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D Hwang

Publications and source records attributed to D Hwang.

At least 37 records · Page 2Linked to original sources
PubMed1999

Receptor-mediated signaling pathways: potential targets of modulation by dietary fatty acids.

Extracellular signals are transmitted to intracellular targets through many signal-transduction pathways. Each signaling pathway is composed of a network of interacting signaling molecules that regulate diverse cellular responses. A modulation of the functional activities of these signaling molecules as a result of altered nutritional status could lead to qualitative and quantitative changes in cellular responses to extracellular signals. Growing evidence now suggests that fatty acids can directly and indirectly modulate signaling pathways at multiple levels. Elucidating the mechanism of this modulation could help us to understand how different types of dietary fat modify the risks of many chronic diseases.

1-Phosphatidylinositol 4-Kinase↗
PubMed1998

Proteolytic processing of rubella virus nonstructural proteins.

The genomic RNA of rubella virus contains two long open reading frames (ORF), a 5'-proximal ORF that codes for the nonstructural proteins and a 3'-proximal ORF that encodes the structural proteins. The cDNA encoding the nonstructural protein ORF of the wild-type M33 strain of rubella virus has been obtained and sequenced. Comparison between the nonstructural proteins of the M33 and Therien strains of rubella virus revealed a 98% homology in nucleotide sequence and 98.1% in deduced amino acid sequence. To examine the processing of rubella virus nonstructural protein, the complete nonstructural protein ORF was expressed in BHK cells using a pSFV expression vector. Three nonstructural protein products (p200, p150, and p90) with molecular weights of 200, 150, and 90 kDa were identified using antisera raised against synthetic peptides corresponding to regions of the nonstructural proteins. p200 is the polyprotein precursor, while p150 and p90 are the cleavage products. Site-directed mutagenesis of the Cys-1151 residue (one of the catalytic dyad residues of the viral protease) and of the Gly-1300 residue (the viral protease cleavage site) abrogated protease activity and p200 precursor cleavage, respectively. Coexpression of mutant constructs in BHK cells indicated that rubella virus protease can function both in cis and in trans.

Animals↗
PubMed1998

Expression of cyclooxygenase-1 and cyclooxygenase-2 in human breast cancer.

BACKGROUND: Numerous studies have demonstrated that the levels of prostaglandins are greater in various cancers, including breast cancer and colon cancer, than in normal tissues. In particular, the inducible form of cyclooxygenase (COX), the rate-limiting enzyme in prostaglandin biosynthesis, is overexpressed in colon tumors. Epidemiologic studies have demonstrated that the use of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce the risk of colon cancer and, to a lesser extent, the risk of breast cancer. NSAIDs are known to inhibit COX, suggesting that the beneficial effect of NSAIDs in colon cancer may be related to COX overexpression in this disease. This possibility led us to ask whether COX is also overexpressed in breast cancers. METHODS: Surgical specimens from 44 patients with breast cancer who had undergone lumpectomy or mastectomy were analyzed by immunoblot analysis and immunohistochemical analysis to determine the expression profile of the constitutively expressed form of cyclooxygenase (COX-1) and the inducible form (COX-2); the specimens from 14 patients included normal breast tissue. RESULTS: Expression of COX-1 protein was substantially higher in 30 of 44 tumor samples than in any of the 14 normal tissue specimens. Immunoblot analysis revealed extremely high levels of COX-2 protein in two tumor samples. Immunohistochemical staining of specimens that expressed COX-1 and/or COX-2 revealed that COX-1 was localized in stromal cells adjacent to the tumor but not in tumor cells. In contrast, COX-2 was localized primarily in tumor cells but also appeared in stromal cells. CONCLUSION: Our results suggest that overexpression of COX may not be unique to colon cancer and may be a feature common to other epithelial tumors.

Breast Neoplasms↗
PubMed1998

Effects of mutations in the rubella virus E1 glycoprotein on E1-E2 interaction and membrane fusion activity.

