics of nuclear protein import.
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PMID:Kinetic characterization of the human retinoblastoma protein bipartite nuclear localization sequence (NLS) in vivo and in vitro. A comparison with the SV40 large T-antigen NLS. 926 57

The purpose of this paper was to clarify critical aspects of the behavior of signal transduction activity in normal and cancer cells. 1. Signal transduction activity in the conversion of phosphatidylinositol through PI and PIP kinases and PLC to IP3 is regulated at multiple sites. In liver, hepatomas and human carcinomas PIP kinase is the rate limiting enzyme and PLC activity is present in great excess. 2. The steady-state signal transduction activity as measured by the three enzyme activities and IP3 concentration was markedly up-regulated in rat hepatomas of different growth rates. The steady-state specific activities of the three signal transduction enzymes were elevated in ovarian carcinomas as compared to normal ovary. Increased enzyme activities were also observed in human breast carcinoma cells as compared to normal human breast parenchymal cells. In breast, ovarian and rat hepatoma cells as they go through lag, log and plateau phases, IP3 concentration in the early lag phase increased 4.5- to 20-fold and PI and PIP kinase activities peaked in mid-log phase. These events returned to baseline levels in the plateau phase. PLC activity did not change. 3. The bone marrow PI and PIP kinase activities in 3-day starvation were decreased to 13% and IP3 concentration was reduced to 24%; at 1-day refeeding they returned to normal. PLC activity changed little. These alterations are in line with the rapid t1/2 degradation rates (12 min) of PI and PIP kinases observed in studies with cycloheximide. By contrast, PLC has a long half-life. 4. The molecular action of tiazofurin entails inhibition of IMP DH activity, decrease in GTP and IP3 concentrations, reduction of ras and myc oncogene expression, and signal transduction enzyme activities. These events are followed by induced differentiation and apoptosis. There are also decreases in enzyme activities which have rapid turnover, including TdR kinase, dTMP synthase, and GPRT. In vitro studies indicated that these events are abrogated by addition of guanine which restores GTP concentrations. Therefore, most or all these events were brought about by the reduced GTP concentration in the tiazofurin target cells. 5. Quercetin and genistein are able to inhibit PI and PIP kinase activities and reduce IP3 concentration in vivo and in tissue culture systems. These flavonoids are also inhibitors of cell proliferation and clonogenic ability in rat hepatoma 3924A and in human OVCAR-5 and MDA-MB-435 cells. Quercetin down-regulated the expression of c-myc and Ki-ras oncogenes and led to induced differentiation and apoptosis in K562 cells. Genistein reduced IP3 concentration in vivo and in the tissue culture system. Genistein is antiproliferative and has cytototoxicity in human carcinoma cells. All three drugs, tiazofurin, quercetin and genistein, act, in part at least, through depression of cellular IP3 concentration although the mechanisms may not be identical. 6. Quercetin and genistein, which attack different targets and different phases of the cell cycle, proved to be synergistic in OVCAR-5 cells. The impact of tiazofurin, genistein and quercetin is of interest because the drugs crucially inhibit the display of the neoplastic program of cells and lead to induced differentiation and apoptosis.
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PMID:Regulation of the signal transduction program by drugs. 938 80

Protein synthesis in rat H35 Reuber hepatoma cells is rapidly inhibited on heat shock. At mild heat-shock temperatures the main cause for inhibition is the inactivation of the guanine nucleotide exchange factor eukaryotic initiation factor 2B (eIF2B); under more severe heat-shock conditions the activity of several initiation factors is compromised. eIF2B is required for GDP/GTP exchange on eIF2, which delivers methionyl-tRNA to the 40 S ribosomal subunit. We have tried to elucidate the mechanism underlying the inactivation of eIF2B by assays in vitro. Incubation of cell extracts at 41 degreesC or higher led to the inactivation of eIF2B. In agreement with observations in cells exposed to mild heat shocks, the thermal inactivation of eIF2B could be ascribed to neither eIF2alpha phosphorylation nor the induction of another inhibitor. With the use of glycerol gradients we show that eIF2B forms aggregates in heat-treated extracts. Furthermore eIF2B activity is protected against heat shock in thermotolerant cells. Taken together, these results suggest a role for chaperones in the control of eIF2B activity.
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PMID:Inactivation of eukaryotic initiation factor 2B in vitro by heat shock. 971 6

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

A novel human DNA virus, TTvirus (TTV), was identified from a patient with posttransfusion hepatitis of unknown etiology. It is thought to be a new hepatitis virus, but the clinical significance of this virus is uncertain. We investigated the frequency of TTV viremia by PCR in 39 non-B, non-C hepatitis (NBNC) patients with hepatocellular carcinoma (HCC), and clinical features of these patients. TTV viremia was detected in 20 (51.3%) of 39 NBNC hepatitis patients with HCC. Liver cirrhosis (LC) were found in 11 (55%) of 20 TTV-positive patients and 16 (84%) of 19 TTV-negative patients (p < 0.05). The levels of AST, LDH, LAP, gamma GTP in TTV-positive patients were significantly higher than those in TTV-negative patients (p < 0.05). (AST: 58 +/- 26 vs 42 +/- 23 IU/l, LDH: 468 +/- 127 vs 366 +/- 123 IU/l, LAP: 339 +/- 242 vs 206 +/- 80 IU/l, gamma GTP: 207 +/- 207 vs 105 +/- 107 IU/l) These results suggest clinical differences between TTV-positive and TTV-negative patients in NBNC hepatitis patients with HCC.
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PMID:[Detection of TT virus (TTV) in non-B, non-C hepatitis patients with hepatocellular carcinoma, and clinical features of these patients]. 1039 Oct

