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Biomedical subjects

M Y Han

Publications and source records attributed to M Y Han.

At least 19 recordsLinked to original sources
PubMed2006

Effects of surface charge, micro-bubble size and particle size on removal efficiency of electro-flotation.

Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar.

Aluminum Chloride↗
PubMed2006

Application of the flotation process to thicken the sludge from a DAF plant.

Dissolved air flotation (DAF) was evaluated for thickening of the sludges from a water treatment plant which uses DAF. Solid flux theory for gravity thickening was applied to the solid flux of DAF sludge. The higher the polymer dosage, at fixed solid concentration, the greater the rising velocity becomes. When applied with solid flux equations, a similar relationship to that of gravity thickening has been found. However, the values were much higher than in gravity thickening, because both the inflow solid concentration and the floating velocity were higher than for settled sludge. With this result, the proper dosage of polymer could be derived from the relationship between total solid flux and withdrawal velocity of DAF sludge.

Models, Chemical↗
PubMed2004

The effect of divalent metal ions on the zeta potential of bubbles.

Micro-bubbles are used in electro-flotation (EF) and dissolved air flotation (DAF) for particle separation. The efficiency of these flotation processes depends on the collision of bubble and particle and the collision efficiency is affected by certain parameters with respect to the size and zeta potential of bubble and particle. Therefore, it is necessary to monitor not only the zeta potential of the particle, but also that of the bubble. Gas bubbles are reported to be generally negatively charged in water. In this paper, we report a study performed to measure the zeta potential of bubbles in solutions containing divalent metals and find factors which can produce positively charged bubbles. Calcium and magnesium ions were selected as divalent metal ions because natural water normally contains an appreciable quantity of them. It was found that bubbles are negatively charged in CaCl2 solutions whereas, under certain conditions, they become positively charged in MgCl2. Charge reversal of bubbles was observed above 10(-2) M Mg, especially above pH 9. A probable principle that explained the charge reversal could be a combined mechanism with both specific adsorption of hydroxylated species and formation of hydroxide precipitates. Creating solution conditions that can produce positively charged bubbles in flotation methods might make it possible to remove particles using lesser amounts of coagulant or even none at all.

Air↗
PubMed2004

Fundamental characteristics of bubbles and ramifications for the flotation process.

Flotation processes involve the use of very small bubbles (micro-bubbles) to separate particles from water. The process has become a good alternative to sedimentation, especially where the particles are small or of low density. Although the flotation process commences with a collision between particles and bubbles, most research has been focused only on the characteristics of the particles. In this paper, recent theoretical and experimental research on the characteristics of bubbles is summarized. The effect on the collision efficiency of the size and charge of bubbles is calculated through trajectory analysis. The size and charge of bubbles are measured under different conditions and the ramifications of the results are discussed. The results may lead to a better understanding and optimization of the existing process. In particular, we discuss an idea that a new advanced flotation process might be possible by the modification of the characteristics of the bubble alone or of both bubble and particle.

Air↗
PubMed2002

Diagnosing and optimizing water treatment processes by using particle counter: a case study in Korea.

The goal of the flocculation process is to change the particle size distribution to best suit the subsequent processes. Although several methods exist to evaluate the flocculation process, no single universally accepted method has yet to be developed. The purpose of this paper is to present experiences whereby particle counting was used in the diagnosis and optimization of the flocculation process. A commercially available on-line continuous particle counter has been used in evaluating the design and the operation of this process at two conventional Water Treatment Plants. The evaluation is based on particle dynamics, i.e., the change of the number of small and large particles. Some design deficiencies in the distribution channel and flocculation process have been identified from this method, and thus some operational parameters are suggested for optimum performance. Because the optimum condition may be site-specific, the method presented in this paper will be beneficial in the evaluation of the flocculation process at other water treatment plants.

Facility Design and Construction↗
PubMed2001

Pleckstrin homology domain interacts with Rkp1/Cpc2, a RACK1 homolog, to modulate Pck2-mediated signaling process in Schizosaccharomyces pombe.

