arthur chiu | United States Environmental Protection Agency (original) (raw)
Papers by arthur chiu
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2010
Hexavalent chromium combines with glutathione in chloride intracellular channel carrier to form t... more Hexavalent chromium combines with glutathione in chloride intracellular channel carrier to form tetravalent and pentavalent chromium in plasma and organelle membranes. It also combines with NADH/NADPH to form pentavalent chromium in mitochondria. Tetravalent- and pentavalent- chromium (directly and indirectly) mediated DNA double strand breaks activate DNA damage signaling sensors: DNA-dependent-protein-kinase signals p53-dependent intrinsic mitochondrial apoptosis, and ataxia-telangiectasia-mutated and ataxia-telangiectasia-Rad3-related signal cell-arrest for DNA repair. Tetravalent chromium may be the most potent species since it causes DNA breaks and somatic recombination, but not apoptosis. Upon further failure of apoptosis and senescence/DNA-repair, damaged cells may become immortal with loss-of-heterozygosity and genetic plasticity.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2001
Inhalation of volatile chemicals released during household water use is a recognized exposure pat... more Inhalation of volatile chemicals released during household water use is a recognized exposure pathway. Models previously developed to estimate inhalation exposure to radon gas, radon progeny, and volatile organic compounds (VOCs) were limited in their ability to predict exposure to compounds of low volatility due to a lack of appropriate experimental data. Recently, a comprehensive series of experimental studies has been completed in which mass-transfer coefficients for a shower, bath, faucet, washing machine, and dishwasher have been measured, making more detailed and accurate predictions possible. In this paper, the theoretical basis for mass transfer between water and air is reviewed and then extended to include the pH-dependent transfer of volatile compounds that participate in rapid acid/base reactions. This class of compound has not previously been considered in exposure assessment models. The evolution of inhalation exposure models is briefly reviewed and an improved version is developed. Sample calculations are made demonstrating the influence of both low volatility and pH on inhalation exposure. The paper concludes with illustrative examples assessing the toxicological implications of exposure to radon and hydrogen cyanide. The analysis confirms that inhalation is an important exposure pathway for waterborne chemicals.
Dna Repair, 2008
Cellular stress and DNA damage up-regulate and activate p53, fundamental for cell cycle control, ... more Cellular stress and DNA damage up-regulate and activate p53, fundamental for cell cycle control, senescence, DNA repair and apoptosis. The specific mechanism(s) that determine whether p53-dependent cell cycle arrest or p53-dependent apoptosis prevails in response to specific DNA damage are poorly understood. In this study, we investigated two types of DNA damage, chromium treatment and gamma irradiation (IR) that induced similar levels of p53, but that mediated two distinct p53-dependent cell fates. Chromium exposure induced a robust DNA-dependent protein kinase (DNA-PK)-mediated apoptotic response that was accompanied by the rapid loss of the cyclin-dependent kinase inhibitor 1A (p21) protein, whereas IR treatment-induced cell cycle arrests that was supported by the rapid induction of p21. Inhibition of DNA-PK effectively blocked chromium-, but not IR-induced p53 stabilization and activation. In contrast, inhibition of ATM and ATR by caffeine had the inverse effect of blocking IR-, but not chromium-induced p53 stabilization and activation. Chromium exposure ablated p21 transcription but PUMA and Bax transcription was significantly enhanced compared to non-damaged cells. In contrast, IR treatment triggered significant p21 mRNA synthesis in addition to PUMA and Bax mRNA production. While chromium treatment enhanced the binding of p53 and RNA polymerase II (RNA Pol II) to both the p21 and PUMA promoters, RNA Pol II elongation was only observed along the PUMA gene and not the p21 gene. In contrast, following IR treatment, RNA Pol II elongation was observed on both p21 and PUMA. Chromium-induced apoptosis therefore involves DNA-PK-mediated p53 activation followed by preferential transcription of pro-apoptotic PUMA over anti-apoptotic p21 genes.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 1998
