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H J Chen

Publications and source records attributed to H J Chen.

At least 91 records · Page 5Linked to original sources
PubMed1998

2,3-epoxy-4-hydroxynonanal, a potential lipid peroxidation product for etheno adduct formation, is not a substrate of human epoxide hydrolase.

Our previous studies have shown that 2,3-epoxy-4-hydroxynonanal, a reactive epoxy aldehyde capable of forming etheno adducts with DNA bases, is mutagenic and tumorigenic (Carcinogenesis, 14, 2073). The epoxy aldehyde can be generated from trans-4-hydroxy-2-nonenal, a lipid peroxidation product of omega-6 polyunsaturated fatty acids, by autoxidation or by incubation with fatty acid hydroperoxides or hydrogen peroxides (Chem. Res. Toxicol., 9, 306). These are plausible in vivo pathways for the formation of 2,3-epoxy-4-hydroxynonanal. The possibility that 2,3-epoxy-4-hydroxynonanal is a tumorigen of endogenous origin is suggested by recent observations that etheno bases are detected as background DNA lesions in untreated rodents and humans. A metabolic pathway critical for detoxification of 2,3-epoxy-4-hydroxynonanal involves the ring-opening by epoxide hydrolase, which abolishes its ability to form cyclic etheno DNA adducts. In this study, we examined whether 2,3-epoxy-4-hydroxynonanal is a substrate of cDNA expressed human epoxide hydrolase. Human epoxide hydrolase was expressed in TK- 143 cells (thymidine kinase-deficient human embryoblast) infected with recombinant vaccinia virus encoding human epoxide hydrolase cDNA. Controls consisted of the cells infected with vaccinia virus in the absence of human epoxide hydrolase cDNA. No hydrolysis occurred when [2,3-(3)H]2,3-epoxy-4-hydroxynonanal was incubated at 37 degrees C for 30 min at pH 7.4 with cells expressing human epoxide hydrolase, as indicated by the presence of a pair of radioactive peaks in reversed-phase HPLC chromatography, which comigrated with the UV standards of the two diastereomers of the epoxy aldehyde. The identity of these compounds as the intact epoxy aldehyde was further supported by derivatization to the 2,4-dinitrophenylhydrazones followed by reversed phase HPLC analysis. Similar results were observed with the control cells or with the heat deactivated human epoxide hydrolase. The epoxide hydrolase activity in the expressed cells was demonstrated by their ability to convert benzo[a]pyrene-4,5-dihydroepoxide to benzo[a]pyrene-trans-4,5-dihydrodiol under the same conditions. These results clearly indicate that 2,3-epoxy-4-hydroxynonanal is not a substrate of human epoxide hydrolase, and, thus strengthen its possible endogenous role in the formation of promutagenic exocyclic etheno adducts in vivo.

Aldehydes↗
PubMed1998

Isolated intracranial Rosai-Dorfman disease: case report and literature review.

Rosai-Dorfman disease, first described in 1969, is a rare idiopathic histioproliferative disease affecting the lymph nodes. Typical clinical features include bilateral painless lymphadenopathy, fever and polyclonal hypergammaglobulinemia. In approximately 43% of cases, extranodal sites may be involved and occasionally represent the initial or sole manifestation of the disease. Central nervous system manifestations are exceedingly rare, and only 17 cases have been recorded, among which there are merely seven isolated intracranial cases without concurrent nodal or other extranodal involvement. Herein, we report a 38-year-old male presenting with generalized tonic-clonic seizure and radiological findings indicative of meningioma. Complete physical examinations and laboratory surveys demonstrate the absence of involvement at other body sites. Microscopically, the lesion consists of proliferative histiocytes exhibiting emperipolesis coupled with the characteristic cytoplasmic staining against S-100 protein. The differential diagnosis of polymorphic inflammatory meningioma-mimicking masses is discussed, and a review of previously reported intracranial Rosai-Dorfman disease is presented.