Rkp1/Cpc2, a fission yeast RACK1 homolog, interacts with Pck2, a PKC homolog, and is involved in the regulation of pck2-mediated signaling process. The N-terminal region of split pleckstrin homology domain (nPH) in human PLC-gamma1 bound to Rkp1/Cpc2 concomitantly with Pck2. nPH inhibited kinase activity of GST-Pck2 purified from Schizosaccharomyces pombe in vitro. The lethality induced by pck2(+) overexpression was suppressed by coexpression of either rkp1(+) or nPH domain. This result suggests that Rkp1/Cpc2 interacts with PH domain-containing protein and regulates the Pck2-mediated signaling process in S. pombe.

Binding Sites↗
PubMed2001

The neuron restrictive silencer factor can act as an activator for dynamin I gene promoter activity in neuronal cells.

The neuron restrictive silencer element (NRSE) has been identified in several neuronal genes and confers neuron specificity by silencing transcription in nonneuronal cells. We have previously reported that Sp1 and an NF-kappaB-like element (NE-1) are required for the promoter activity of mouse dynamin I gene. In the present study, we found that the upstream regulatory region of the dynamin I promoter has an NRSE-like sequence and showed that neuron restrictive silencer factor (NRSF) binds to this element in neuronal cells as well as in nonneuronal cells. We also showed that NRSF activates the promoter activity of dynamin I gene in neuronal cells. From the results in this study, we suggest that NRSE might be involved in the neuron restriction of dynamin I expression, and NRSF could act as an activator for promoter activity of dynamin I gene in neuronal cells.

Animals↗
PubMed2001

Negative regulation of YY1 transcription factor on the dynamin I gene promoter.

Dynamin I is highly expressed in brain and plays a critical role in clathrin-mediated endocytosis and synaptic vesicle recycling. To elucidate the molecular mechanism by which expression of dynamin I is tissue-specifically regulated, we previously cloned and characterized the promoter of the mouse dynamin I gene and suggested that there is a negative regulatory element in this promoter region. In the present study, we showed that YY1 binds to this negative regulatory element located at -111 to -107 by using the EMSA and supershift analyses. Cotransfection experiment using an YY1 expression vector revealed that YY1 exerts a repressive role on the dynamin I gene promoter activity. These results demonstrate that transcription factor YY1 negatively regulates dynamin I expression via binding to the negative regulatory element.

Animals↗
PubMed2001

Increased GTP-binding to dynamin II does not stimulate receptor-mediated endocytosis.

Regarding the molecular mechanism of dynamin in receptor-mediated endocytosis, GTPase activity of dynamin has been thought to have a critical role in endocytic vesicle internalization. However, a recent report suggested that GTP-binding to dynamin itself activates the dynamin to recruit molecular machinery necessary for endocytosis. In this study, to investigate the role of GTP binding to dynamin II, we generated two mutant dynamin II constructs: G38V and K44E. G38V, its GTP binding site might be mainly occupied by GTP caused by reduced GTPase activity, and K44E mutant, its GTP binding site might be vacant, caused by its decreased affinity for GTP and GDP. From the analysis of the ratio of GTP vs GDP bound to dynamin, we confirmed these properties. To test the effect of these mutant dynamins on endocytosis, we performed flow cytometry and confocal immunofluorescence analysis and found that these two mutants have inhibitory effect on transferrin-induced endocytosis. Whereas fluorescent transferrin was completely internalized in wild-type (WT) dynamin II expressing cells, no intracellular accumulation of fluorescent transferrin was found in the cells overexpressing K44E and G38V mutant. Interestingly, the amount of GTP bound to K44E was increased when endocytosis was induced than that bound to WT. The present results suggested that the GTPase activity of dynamin II is required for formation of endocytic vesicle and GTP-binding to dynamin II per se is not sufficient for stimulating endocytosis.

3T3 Cells↗
PubMed2001

Grb2 dominantly associates with dynamin II in human hepatocellular carcinoma HepG2 cells.