Chromate is a human carcinogen. Since it does not form a covalent DNA adduct in vitro under physi... more Chromate is a human carcinogen. Since it does not form a covalent DNA adduct in vitro under physiological conditions, and is not mutagenic in vitro in the presence of cytochrome P450 preparations from liver, reduction of Cr6+ by cellular reductants to lower oxidation states such as Cr5+, Cr4+ is considered to be a critical step in the mechanism of carcinogenesis.Long‐lived paramagnetic chromium species, Cr5+, Cr4+, Cr3+ are formed in the presence of coenzymes such as NAD(P)H, GSH, and cytochromes. These anionic complexes of reduced chromium are considered potential “penultimate” carcinogens. Various in vitro and in vivo studies from our group have demonstrated the formation of these ionic species using a modified paramagnetic spectroscopy approach. In this review, information is provided on the half‐lives of formation and decay, free energy changes, atomic structures and reaction mechanisms of these compounds in situ, in vivo and in vitro, at the molecular, cellular and organismic levels.Hydroxyl radical (·OH) can be generated from the reaction of these Cr5+, Cr4+ compounds with H2O2 by a Fenton‐like reaction, as can be demonstrated by molecular spin traps. In addition to ·OH radical, a number of other free radicals may be generated from reaction of chromium with cellular reductants and peroxides. These radicals, particularly the hydroxyl radical, are considered the ultimate agents in chromium carcinogenesis. They may break phosophodiester bonds of the DNA double strands, and modify 2'‐deoxyguanosine to form promutagenic 8‐hydroxy‐2'‐deoxyguanosine (8‐OHdG) in the DNA structure. Genetic expressions are changed at the transcription level. Changes in genetic information may also be passed onto future generations through cell replications to the daughter cells. Thus, ·OH from the interaction of Cr5+, Cr4+ with H2O2 affects not only differentiation but also cell division, and leads to the development of cancer as a result.
Dna Repair, 2008
The cyclin-dependent kinase inhibitor p21CIP1/WAF1 is a key component in cell cycle control and a... more The cyclin-dependent kinase inhibitor p21CIP1/WAF1 is a key component in cell cycle control and apoptosis, directing an anti-apoptotic response following DNA damage. Chromium exposure resulted in a 500–1000 fold increase in apoptosis-induced cell death in p21−/− HCT116 cells compared to wild-type or p53−/− cells. p53 shRNA (or transient p53 siRNA) into p21−/− HCT116 cells reduced Cr(VI) sensitivity, suggesting the enhanced apoptosis in p21−/− cells is p53-dependent. Under non-DNA damage conditions, the p53 level in p21−/− cells was significantly higher than in wild-type cells, due to enhanced p53 phosphorylation and stabilization rather than elevated p53 transcription. Wild-type cells showed significant p53 protein induction upon DNA damage whereas p21−/− cells showed no p53 increase. p21−/− cells display the constitutive activation of upstream p53 kinases (ATM, DNA-PK, ATR, AKT and p38). 2D gel analysis revealed p53 patterns in p21−/− cells were distinct from those in wild-type cells before and after chromium exposure. Our results suggest that p21 has an important role in the cellular response to normal replicative stress and its absence leads to a “chronic DNA damage” state that primes the cell for p53-dependent apoptosis.
