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)

The myelotoxicity, including leukemia, associated with benzene exposure has been attributed to the further activation of benzene-derived metabolites. In a previous study, we observed that (Cu(II) strongly mediates the oxidation of hydroquinone (HQ) producing benzoquinone (BQ) and H2O2 through Cu(II)/Cu(I) redox mechanism. Since copper exists in the nucleus and is closely associated with chromosomes and DNA, in this study we investigated whether this chemical--metal redox system induces strand breaks in phi X-174 RFI plasmid DNA. In the presence of micromolar concentrations of Cu(II) and HQ, both single and double strand breaks were induced, whereas HQ, Cu(II), H2O2 or BQ alone at the employed concentrations elicited no significant damage to DNA. The HQ/Cu(II) system was at least twice as efficient as a H2O2/Cu(II) system at inducing DNA strand breaks. Of Cu(II), Fe(III), Mn(II), Cd(II) and Zn(II), only HQ/Cu(II) induced extensive DNA strand breaks. Among HQ, 1,2,4-benzenetriol (BT), catechol and phenol, HQ/Cu(II) and BT/Cu(II) were the two most efficient DNA cleaving systems. The presence of bathocuproinedisulfonic acid (BCS) or catalase prevented the HQ/Cu(II)-induced DNA strand breaks. In addition, the HQ/Cu(II)-induced DNA strand breaks could be completely blocked by reduced glutathione and dithiothreitol, but not by L-cysteine. The interaction of L-cysteine with copper in the absence of HQ induced significant DNA strand breaks with the same pattern of DNA strand breaks as that of HQ/Cu(II) plus L-cysteine. In contrast to the HQ/Cu(II) system, a HQ/myeloperoxidase (MPO)/H2O2 system did not induce any DNA strand breaks, and furthermore, the presence of MPO inhibited the HQ/Cu(II)-induced DNA strand breaks. When DNA pretreated with Cu(II) was exposed to HQ, DNA strand breaks were formed that could be prevented by BCS or catalase, indicating that DNA-bound copper can undergo redox cycling in the presence of HQ, generating H2O2. Similar to the H2O2/Cu(II) system, the HQ/Cu(II)-induced DNA strand breaks could not be efficiently inhibited by hydroxyl radical scavengers but could be protected by singlet oxygen scavengers, indicating that the localized generation of singlet oxygen or a singlet oxygen-like entity, possibly a copper-peroxide complex, rather than free hydroxyl radical probably plays a role in the HQ/Cu(II)-induced DNA strand breaks. The above results suggest that macromolecule-associated copper and reactive oxygen generation may be important factors in the mechanism of HQ-induced DNA damage in target cells.
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PMID:DNA damage resulting from the oxidation of hydroquinone by copper: role for a Cu(II)/Cu(I) redox cycle and reactive oxygen generation. 839 44

The forward and reverse reactions for integration were characterized for the Moloney murine leukemia virus integrase (M-MuLV IN) protein. The M-MuLV IN was recombinantly produced in Escherichia coli, and was purified to greater than 90% homogeneity by a one-step affinity purification scheme. M-MuLV IN was highly active for integration as measured by in vitro cleavage and strand transfer assays. Furthermore, the integration of a model viral substrate into lambda concatamers by IN correctly produced the flanking 4-base pair duplications characteristic of M-MuLV IN. The reverse reaction of integration, disintegration, was also catalyzed by the recombinant M-MuLV IN. Two products were generated, a 3'-recessed long terminal repeat and a ligated target DNA, from a model integration-intermediate substrate in the presence of M-MuLV IN. The requirements and optimal conditions for maximal integration and disintegration activity for M-MuLV IN were determined. The forward and reverse reactions required different concentrations of manganese ion and reductant. Salt was also titrated for the forward and reverse reactions. Sodium chloride inhibited integration, but had little affect on disintegration. Low concentrations of potassium chloride enhanced integration, but had no affect on disintegration. The dinucleotide cleavage, strand transfer, and the disintegration reactions each had a unique pH profile of activity.
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PMID:Characterization of the forward and reverse integration reactions of the Moloney murine leukemia virus integrase protein purified from Escherichia coli. 841 46