Rubella virus (RV) virions contain two glycosylated membrane proteins, E1 and E2, that exist as a heterodimer and form the viral spike complexes on the virion surface. Formation of an E1-E2 heterodimer is required for transport of E1 out of the endoplasmic reticulum lumen to the Golgi apparatus and plasma membrane. To investigate the nature of the E1-E2 interaction, we have introduced mutations in the internal hydrophobic region (residues 81 to 109) of E1. Substitution of serine at Cys82 (mutant C82S) or deletion of this hydrophobic domain (mutant dt) of E1 resulted in a disruption of the E1 conformation that ultimately affected E1-E2 heterodimer formation and cell surface expression of both E1 and E2. Substitution of either aspartic acid at Gly93 (G93D) or glycine at Pro104 (P104G) was found to impair neither E1-E2 heterodimer formation nor the transport of E1 and E2 to the cell surface. Fusion of RV-infected cells is induced by a brief treatment at a pH below 6. 0. To test whether this internal hydrophobic domain is involved in the membrane fusion activity of RV, transformed BHK cell lines expressing either wild-type or mutant spike proteins were exposed to an acidic pH and polykaryon formation was measured. No fusion activity was observed in the C82S, dt, and G93D mutants; however, the wild type and the P104G mutant exhibited fusogenic activities, with greater than 60% and 20 to 40% of the cells being fused, respectively, at pH 4.8. These results suggest that it is likely that the region of E1 between amino acids 81 and 109 is involved in the membrane fusion activity of RV and that it may be important for the interaction of that protein with E2 to form the E1-E2 heterodimer.

Amino Acid Sequence↗
PubMed1998

Age-associated increase in PGE2 synthesis and COX activity in murine macrophages is reversed by vitamin E.

We previously showed that increased macrophage and PGE2 production with age is due to enhanced cyclooxygenase (COX) activity and COX-2 expression. This study determined the effect of vitamin E supplementation on macrophage PGE2 synthesis in young and old mice and its underlying mechanism. Mice were fed 30 or 500 parts per million vitamin E for 30 days. Lipopolysaccharide (LPS)-stimulated macrophages from old mice produced significantly more PGE2 than those from young mice. Vitamin E supplementation reversed the increased PGE2 production in old mice but had no effect on macrophage PGE2 production in young mice. In both LPS-stimulated and unstimulated macrophages, COX activity was significantly higher in old than in young mice at all intervals. Vitamin E supplementation completely reversed the increased COX activity in old mice to levels comparable to those of young mice but had no effect on macrophage COX activity of young mice or on COX-1 and COX-2 protein or COX-2 mRNA expression in young or old mice. Thus vitamin E reverses the age-associated increase in macrophage PGE2 production and COX activity. Vitamin E exerts its effect posttranslationally, by inhibiting COX activity.

Aging↗
PubMed1998

Supercomputer description of human lung morphology for imaging analysis.

A supercomputer code that describes the three-dimensional branching structure of the human lung has been developed. The algorithm was written for the Cray C94. In our simulations, the human lung was divided into a matrix containing discrete volumes (voxels) so as to be compatible with analyses of SPECT images. The matrix has 3840 voxels. The matrix can be segmented into transverse, sagittal and coronal layers analogous to human subject examinations. The compositions of individual voxels were identified by the type and respective number of airways present. The code provides a mapping of the spatial positions of the almost 17 million airways in human lungs and unambiguously assigns each airway to a voxel. Thus, the clinician and research scientist in the medical arena have a powerful new tool to be used in imaging analyses. The code was designed to be integrated into diverse applications, including the interpretation of SPECT images, the design of inhalation exposure experiments and the targeted delivery of inhaled pharmacologic drugs.

Computer Simulation↗
PubMed1997

The binding of two dimers of IciA protein to the dnaA promoter 1P element enhances the binding of RNA polymerase to the dnaA promoter 1P.