Molecular and Cellular Biochemistry, 2004
Genetic and environmental interactions determine cancer risks but some cancer incidence is primar... more Genetic and environmental interactions determine cancer risks but some cancer incidence is primarily a result of inherited genetic deficits alone. Most cancers have an occupational, viral, nutritional, behavioral or iatrogenic etiology. Cancer can sometimes be controlled through broad public health interventions including industrial hygiene and engineering controls. Chromium and nickel are two human carcinogens associated with industrial exposures where public health measures apparently work. Carcinogenic mechanisms of these metals are examined by electron-spin-resonance-spectroscopy and somatic-mutation-and-recombination in Drosophila melanogaster in this report. Both metals primarily affect initiation processes in cancer development suggesting important theoretical approaches to prevention and followup.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 1996
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2000
Wildlife populations are adversely affected in polluted environments. Nevertheless, a cause‐and‐e... more Wildlife populations are adversely affected in polluted environments. Nevertheless, a cause‐and‐effect relationship between excessive exposure to chlorinated hydrocarbons and induction of pathologic disorders in animals, is difficult to demonstrate without verification from experiments following the rationale of Koch's postulates. Deleterious effects of chlorinated chemicals such as DDT on songbird reproduction, as demonstrated by the clutch size of eggs in a
Mutation Research-fundamental and Molecular Mechanisms of Mutagenesis, 2004
Hexavalent chromium (Cr[VI]) is a common industrial waste product, an environmental pollutant, an... more Hexavalent chromium (Cr[VI]) is a common industrial waste product, an environmental pollutant, and a recognized human carcinogen. Following cellular uptake, Cr[VI] can cause DNA damage, however, the mechanisms by which mammalian cells respond to Cr-induced DNA damage remain to be elucidated. Using single cell gel electrophoresis (e.g., Comet Assay) and immunofluoresence microscopy to detect the presence of γ-H2AX foci, we find that Cr[VI] induces DNA double-strand breaks similar to ionizing radiation (IR). We also demonstrated that ataxia telangiectasia mutated (ATM) is activated in response to Cr[VI] and exposure to Cr[VI] triggers a dose and ATM-dependent S-phase arrest. Further, we document that ATM is required for phosphorylation of the structural maintenance of chromosome protein 1 (SMC1). Finally, we find that ATM-dependent phosphorylation of SMC1 is required to facilitate S-phase cell-cycle arrest in response to Cr[VI] exposure. Collectively, these results indicate that the ATM-SMC1 pathway plays a critical role in cellular response to Cr[VI].
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2004
Long range atmospheric and stream transport and oceanic currents drive the ecologic process of PC... more Long range atmospheric and stream transport and oceanic currents drive the ecologic process of PCB deposition in the abiotic environment. In contrast short range transport via bioaccumulation–biomagnification up the food chain determines PCB congener profiles and concentrations and their adverse effects in biological organisms. Two research approaches to congeners, with potential to associate specific adverse human health effects with PCB concentrations in indigenous small populations, are summarized in this study. The field epidemiologic approach includes giving questionnaires to target population groups in conjunction with sampling for PCBs (and selected persistent organic pollutants and metals), in foods purchased or hunted and collected by Inuit peoples. Direct determination of contaminant levels in food sources and among individuals in selected comparative subpopulations is also presented.
Journal of Molecular Biology, 1975
Tetrahymena mitochondrial and cytoplasmic tRNAs for valine, lysine, arginine and phenylalanine pr... more Tetrahymena mitochondrial and cytoplasmic tRNAs for valine, lysine, arginine and phenylalanine produced identical or different isoacceptor patterns on reversed-phase chromatography. Positive bindings of individual isoacceptors to Escherichia coli ribosomes were demonstrated in response to trinucleoside diphosphates and polynucleotides. It was shown that different isoacceptors exhibited different but degenerate coding recognition patterns. One of two phenylalanyl-tRNA species in mitochondria, however, showed no recognition toward either phenylalanine codon triplets or poly(U).Under suitable annealing conditions, two phenylalanyl-tRNA species could hybridize with mitochondrial DNA. The other mitochondrial tRNAs for valine, lysine and arginine showed no hybridization with mitochondrial DNA but produced significant binding to nuclear DNA-immobilized filters.From these and other coding data presented here, it is postulated that there are two classes of tRNA in Tetrahymena pyriformis mitochondria; the one, “native” tRNA, is mitochondrial DNA-transcript whose coding specificity is unique to mitochondrial tRNA. The other, termed “imported” tRNA, is transcribed from the nuclear DNA and probably transported into mitochondria. This class of tRNA exhibits the same or similar coding specificity as the corresponding cytoplasmic tRNA.
