Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

ELP, the embryonal LTR binding protein, is a member of the nuclear receptor superfamily and a mouse homologue of Drosophila FTZ-F1. ELP is expressed specifically in undifferentiated mouse embryonal carcinoma cells and participates in suppression of the Moloney murine leukemia virus genome. The zinc finger domain of the protein was fused with glutathione S-transferase and was successfully used for isolating genomic targets. Sixteen genomic fragments were isolated and twelve of them strongly interacted with ELP. Six of the ELP binding fragments were analyzed further. All of these contained the multiple binding sites for ELP, which matched well with the consensus binding sequence for FTZ-F1, YCAAGGYCR. Among these, three fragments functioned as negative regulatory elements in response to ELP, when placed upstream to the promoter region of the Moloney leukemia virus. These results indicate that ELP may function as a negative transcription factor for a variety of cellular sequences, in addition to suppressing expression of Moloney leukemia virus in early embryonal cells. It was also shown that the procedure employed here works well for isolation of genomic targets of transcription factors.
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PMID:Isolation of high affinity cellular targets of the embryonal LTR binding protein, an undifferentiated embryonal carcinoma cell-specific repressor of Moloney leukemia virus. 157 38

The 27-kDa Rex trans-acting protein appears to be essential for replication of human T-cell leukemia virus type I. Mutations introduced outside of the Rex RNA-binding domain-nucleolar localization signal display either wild-type activity or, conversely, yield dominant-negative proteins. We generated missense mutations in a particular domain of the Rex protein (amino acid residues 54 to 69) which is characterized by a cluster of dominant-negative mutants. Our results indicate that amino acids 57 to 67 are critically important for Rex function mediated through the RxRE cis-acting RNA sequence. Within this domain, only amino acids 61 to 63 could be mutated without loss of function. All other missense and deletion mutants yielded dominant-negative proteins. In vitro RNA-binding studies performed with glutathione S-transferase-Rex fusion proteins demonstrated that all of the mutant Rex proteins interacted specifically with RxRE RNA. Analysis of chimeric Rex-Rev proteins suggests that this Rex domain is important for oligomerization.
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PMID:Dominant-negative mutants are clustered in a domain of the human T-cell leukemia virus type I Rex protein: implications for trans dominance. 160 59

Resistance to multiple chemotherapeutic agents is a common clinical problem in the treatment of cancer: such resistance may occur in primary therapy or be acquired during treatment. The most commonly used antineoplastic agents in the treatment of disseminated breast cancer are adriamycin, methotrexate and cyclophosphamide. Cell lines selected for resistance to adriamycin often develop cross-resistance to structurally dissimilar antineoplastic drugs with different mechanisms of cytotoxic action; this phenomenon has been called pleiotropic or multidrug resistance (MDR). In vitro models of MDR have shown that this type of resistance is accompanied by a decrease in cellular drug accumulation, mediated by the over-expression of a 170 kD plasma membrane glycoprotein referred to as P170. Glycoprotein P170 is an energy-dependent multidrug efflux pump, whose activity can be inhibited in vitro by a variety of agents including verapamil, quinidine and reserpine. P170 is over-expressed also in some human malignancies, and evidence exists about its role in examples of clinical resistance in vitro. Clinical trials using verapamil, a calcium channel blocker which selectively enhances drug cytotoxicity in MDR cell lines, have been prompted for leukemia and ovarian cancer. In addition other approaches are the subject of current preclinical investigations. Several observations as well the phenomenon of "atypical" MDR in cell lines which do not overexpress P170, suggest that also other factors are involved in multidrug resistance. Qualitative or quantitative changes in the activity of topoisomerases, protein kinase-related systems and glutathione S-transferase, may confer pleiotropic resistance. As the role of these genes and their regulation is clarified, they may also serve as useful targets for pharmacologic intervention in the treatment of drug-resistant human tumors. The mechanisms involved in resistance to methotrexate and cyclophosphamide are less studied, particularly in vivo samples. Methotrexate resistance is probably a complex multifactorial phenomenon; in some cases it is due to an increase in the expression of the drug target dihydrofolate reductase, often as a result of gene amplification, but in other cases a transport defect of the methotrexate or alterations of the activity of different enzymes have been reported. Cyclophosphamide (CP) resistance has been attributed to an increased activity of two different enzymes, glutathione S-transferase, also involved in MDR phenotype, and aldehyde dehydrogenase, which catalyzes inactivation of CP in non cytotoxic metabolites. This paper reviews the current state of our knowledge of chemo-resistance and the utility of available markers to identify potentially resistant tumors in vivo; the strategies that might be used to overcome this phenomenon are also described.
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PMID:Chemoresistance in breast tumors. 168 Jun 89

