The influence of graphitization of carbon support on the electrochemical corrosion of carbon and ... more The influence of graphitization of carbon support on the electrochemical corrosion of carbon and sintering of Pt particles are investigated by measuring emission at a constant potential of 1.4 V for 30 min using on-line mass spectrometry and cyclic voltammogram. In comparison to commercial Pt/C (from Johnson Matthey), highly graphitized carbon nanofiber (CNF) supported Pt catalyst exhibits lower performance degradation and emission. As the more carbon corrosion occurred, the more prominent changes were detected in electrochemical characteristics of fuel cell. This indicates that the carbon corrosion affects significantly the fuel cell durability. From the observed results, CNF is considered to be more corrosion resistant material as a catalyst support. However, CNF shows higher aggregation of Pt particles under repeated cyclic voltammetry between 0 and 0.8 V where the carbon corrosion is not initiated.
Pt catalyst was adsorbed on Carbon nanofiber (CNF) by modified polyol method after acid treatment... more Pt catalyst was adsorbed on Carbon nanofiber (CNF) by modified polyol method after acid treatment of the carbon support with and . As the time for acid treatment increases, more oxygen functional groups on carbon surface were produced which improve the loading amount and dispersion of Pt catalyst on carbon supports. In order to inspect the effect of CNF acid treatment time on electrochemical corrosion, constant potential of 1.4 V was applied to a single cell for 30 min and the amount of emitted was monitored with on-line mass spectrometry. According to the results of our experiment, more was produced with Pt/ oxidized-CNF catalyst in compared to that with unoxidized-CNF. Increasing acid treatment time also induces the more emission. Besides, performance degradation after corrosion test expanded with severer carbon corrosion. From the observed results, it can be concluded that the acid treatment of CNF is beneficial to catalyst loading, but it also is a significant factor declining t...
Angewandte Chemie (International ed. in English), Jan 29, 2015
This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reactio... more This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon-based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO2 to CO/H2 mixtures outperforming a low-area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low-cost, abundant electrocatalysts for synthetic fuel production from CO2 .
We have shown previously that A-type lamins and intranuclear localization of the herpes simplex v... more We have shown previously that A-type lamins and intranuclear localization of the herpes simplex virus (HSV) genome are critical for the formation of the VP16 activator complex on HSV immediate-early (IE) gene promoters in murine cells, which implies a critical role for lamin A and its associated proteins in HSV gene expression. Because barrier-to-autointegration factor 1 (BAF/BANF1) has been thought to bridge chromosomes to the nuclear lamina, we hypothesized that BAF might mediate viral genome targeting to the nuclear lamina. We found that overexpression of BAF enhances HSV-1 replication and knockdown of BAF decreases HSV gene expression, delays the kinetics of viral early replication compartment formation, and reduces viral yield compared to those in control small interfering RNA-transfected cells. However, BAF depletion did not affect genome complex targeting to the nuclear periphery. Instead, we found that the levels of a histone-modifying enzyme, SETD1A methyltransferase, and h...
ABSTRACT The addition of a small amount of Al2O3 (6 wt%) to the catalyst layer of high temperatur... more ABSTRACT The addition of a small amount of Al2O3 (6 wt%) to the catalyst layer of high temperature-polymer electrolyte membrane fuel cells (HT-PEMFCs) using phosphoric acid-doped membranes was proved to be an effective way to increase durability and performance. It was confirmed from the XRD study that Al2O3 reacts with phosphoric acid diffusing from the membrane to the electrode and produces aluminum dihydrophosphate (Al(H2PO4)3), which has proton conductivity. As a result, the formation of Al(H2PO4)3 not only reduces the loss of phosphoric acid and the resistance in fuel cells but also enhances the electrochemical surface area of catalysts.