Journal of Inorganic Biochemistry, 1999
Electrophoretic mobility shift, DNA strand breakage assays and electron spin resonance (ESR) spin... more Electrophoretic mobility shift, DNA strand breakage assays and electron spin resonance (ESR) spin trapping were used to investigate the activation of nuclear transcription factor (NF)-κB, DNA strand breakage and 2′-deoxyguanosine hydroxylation induced by Cr(IV), as well the role of free radical reactions in these processes. Incubation of synthesized Cr(IV)-glutathione complex with cultured Jurkat cells resulted in activation of DNA binding activity of NF-κB. Cr(VI) is also able to induce NF-κB activation through Cr(V) and Cr(IV) intermediates generated during the reduction of Cr(VI) by the cells. Cr(III) did not cause observable NF-κB activation due to its inability to cross cell membranes. Cr(IV)-induced NF-κB activation is dose-dependent. Catalase inhibited the activation while superoxide dismutase enhanced it. The metal chelator, deferoxamine, and hydroxyl (OH) radical scavengers, sodium formate and aspirin, also inhibited the NF-κB activation. Electrophoretic assays using λ Hind III linear DNA showed that, in the presence of H2O2, Cr(IV) is capable of causing DNA strand breaks. Deferoxamine, sodium formate and aspirin inhibited the DNA strand breaks. HPLC measurements also show that OH radical generated by the Cr(IV)-mediated reaction with H2O2 was capable of causing 2′-deoxyguanosine (dG) hydroxylation to generate 8-hydroxyguanosine (8-OHdG). The relative magnitude of 8-OHdG formation correlated with the generation of OH radicals. ESR spin trapping measurements showed that reaction of Cr(IV) with H2O2 generated OH radicals, which were inhibited by deferoxamine, sodium formate and aspirin. The results show that Cr(IV) can cause NF-κB activation, DNA strand breaks and dG hydroxylation through OH radical-initiated reactions. This reactive chromium intermediate may play an important role in the mechanism of Cr(VI)-induced carcinogenesis. The results also suggest that the Cr(IV)-glutathione complex may be used as a model compound to study the role of Cr(IV) in Cr(VI) carcinogenicity.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2010
Hexavalent chromium combines with glutathione in chloride intracellular channel carrier to form t... more Hexavalent chromium combines with glutathione in chloride intracellular channel carrier to form tetravalent and pentavalent chromium in plasma and organelle membranes. It also combines with NADH/NADPH to form pentavalent chromium in mitochondria. Tetravalent- and pentavalent- chromium (directly and indirectly) mediated DNA double strand breaks activate DNA damage signaling sensors: DNA-dependent-protein-kinase signals p53-dependent intrinsic mitochondrial apoptosis, and ataxia-telangiectasia-mutated and ataxia-telangiectasia-Rad3-related signal cell-arrest for DNA repair. Tetravalent chromium may be the most potent species since it causes DNA breaks and somatic recombination, but not apoptosis. Upon further failure of apoptosis and senescence/DNA-repair, damaged cells may become immortal with loss-of-heterozygosity and genetic plasticity.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2001
Inhalation of volatile chemicals released during household water use is a recognized exposure pat... more Inhalation of volatile chemicals released during household water use is a recognized exposure pathway. Models previously developed to estimate inhalation exposure to radon gas, radon progeny, and volatile organic compounds (VOCs) were limited in their ability to predict exposure to compounds of low volatility due to a lack of appropriate experimental data. Recently, a comprehensive series of experimental studies has been completed in which mass-transfer coefficients for a shower, bath, faucet, washing machine, and dishwasher have been measured, making more detailed and accurate predictions possible. In this paper, the theoretical basis for mass transfer between water and air is reviewed and then extended to include the pH-dependent transfer of volatile compounds that participate in rapid acid/base reactions. This class of compound has not previously been considered in exposure assessment models. The evolution of inhalation exposure models is briefly reviewed and an improved version is developed. Sample calculations are made demonstrating the influence of both low volatility and pH on inhalation exposure. The paper concludes with illustrative examples assessing the toxicological implications of exposure to radon and hydrogen cyanide. The analysis confirms that inhalation is an important exposure pathway for waterborne chemicals.