This paper presents an analysis of glutathione S-transferase (GST) activity of leukemic cells in 30 patients with acute leukemias and its predictive value for therapy. Blast cells were isolated from peripheral blood or bone marrow before induction therapy using Ficoll density gradient. GST activity was measured according to the spectrophotometric assay based on the use of 1-chloro-2,4-dinitrobenzene as a substrate. The results did not show any significant differences between activities of the enzyme within the different leukemia types according to the French-American-British (FAB) classification. The patients who achieved complete remission demonstrated the lowest value of enzyme activity. The highest enzyme activity was observed in those patients who achieved partial remission and the non-responsive patients presented a GST value within the median of these two groups. Two categories of patients were represented within the non-responsive treatment group. One was resistant to the conventional therapy and in the other death was caused by infectious or hemorrhagic complications. The mean GST activity in these two groups of patients differ greatly. These results suggest that low GST activity of leukemic cells could be a favourable prognostic factor whereas high GST values could help to find out the group of patients who should be further analysed prior to induction therapy.
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PMID:Glutathione S-transferase activity of leukemic cells as a prognostic factor for response to chemotherapy in acute leukemias. 204 80

The glutathione S-transferases are a group of enzymes involved in the detoxification of a wide range of xenobiotics. Elevation of the level of activity of glutathione S-transferases within the cytosol has been associated with the development of resistance to a number of cytotoxic drugs, including some commonly used in the treatment of leukaemia. In this paper we describe the purification and characterization of an anionic (p class) form of the enzyme from the peripheral blood of patients with acute myeloid leukemia, chronic myeloid leukaemia, and acute lymphocytic leukaemia and the spleen of a patient with chronic lymphocytic leukaemia. We present evidence that the form of enzyme purified closely resembles pi class glutathione S-transferase purified from human placenta. Immunoblotting performed on cytosol from the leukaemic cells from a range of cases of leukaemia at presentation, or on treatment, demonstrated that this form of glutathione S-transferase was the predominant isoenzyme expressed in all cases studied. However, in the limited number of cases studied there was no correlation between the level of expression and response to chemotherapy, suggesting that increased expression of pi class GST is not the sole cause of resistance to bifunctional alkylating agent in human leukaemias.
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PMID:Purification and characterization of a pi class glutathione S-transferase from human leukaemic cells. 226 12

Glutathione (GSH) levels and glutathione S-transferase (GST) activities were measured in the leukemia cells of 12 patients with chronic lymphocytic leukemia. Both were correlated with prior clinical exposure to alkylating agents and with DNA cross-link formation by chlorambucil in these cells in vitro. No correlation was observed between prior exposure to alkylating agents and GSH level or GST activity. An inverse correlation was observed between GST activity and cross-linking by chlorambucil, which was enhanced if both GST activity and GSH level were related to cross-linking. These findings suggest that the combination of GST and GSH protects the DNA of leukemia cells from chlorambucil, but the role of this combination in clinical resistance remains to be determined.
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PMID:Glutathione S-transferase activity, sulfhydryl group and glutathione levels, and DNA cross-linking activity with chlorambucil in chronic lymphocytic leukemia. 232 47