Adult↗
PubMed1998

Use of DNA transfer in the induction of metastasis in experimental mammary systems.

The metastatic spread of cancer is a little understood process, in part because it is difficult to model the entire process using experimental approaches in vitro. The ability to transfer DNA into non-metastatic mammary cells and to observe the induction of metastasis in vivo provides a means for identifying DNA sequences that are associated with the development of metastatic capability. Using these techniques, a metastasis-associated cytoskeletal calcium binding protein, S100A4 (p9Ka), has been identified as an inducer of metastatic capability in benign rat mammary epithelial cells. Metastasis can also be induced in the rat mammary epithelial cells by fragments of DNA from metastatic, but not from benign, human breast tumour cells. These non-coding fragments of DNA act via the induction of osteopontin, an extracellular, integrin binding, calcium binding protein. Since both osteopontin and S100A4 are thought to be associated with malignancy in human breast cancer specimens, gene transfer techniques can identify genes for metastasis-inducing proteins that may play a role in breast cancer, and further suggest that cell migration/motility might be important in the metastatic process.

Animals↗
PubMed1998

Optimal timing of retina examinations for premature infants.

Developments in modern neonatal intensive care have resulted in increased survival of very premature infants. Along with this increase in survival, there has been a concomitant increase in the frequency of retinopathy of prematurity (ROP). We investigated the relationship between the severity and the time course of ROP as well as the optimal time for retinal examinations of premature infants of various birth weights and gestational ages. A total of 80 premature infants were enrolled for analysis. The mean postnatal age of infants at the time of diagnosis was 7.3 +/- 3.4 weeks for stage 1 retinopathy, 9.2 +/- 5.8 for stage 2 retinopathy, 9.5 +/- 3.8 for stage 3 retinopathy, 10.7 +/- 3.7 for threshold disease, and 11.7 +/- 3.2 for stage 4 retinopathy. The mean postconceptional age of infants at the time of diagnosis was 35 +/- 3 for stage 1 retinopathy, 36.4 +/- 3 for stage 2 retinopathy, 37.6 +/- 3.5 for stage 3 retinopathy, 38.4 +/- 3.5 for threshold disease, and 40 +/- 3.7 for stage 4 retinopathy. The age at the time of the initial detection of ROP was from the ninth to 10th week among infants weighing less than 1,000 g at birth and from the fifth to seventh week among those weighing 1,000 g or more at birth. However, the postconceptional age at the time of initial detection of ROP for the whole group was 36 weeks and was not influenced by birth weight or gestational age. Therefore, we suggest that postconceptional age, rather than postnatal age, should be used to decide the timing of retinal examinations for premature infants.

Female↗
PubMed1998

Molecular characterization of germline mutations in neurofibromatosis 2 in two families.

Neurofibromatosis 2 (NF2) is an autosomal dominant disorder that predisposes patients to central nervous system tumors. It is caused by mutations in the NF2 tumor suppressor gene, which is located on chromosome 22q12. We studied 2 multigenerational NF2 families (three members of family 1 and the proband of the family) by gene mutation analysis and clinical assessment. One member of family 1 had a 169 C-->T point mutation at codon 57 of exon 2 and had a severe phenotype. His father had a silent 1113 C-->T point mutation at codon 371 of exon 11 and had a normal phenotype. The proband of family 2 had a deletion at nucleotide 720 G (codon 240) of exon 8. This led to a frameshift and termination at codon 250, and a severe NF2 phenotype. Our results indicate that clinical abnormalities can be present in carriers. Nonsense and frameshift mutations in the NF2 tumor suppressor gene are associated with phenotypes. The clinical abnormalities can develop at a young age.

Adult↗
PubMed1997

Drosophila Mad binds to DNA and directly mediates activation of vestigial by Decapentaplegic.