The herpes simplex virus 1 VP16 tegument protein forms a transactivation complex with the cellula... more The herpes simplex virus 1 VP16 tegument protein forms a transactivation complex with the cellular proteins HCF-1 and Oct-1 upon entry into the host cell. VP16 has also been shown to interact with a number of virion tegument proteins and viral glycoprotein H to promote viral assembly, but no comprehensive study of the VP16 proteome has been performed at early times post-infection. We therefore performed a proteomic analysis of VP16-interacting proteins at 3 hours post-infection. We confirmed the interaction of VP16 with HCF-1 and a large number of cellular Mediator complex proteins, but most surprisingly, we found that the major viral protein associating with VP16 is the ICP4 immediate-early transactivator protein. These results raise the potential for a new function for VP16 in associating with the immediate-early ICP4 and playing a role in transactivation of early and late gene expression, in addition to its well-documented function in transactivation of immediate-early gene expre...
Active and highly stable oxide-supported IrNiO x core-shell catalysts for electrochemical water s... more Active and highly stable oxide-supported IrNiO x core-shell catalysts for electrochemical water splitting are presented. IrNi x @IrO x nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiO x / Meso-ATO) were synthesized from bimetallic IrNi x precursor alloys (PA-IrNi x /Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNi x /Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of coreshell particles. The core-shell IrNiO x /Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.
The effect of urea hydrolysis was studied on the preparation and properties of Pt/C catalyst. The... more The effect of urea hydrolysis was studied on the preparation and properties of Pt/C catalyst. The hydrolysis of urea provided hydroxyl ions in a controlled manner that prevented the localized pH change in the solution and only surface precipitation is resulted in a particle growth. From rotating ring disk electrode (RRDE) experiments, the Pt/C prepared in the presence of urea showed better exchange current density toward the oxygen reduction reaction. The rate of H 2 O 2 formation was reduced when urea was used in the alcohol reduction process and it was further decreased in the Pt/C catalyst prepared by the polyol process combined with urea.
Preparation of carbon-supported nano-MnO 2 composite (MnO 2 /C) by microemulsion process is repor... more Preparation of carbon-supported nano-MnO 2 composite (MnO 2 /C) by microemulsion process is reported. As evidenced by highresolution transmission electron microscopy (HR-TEM) micrographs, highly dispersed MnO 2 nanorods over carbon surface with clear inter-phase boundaries are obtained. X-ray diffraction results of as grown composite powder confirm the aMnO 2 phase of manganese oxide that on annealing at elevated temperatures undergo oxidative transformation to Mn 3 O 4 and Mn 2 O 3 phases. The small size and high dispersion of MnO 2 nanorods in the composite material exhibited high capacitance of 165 Fg À1 for MnO 2 /C and 458 Fg À1 for pure MnO 2 .
Purpose To explore surface-immobilized and suspended modalities of the hydrophobic polycation N,N... more Purpose To explore surface-immobilized and suspended modalities of the hydrophobic polycation N,N-dodecyl, methyl-polyethylenimine (DMPEI) for the ability to reduce viral infectivity in aqueous solutions containing herpes simplex viruses (HSVs) 1 and 2. Methods Surface-immobilized (coated onto surfaces) and suspended DMPEI were incubated with aqueous solutions containing HSV-1 or -2 to measure the antiviral effect of the hydrophobic polycation's formulations on HSVs.
Little is known about the mechanisms of gene targeting within the nucleus and its effect on gene ... more Little is known about the mechanisms of gene targeting within the nucleus and its effect on gene expression, but most studies have concluded that genes located near the nuclear periphery are silenced by heterochromatin. In contrast, we found that early herpes simplex virus (HSV) genome complexes localize near the nuclear lamina and that this localization is associated with reduced heterochromatin on the viral genome and increased viral immediate-early (IE) gene transcription. In this study, we examined the mechanism of this effect and found that input virion transactivator protein, virion protein 16 (VP16), targets sites adjacent to the nuclear lamina and is required for targeting of the HSV genome to the nuclear lamina, exclusion of heterochromatin from viral replication compartments, and reduction of heterochromatin on the viral genome. Because cells infected with the VP16 mutant virus in1814 showed a phenotype similar to that of lamin A/C ؊/؊ cells infected with wild-type virus, we hypothesized that the nuclear lamina is required for VP16 activator complex formation. In lamin A/C ؊/؊ mouse embryo fibroblasts, VP16 and Oct-1 showed reduced association with the viral IE gene promoters, the levels of VP16 and HCF-1 stably associated with the nucleus were lower than in wild-type cells, and the association of VP16 with HCF-1 was also greatly reduced. These results show that the nuclear lamina is required for stable nuclear localization and formation of the VP16 activator complex and provide evidence for the nuclear lamina being the site of assembly of the VP16 activator complex.