The two SH3 domains and one SH2 domain containing adaptor protein Grb2 is an essential element of the Ras signaling pathway in multiple systems. The SH2 domain of Grb2 recognizes and interacts with phosphotyrosine residues on activated tyrosine kinases, whereas the SH3 domains bind to several proline-rich domain-containing proteins such as Sos1. To define the difference in Grb2-associated proteins in hepatocarcinoma cells, we performed coprecipitation analysis using recombinant GST-Grb2 fusion proteins and found that several protein components (p170, p125, p100, and p80) differently associated with GST-Grb2 proteins in human Chang liver and hepatocarcinoma HepG2 cells. Sos1 and p80 proteins dominantly bind to Grb2 fusion proteins in Chang liver, whereas p100 remarkably associate with Grb2 in HepG2 cells. Also GST-Grb2 SH2 proteins exclusively bound to the p46(Shc), p52(Shc), and p66(Shc) are important adaptors of the Ras pathway in HepG2 cells. The p100 protein has been identified as dynamin II. We observed that the N-SH3 and C-SH3 domains of Grb2 fusion proteins coprecipitated with dynamin II besides Sos1. These results suggest that dynamin II may be a functional molecule involved in Grb2-mediated signaling pathway on Ras activation for tumor progression and differentiation of hepatocarcinoma cells.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Role of protein kinase Cdelta in transmitting hypoxia signal to HSF and HIF-1.

An hypoxic microenvironment is an important modulator of gene expression in many pathophysiological conditions. In this study, we show a coordinate activation of heat shock transcription factor (HSF) and hypoxia-inducible factor-1 (HIF-1) in RIF tumor cells by hypoxia. Since heat shock protein (hsp) and angiogenic factor genes that are regulated by HSF and HIF-1 are thought to contribute to the malignant progression of hypoxic tumor cells, it was of our major interest to identify the components that are responsible for the activation of both HSF and HIF-1. Our finding that a bioflavonoid quercetin (QCT), a well known inhibitor of hsp gene expression, significantly inhibited the transcriptional activation of HSF and HIF-1 strongly suggests that QCT-sensitive molecule(s) is involved in the transcriptional activation of HSF and HIF-1 by hypoxia. Our results revealed that PCKalpha, delta and epsilon isoforms are expressed in RIF cells, but only PKCdelta was specifically translocated to the membrane by hypoxia. Our results also revealed that the translocation of PKCdelta was completely abrogated by QCT. Moreover, inhibiting the PKCdelta activation, either pharmacologically with phorbol 12-myristate 13-acetate or with bisindolymaleimide II or genetically by transient transfection of a dominant negative PKCdelta, significantly inhibited the transcriptional activation of HSF and HIF-1 by hypoxia. These results strongly substantiate a view that the PKCdelta isozyme is the QCT-sensitive molecule that plays an important role in transmitting hypoxia signals to both HSF and HIF-1. Here we show that the membrane translocation of PKCdelta is dependent on the activation of phosphoinositol 3-kinase (PI3K). Treatment with PI3K inhibitor, wortmannin or LY294002, abrogated not only PKCdelta translocation but the subsequent transcriptional activation of HSF and HIF-1 by hypoxia. Together, our study shows that the PKCdelta isozyme acts as a shared component in transmitting hypoxia-induced signals to both HSF and HIF-1, and that the upstream regulator of PKCdelta is PI3K.

Cell Hypoxia↗
PubMed2000

Induction of early growth response-1 gene expression by calmodulin antagonist trifluoperazine through the activation of Elk-1 in human fibrosarcoma HT1080 cells.