We have previously described the in vitro and in vivo characterization of a panel of mutations affecting the RNase H domain of Moloney murine leukemia virus reverse transcriptase (Blain, S. W., and Goff, S.P. (1993) J. Biol. Chem. 268, 23585-23592; Blain, S. W., and Goff, S. P. (1995) J. Virol. 69, 4440-4452). We were intrigued by a discrepancy between in vitro and in vivo RNase H results for two of the mutants. While delta C and delta 5E appeared to have nearly wild-type RNase H activity in vitro, they were unable to degrade their genomic RNA in vivo and thus were effectively RNase H null mutants in this context. In this present report, we describe the differential effects of these mutations on RNase H activity in vitro in the presence of Mg2+ versus Mn2+: mutants delta C and delta 5E were active in the presence of the less biologically relevant Mn2+ and not in the presence of Mg2+. We also describe three mutants with only partial activity in Mg2+. The presence of the different cations can also affect DNA polymerization and processivity of an RNase H-deficient mutant.
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PMID:Differential effects of Moloney murine leukemia virus reverse transcriptase mutations on RNase H activity in Mg2+ and Mn2+. 857 37

We have characterized a Ca2+ current activated by depletion of intracellular Ca2+ stores (capacitative Ca2+ entry current) as a first step to investigate the mechanisms underlying communication between the intracellular Ca2+ stores and the plasma membrane Ca2+ permeability. Whole cell currents in response to voltage ramps from -125 to +60 mV from a holding potential of -40 mV were recorded in rat basophilic leukemia cells (RBL-1 cells) in solutions designed to optimize detection of a Ca2+ current. An inwardly rectifying current could be activated upon dialysis of the cell interior with pipette solutions devoid of Ca2+ and containing 20 mm BAPTA, a procedure expected to passively deplete intracellular Ca2+ stores. The current was maximally activated within 2 min, was sensitive to extracellular Ca2+ concentration and was abolished by removal of extracellular Ca2+. The current was markedly reduced in the presence of Ni2+ or La3+. The pathway activated by this protocol was permeant to Ba2+, displaying complex permeability characteristics at negative potentials. A small inward Mn2+ current consistent with a finite permeability of the pathway to Mn2+ was detected. In contrast Ni2+ displayed no detectable current carrying ability. Extracellular Na+ permeated the pathway in the absence of extracellular Ca2+. Under conditions designed to reduce passive depletion of intracellular Ca2+ stores, a Ca2+ current indistinguishable from that described above was activated by addition of ionomycin. This observation is consistent with the activation of the Ca2+ influx pathway occurring as a result of events associated with depletion of intracellular Ca2+ stores. Importantly, application of extracellular Ni2+ in the presence of ionomycin irreversibly inhibited the current. The presence of an inwardly rectifying K+ current in RBL cells could confound studies of the capacitative Ca2+ entry current when recorded using pipette solutions devoid of K+ since this current would be inward over the voltage range used to investigate the capacitative Ca2+ entry current. This study compares an inward rectifying K+ current and the capacitative Ca2+ entry current in RBL cells and highlights some similarities and differences between the two currents. The results demonstrate that caution should be exercised in interpreting recordings made using extracellular solutions containing even modest amounts of K+ when studying the capacitative Ca2+ entry current in RBL cells.
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PMID:A Ca2+ current activated by release of intracellular Ca2+ stores in rat basophilic leukemia cells (RBL-1). 884 17