The TGF-beta (transforming growth factor-beta)-related signalling proteins, including Decapentaplegic (Dpp) in Drosophila-and bone morphogenic proteins and activin in vertebrates, affect the growth and patterning of a great variety of structures. However, the mechanisms by which these ligands regulate gene expression are not understood. Activation of complexes of type I with type II receptors results in the phosphorylation and nuclear localization of members of the SMAD protein family, which are thought to act as co-activators of transcription, perhaps in conjunction with sequence-specific cofactors. Here we show that the amino-terminal domain of the Drosophila Mothers against dpp protein (Mad), a mediator of Dpp signalling, possesses a sequence-specific DNA-binding activity that becomes apparent when carboxy-terminal residues are removed. Mad binds to and is required for the activation of an enhancer within the vestigial wing-patterning gene in cells across the entire developing wing blade. Mad also binds to Dpp-response elements in other genes. These results suggest that Dpp signalling regulates gene expression by activating Mad binding to target gene enhancers.

Animals↗
PubMed1997

Human acetyltransferase polymorphisms.

Conjugation of primary amino and hydroxylamino groups with acetate, catalyzed by acetyl CoA-dependent arylamine acetyltransferase (NAT) enzymes, may play an important role in the intricate series of metabolic pathways that produce or prevent toxicity following exposure to homo- and heterocyclic arylamine and hydrazine xenobiotics. Two independently regulated and kinetically distinct human acetyltransferases are now known to exist, namely NAT1 and NAT2. Interindividual variation in NAT2 function is associated with the classical isoniazid acetylation polymorphism which was discovered over forty years ago. At last count, fifteen variant alleles at the NAT2 gene locus have been linked to the isoniazid 'acetylator phenotype', and each of these can be identified in population studies using specific PCR-based genotyping tests. On the other hand, NAT1 shows kinetic selectivity for compounds whose disposition is unrelated to the classical isoniazid acetylation polymorphism. NAT1 expression is also phenotypically variable in human populations, at least in part due to allelic differences at the NAT1 gene locus. Nine NAT1 variant alleles have been described to date, of which NAT1* 14 and NAT1* 15 clearly produce defective NAT1 proteins and lead to functional impairment in the metabolism of NAT1-selective substrates both in vivo and in vitro. On the other hand, it has been reported that the NAT1* 10 variant associates with elevated NAT1 activity and increased risk for cancers of the bladder and colon. Because of the important toxicologic consequences of allelic variation in NAT1 and NAT2 function for the metabolic activation of arylamine and heterocyclic amine procarcinogens, further studies are needed to improve our understanding of the extent of NAT allelic variation, to determine the functional capacity of each variant gene product, and to develop accurate methods of detecting them in population and epidemiological studies.

Acetylation↗
PubMed1997

Systematic mutational analysis of the cation-independent mannose 6-phosphate/insulin-like growth factor II receptor cytoplasmic domain. An acidic cluster containing a key aspartate is important for function in lysosomal enzyme sorting.

We have used systematic mutational analysis to identify signals in the 166-residue murine cation-independent mannose 6-phosphate/insulin-like growth factor II receptor cytoplasmic domain required for efficient sorting of lysosomal enzymes. Alanine cluster mutagenesis on all conserved residues apart from the endocytosis signal demonstrates that the major sorting determinant is a conserved casein kinase II site followed by a dileucine motif (157DDSDEDLL164). Small deletions or additions outside this region have severe to mild effects, indicating that context is important. Single residue mutagenesis indicates that cycles of serine phosphorylation/dephosphorylation are not obligatory for sorting. In addition, the two leucine residues and four of the five negatively charged residues can readily tolerate conservative substitutions. In contrast, aspartate 160 could not tolerate isoelectric or isosteric substitutions, implicating it as a critical component of the sorting signal.

Amino Acid Sequence↗
PubMed1997

Cloning and characterization of a rhamnogalacturonan hydrolase gene from Botrytis cinerea.