Herpes simplex virus (HSV) utilizes and subverts host chromatin mechanisms to express its lytic g... more Herpes simplex virus (HSV) utilizes and subverts host chromatin mechanisms to express its lytic gene products in mammalian cells. The host cell attempts to silence the incoming viral genome by epigenetic mechanisms, but the viral VP16 and ICP0 proteins promote active chromatin on the viral genome by recruiting other host epigenetic factors. However, the dependence on VP16 and ICP0 differs in different cell lines, implying cell type-dependent functional contributions of epigenetic factors for HSV gene expression. In this study, we performed a targeted RNA interference (RNAi) screen for cellular chromatin factors that are involved in regulation of herpes simplex virus (HSV) gene expression in U2OS osteosarcoma cells, a cell line that complements ICP0 mutant and VP16 mutant virus replication. In this screen, we found the same general classes of chromatin factors that regulate HSV gene expression in U2OS cells as in other cell types, including histone demethylases (HDMs), histone deacetylases (HDACs), histone acetyltransferases (HATs), and chromatin-remodeling factors, but the specific factors within these classes are different from those identified previously for other cell types. For example, KDM3A and KDM1A (LSD1) both demethylate mono-and dimethylated H3K9, but KDM3A emerged in our screen of U2OS cells. Further, small interfering RNA (siRNA) and inhibitor studies support the idea that KDM1A is more critical in HeLa cells, as observed previously, while KDM3A is more critical in U2OS cells. These results argue that different cellular chromatin factors are critical in different cell lines to carry out the positive and negative epigenetic effects exerted on the HSV genome. IMPORTANCE Upon entry into the host cell nucleus, the herpes simplex virus genome is subjected to host epigenetic silencing mechanisms. Viral proteins recruit cellular epigenetic activator proteins to reverse and counter the cellular silencing mechanisms. Some of the host silencing and activator functions involved in HSV gene expression have been identified, but there have been indications that the host cell factors may vary in different cell types. In this study, we performed a screen of chromatin factors involved in HSV gene regulation in osteosarcoma cells, and we found that the chromatin factors that are critical for HSV gene expression in these cells are different from those for previously studied cell types. These results argue that the specific chromatin factors operative in different cell lines and cell types may differ. This has implications for epigenetic drugs that are under development. Citation Oh HS, Bryant KF, Nieland TJF, Mazumder A, Bagul M, Bathe M, Root DE, Knipe DM. 2014. A targeted RNA interference screen reveals novel epigenetic factors that regulate herpesviral gene expression. mBio 5(1):e01086-13.
A poliovirus (PV) mutant (termed GG), which is incapable of producing 3AB, VPg, and 3CD proteins ... more A poliovirus (PV) mutant (termed GG), which is incapable of producing 3AB, VPg, and 3CD proteins due to a defective cleavage site between the 3B and 3C proteins, replicated, producing 3BC-linked RNA rather than the VPg-linked RNA produced by the wild type (WT). GG PV RNA is quasi-infectious. The yield of infectious GG PV relative to replicated RNA is reduced by almost 5 logs relative to that of WT PV. Proteolytic activity required for polyprotein processing is normal for the GG mutant. 3BC-linked RNA can be encapsidated as efficiently as VPg-linked RNA. However, a step after genome replication but preceding virus assembly that is dependent on 3CD and/or 3AB proteins limits production of infectious GG PV. This step may involve release of replicated genomes from replication complexes. A pseudorevertant (termed EG) partially restored cleavage at the 3B-3C cleavage site. The reduced rate of formation of 3AB and 3CD caused corresponding reductions in the observed rate of genome replication and infectious virus production by EG PV without impacting the final yield of replicated RNA or infectious virus relative to that of WT PV. Using EG PV, we showed that genome replication and encapsidation were distinct steps in the multiplication cycle. Ectopic expression of 3CD protein reversed the genome replication phenotype without alleviating the infectious-virus production phenotype. This is the first report of a trans-complementable function for 3CD for any picornavirus. This observation supports an interaction between 3CD protein and viral and/or host factors that is critical for genome replication, perhaps formation of replication complexes.