An ultra-sensitive assay for reverse transcriptase (RT) activity called Amp-RT has been developed. An in vitro transcribed heteropolymeric RNA sequence was used as a template, and polymerase chain reaction (PCR) amplification with Southern-blot hybridization served as a detection system for the cDNA product of the reaction. Titration of Mg2+ and Mn2+ concentrations using the human immunodeficiency virus type 1 (HIV-1) and the human T lymphotropic virus type 1 (HTLV-I), respectively, showed optimal assay reactivity for both viruses at 2-20 mM of Mg2+. Analysis of density banded HIV-1 showed that the peak RT activity of the assay was associated with the fractions consistent with retrovirus particles. The sensitivity of Amp-RT was also compared with that of three conventional RT assays by using seven different retroviruses including HIV-1, simian immunodeficiency virus (SIV), caprine arthritis-encephalitis virus (CAEV), HTLV-I and HTLV-II, simian retrovirus type 2 (SRV-2), and gibbon ape leukemia virus (GALV). HTLV-I, HTLV-II, and GALV could not be detected by the three conventional RT assays. Amp-RT was able to detect all these viruses in 10(1)-10(3)-fold dilutions. Similarly, Amp-RT was found to be 10(3)-10(6)-fold more sensitive than the other RT assays in detecting HIV-1, SIV< or CAEV. Culture supernatants from uninfected cell lines were all Amp-RT negative. A quantitative Amp-RT assay was also developed by using recombinant HIV-1 RT and signal quantitation. The assay was found to have a 5 log linear range, and therefore, provides a useful tool for quantitating RT and retroviruses. Amp-RT offers a sensitive generic tool for the qualitative and quantitative detection of known and unknown retroviruses.
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PMID:Highly sensitive qualitative and quantitative detection of reverse transcriptase activity: optimization, validation, and comparative analysis with other detection systems. 888 46

Aggregation of the high-affinity receptor for IgE (Fc eta RI) on the surface of intact or permeabilized rodent mast cells results in tyrosine phosphorylation of phospholipase C-gamma 1 (PLC gamma 1) and PLC gamma 2, and translocation of both isozymes to the particulate fraction. We report here that activation of resident tyrosine kinases by the addition of adenosine triphosphate (ATP), orthovanadate, and Mg2+ to rat basophilic leukemia cell (RBL) lysates induces an association of PLC gamma 2 with the Triton-insoluble particulate fraction, with a parallel increase in tyrosine phosphorylation of cellular proteins. Both PLC gamma 2 translocation and tyrosine phosphorylation are supported by millimolar Mg2+ or Mn2+ but not by Ca2+. Both tyrosine phosphorylation and PLC gamma 2 translocation are inhibited by genistein. These data suggest that in vitro activation of tyrosine kinase activity in broken cell preparations induces the formation of association between PLC gamma 2 and ligands with the Triton-insoluble fraction.
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PMID:Translocation of phospholipase C-gamma 2 induced by in vitro activation of protein tyrosine kinase activity in mast cell lysates. 895 50

The reverse transcriptase-associated RNase H activity of Moloney murine leukemia virus specifically cleaves within the polypurine tract region of the viral genome to generate the primer for plus-strand DNA synthesis and removes the tRNA primer after minus-strand initiation by preferentially cleaving the RNA one nucleotide before the RNA-DNA junction. Moreover, the enzyme is unable to cleave the extended tRNA substrate at the RNA-DNA junction even at high enzyme concentrations. The RNase H domain of the reverse transcriptase was expressed as a glutathione S-transferase fusion protein and purified from Escherichia coli extracts. Following removal of the glutathione S-transferase portion of the protein, the specificity of the isolated RNase H domain was determined in the plus-strand primer reaction and in the tRNA primer removal reaction. Although the isolated domain lacked specificity in both cases, it was still unable to cleave the tRNA substrate precisely at the RNA-DNA junction. Specificity in both cases could be restored by adding back a truncated form of Moloney murine leukemia virus reverse transcriptase lacking the RNase H domain. These results implicate the polymerase domain as a specificity determinant for the RNase H activity of reverse transcriptase. The isolated RNase H domain had higher activity in the presence of Mn2+ than in the presence of Mg2+, but neither the RNase H domain alone nor the RNase H domain coupled to the polymerase domain in wild-type protein exhibited the normal cleavage specificities in the presence of the nonphysiological divalent cation.
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PMID:RNase H domain of Moloney murine leukemia virus reverse transcriptase retains activity but requires the polymerase domain for specificity. 897 Sep 88