Two G protein-coupled receptors (Edg-2) and (Edg-4) for the lysolipid phosphoric acid mediator lysophosphatidic acid have been described by molecular cloning. However, the calcium-mobilizing receptor Edg-4 is not expressed in some cell lines that exhibit robust calcium responses to this ligand, thus predicting the existence of additional receptor subtypes. We report here on the characterization of a third human lysophosphatidic acid receptor subtype, Edg-7, which mediates lysophosphatidic acid-evoked calcium mobilization. In a rat hepatoma Rh7777 cell line that lacks endogenous responses to lysophosphatidic acid, this lipid mediator, but not others, evokes calcium transients when the cells have been transfected with Edg-7 or Edg-4 DNAs. Furthermore, frog oocytes exhibit a calcium-mediated chloride conductance in response to mammalian-selective lysophosphatidic acid mimetics after injection of Edg-7 mRNA. Edg-7-expressing Rh7777 cells do not show inhibition of forskolin-driven rises in cAMP in response to lysophosphatidic acid. However, membranes from HEK293T cells cotransfected with Edg-7 and G(i2)alpha protein DNAs show lysophosphatidic acid dose-dependent increases in [gamma-(35)S]GTP binding with an EC(50) value of 195 nM. When we used this assay to compare various synthetic LPA analogs at Edg-2, Edg-4, and Edg-7 receptors, we found that ethanolamine-based compounds, which are full LPA mimetics at Edg-2 and Edg-4, exhibit little activity at the Edg-7 receptor. Edg-7 RNA was detected in extracts of several rat and human tissues including prostate. Together, our data indicate that Edg-7 is a third lysophosphatidic acid receptor that couples predominantly to G(q/11)alpha proteins.
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PMID:Molecular cloning and characterization of a lysophosphatidic acid receptor, Edg-7, expressed in prostate. 1072 22

Pancreastatin, a chromogranin A-derived peptide widely distributed throughout the neuroendocrine system, has a general inhibitory effect on endocrine secretion and a counterregulatory effect on insulin action. We have recently described the cross-talk of pancreastatin with insulin signaling in rat hepatoma cells (HTC), where it inhibits insulin action and signaling through the serine phosphorylation of the insulin receptor, thereby impairing tyrosine kinase activity. Here, we have characterized pancreastatin receptors and signaling in HTC cells. The pancreastatin effector systems were studied by determining phospholipase C activity in HTC membranes and mitogen-activated protein kinase (MAPK) phosphorylation activity in HTC cells. Binding studies with radiolabeled pancreastatin showed a population of high affinity binding sites, with a B(max) of 8 fmol/mg protein and a K(d) of 0.6 nM. Moreover, we assessed the coupling of the receptor with a G protein system by inhibiting the binding with guanine nucleotide and by measuring the GTP binding to HTC membranes. We found that pancreastatin receptor was coupled with a G alpha(q/11) protein which activates phospholipase C-beta(1) and phospholipase C-beta(3), in addition to MAPK via both beta gamma and alpha(q/11).
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PMID:Characterization of pancreastatin receptor and signaling in rat HTC hepatoma cells. 1084 19

The regulation of phosphatidylcholine-specific phospholipase D by purine nucleotides and protein kinase A were studied in vitro using an enzyme preparation partially purified from the membranous fraction of 7721 hepatocarcinoma cells. It was found that the enzyme activity was elevated by low concentrations of some purine nucleotides, but the activating effects were decreased when the concentrations of the nucleotides were higher. The optimal concentrations of GTP, GTPgamma[S], GDP and ATP for maximal activation were 0.1 mM, 5 microM, 1 mM and 1 mM respectively. The activation caused by 1 mM ADP was lower. The enzyme was not activated by 1 mM AMP, but significant activation was observed by the addition of 1 mM cAMP. The latter was mediated by protein kinase A, as a specific inhibitor of protein kinase A abolished the activation. There were synergic effects between ATP and GTP, ATP and PIP2, but not between ATP and GTPgamma[S], or PIP2 and GTPgamma[S]. The activating effects of GTP and ATP were abolished by neomycin, a PIP2 scavenger. These results suggest that phospholipase D is regulated by GTP-binding protein and the presence of PIP2 is required for the activation induced by GTP. Protein kinase A may be another protein kinase in addition to protein kinase C and protein tyrosine kinase which regulate the activity of phospholipase D, when the intracellular concentration of cAMP is increased.
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PMID:Regulation of phospholipase D from human hepatocarcinoma cell line by purine nucleotides and protein kinase A. 1088 20


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