Cell lysates of mouse peritoneal macrophages, in the presence of reduced glutathione, converted leukotriene LTA4 to LTC4, and neither LTD4 nor LTE4 was detected. Therefore, like cultured rat basophilic leukemia cells (RBL cells), the peritoneal macrophage contains LTC4 synthetase and appears to contain little, if any, gamma-glutamyl transpeptidase. When LTA4 was added to subcellular fractions of mouse macrophage lysate, the highest specific activity of LTC4 synthetase (nmol LTC4/mg protein per 10 min) was associated with the particulate or membrane fractions (i.e., 10(4) and 10(5) X g pellets). The 10(5) X g supernatant contains approx. 1% of the specific activity and 6% of the total LTC4 synthetase activity compared with that of the 10(5) X g pellet. Conversely, the 10(5) X g supernatant had four-times more specific activity and 19-times more total GSH S-transferase activity than did the 10(5) X g pellet when evaluated using 1-chloro-2,4-dinitrobenzene (DNCB) as the substrate. LTA4 was converted to LTC4 by the membrane enzyme LTC4 synthetase in a dose-dependent manner at low LTA4 concentrations (3-50 microM) and reached a plateau of approx. 30 microM LTA4 using the macrophage 10(5) X g pellet as an enzyme source. The apparent Km value of LTC4 synthetase for LTA4 was estimated to be 5 microM based on Lineweaver-Burk plots. Enzyme in the 10(5) X g supernatant produced negligible quantities of LTC4 (1% or less of the particulate fractions) over a wide range of LTA4 concentrations. However, an enzyme in the 10(5) X g supernatant fraction presumed to be GSH S-transferase effectively catalyzes the conjugation of glutathione (GSH) with the aromatic compound DNCB. The apparent Km value of GSH S-transferase for DNCB was estimated to be 1.0-1.5 mM. On the other hand, enzyme from the membrane fraction (i.e., 10(5) X g pellet) catalyzed this reaction at a negligible rate over a wide range of DNCB concentrations. The apparent Km value of LTC4 synthetase for GSH was estimated to be 0.36 mM and the corresponding Km value estimated for the glutathione S-transferase was 0.25-0.76 mM. These values indicate similar kinetics for GSH utilization by both enzymes. These Km values are also significantly lower than the intracellular GSH levels of 2 to 5 mM. Therefore, it is suggested that the substrate limiting LTC4 synthetase activity is LTA4 and not GSH. Our results indicate that LTC4 synthetase from mouse peritoneal macrophages is a particulate or membrane-bound enzyme, as was reported by Bach et al.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Characterization of leukotriene C4 synthetase in mouse peritoneal exudate cells. 283 15

Sulfasalazine inhibited the formation of sulfidopeptide leukotrienes in ionophore A23187-challenged rat basophil leukemia cells in a dose-dependent fashion (EC50 = 0.11 mM). This compound also inhibited the solubilized, particulate LTC synthetase of RBL cells (EC50 = approximately 0.4 mM in the presence of a standard substrate mixture). The inhibition of LTC synthetase was paralleled by the capacity of sulfasalazine to potently inhibit several subfractions of the cytosolic rat liver glutathione S-transferases. The kinetics of the inhibition of the glutathione S-transferases, with 2,4-dinitrochlorobenzene as the substrate, were consistent with competitive inhibition with respect to glutathione (Ki values 0.21 +/- 0.05 to 0.46 +/- 0.096 microM in three discrete fractions). Inhibition with respect to the chromophoric substrate was uncompetitive in two of the three fractions examined (K'i values 0.61 +/- 0.13 and 1.05 +/- 0.14 microM) and non-competitive in the third (Ki = 0.72 microM). The inhibition of the LTC synthetase of RBL cells was also competitive with respect to glutathione (Ki = 120 microM). Both 5-aminosalicyclic acid and N'-2-pyridylsulfanilamide inhibited the one glutathione S-transferase fraction which was examined, and N'-2-pyridylsulfanilamide also inhibited the LTC synthetase. However, the kinetics of the inhibition of the liver enzyme by these compounds were not consistent with a competitive mechanism relative to glutathione, and the Ki values were at least 100 times greater than the ones for sulfasalazine on the same enzyme.
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PMID:Inhibition by sulfasalazine of LTC synthetase and of rat liver glutathione S-transferases. 286 22