Poliovirus (PV) requires membranes of the host cell's secretory pathway to generate replication c... more Poliovirus (PV) requires membranes of the host cell's secretory pathway to generate replication complexes (RCs) for viral RNA synthesis. Recent work identified the intermediate compartment and the Golgi apparatus as the precursors of the replication "organelles" of PV (N. Y. Hsu et al., Cell 141:799 -811, 2010).
Carbon-supported MnO 2 nanorods are synthesized using a microemulsion process and a manganese oxi... more Carbon-supported MnO 2 nanorods are synthesized using a microemulsion process and a manganese oxide/carbon (MnO 2 /C) composite is investigated for use in a supercapacitor. As shown by high-resolution transmission electron microscopy the 2 nm × 10 nm MnO 2 nanorods are uniformly dispersed on the carbon surface. Cyclic voltammograms recorded for the MnO 2 /C composite electrode display ideal capacitive behaviour between −0.1 and 0.8 V (vs. saturated calomel electrode) with high reversibility. The specific capacitance of the MnO 2 /C composite electrode found to be 165 F g −1 and is estimated to be as high as 458 F g −1 for the MnO 2 . Based on cyclic voltammetric life-cycle tests, the MnO 2 /C composite electrode gives a highly stable and reversible performance for up to 10,000 cycles.
A modified polyol process is developed to enhance the Pt loading during the preparation of carbon... more A modified polyol process is developed to enhance the Pt loading during the preparation of carbonsupported platinum (Pt/C) catalysts. With the help of the zeta potential, the effect of pH on the electrostatic forces between the support and the Pt colloid is investigated. It is shown experimentally that the surface charge on the carbon support becomes more electropositive when the solution pH is changed from alkaline to acidic. This change does not, however, affect the electronegative surface charge of Pt colloids already attained and stabilized by glycolate anions. This new behaviour caused by the change in solution pH accounts for the enhanced yield of the process and does not affect the Pt particle size. All the experimental results reveal that this simple modification is a cost-effective method for the synthesis of highly Pt-loaded Pt/C catalysts for fuel cells.
ABSTRACT This study examines the effect of heat-treatment temperature on the electrochemical corr... more ABSTRACT This study examines the effect of heat-treatment temperature on the electrochemical corrosion of carbon nanofibers (CNFs) in polymer electrolyte membrane (PEM) fuel cells. Corrosion is investigated by monitoring the generation of CO2 using an on-line mass spectrometer at a constant potential of 1.4 V for 30 min. The experimental results show that the generation of CO2 decreases with increasing heat-treatment temperature, indicating that less electrochemical carbon corrosion occurs. In particular, when the heat-treatment temperature is 2400 °C, the change intensifies. X-ray photoelectron spectroscopic analysis shows that oxygen functional groups on the carbon surface decrease with increasing heat-treatment temperature. A reduction in oxygen functional groups increases the hydrophobic nature of the carbon surface, which is responsible for the increased corrosion resistance of CNFs.