Dna Repair, 2008
Cellular stress and DNA damage up-regulate and activate p53, fundamental for cell cycle control, ... more Cellular stress and DNA damage up-regulate and activate p53, fundamental for cell cycle control, senescence, DNA repair and apoptosis. The specific mechanism(s) that determine whether p53-dependent cell cycle arrest or p53-dependent apoptosis prevails in response to specific DNA damage are poorly understood. In this study, we investigated two types of DNA damage, chromium treatment and gamma irradiation (IR) that induced similar levels of p53, but that mediated two distinct p53-dependent cell fates. Chromium exposure induced a robust DNA-dependent protein kinase (DNA-PK)-mediated apoptotic response that was accompanied by the rapid loss of the cyclin-dependent kinase inhibitor 1A (p21) protein, whereas IR treatment-induced cell cycle arrests that was supported by the rapid induction of p21. Inhibition of DNA-PK effectively blocked chromium-, but not IR-induced p53 stabilization and activation. In contrast, inhibition of ATM and ATR by caffeine had the inverse effect of blocking IR-, but not chromium-induced p53 stabilization and activation. Chromium exposure ablated p21 transcription but PUMA and Bax transcription was significantly enhanced compared to non-damaged cells. In contrast, IR treatment triggered significant p21 mRNA synthesis in addition to PUMA and Bax mRNA production. While chromium treatment enhanced the binding of p53 and RNA polymerase II (RNA Pol II) to both the p21 and PUMA promoters, RNA Pol II elongation was only observed along the PUMA gene and not the p21 gene. In contrast, following IR treatment, RNA Pol II elongation was observed on both p21 and PUMA. Chromium-induced apoptosis therefore involves DNA-PK-mediated p53 activation followed by preferential transcription of pro-apoptotic PUMA over anti-apoptotic p21 genes.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 1998
Chromate is a human carcinogen. Since it does not form a covalent DNA adduct in vitro under physi... more Chromate is a human carcinogen. Since it does not form a covalent DNA adduct in vitro under physiological conditions, and is not mutagenic in vitro in the presence of cytochrome P450 preparations from liver, reduction of Cr6+ by cellular reductants to lower oxidation states such as Cr5+, Cr4+ is considered to be a critical step in the mechanism of carcinogenesis.Long‐lived paramagnetic chromium species, Cr5+, Cr4+, Cr3+ are formed in the presence of coenzymes such as NAD(P)H, GSH, and cytochromes. These anionic complexes of reduced chromium are considered potential “penultimate” carcinogens. Various in vitro and in vivo studies from our group have demonstrated the formation of these ionic species using a modified paramagnetic spectroscopy approach. In this review, information is provided on the half‐lives of formation and decay, free energy changes, atomic structures and reaction mechanisms of these compounds in situ, in vivo and in vitro, at the molecular, cellular and organismic levels.Hydroxyl radical (·OH) can be generated from the reaction of these Cr5+, Cr4+ compounds with H2O2 by a Fenton‐like reaction, as can be demonstrated by molecular spin traps. In addition to ·OH radical, a number of other free radicals may be generated from reaction of chromium with cellular reductants and peroxides. These radicals, particularly the hydroxyl radical, are considered the ultimate agents in chromium carcinogenesis. They may break phosophodiester bonds of the DNA double strands, and modify 2'‐deoxyguanosine to form promutagenic 8‐hydroxy‐2'‐deoxyguanosine (8‐OHdG) in the DNA structure. Genetic expressions are changed at the transcription level. Changes in genetic information may also be passed onto future generations through cell replications to the daughter cells. Thus, ·OH from the interaction of Cr5+, Cr4+ with H2O2 affects not only differentiation but also cell division, and leads to the development of cancer as a result.