Rhamnogalacturonan hydrolase (Rgase A) cleaves alpha 1--2 linkages between rhamnosyl and galacturonosyl residues in pectin. A 1.9 kb RGase A cDNA clone (BCRHGA) was isolated from a B. cinerea cDNA library using a PCR-amplified Aspergillus aculeatus RGase A probe. It's 1.7 kb open reading frame had 62% identity at the amino acid level with A. aculeatus RGase A. Northern blots of B. cinerea total RNA probed with BCRHGA revealed a 2 kb band, suggesting the cDNA clone is full or nearly-full length. To determine mRNA expression of the gene, B. cinerea was grown in media containing 0.5% apple pectin, 0.5% rhamnogalacturonan-I and 1% glucose carbon sources. Northern analysis revealed the BCRHGA gene was expressed on all carbon sources, but with different patterns of expression. B. cinerea RGase A appeared to be coded for by a single or low copy number gene based on Southern analysis.

Amino Acid Sequence↗
PubMed1997

Effects of S-dC28 on vascular smooth muscle cell adhesion and plasminogen activator production.

We sought to examine phosphorothioate oligodeoxynucleotide (PS oligo) non-G-quartet, nonsequence specific effects on smooth muscle cell (SMC) adhesion by using S-dC28, a 28-mer cytidine homopolymer that lacks contiguous guanosine residues. Human aortic SMC were incubated with vehicle or various doses of S-dC28, and the number of SMC adhered to noncoated plates was determined using a Coulter Counter. S-dC28 significantly inhibited SMC adhesion. SMC adhesion dramatically improved with S-dC28 in fibronectin-coated plates. When laminin-coated plates were used, the inhibition of SMC adhesion by S-dC28 was completely reversed. Replacement of serum-free medium with 5% fetal bovine serum medium for SMC cultured on non-coated plates also greatly attenuated inhibition of adhesion by S-dC28. Human SMC TPA, UPA, and PAI-1 antigen levels were determined by ELISAs. PDGF significantly induced SMC TPA antigen production measured by an ELISA. Coincubation of PDGF with S-dC28 significantly attenuated SMC TPA antigen levels. SMC UPA antigen levels after coincubation with PDGF and S-dC28 were significantly greater than the values observed in SMC incubated in medium containing PDGF alone. SMC PAI-1 antigen levels were not altered by the addition of S-dC28. We conclude that S-dC28 inhibits human SMC adhesion and that this inhibition can be diminished by fibronectin or laminin coating of culture plates or by the presence of serum in the culture medium. Furthermore, S-dC28 attenuates SMC TPA production, thereby inhibiting SMC migration, whereas S-dC28 augments SMC UPA production, thus diminishing SMC cellular adhesion.

Analysis of Variance↗
PubMed1997

Inhibitory nonsequence-specific effects of cytidine homopolymers on in vivo neointimal formation.

Phosphorothioate oligodeoxynucleotides (PS oligos) manifest both antisense and G-quartet aptameric inhibitory effects on vascular smooth muscle cell (SMC) proliferation. In this study, we examined the effects of three cytidine (S-dC) homopolymers lacking any guanosines of various chain length-S-dC28, S-dC18 and S-dC12-on in vitro SMC proliferation and in vivo neointimal formation. S-dC18 significantly inhibited human vascular SMC proliferation, although it had only half the potency as the same dose of S-dC28. Furthermore, S-dC12 at the same concentrations as S-dC18 did not significantly inhibit vascular SMC proliferation. S-dC28 and S-dC18 inhibited PDGF-induced in vitro SMC migration, whereas D-dC12 had no significant effect on PDGF-induced in vitro SMC migration. We determined the effects of S-dC28, S-dC18, and S-dC12 on neointimal SMC formation in the rat carotid balloon injury model. Rat carotid artery neointimal formation after balloon injury was significantly attenuated by S-dC28 treatment compared with the control group and by S-dC18 treatment compared with the control group. S-dC28 and S-dC18 treatment significantly reduced the intima/media area ratio compared with the values of the control groups. However, S-dC12 did not significantly inhibit neointimal formation. We investigated the time course of the inhibitory effects of S-dC28 on rat carotid artery neointimal formation. S-dC28 significantly inhibited rat carotid artery intimal area and intima/media area ratio at 4 weeks and 8 weeks. Fluoresceinated S-dC28 (FITC-S-dC28) was found to be present throughout the rat carotid arterial wall within 6 hours after balloon injury. Taken together, the potent non-G-quartet, nonsequence-specific inhibitory effects of S-dC compounds on in vitro SMC proliferation and in vivo neointimal formation in the rat carotid balloon injury model are chain length dependent and long lasting.