The influence of humidity, cell temperature and gas-phase O2 on the electrochemical corrosion of ... more The influence of humidity, cell temperature and gas-phase O2 on the electrochemical corrosion of carbon in polymer electrolyte membrane fuel cells is investigated by measuring CO2 emission at a constant potential of 1.4V for 30min using on-line mass spectrometry. Carbon corrosion shows a strong positive correlation with humidity and cell temperature. The presence of water is indispensable for electrochemical carbon
The influence of graphitization of carbon support on the electrochemical corrosion of carbon and ... more The influence of graphitization of carbon support on the electrochemical corrosion of carbon and sintering of Pt particles are investigated by measuring emission at a constant potential of 1.4 V for 30 min using on-line mass spectrometry and cyclic voltammogram. In comparison to commercial Pt/C (from Johnson Matthey), highly graphitized carbon nanofiber (CNF) supported Pt catalyst exhibits lower performance degradation and emission. As the more carbon corrosion occurred, the more prominent changes were detected in electrochemical characteristics of fuel cell. This indicates that the carbon corrosion affects significantly the fuel cell durability. From the observed results, CNF is considered to be more corrosion resistant material as a catalyst support. However, CNF shows higher aggregation of Pt particles under repeated cyclic voltammetry between 0 and 0.8 V where the carbon corrosion is not initiated.
Pt catalyst was adsorbed on Carbon nanofiber (CNF) by modified polyol method after acid treatment... more Pt catalyst was adsorbed on Carbon nanofiber (CNF) by modified polyol method after acid treatment of the carbon support with and . As the time for acid treatment increases, more oxygen functional groups on carbon surface were produced which improve the loading amount and dispersion of Pt catalyst on carbon supports. In order to inspect the effect of CNF acid treatment time on electrochemical corrosion, constant potential of 1.4 V was applied to a single cell for 30 min and the amount of emitted was monitored with on-line mass spectrometry. According to the results of our experiment, more was produced with Pt/ oxidized-CNF catalyst in compared to that with unoxidized-CNF. Increasing acid treatment time also induces the more emission. Besides, performance degradation after corrosion test expanded with severer carbon corrosion. From the observed results, it can be concluded that the acid treatment of CNF is beneficial to catalyst loading, but it also is a significant factor declining t...
Angewandte Chemie (International ed. in English), Jan 29, 2015
This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reactio... more This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon-based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO2 to CO/H2 mixtures outperforming a low-area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low-cost, abundant electrocatalysts for synthetic fuel production from CO2 .
We have shown previously that A-type lamins and intranuclear localization of the herpes simplex v... more We have shown previously that A-type lamins and intranuclear localization of the herpes simplex virus (HSV) genome are critical for the formation of the VP16 activator complex on HSV immediate-early (IE) gene promoters in murine cells, which implies a critical role for lamin A and its associated proteins in HSV gene expression. Because barrier-to-autointegration factor 1 (BAF/BANF1) has been thought to bridge chromosomes to the nuclear lamina, we hypothesized that BAF might mediate viral genome targeting to the nuclear lamina. We found that overexpression of BAF enhances HSV-1 replication and knockdown of BAF decreases HSV gene expression, delays the kinetics of viral early replication compartment formation, and reduces viral yield compared to those in control small interfering RNA-transfected cells. However, BAF depletion did not affect genome complex targeting to the nuclear periphery. Instead, we found that the levels of a histone-modifying enzyme, SETD1A methyltransferase, and h...
ABSTRACT The addition of a small amount of Al2O3 (6 wt%) to the catalyst layer of high temperatur... more ABSTRACT The addition of a small amount of Al2O3 (6 wt%) to the catalyst layer of high temperature-polymer electrolyte membrane fuel cells (HT-PEMFCs) using phosphoric acid-doped membranes was proved to be an effective way to increase durability and performance. It was confirmed from the XRD study that Al2O3 reacts with phosphoric acid diffusing from the membrane to the electrode and produces aluminum dihydrophosphate (Al(H2PO4)3), which has proton conductivity. As a result, the formation of Al(H2PO4)3 not only reduces the loss of phosphoric acid and the resistance in fuel cells but also enhances the electrochemical surface area of catalysts.