When leukotriene (LT) A4 was incubated with subcellular fractions of sonicated rat basophilic leukemia (RBL) cells in the presence of glutathione, the enzyme producing LTC4, designated LTC4 synthetase, was found in the 105,000 X g pellet (microsomes) with a 3-fold enrichment in specific activity over that of the sonicate. The identification of the reaction product as LTC4 was confirmed by its identical retention time on reverse-phase HPLC to that of synthetic LTC4, the incorporation of [3H]glutathione into the product, its reactivity in a radioimmunoassay, and its UV absorption spectrum. In contrast, glutathione S-transferase activity, measured spectrophotometrically with 1-chloro-2,4-dinitrobenzene, was detected predominantly in the 105,000 X g supernatant (89%) and also in the microsomes (7%). The microsomal glutathione S-transferase and LTC4 synthetase were solubilized with 0.4% Triton X-102 and separated by DEAE-Sephacel chromatography; the former appeared in the effluent and the latter in the eluate after the addition of 0.16 M NaCl to the equilibration buffer. Solubilized, microsomal glutathione S-transferase was inhibited by S-hexylglutathione with an IC50 of 36 microM and was stable at 40 degrees C for 5 min, whereas LTC4 synthetase was only slightly inhibited (IC50, 2.3 mM) by S-hexylglutathione and retained no activity after incubation at 40 degrees C for 5 min. The partially purified LTC4 synthetase showed a specific activity of 1.34 +/- 0.51 nmol of LTC4 per 10 min per mg of protein (mean +/- SD, n = 9), representing a 10-fold purification from the sonicate and catalyzed the dose- and time-dependent production of LTC4 from LTA4 and glutathione. The apparent Km values for LTA4 and glutathione were estimated by Lineweaver-Burk plots to be 5-10 microM and 3-6 mM, respectively. These results indicate that the conjugation of LTA4 with glutathione to form LTC4 is catalyzed by a unique microsomal enzyme.
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PMID:Isolation and characterization of leukotriene C4 synthetase of rat basophilic leukemia cells. 386 31

Rat basophil leukemia cell homogenates effectively catalyze the conversion of leukotriene A4 to a mixture of leukotrienes C4 and D4 in the presence of glutathione. These homogenates also catalyze the formation of adducts of halogenated nitrobenzene with glutathione, as determined spectrophotometrically. While all the classical glutathione S-transferase activity resides in the soluble fraction of the homogenates, the thiol ether leukotriene-generating activity is found in the particulate fraction. This "leukotriene C synthetase" activity has been solubilized from a crude high-speed particulate fraction by means of the nonionic detergent, Triton X-100. The solubilized enzyme is incapable of converting 2,4-dinitrochlorobenzene to a colored product in the presence of glutathione. Nor will it react with 3,4-dichloronitrobenzene. On the other hand, under optimal conditions, this enzyme preparation is capable of generating about 0.1 nmol leukotriene C mg protein-1 min-1 in a reaction which continues in linear fashion for at least 10 min. This dissociation in substrate specificity, as well as differences in the inhibition profile, distinguish the enzyme activity in the particulate fraction from rat basophil leukemia cell homogenates from the microsomal glutathione S-transferase which has been described in rat liver homogenates, suggesting that this "leukotriene C synthetase" is a new and unique enzyme.
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PMID:Solubilization and characterization of the leukotriene C4 synthetase of rat basophil leukemia cells: a novel, particulate glutathione S-transferase. 632 87


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