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

Antineoplastic ether lipids have entered phase I clinical trial and, although their mechanism of action remains unclear, it is widely believed that the plasma membrane is the primary cellular drug target. In the present study the hypothesis was tested that metabolism of ether lipids acts as a detoxification process. [31P]-nuclear magnetic resonance (NMR) spectroscopy was used to study the metabolism of the ether lipid SRI 62-834 (SRI) and the phosphate ester hexadecylphosphocholine (HPC) in the presence of both isolated phospholipases C and D and post-mitochondrial rat liver homogenate. Both SRI and HPC were slowly metabolised by phospholipase D to their alkyl phosphates and choline, and the alkyl phosphates were subsequently metabolised by phosphatase to yield the alcohols and inorganic phosphate. These studies failed to detect any metabolism of either SRI or HPC by phospholipase C, and the metabolism of platelet-activating factor (PAF) by this enzyme was not inhibited by the addition of either compound. The cytotoxicity of SRI, the related compound HPC and their metabolites was determined in vitro using three cell lines. Cytotoxicity was measured by analysis of cell growth kinetics, MTT assay and lactate dehydrogenase release. Closely similar results were obtained in the JB1 rat hepatoma cell line, in the non-transformed BL8 rat hepatocyte cell line, and in A549 human lung adenocarcinoma cells. SRI was the most toxic of the compounds analysed, the concentration required to produce 50% toxicity or growth inhibition (IC50) being 6-9 microM. The putative metabolite of SRI, 2,2'-bis(hydroxymethyl)tetrahydrofuran, and the known metabolites [2'-(octadecyloxymethyl)tetrahydrofuran-2'-yl]methyl phosphate and 2-hydroxymethyl-2-octadecyloxymethyltetrahydrofuran exhibited IC50 values of > 200, > 100 and 40-70 microM, respectively, consistent with metabolic detoxification. HPC was more cytotoxic (IC50, 37 microM) than its phosphate metabolite (IC50, 140 microM), but its toxicity was similar to that of its metabolite hexadecanol (IC50, 28 microM), suggesting that only the former metabolic route leads to detoxification.
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PMID:Is metabolism an important arbiter of anticancer activity of ether lipids? Metabolism of SRI 62-834 and hexadecylphosphocholine by [31P]-NMR spectroscopy and comparison of their cytotoxicities with those of their metabolites. 145 Dec 37

1. We report the first demonstration of the pathophysiological importance and clinical applications of the relatively recently discovered circulating enzyme, phosphoinositol-specific phospholipase D. This enzyme is known to cleave the large variety of important cell-surface molecules linked to the cell membrane by glycan-phosphatidylinositol linkages (glycan-phosphatidylinositol anchors). 2. When measured in the sera of healthy individuals, phosphoinositol-specific phospholipase D activity was found to show a strong negative correlation with age, the degree of depreciation being greater than that measured for most other analytes. 3. Serum phosphoinositol-specific phospholipase D activity was considerably depressed in patients presenting with conditions leading to reduced liver synthetic reserve, such as hepatocellular carcinoma or liver cirrhosis caused by chronic viral hepatitis, and correlated with reduced albumin levels in these conditions, indicating that the liver is the site of phosphoinositol-specific phospholipase D synthesis and that phosphoinositol-specific phospholipase D may be used as an additional marker of liver synthetic reserve. 4. When measured in patients with acute liver disease, such as acute viral hepatitis, or in patients with bronchopneumonia, phosphoinositol-specific phospholipase D activity was found to be significantly raised, demonstrating features characteristic of an acute-phase reactant. 5. These findings indicate that, besides its pathophysiological importance, phosphoinositol-specific phospholipase D and the measurement of its activity in serum may have a useful place in the investigation of a range of clinical conditions, including tissue injury and inflammation.
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PMID:Inositol-specific phospholipase D activity in health and disease. 816 40

A culture model for invasion of rat mesothelial cell layer by rat ascites hepatoma cells has been developed. By using this quantitative model, we have recently found that the invasiveness of tumor cells is not only genetically determined but is greatly influenced by their interactions with host cells and host mediators. The preculture with macrophages was found to enhance both the in vitro and in vivo invasive potentials of the tumor cells. This potentiation appears to be mediated partly by oxygen radicals generated by the cocultured macrophages. The in vitro invasive capacity was also augmented by pretreating the tumor cells with TGF-beta, or with activated platelets. In the in vitro invasion assay system, tumor cells did not invade against cultured mesothelial cell monolayers without fetal calf serum. Serum could be completely substituted by oleoyl-lysophosphatidic acid (LPA) or bacterial phospholipase D (PLD), suggesting a possible participation of particular signaling cascade, PLD-LPA(PA) system, in the invasion of certain tumor cells.
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PMID:[Mechanism of tumor cell invasion studied by a culture model--modification of invasiveness by host mediators]. 829 16