Angioplasty, Balloon↗
PubMed1997

T cell lymphokines modulate bFGF-induced smooth muscle cell fibrinolysis and migration.

Smooth muscle cell (SMC) fibrinolysis is necessary for SMC migration. To determine whether the T cell lymphokines interleukin 4 (IL-4) and interferon-gamma (IFN-gamma) modulate SMC fibrinolysis and migration induced by basic fibroblast growth factor (bFGF), we examined the effects of IL-4 and IFN-gamma on human SMC tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (UPA), and plasminogen activator inhibitor 1 (PAI-1) antigen production, determined by enzyme-linked immunosorbent assays. Although IL-4 had no effects on SMC tPA, UPA, and PAI-1 production, it potentiated bFGF-induced tPA, UPA, and PAI-1 antigens. IL-4 plus bFGF resulted in a net increase in SMC fibrinolytic activity. IFN-gamma did not significantly affect bFGF induction of SMC tPA and PAI-1 antigens. However, IFN-gamma significantly decreased bFGF-mediated induction of SMC UPA antigen. IFN-gamma decreased the IL-4 plus bFGF induction of both tPA and UPA antigens. IL-4 increased and IFN-gamma abrogated bFGF induction of in vitro SMC migration through a modified micro-Boyden chamber. Therefore, IL-4 and IFN-gamma modulate bFGF-mediated induction of in vitro vascular SMC fibrinolysis and migration.

Antigens↗
PubMed1996

Sequence-independent inhibition of in vitro vascular smooth muscle cell proliferation, migration, and in vivo neointimal formation by phosphorothioate oligodeoxynucleotides.

Phosphorothioate oligodeoxynucleotides (PS oligos) are antisense (sequence-specific) inhibitors of vascular smooth muscle cell (SMC) proliferation when targeted against different genes. Recently an aptameric G-quartet inhibitory effect of PS oligos has been demonstrated. To determine whether PS oligos manifest non-G-quartet, non-sequence-specific effects on human aortic SMC, we examined the effects of S-dC28, a 28-mer phosphorothioate cytidine homopolymer, on SMC proliferation induced by several SMC mitogens. S-dC28 significantly inhibited SMC proliferation induced by 10% FBS as well as the mitogens PDGF, bFGF, and EGF without cytotoxicity. Moreover, S-dC28 abrogated PDGF-induced in vitro migration in a modified micro-Boyden chamber. Furthermore, S-dC28 manifested in vivo antiproliferative effects in the rat carotid balloon injury model. S-dC28 suppressed neointimal cross-sectional area by 73% and the intima/media area ratio by 59%. Therefore, PS oligos exert potent non-G-quartet, non-sequence-specific effects on in vitro SMC proliferation and migration as well as in vivo neointimal formation.

Animals↗
PubMed1996

Identification of a potential physiological substrate for oncogenic Ras-activated protein kinases in activated Xenopus egg extracts: correlation with oncogenic Ras-induced cell cycle arrest.