The herpes simplex virus 1 VP16 tegument protein forms a transactivation complex with the cellula... more The herpes simplex virus 1 VP16 tegument protein forms a transactivation complex with the cellular proteins HCF-1 and Oct-1 upon entry into the host cell. VP16 has also been shown to interact with a number of virion tegument proteins and viral glycoprotein H to promote viral assembly, but no comprehensive study of the VP16 proteome has been performed at early times post-infection. We therefore performed a proteomic analysis of VP16-interacting proteins at 3 hours post-infection. We confirmed the interaction of VP16 with HCF-1 and a large number of cellular Mediator complex proteins, but most surprisingly, we found that the major viral protein associating with VP16 is the ICP4 immediate-early transactivator protein. These results raise the potential for a new function for VP16 in associating with the immediate-early ICP4 and playing a role in transactivation of early and late gene expression, in addition to its well-documented function in transactivation of immediate-early gene expre...
Active and highly stable oxide-supported IrNiO x core-shell catalysts for electrochemical water s... more Active and highly stable oxide-supported IrNiO x core-shell catalysts for electrochemical water splitting are presented. IrNi x @IrO x nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiO x / Meso-ATO) were synthesized from bimetallic IrNi x precursor alloys (PA-IrNi x /Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNi x /Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of coreshell particles. The core-shell IrNiO x /Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.
The effect of urea hydrolysis was studied on the preparation and properties of Pt/C catalyst. The... more The effect of urea hydrolysis was studied on the preparation and properties of Pt/C catalyst. The hydrolysis of urea provided hydroxyl ions in a controlled manner that prevented the localized pH change in the solution and only surface precipitation is resulted in a particle growth. From rotating ring disk electrode (RRDE) experiments, the Pt/C prepared in the presence of urea showed better exchange current density toward the oxygen reduction reaction. The rate of H 2 O 2 formation was reduced when urea was used in the alcohol reduction process and it was further decreased in the Pt/C catalyst prepared by the polyol process combined with urea.
Preparation of carbon-supported nano-MnO 2 composite (MnO 2 /C) by microemulsion process is repor... more Preparation of carbon-supported nano-MnO 2 composite (MnO 2 /C) by microemulsion process is reported. As evidenced by highresolution transmission electron microscopy (HR-TEM) micrographs, highly dispersed MnO 2 nanorods over carbon surface with clear inter-phase boundaries are obtained. X-ray diffraction results of as grown composite powder confirm the aMnO 2 phase of manganese oxide that on annealing at elevated temperatures undergo oxidative transformation to Mn 3 O 4 and Mn 2 O 3 phases. The small size and high dispersion of MnO 2 nanorods in the composite material exhibited high capacitance of 165 Fg À1 for MnO 2 /C and 458 Fg À1 for pure MnO 2 .
Purpose To explore surface-immobilized and suspended modalities of the hydrophobic polycation N,N... more Purpose To explore surface-immobilized and suspended modalities of the hydrophobic polycation N,N-dodecyl, methyl-polyethylenimine (DMPEI) for the ability to reduce viral infectivity in aqueous solutions containing herpes simplex viruses (HSVs) 1 and 2. Methods Surface-immobilized (coated onto surfaces) and suspended DMPEI were incubated with aqueous solutions containing HSV-1 or -2 to measure the antiviral effect of the hydrophobic polycation's formulations on HSVs.
Little is known about the mechanisms of gene targeting within the nucleus and its effect on gene ... more Little is known about the mechanisms of gene targeting within the nucleus and its effect on gene expression, but most studies have concluded that genes located near the nuclear periphery are silenced by heterochromatin. In contrast, we found that early herpes simplex virus (HSV) genome complexes localize near the nuclear lamina and that this localization is associated with reduced heterochromatin on the viral genome and increased viral immediate-early (IE) gene transcription. In this study, we examined the mechanism of this effect and found that input virion transactivator protein, virion protein 16 (VP16), targets sites adjacent to the nuclear lamina and is required for targeting of the HSV genome to the nuclear lamina, exclusion of heterochromatin from viral replication compartments, and reduction of heterochromatin on the viral genome. Because cells infected with the VP16 mutant virus in1814 showed a phenotype similar to that of lamin A/C ؊/؊ cells infected with wild-type virus, we hypothesized that the nuclear lamina is required for VP16 activator complex formation. In lamin A/C ؊/؊ mouse embryo fibroblasts, VP16 and Oct-1 showed reduced association with the viral IE gene promoters, the levels of VP16 and HCF-1 stably associated with the nucleus were lower than in wild-type cells, and the association of VP16 with HCF-1 was also greatly reduced. These results show that the nuclear lamina is required for stable nuclear localization and formation of the VP16 activator complex and provide evidence for the nuclear lamina being the site of assembly of the VP16 activator complex.