Retroviral RNases H are similar in sequence and structure to Escherichia coli RNase HI and yet have differences in substrate specificities, metal ion requirements, and specific activities. Separation of reverse transcriptase (RT) into polymerase and RNase H domains yields an active RNase H from murine leukemia virus (MuLV) but an inactive human immunodeficiency virus (HIV) RNase H. The "handle region" present in E. coli RNase HI but absent in HIV RNase H contributes to the binding to its substrate and when inserted into HIV RNase H results in an active enzyme retaining some degree of specificity. Here, we show MuLV protein containing the C-terminal 175 amino acids with its own handle region or that of E. coli RNase HI has the same specific activity as the RNase H of RT, retains a preference for Mn2+ as the cation required for activity, and has association rate (KA) 10% that of E. coli RNase HI. However, with model substrates, specificities for removal of the tRNAPro primer and polypurine tract stability are lost, indicating specificity of RNase H of MuLV requires the remainder of the RT. Differences in KA, while significant, appear insufficient to account for the differences in specific activities of the bacterial and viral RNases H.
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PMID:The isolated RNase H domain of murine leukemia virus reverse transcriptase. Retention of activity with concomitant loss of specificity. 926 41

We investigated the effect of diphenylthiocarbazone (dithizone) and its structurally related compounds on the differentiation and apoptosis of two human myeloid leukemia cell lines. Dithizone caused a time- and concentration-dependent induction of differentiation in both the promyelocytic leukemia cell line HL-60 cells and the myeloblastic leukemia cell line ML-1 cells, as measured by nitroblue tetrazolium (NBT) reducing activity. Morphological changes and esterase activities confirmed that this differentiation took place. The induction of differentiation required the addition of dithizone to the culture medium for at least 12 h. The differentiation inducing activity was inhibited by the preincubation of dithizone with various metal ions such as Pb2+, Zn2+, Cu2+ and Mn2+ ions, but not with Fe3+ and Mg2+ ions. In addition, the DNA extracted from dithizone-treated HL-60 cells showed a typical ladder pattern characteristic of apoptosis in agarose gel electrophoresis. A quantitative analysis of DNA fragmentation revealed that this apoptosis was concentration- and time-dependent in both the HL-60 and ML-1 cells. Dithizone-induced apoptosis was also inhibited by preincubation with Mn2+ ions, but not with Mg2+ ions. These results indicate that dithizone induces both differentiation and apoptosis in HL-60 and ML-1 cells through a unique mechanism including metal chelation.
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PMID:Induction of differentiation and apoptosis by dithizone in human myeloid leukemia cell lines. 965 26

Retroviral reverse transcriptase-associated RNase H enzymes are responsible for degradation of viral RNA, including removal of the tRNA primer after plus-strand strong-stop synthesis and cleavage of the polypurine tract primer. These activities are required for the complex viral replication and result in generation of the long terminal repeats. The human immunodeficiency virus type 1 (HIV-1) RNase H domain has been expressed independently of the polymerase domain and possesses Mn2+-dependent activity with a hexahistidine tag. The isolated domain maintains the ability to specifically remove a tRNA primer mimic. In this study, the substrate determinants for recognition of the cognate tRNA3Lys are defined. Model substrates were constructed which mimic the RNA-DNA hybrid obtained from plus-strand strong-stop synthesis. Deletion substrates containing only 12, 9, or 6 positions of the tRNA primer were capable of being cleaved by the isolated RNase H domain. Mismatch and bromodeoxyuridine mutagenesis analysis indicated that positions 2, 3, 4, and 6, when mutated, affected the specificity of RNase H activity. Substitution substrates indicated that positions 4 and 6 within the RNA primer were important for recognition and cleavage by the HIV-1 isolated RNase H domain. Moloney murine leukemia virus-HIV-1 hybrid substrates were constructed which demonstrated that changes to HIV-1 sequences at positions 4 and 6 were sufficient but not optimal for regaining cleavage by the isolated HIV-1 RNase H domain. Optimal site-specific cleavage between the terminal ribonucleotide A and ribonucleotide C requires additional sequences beyond the first six positions but less than nine.
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PMID:Sequence requirements for removal of tRNA by an isolated human immunodeficiency virus type 1 RNase H domain. 965 29


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