The early growth response gene-1 (Egr-1) is a transcription factor that plays an important role in cell growth and differentiation. It has been known that Egr-1 expression is down-regulated in many types of tumor tissues, including human fibrosarcoma HT1080 cells, and introduction of the Egr-1 gene into HT1080 cells inhibits cell growth and tumorigenic potential. Trifluoperazine (TFP), a phenothiazine class calmodulin antagonist, is known to inhibit DNA synthesis and cell proliferation and potentially important in antitumor activities. To understand the regulatory mechanism of Egr-1, we investigated the effect of TFP on expression of Egr-1 in HT1080 cells. Herein, we report that Egr-1 expression was increased by TFP in synergy with serum at the transcriptional level. Both the Ca(2+)/calmodulin-dependent protein kinase II inhibitor KN62 and the calcineurin inhibitor cyclosporin A enhanced TFP-dependent increase of Egr-1, suggesting that the Ca(2+)/calmodulindependent pathway plays a role in regulation of Egr-1 expression in HT1080 cells. The TFP-stimulated increase of the Egr-1 protein was preferentially inhibited by the MEK-specific inhibitor PD98059. In addition, activation of human Egr-1 promoter and the transcriptional activation of the ternary complex factor Elk-1 induced by TFP were inhibited both by pretreatment of PD98059 and by expression of the dominant-negative RasN17. These results indicate that the Ras/MEK/Erk/Elk-1 pathway is necessary for TFP-induced Egr-1 expression. We propose that the calmodulin antagonist TFP stimulates Egr-1 gene expression by modulating Ras/MEK/Erk and activation of the Elk-1 pathway in human fibrosarcoma HT1080 cells.

Calmodulin↗
PubMed2000

Regulation of rat heat shock factor 2 expression during the early organogenic phase of embryogenesis.

A central step in the transcriptional regulation of heat shock protein (hsp) genes is the binding of the heat shock factor (HSF) to the upstream heat shock elements (HSEs). In vertebrates, HSF2 has been suggested to mediate the transcriptional regulation of hsp gene expression during development and differentiation. The expression levels of HSF2 were shown to vary widely among fully developed mouse organs. However, there exists limited information on the regulation of HSF2 expression during the inductive stage of organ formation in mammalian development. In this study, we have cloned the rat HSF2 cDNA and examined embryos for HSF2 expression from days 9.5 (E9.5) to 15.5 (E15.5) of gestation that correspond to the period when the major organ primordia are being actively established. We show that rat HSF2 has 94.6 and 96.3% identity to mouse HSF2 in nucleotide and amino acid sequences, respectively. By establishing a competitive RT-PCR, we show that about 503.6 pg of HSF2 mRNA were present per microgram of embryonic RNA in the primitive streak stage E9.5 embryos. The amounts of HSF2 mRNA then gradually decreased, resulting in an approximately 300-fold reduction in E15.5 embryos. The amounts of HSF2 mRNA in the embryos were found to be closely correlated with those of HSF2 protein and their HSE-binding activities. To our knowledge, this is the first detailed report on the structure and regulation of the rat HSF2 during the early organogenic period of mammalian embryogenesis.

Amino Acid Sequence↗
PubMed2000

Characterization of the mouse dynamin I gene promoter and identification of sequences that direct expression in neuronal cells.

Dynamin I is expressed at high levels in brain and its expression is regulated during the developmental stages of brain. To elucidate the molecular mechanism by which the expression is tissue-specifically regulated, we cloned the 5'-flanking region of the mouse dynamin I gene and determined the nucleotide sequence of 1036 bases upstream from the translation start site. Transient transfection studies with a chloramphenicol acetyltransferase reporter gene in neuroblastoma NS20Y and Lewis lung cells demonstrated that the 5'-flanking region has a cell-type-specific promoter activity. Deletion analyses demonstrated that the minimal promoter activity was detected in the proximal region 195 bp upstream of the translation initiation codon (-90 to +105). The minimal promoter was embedded in a GC-rich region (75% GC content), in which an Sp1-binding motif and a nuclear factor (NF)-kappa B-like element (NE-1) were found, but it lacked TATA and CAAT boxes. Mutational analysis and electrophoretic mobility-shift assay analysis revealed that Sp1 binds to the Sp1 site and that this element is critical for the promoter activity of the dynamin I gene. We found that the NE-1 sequence is required for the expression of the dynamin I gene but NEBP (NE-1-binding protein), which binds to the NE-1 sequence, is not NF-kappa B. We also found that one base in the NE-1 sequence (the underlined G residue in GGGATTCGCGGA) is critical for binding specificity to discriminate between NEBP and NF-kappa B. By UV cross-linking analysis, we found that NEBP is an approx. 104 kDa nuclear protein.