Herpes simplex virus (HSV) utilizes and subverts host chromatin mechanisms to express its lytic g... more Herpes simplex virus (HSV) utilizes and subverts host chromatin mechanisms to express its lytic gene products in mammalian cells. The host cell attempts to silence the incoming viral genome by epigenetic mechanisms, but the viral VP16 and ICP0 proteins promote active chromatin on the viral genome by recruiting other host epigenetic factors. However, the dependence on VP16 and ICP0 differs in different cell lines, implying cell type-dependent functional contributions of epigenetic factors for HSV gene expression. In this study, we performed a targeted RNA interference (RNAi) screen for cellular chromatin factors that are involved in regulation of herpes simplex virus (HSV) gene expression in U2OS osteosarcoma cells, a cell line that complements ICP0 mutant and VP16 mutant virus replication. In this screen, we found the same general classes of chromatin factors that regulate HSV gene expression in U2OS cells as in other cell types, including histone demethylases (HDMs), histone deacetylases (HDACs), histone acetyltransferases (HATs), and chromatin-remodeling factors, but the specific factors within these classes are different from those identified previously for other cell types. For example, KDM3A and KDM1A (LSD1) both demethylate mono-and dimethylated H3K9, but KDM3A emerged in our screen of U2OS cells. Further, small interfering RNA (siRNA) and inhibitor studies support the idea that KDM1A is more critical in HeLa cells, as observed previously, while KDM3A is more critical in U2OS cells. These results argue that different cellular chromatin factors are critical in different cell lines to carry out the positive and negative epigenetic effects exerted on the HSV genome. IMPORTANCE Upon entry into the host cell nucleus, the herpes simplex virus genome is subjected to host epigenetic silencing mechanisms. Viral proteins recruit cellular epigenetic activator proteins to reverse and counter the cellular silencing mechanisms. Some of the host silencing and activator functions involved in HSV gene expression have been identified, but there have been indications that the host cell factors may vary in different cell types. In this study, we performed a screen of chromatin factors involved in HSV gene regulation in osteosarcoma cells, and we found that the chromatin factors that are critical for HSV gene expression in these cells are different from those for previously studied cell types. These results argue that the specific chromatin factors operative in different cell lines and cell types may differ. This has implications for epigenetic drugs that are under development. Citation Oh HS, Bryant KF, Nieland TJF, Mazumder A, Bagul M, Bathe M, Root DE, Knipe DM. 2014. A targeted RNA interference screen reveals novel epigenetic factors that regulate herpesviral gene expression. mBio 5(1):e01086-13.
A poliovirus (PV) mutant (termed GG), which is incapable of producing 3AB, VPg, and 3CD proteins ... more A poliovirus (PV) mutant (termed GG), which is incapable of producing 3AB, VPg, and 3CD proteins due to a defective cleavage site between the 3B and 3C proteins, replicated, producing 3BC-linked RNA rather than the VPg-linked RNA produced by the wild type (WT). GG PV RNA is quasi-infectious. The yield of infectious GG PV relative to replicated RNA is reduced by almost 5 logs relative to that of WT PV. Proteolytic activity required for polyprotein processing is normal for the GG mutant. 3BC-linked RNA can be encapsidated as efficiently as VPg-linked RNA. However, a step after genome replication but preceding virus assembly that is dependent on 3CD and/or 3AB proteins limits production of infectious GG PV. This step may involve release of replicated genomes from replication complexes. A pseudorevertant (termed EG) partially restored cleavage at the 3B-3C cleavage site. The reduced rate of formation of 3AB and 3CD caused corresponding reductions in the observed rate of genome replication and infectious virus production by EG PV without impacting the final yield of replicated RNA or infectious virus relative to that of WT PV. Using EG PV, we showed that genome replication and encapsidation were distinct steps in the multiplication cycle. Ectopic expression of 3CD protein reversed the genome replication phenotype without alleviating the infectious-virus production phenotype. This is the first report of a trans-complementable function for 3CD for any picornavirus. This observation supports an interaction between 3CD protein and viral and/or host factors that is critical for genome replication, perhaps formation of replication complexes.