Dna Repair, 2008
The cyclin-dependent kinase inhibitor p21CIP1/WAF1 is a key component in cell cycle control and a... more The cyclin-dependent kinase inhibitor p21CIP1/WAF1 is a key component in cell cycle control and apoptosis, directing an anti-apoptotic response following DNA damage. Chromium exposure resulted in a 500–1000 fold increase in apoptosis-induced cell death in p21−/− HCT116 cells compared to wild-type or p53−/− cells. p53 shRNA (or transient p53 siRNA) into p21−/− HCT116 cells reduced Cr(VI) sensitivity, suggesting the enhanced apoptosis in p21−/− cells is p53-dependent. Under non-DNA damage conditions, the p53 level in p21−/− cells was significantly higher than in wild-type cells, due to enhanced p53 phosphorylation and stabilization rather than elevated p53 transcription. Wild-type cells showed significant p53 protein induction upon DNA damage whereas p21−/− cells showed no p53 increase. p21−/− cells display the constitutive activation of upstream p53 kinases (ATM, DNA-PK, ATR, AKT and p38). 2D gel analysis revealed p53 patterns in p21−/− cells were distinct from those in wild-type cells before and after chromium exposure. Our results suggest that p21 has an important role in the cellular response to normal replicative stress and its absence leads to a “chronic DNA damage” state that primes the cell for p53-dependent apoptosis.
Molecular and Cellular Biochemistry, 2004
Genetic and environmental interactions determine cancer risks but some cancer incidence is primar... more Genetic and environmental interactions determine cancer risks but some cancer incidence is primarily a result of inherited genetic deficits alone. Most cancers have an occupational, viral, nutritional, behavioral or iatrogenic etiology. Cancer can sometimes be controlled through broad public health interventions including industrial hygiene and engineering controls. Chromium and nickel are two human carcinogens associated with industrial exposures where public health measures apparently work. Carcinogenic mechanisms of these metals are examined by electron-spin-resonance-spectroscopy and somatic-mutation-and-recombination in Drosophila melanogaster in this report. Both metals primarily affect initiation processes in cancer development suggesting important theoretical approaches to prevention and followup.
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 1996
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2000
Wildlife populations are adversely affected in polluted environments. Nevertheless, a cause‐and‐e... more Wildlife populations are adversely affected in polluted environments. Nevertheless, a cause‐and‐effect relationship between excessive exposure to chlorinated hydrocarbons and induction of pathologic disorders in animals, is difficult to demonstrate without verification from experiments following the rationale of Koch's postulates. Deleterious effects of chlorinated chemicals such as DDT on songbird reproduction, as demonstrated by the clutch size of eggs in a
Mutation Research-fundamental and Molecular Mechanisms of Mutagenesis, 2004
Hexavalent chromium (Cr[VI]) is a common industrial waste product, an environmental pollutant, an... more Hexavalent chromium (Cr[VI]) is a common industrial waste product, an environmental pollutant, and a recognized human carcinogen. Following cellular uptake, Cr[VI] can cause DNA damage, however, the mechanisms by which mammalian cells respond to Cr-induced DNA damage remain to be elucidated. Using single cell gel electrophoresis (e.g., Comet Assay) and immunofluoresence microscopy to detect the presence of γ-H2AX foci, we find that Cr[VI] induces DNA double-strand breaks similar to ionizing radiation (IR). We also demonstrated that ataxia telangiectasia mutated (ATM) is activated in response to Cr[VI] and exposure to Cr[VI] triggers a dose and ATM-dependent S-phase arrest. Further, we document that ATM is required for phosphorylation of the structural maintenance of chromosome protein 1 (SMC1). Finally, we find that ATM-dependent phosphorylation of SMC1 is required to facilitate S-phase cell-cycle arrest in response to Cr[VI] exposure. Collectively, these results indicate that the ATM-SMC1 pathway plays a critical role in cellular response to Cr[VI].