We have previously reported that a microcarrier-attached human hepatoma (Hep G2) cell line responds to hydrodynamic shear upon transfer to an agitated, clean, autoclaved spinner flask with a transient increase in cytochrome P450IA1 (CYPIA1) activity. Physiological changes induced by hydrodynamic stress could be problematic in the scaleup of microcarrier cultures. A better understanding of how stress alters cell physiology may assist in reactor scaleup. The induction of CYPIA1 activity was dependent on the agitation level of the cultures, and the level of CYPIA1 induction was comparable to that obtained with exposure to approximately 0.1 nM TCDD (2, 3, 7, 8-tetrachlorodibenzo-p-dioxin). It has been well documented that hydrodynamic shear stress can cause alterations in the metabolism of phospholipid membrane-bound arachidonic acid (AA) in adherent cells in a parallel plate system. The present study was carried out to determine if either AA or a metabolite of AA was involved in the induction of CYPIA1 activity in the microcarrier cultures of Hep G2 cells. Addition of exogenous AA followed by initiation of the stress resulted in an increase in the level of CYPIA1 activity. Pretreatment of the cultures with quinacrine, an inhibitor of phospholipase A2, reduced the stress-induced CYPIA1 activity. Furthermore, addition of propranolol, an inhibitor of phosphatidic acid phosphohydrolase, resulted in an increase in the response in addition to sustaining the induced enzyme activity. Pretreatment with the cyclooxygenase inhibitor, indomethacin, or the lipoxygenase inhibitor, caffeic acid, had no effect on the response, suggesting that the cyclooxygenase and lipoxygenase pathways were not involved in generating AA metabolites that alter CYPIA1 activity. The agent, nordihydroguaiaretic acid, blocks the monooxygenase pathway and blocks CYPIA1 activity increases. These observations suggest a possible mechanism where the stress on the cells induces phospholipase D, resulting in the formation of phosphatidic acid which then activates phospholipase A2, resulting in the release of AA. Further, these results are consistent with a mechanism in which the metabolism of AA, most likely through the monooxygenase pathway, results in a metabolite that by a yet unknown mechanism induced CYPIA1.
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PMID:Possible role of arachidonic acid in stress-induced cytochrome P450IA1 activity. 898 9

Two forms of phospholipase D (PLD) have been found to be present in nuclei isolated from rat hepatocytes by measuring phosphatidylbutanol produced from exogenous radiolabeled phosphatidylcholine in the presence of butanol. In nuclear lysates from either rat liver or ascites hepatoma AH 7974 cells, the PLD activity was markedly stimulated by a recombinant ADP-ribosylation factor (rARF) in the presence of the guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) and phosphatidylinositol 4, 5-bisphosphate. ATP and phorbol-12-myristate 13-acetate had no synergistic effect on this PLD activity. On the other hand, the nuclear PLD was stimulated by unsaturated fatty acids, especially by oleic acid. The ARF-dependent nuclear PLD activity was increased in the S-phase of the regenerating rat liver after partial hepatectomy and also was much higher in AH 7974 cells than in the resting rat liver. In contrast, the levels of the oleate-dependent PLD activity remained constant throughout the cell cycle in liver regeneration. The intranuclear levels of the stimulating proteins of the nuclear PLD activity, e.g. ARF, RhoA, and protein kinase Cdelta increased in the S-phase of the regenerating liver. These results suggested that the nuclear ARF-dependent PLD activity may be associated with cell proliferation.
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PMID:Nuclear ADP-ribosylation factor (ARF)- and oleate-dependent phospholipase D (PLD) in rat liver cells. Increases of ARF-dependent PLD activity in regenerating liver cells. 903 May 90

The kinetics of phosphatidylcholine-specific phospholipase D activated by phosphatidylinositol 4,5-bisphosphate (PIP2) and inhibition by neomycin were studied in an enzyme preparation partially purified from human hepatocarcinoma cell line. It was found that phospholipase D was marginally activated by phosphatidyl-4-phosphate (PIP) and phosphatidylethanolamine (PE). In contrast, it was considerably activated by PIP2 in different concentration of phosphatidylcholine (PC). Sphingomyelin (SM), lysophosphatidylcholine (LPC) and phosphatidylserine (PS) were neither substrates nor inhibitors of the phospholipase D. PIP, induced an allosteric effect on phospholipase D and a negative cooperative effect with respect to phosphatidylcholine as indicated in the Lineweaver-Burk plot. In the absence of PIP2, a straight line was obtained, whereas a downward concave curve was observed in the presence of 25 microM of PIP2. The Hill coefficient and the apparent K(m) of phosphatidylcholine in the presence of 25 microM PIP, were calculated to be 0.631 and 10.79 mM, respectively. PIP2 also increased the maximal velocity (Vmax) of the phospholipase D reaction, suggesting that the affinity of substrate to enzyme was decreased, and the turnover number of the enzyme (kcat) was increased by PIP2. The activation of phospholipase D by PIP2 was dose dependent up to 50 microM of PIP2. The Ka of PIP2 was 15.8 mM. Neomycin, a polycationic glycoside, was shown to be an uncompetitive inhibitor of phospholipase D, and revealed the formation of a neomycin-PIP2 complex. The Ki of neomycin was estimated to be 8.7 mM.
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PMID:Effects of phosphatidylinositol 4,5-bisphosphate and neomycin on phospholipase D: kinetic studies. 1048 39