Poliovirus (PV) requires membranes of the host cell's secretory pathway to generate replication c... more Poliovirus (PV) requires membranes of the host cell's secretory pathway to generate replication complexes (RCs) for viral RNA synthesis. Recent work identified the intermediate compartment and the Golgi apparatus as the precursors of the replication "organelles" of PV (N. Y. Hsu et al., Cell 141:799 -811, 2010).
Carbon-supported MnO 2 nanorods are synthesized using a microemulsion process and a manganese oxi... more Carbon-supported MnO 2 nanorods are synthesized using a microemulsion process and a manganese oxide/carbon (MnO 2 /C) composite is investigated for use in a supercapacitor. As shown by high-resolution transmission electron microscopy the 2 nm × 10 nm MnO 2 nanorods are uniformly dispersed on the carbon surface. Cyclic voltammograms recorded for the MnO 2 /C composite electrode display ideal capacitive behaviour between −0.1 and 0.8 V (vs. saturated calomel electrode) with high reversibility. The specific capacitance of the MnO 2 /C composite electrode found to be 165 F g −1 and is estimated to be as high as 458 F g −1 for the MnO 2 . Based on cyclic voltammetric life-cycle tests, the MnO 2 /C composite electrode gives a highly stable and reversible performance for up to 10,000 cycles.
A modified polyol process is developed to enhance the Pt loading during the preparation of carbon... more A modified polyol process is developed to enhance the Pt loading during the preparation of carbonsupported platinum (Pt/C) catalysts. With the help of the zeta potential, the effect of pH on the electrostatic forces between the support and the Pt colloid is investigated. It is shown experimentally that the surface charge on the carbon support becomes more electropositive when the solution pH is changed from alkaline to acidic. This change does not, however, affect the electronegative surface charge of Pt colloids already attained and stabilized by glycolate anions. This new behaviour caused by the change in solution pH accounts for the enhanced yield of the process and does not affect the Pt particle size. All the experimental results reveal that this simple modification is a cost-effective method for the synthesis of highly Pt-loaded Pt/C catalysts for fuel cells.
ABSTRACT This study examines the effect of heat-treatment temperature on the electrochemical corr... more ABSTRACT This study examines the effect of heat-treatment temperature on the electrochemical corrosion of carbon nanofibers (CNFs) in polymer electrolyte membrane (PEM) fuel cells. Corrosion is investigated by monitoring the generation of CO2 using an on-line mass spectrometer at a constant potential of 1.4 V for 30 min. The experimental results show that the generation of CO2 decreases with increasing heat-treatment temperature, indicating that less electrochemical carbon corrosion occurs. In particular, when the heat-treatment temperature is 2400 °C, the change intensifies. X-ray photoelectron spectroscopic analysis shows that oxygen functional groups on the carbon surface decrease with increasing heat-treatment temperature. A reduction in oxygen functional groups increases the hydrophobic nature of the carbon surface, which is responsible for the increased corrosion resistance of CNFs.
The influence of humidity, cell temperature and gas-phase O2 on the electrochemical corrosion of ... more The influence of humidity, cell temperature and gas-phase O2 on the electrochemical corrosion of carbon in polymer electrolyte membrane fuel cells is investigated by measuring CO2 emission at a constant potential of 1.4V for 30min using on-line mass spectrometry. Carbon corrosion shows a strong positive correlation with humidity and cell temperature. The presence of water is indispensable for electrochemical carbon
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Papers by Hyung-Suk Oh