Transcription of the dnaA gene from the promoter 1P has been shown to be activated in vitro and in vivo by the binding of IciA protein to two sites on the dnaA promoter region [Lee, Y. S., Kim, H., and Hwang, D. S. (1996) Mol. Microbiol . 19, 389-396; Lee, Y. S., and Hwang, D. S. (1997) J. Biol. Chem. 272, 83-88]. In vitro transcription assays using DNA fragments carrying variable combinations of two IciA binding sites revealed that IciA binding site I (IciA I site), which is located upstream of the promoter 1P, is responsible for the transcriptional activation. Binding of one dimeric IciA protein to the IciA I site is followed by binding of the second dimer. Two dimers of IciA protein, rather than one dimer, on the IciA I site appeared to enhance the binding of RNA polymerase to the promoter 1P, resulting in the activation of transcription from the promoter 1P.

Bacterial Proteins↗
PubMed1997

Enhanced expression of inducible cyclooxygenase with age in murine macrophages.

Macrophages (Mphi) from old mice produce more PGE2 than those from young mice, contributing to the dysregulation of the immune and inflammatory responses with age. This study was conducted to determine the mechanisms of the age-associated increase in Mphi PGE2 production. PGE2 production is influenced by the availability of the substrate arachidonic acid and by activity of the enzyme cyclooxygenase (Cox). We demonstrate that when the substrate is not the limiting factor, Mphi from old mice have significantly higher LPS-stimulated Cox activity than young mice, indicating that the age-associated increase in PGE2 production is due to increased enzyme activity and not to changes in substrate level. Cox activity is determined by the enzyme level and requires hydroperoxide for activation. Of the two Cox isoforms, Cox 1 is constitutively expressed in nearly all cells; whereas Cox 2 is induced by a wide range of ligands. Analysis of accumulated and de novo synthesis of constitutive Cox 1 and inducible Cox 2 proteins showed no age-related difference in Cox 1 protein levels, but Mphi from old mice had higher accumulated and newly synthesized LPS-stimulated Cox 2 protein levels than young mice. Furthermore, Mphi from old mice had higher LPS-stimulated levels of Cox 2 mRNA compared with those from young mice. Clearly, the age-associated increase in LPS-stimulated PGE2 production is due to increased Cox activity resulting from higher Cox 2 protein and mRNA expression. These findings have significant implications for age-associated immune and inflammatory dysregulation as well as the development of preventive and therapeutic strategies against them.

Aging↗
PubMed1997

Expression of mitogen-inducible cyclooxygenase induced by lipopolysaccharide: mediation through both mitogen-activated protein kinase and NF-kappaB signaling pathways in macrophages.

The mitogen-inducible cyclooxygenase (COX-2) is selectively expressed in lipopolysaccharide (LPS)-stimulated macrophages. However, the signaling pathways that lead to the expression of COX-2 in LPS-stimulated macrophages are not well understood. LPS activates members of mitogen-activated protein kinases (MAPKs) and NF-kappaB transcription factor in macrophages. We have shown that protein tyrosine kinase (PTK) inhibitors suppress the LPS-induced expression of COX-2 in macrophages (Chanmugam et al., J Biol Chem 270: 5418-5426, 1995). These PTK inhibitors also inhibit LPS-induced activation of MAPKs. Thus, in the present study, we determined whether the activation of MAPKs and NF-kappaB is necessary for the signaling pathway for the LPS-induced expression of COX-2 in the murine macrophage cell line RAW 264.7. The findings demonstrated that inhibition of extracellular signal-regulated protein kinases 1 and 2 (ERK-1 and -2) by the selective inhibitor PD98059 or inhibition of P38 by the specific inhibitor SB203580 results in partial suppression of COX-2 expression. However, activation of MAPKs by phorbol 12-myristate 13-acetate, H2O2, sorbitol, sodium vanadate, or a combination of these agents failed to induce the expression of COX-2. Inhibitors of NF-kappaB suppressed COX-2 expression without affecting tyrosine phosphorylation of MAPKs. The PTK inhibitors that suppressed the activation of MAPKs and COX-2 expression also inhibited the degradation of IkappaB-alpha. Together, these results indicate that the activation of NF-kappaB is required to induce the expression of COX-2 in LPS-stimulated RAW 264.7 cells. Inhibition of ERK-1 and 2 or P38 results in partial suppression of COX-2 expression. However, the activation of MAPKs alone is not sufficient to induce the expression of COX-2 in these cells.