Animals↗
PubMed2000

Natural and synthetic analogues of actinomycin D as Grb2-SH2 domain blockers.

Natural analogues (D, C2, and VII) of actinomycin inhibit Grb2 SH2 domain binding with phosphopeptide-derived from Shc in vitro and in intracellular system. To study structure-activity relationships, 13 actinomycin analogues were synthesized and we found that the inhibition activity depended on the substituents of cyclic peptide groups in actinomycin and two analogues with Tyr residue are the most potent inhibitors with IC50 value of 0.5 and 0.8 microM, respectively.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Reduced glutathione oxidation ratio and 8 ohdG accumulation by mild ischemic pretreatment.

A critical role of oxidative stress has been implicated in ischemic brain damage. Mild ischemic pretreatment and/or synthesis of heat shock proteins (HSPs) has been suggested to protect against oxidative brain damage. However, experimental support of this suggestion have proven to be difficult partly because sensitive indices to assess oxidative consequences of ischemic brain damage were few. In this study, we have attempted to establish biochemical assay systems to quantitate oxidative brain damage following ischemia. We produced experimental brain ischemia in the Mongolian gerbil (Meriones unguiculatus) and examined the hippocampus for ischemic brain damage. The results obtained from ischemic gerbil hippocampus demonstrated that oxidative brain damage can be quantitated by determining glutathione oxidation ratio together with the accumulation of the oxidative DNA damage product, 8-hydroxy-2'-deoxyguanosine (8 ohdG). Our results also demonstrated a role for mild ischemic pretreatment and synthesis of HSPs against oxidative brain damage. We showed that mild 2-min ischemic pretreatment reduced the degree of both glutathione oxidation ratio and 8 ohdG accumulation in gerbil hippocampus subsequent to 10 min ischemic challenge. We also showed that the accumulation of HSP70 was closely associated with the reduction of oxidative brain damage. To our knowledge, this is the first report to investigate glutathione redox states and oxidative DNA damage levels to evaluate a protective role of mild ischemic pretreatment and HSP synthesis following brain ischemia. Our data validate the previous suggestions and provide new additional data that argue for the protective role of mild ischemic pretreatment and HSP70 synthesis against oxidative brain damage.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2000

Role of small heat shock protein HSP25 in radioresistance and glutathione-redox cycle.

Expression of heat shock proteins (HSPs) has been shown to protect mammalian cells exposed to a variety of stress stimuli. Among various HSPs, small HSPs from diverse species were shown to protect cells against oxidative stress. Here, we show that the overexpression of the mouse small hsp gene, hsp25, provides protection against ionizing radiation. Our results demonstrate that the radiation survival of the L929 cells stably transfected with hsp25 was enhanced compared with that of the parental or vector transfected control, L25#1 cells. Our results also demonstrate that the radiation-induced apoptosis was reduced in HSP25 overexpressors. A detailed analysis of glutathione composition of those clones that overexpressed HSP25 revealed the increases of the glutathione pool, which primarily resulted from the increase of reduced glutathione. Our data suggest that higher content of GSH in HSP25 overexpressors was because of a faster reduction of oxidized glutathione (GSSG) to GSH rather than an increased de novo synthesis of GSH. The activities of glutathione reductase (GRd) and glutathione peroxidase (GPx) were greater in HSP25 overexpressors but the activity of gamma-glutamylcysteine synthetase was similar between the transfectants and the control cells. Consistent with our view, a steady state ratio of the GSH/GSSG was greater in the transfectants in comparison with the control L25#1 cells. A difference in the relative ratio became more significant after exposure to the ionizing radiation. To our knowledge, this study provides the first experimental evidence in support of the hypothesis that small HSP plays a key role in radioresistance by modulating the metabolism of glutathione. Based on the results obtained from the current investigation, we propose that HSP25 helps facilitate the glutathione-redox cycle and therefore, enhances glutathione utilization and maintains the cellular glutathione pool in favor of the reduced states.

Animals↗