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

In order to elucidate the relation between cell signal transduction and cell differentiation, the effect of two differentiation inducers--all trans-retinoic acid (ATRA) and 13 cis-retinoic acid (13 cis-RA) on the specific activities (nmol/hr.mg protein) of phosphatidyl choline specific phospholipase D (PC-PLD) in 7721 human hepatocarcinoma cell line was studied. It was found that ATRA and 13 cis-RA increased the specific activities of membrane bound PC-PLD on 2nd and 4th day of cell culture respectively. If the PC-PLD activities were calculated as activity per bottle cells, the effect of ATRA on the 2nd day was also higher than that of 13 cis-RA, while the reverse was true on the 4th day, revealing a postponed effect of 13 cis-RA as compared with ATRA. The increase of PC-PLD was higher when the culture medium was refreshed every day than that when the medium was unrefreshed, suggesting that a factor might be existed in the fresh medium which could enhance the stimulating effect of retinoic acids on PC-PLD. The effect of ATRA on PC-PLD specific activity were higher on 2nd day than that on 4th day, owing to the accelerated proliferation of the cells on 4th day, leading to the increase of protein contents and decrease of the enzyme specific activity calculated on the base of protein contents. Whereas, the effect of 13 cis-RA on PC-PLD specific activity were higher on 4th day than that on 2nd day, because the increase of enzyme activity was higher than the increase of protein contents on 4th day. The relation between the elevation of PC-PLD and protein kinases was further studied and discovered that ATRA decreased both the specific activities of membrane bound and cytosolic protein kinase C (PKC) as well as tyrosine protein kinase (TPK) either in 2nd or 4th day of cell culture, which indicated that the increasing effect of ATRA on membrane bound PC-PLD was not resulted from the stimulating effect of PKC and TPK on PC-PLD, and its mechanism remains to be further investigated.
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PMID:[Effect of retinoic acids on phosphatidylcholine specific phospholipase D in 7721 human hepatocarcinoma cell line]. 1103 15

The effects of some inhibitors of protein kinase C(PKC) and tyrosine protein kinase(TPK)as well as the antibodies to PKC isotypes on the activity of phosphatidylcholine-specific phospholipase D(PLD)in 7721 human hepatocarcinoma cells were determined in order to study the regulation of PKC and TPK on PLD in these cells. It was found that all of the four inhibitors of PKC (chelerythrine, H-7, calphostin C and stausporine) and two inhibitors of TPK (tyrphostin 46 and genistein) partially inhibited the basal activity of PLD. Among them, the inhibition rates of staurosporine and calphostin C were the highest. The effects of TPK inhibitors were less than that of PKC inhibitors. When the inhibitors of PKC and TPK were added in combination, the inhibitory effect was greater than that used separately. A well known physiological inhibitor of PKC, D-sphingosine, did not show any inhibition, but did show stimulation on PLD activity. The mechanism is probably related to the transformation of D-sphingosine to D-sphingosine 1-phosphate, a stimulator of PLD via the activation TPK (and probably also PKC). The stimulating effects of both D-sphingosine and D-sphingosine 1-phosphate were blocked by TPK inhibitors and other PKC inhibitors. Among the 3 common PKC isotypes in human hepatocarcinoma cells, PKCalpha and PKCbetaI may be the main isotypes of PKC in the regulation of PLD.
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PMID:Regulation of Phospholipase D Activity in Human Hepatocacinoma Cells by Protein Kinases and D-sphingosine. 1211 73

The effect of phorbol 12-myristate-13-acetate (PMA) on the hydrolysis of phosphatidylcholine (PC) in rat hepatoma cell line CRBH7919 has been studied. It was found that PMA stimulated PC hydrolysis in CRBH7919 cells in a dose-dependent manner after treatment for 15 min. The product of PC hydrolysis was choline, not phosphocholine. The activity of the membrane bound PC-specific phospholipase D (PC-PLD) was determined. The results showed that the activity of PC-PLD increased after 10 min with 100 nM PMA treatment, and reached a level 3.25 times the control after 30 min. The fact that the PC-PLD activation preceded the hydrolysis of PC, suggests that PC-PLD is involved in the PC hydrolysis into phosphatidic acid and choline in CRBH7919 cells in the presence of PMA.
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PMID:PMA Stimulated Hydrolysis of Phosphatidylcholine in CRBH7919 Cell and Its Enzymatic Basis. 1221 68


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