Animals↗
PubMed1997

Calcium sensing receptor gene: analysis of polymorphism frequency.

The role that the Calcium Sensing Receptor (CASR) plays in extracellular calcium regulation had been ascertained through studies of inactivating as well as activating mutations of CASR gene in a number of multiplex families. We have extended these observations to a polymorphism analysis of the intercellular domain of CASR in a cohort of healthy young women. The results demonstrate significant allelic polymorphism as a result of nonconservative changes at two specific sites. Further studies will be required to determine what, if any, relationship this may have to CASR phenotype.

Adolescent↗
PubMed1997

Excretion of epidermal growth factor in human adult polycystic kidney disease.

In chronic renal failure, epidermal growth factor (EGF) excretion is decreased. In this study, asymptomatic adult polycystic kidney disease (APKD) patients with a relatively preserved glomerular filtration rate were examined. Excretion of EGF was studied in 6 patients with APKD (median age 42 years; serum creatinine [median] 95 [range-80-133] mumol/l) and compared with that of 28 healthy controls. EGF was determined in a spot morning urine by using a specific radioimmunoassay, and expressed in relation to creatinine excretion. Excretion of EGF in APKD was (median) 157 (range-13-359) and in the controls (median) 546 (range-238-1199) pmol/mmol creatinine (p < 0.001). Low excretion of EGF in APKD patients with preserved kidney function suggests a distal abnormality at an early stage of the disease, prior to the development of renal failure.

Adult↗
PubMed1996

Inhibition of the expression of inducible cyclooxygenase and proinflammatory cytokines by sesquiterpene lactones in macrophages correlates with the inhibition of MAP kinases.

In our previous studies (Refs. 1 and 2), it was shown that protein tyrosine kinase (PTK) inhibitors, radicicol and herbimycin A, inhibit the expression of the mitogen-inducible cyclooxygenase (COX-2) and proinflammatory cytokines. Radicicol and herbimycin A possess polarized double bonds which can conjugate sulphydryl groups of proteins. Parthenolide, the predominant sesquiterpene lactone in European feverfew (Tanacetum parthenium), contains alpha-methylene-gamma-lactone (MGL) and an epoxide in its structure. These moieties can interact with biological nucleophiles such as a sulfhydryl group. Parthenolide inhibited the expression of COX-2 and proinflammatory cytokines (TNF alpha and IL-1) in lipopolysaccharide (LPS)-stimulated macrophages. The structure-function relationship indicates that the MGL moiety confers the inhibitory effect. Parthenolide suppressed LPS-stimulated protein tyrosine phosphorylation in the murine macrophage cell line (RAW 264.7). This suppression was correlated with its inhibitory effect on the expression of COX-2 and the cytokines. Among tyrosine phosphorylated proteins, mitogen-activated protein kinases (MAPKs) exhibited the most dramatic inhibition.

Animals↗
PubMed1996

Dimerization of rubella virus capsid protein is not required for virus particle formation.

Rubella virus (RV) virions contain, in addition to the RNA genome, a capsid protein (C) and two envelope glycoproteins (E1 and E2). The C protein in isolated virions has been reported to be a disulfide-linked dimer (C2). There are two cysteine residues (Cys-152 and Cys-196) within the C protein. To define the role of disulfide-linked C2 dimer in virion formation, site-directed mutagenesis was used to alter the Cys-152 residue to serine. The association of mutant C protein with envelope glycoproteins was examined by transient expression of the cDNAs in COS cells. Mutation at the Cys-152 residue completely abolished the formation of C2 dimer. However, C2 dimerization does not appear to be important for the assembly of RV structural proteins into virus-like particles.

Animals↗
PubMed1995

Computer simulations of human lung structures for medical applications.