Journal of Environmental Science and Health Part C-environmental Carcinogenesis & Ecotoxicology Reviews, 2004
Long range atmospheric and stream transport and oceanic currents drive the ecologic process of PC... more Long range atmospheric and stream transport and oceanic currents drive the ecologic process of PCB deposition in the abiotic environment. In contrast short range transport via bioaccumulation–biomagnification up the food chain determines PCB congener profiles and concentrations and their adverse effects in biological organisms. Two research approaches to congeners, with potential to associate specific adverse human health effects with PCB concentrations in indigenous small populations, are summarized in this study. The field epidemiologic approach includes giving questionnaires to target population groups in conjunction with sampling for PCBs (and selected persistent organic pollutants and metals), in foods purchased or hunted and collected by Inuit peoples. Direct determination of contaminant levels in food sources and among individuals in selected comparative subpopulations is also presented.
Journal of Molecular Biology, 1975
Tetrahymena mitochondrial and cytoplasmic tRNAs for valine, lysine, arginine and phenylalanine pr... more Tetrahymena mitochondrial and cytoplasmic tRNAs for valine, lysine, arginine and phenylalanine produced identical or different isoacceptor patterns on reversed-phase chromatography. Positive bindings of individual isoacceptors to Escherichia coli ribosomes were demonstrated in response to trinucleoside diphosphates and polynucleotides. It was shown that different isoacceptors exhibited different but degenerate coding recognition patterns. One of two phenylalanyl-tRNA species in mitochondria, however, showed no recognition toward either phenylalanine codon triplets or poly(U).Under suitable annealing conditions, two phenylalanyl-tRNA species could hybridize with mitochondrial DNA. The other mitochondrial tRNAs for valine, lysine and arginine showed no hybridization with mitochondrial DNA but produced significant binding to nuclear DNA-immobilized filters.From these and other coding data presented here, it is postulated that there are two classes of tRNA in Tetrahymena pyriformis mitochondria; the one, “native” tRNA, is mitochondrial DNA-transcript whose coding specificity is unique to mitochondrial tRNA. The other, termed “imported” tRNA, is transcribed from the nuclear DNA and probably transported into mitochondria. This class of tRNA exhibits the same or similar coding specificity as the corresponding cytoplasmic tRNA.
Journal of Inorganic Biochemistry, 1999
Electrophoretic mobility shift, DNA strand breakage assays and electron spin resonance (ESR) spin... more Electrophoretic mobility shift, DNA strand breakage assays and electron spin resonance (ESR) spin trapping were used to investigate the activation of nuclear transcription factor (NF)-κB, DNA strand breakage and 2′-deoxyguanosine hydroxylation induced by Cr(IV), as well the role of free radical reactions in these processes. Incubation of synthesized Cr(IV)-glutathione complex with cultured Jurkat cells resulted in activation of DNA binding activity of NF-κB. Cr(VI) is also able to induce NF-κB activation through Cr(V) and Cr(IV) intermediates generated during the reduction of Cr(VI) by the cells. Cr(III) did not cause observable NF-κB activation due to its inability to cross cell membranes. Cr(IV)-induced NF-κB activation is dose-dependent. Catalase inhibited the activation while superoxide dismutase enhanced it. The metal chelator, deferoxamine, and hydroxyl (OH) radical scavengers, sodium formate and aspirin, also inhibited the NF-κB activation. Electrophoretic assays using λ Hind III linear DNA showed that, in the presence of H2O2, Cr(IV) is capable of causing DNA strand breaks. Deferoxamine, sodium formate and aspirin inhibited the DNA strand breaks. HPLC measurements also show that OH radical generated by the Cr(IV)-mediated reaction with H2O2 was capable of causing 2′-deoxyguanosine (dG) hydroxylation to generate 8-hydroxyguanosine (8-OHdG). The relative magnitude of 8-OHdG formation correlated with the generation of OH radicals. ESR spin trapping measurements showed that reaction of Cr(IV) with H2O2 generated OH radicals, which were inhibited by deferoxamine, sodium formate and aspirin. The results show that Cr(IV) can cause NF-κB activation, DNA strand breaks and dG hydroxylation through OH radical-initiated reactions. This reactive chromium intermediate may play an important role in the mechanism of Cr(VI)-induced carcinogenesis. The results also suggest that the Cr(IV)-glutathione complex may be used as a model compound to study the role of Cr(IV) in Cr(VI) carcinogenicity.