Activated Xenopus egg extracts are capable of undergoing cell-free cell cycling. Using these activated extracts, we previously showed that purified, bacterially expressed oncogenic human RasH protein arrests cell cycle progression. Because oncogenic Ras activates many serine/threonine protein kinases in Xenopus oocytes and egg extracts, it is possible that induction of cell cycle arrest involves the action of oncogenic Ras-activated kinases. Thus, the identification of the physiological substrates for oncogenic Ras-activated kinases is important for elucidating the molecular mechanism underlying oncogenic Ras-induced cell cycle arrest. We used 32P-orthophosphate as a label to identify the potential substrates. Our results demonstrated that the 32P-labeling of both a 32 and a 33 kDa protein were greatly enhanced by oncogenic Ras during the incubation of activated Xenopus egg extracts. The enhanced labeling correlated with the induced cell cycle arrest and was contributed by serine phosphorylation. Moreover, the 33 kDa protein was detected only in the presence of oncogenic Ras and was a serine-hyperphosphorylated form of the 32 kDa protein. Furthermore, new protein synthesis was not required for the enhanced labeling, consistent with the concept that the enhanced serine phosphorylation of the 32 kDa protein is by oncogenic Ras-activated protein kinases. In addition to serine phosphorylation, our results also suggested that an as yet unidentified modification of the 32 kDa protein might also be induced by oncogenic Ras. Our results suggest that the 32 kDa protein is a potential physiological substrate for oncogenic Ras-activated protein kinases.

14-3-3 Proteins↗
PubMed1996

Lipid peroxidation as a potential endogenous source for the formation of exocyclic DNA adducts.

A number of promutagenic exocyclic DNA adducts have recently been detected in both humans and rodents without carcinogen treatment. These observations raised questions about their origins and potential significance in carcinogenesis. In this commentary, we present our views pertaining to the in vivo sources of these cyclic adducts, specifically the cyclic propano and etheno adducts. The basis for our discussion comes mainly from the information generated through a span of more than a decade from several laboratories, including ours. This commentary summarizes the data from the chemical and biochemical studies that provide support for the hypothesis that lipid peroxidation is involved in the endogenous formation of these exocyclic adducts.

Aldehydes↗
PubMed1996

On the consistency of a physical mapping method to reconstruct a chromosome in vitro.

During recent years considerable effort has been invested in creating physical maps for a variety of organisms as part of the Human Genome Project and in creating various methods for physical mapping. The statistical consistency of a physical mapping method to reconstruct a chromosome, however, has not been investigated. In this paper, we first establish that a model of physical mapping by binary fingerprinting of DNA fragments is identifiable using the key assumption-for a large randomly generated recombinant DNA library, there exists a staircase of DNA fragments across the chromosomal region of interest. Then we briefly introduce epi-convergence theory of variational analysis and transform the physical mapping problem into a constrained stochastic optimization problem. By doing so, we prove epi-convergence of the physical mapping model and epi-convergence of the physical mapping method. Combining the identifiability of our physical mapping model and the epi-convergence of a physical mapping method, finally we establish strong consistency of a physical mapping method.

Aspergillus nidulans↗
PubMed1996

Functional and genetic characterization of the oligomerization and DNA binding properties of the Drosophila doublesex proteins.

The doublesex (dsx) gene of Drosophila melanogaster encodes both male-specific (DSXM) and female-specific (DSXF) polypeptides, which are required for normal differentiation of numerous sexually dimorphic somatic traits. The DSX polypeptides are transcription factors and have been shown previously to bind through a zinc finger-like domain to specific sites in an enhancer regulating sex-specific expression of yolk protein genes. We have determined the consensus target sequence for this DNA binding domain to be a palindromic sequence AGNNACTAAATGTNNTC composed of two half-sites around a central (A/T) base pair. As predicted by the symmetric nature of this site, we have found that the DSX proteins exist as dimers in vivo and have mapped two independent dimerization domains by the yeast two-hybrid method; one in the non-sex-specific amino-terminal region of the protein and one that includes the partially sex-specific carboxy-terminal domains of both the male and female polypeptides. We have further identified a missense mutation that eliminates dsx function in female flies, and shown that the same mutation prevents dimerization of DSXF in the yeast two-hybrid system, indicating a critical role for dimerization in dsx function in vivo.

Animals↗