Knowledge of the structure of the human lung has salient health effects applications. The clinical issues encompass: (1) aerosol therapy, the targeted delivery of inhaled particles to enhance the efficacies of pharmacologic drugs; and (2) nuclear medicine, where planar gamma camera imaging, Single Photon Emission Computer Tomography (SPECT) and Positron Emission Tomography (PET) assess the distribution patterns of radiolabeled diagnostic particles and gases. If the resolution of such images could be enhanced, medical regimens would greatly benefit. Therefore, the focused objective of our work was to develop 3-D mathematical descriptions of the complex airway networks within the lung. A Silicon Graphics workstation was used to depict the daedal structures. The computer-generated color illustrations presented herein are intended to complement medical investigation. They will assist the clinician by serving as templates for the lung and, thereby, providing a real basis for the analysis of relatively abstract images. The illustrations identify individual airways and could be of great importance to physicians in the treatment of airway diseases occurring at well defined locations (e.g. bronchogenic carcinomas). To demonstrate that computers can be actively integrated into medical research and practice we have addressed SPECT images of a subject. Computer templates will aid future clinical investigators in two major ways: (1) the interpretation of a planar gamma camera, SPECT and PET images; and (2) the design of drug testing protocols using inhalation exposures. Considering their usefulness for demonstration, the lung simulations have the potential of playing a substantive role in education.

Administration, Inhalation↗
PubMed1995

Computer model of human lung morphology to complement SPECT analyses.

Aerosol therapy protocols could be improved if inhaled pharmacologic drugs were selectively deposited within the human lung. The targeted delivery to specific sites, such as receptors and sensitive airway cells, would enhance the efficacies of airborne pharmaceuticals. The high spatial discrimination of deposition patterns of inhaled particles can be determined via Single Photon Emission Computer Tomography (SPECT). However, major problems continue to compromise SPECT protocols. Our work focuses on two issues: how can the spatial discrimination be improved; and how are the images to be interpreted? We present a methodology, described by a mathematical model and supercomputer code, for systematically slicing through the human lung in a prescribed manner that is conducive to implementation into SPECT analyses. The lung is divided into concentric shells, or annuli, and the airway generation-by-generation composition of the respective shells determined. This identification was accomplished by superimposing the new shell structure with the 3-D branching network presented by Martonen et al. [23]. Perhaps the key aspect of the model-code is that the supercomputer is instructed to determine the 3-D spatial coordinates of each of the airways (over 16 million) of the lung with respect to the clinician-selected contours of shells within the lung.

Administration, Inhalation↗
PubMed1995

Involvement of reactive oxygen intermediates in cyclooxygenase-2 expression induced by interleukin-1, tumor necrosis factor-alpha, and lipopolysaccharide.

Reactive oxygen intermediates (ROIs) play an important role in inflammatory processes as mediators of injury and potentially in signal transduction leading to gene expression. Cyclooxygenase (COX) is a rate-limiting enzyme in prostanoid biosynthesis, and its recently cloned inducible form, COX-2, is induced by proinflammatory cytokines. This study linked ROIs to the signaling pathways that induce COX-2 expression. The hydroxyl radical scavengers DMSO (1%), as well as di- and tetramethylthiourea, inhibited IL-1-, TNF alpha-, and LPS-induced COX-2 expression in rat mesangial cells. The suppression of COX-2 mRNA expression correlated with the COX-2 protein level. In comparison with the prolonged induction of the inducible gene encoding protein-tyrosine phosphatase by hydrogen peroxide, the COX-2 gene was only transiently induced. Protein-tyrosine phosphatase is also induced by heat shock and chemical stress, whereas COX-2 is not. Superoxide was a more potent inducer for COX-2 than hydrogen peroxide. In addition, NADPH stimulated COX-2 expression, and an inhibitor of NADPH oxidase blocked COX-2 expression induced by TNF alpha. COX-2 and KC gene expression costimulated by IL-1 were inhibited differentially by the scavengers. These studies demonstrate that oxidant stress is a specific and important inducer of COX-2 gene expression. This induction may contribute to the deleterious amplification of prostanoids in inflammation and compound the direct effects of ROI production.

Animals↗