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Biomedical subjects

W Chen

Publications and source records attributed to W Chen.

At least 1,009 records · Page 56Linked to original sources
PubMed1994

Association of Epstein-Barr virus, human papilloma virus, and cytomegalovirus with nine nasopharyngeal carcinoma cell lines.

BACKGROUND: Epstein-Barr virus (EBV) has been proposed to be closely associated with nasopharyngeal carcinoma (NPC). To evaluate the actual relationship, EBV was analyzed in nine established NPC cell lines and in four original NPC biopsy specimens. EXPERIMENTAL DESIGN: We used Southern blot analysis alone or after polymerase chain reaction to determine whether EBV was present in our NPC cell lines. We also used in situ nucleic acid hybridization and in situ polymerase chain reaction to identify EBV in 4 original biopsy specimens. For comparison, we investigated the cell lines for the presence of human papilloma virus type 16 (HPV-16) and human cytomegalovirus (HCMV). RESULTS: Southern blots alone for detection of 3 viruses in 9 cell lines were all negative. PCR plus Southern blotting revealed that 5 cell lines contained EBV in earlier passages, and all became negative in later passages. Some cell lines also contained HPV-16 and HCMV. At earlier passages, some cell lines contained EBV, HPV-16, and HCMV concurrently. Three out of four biopsy specimens contained EBV in certain tumor cells, lymphocytes, and glandular epithelia. CONCLUSIONS: These findings indicate that EBV, HPV-16, and HCMV may be present in certain NPC cell lines and in only a small fraction of each positive cell line, and that a cell line may contain these three viruses concurrently. EBV is present not only in a fraction of tumor cells, but also in some lymphocytes and glandular epithelia in biopsy specimens. It is present as an episomal form but not as an integrated form in the infected cells, suggesting that the carcinogenesis of non-EBV containing NPC tumor cells is not related to EBV infection.

Base Sequence↗
PubMed1994

[1,017 cases of posterior chamber IOL implantation].

Based on 1,017 consecutive cases (1,119 eyes) of modern extracapsular extraction with posterior chamber IOL implantation, the authors report their experience in the management of 11 complications, such as turbid posterior capsule, iris synechiae, pupil capture, etc. The period of follow-up ranged from 2 to 68 months, averaging 18.4 months. Disregarding 76 eyes of low vision due to preoperative fundus diseases, 981 (94.1%) of the 1,043 eyes operated achieved corrected vision of 0.5 or better.

Adolescent↗
PubMed1994

[Scanning electron microscopical study of trachea vasculature in the human fetus].

The microvasculature of the human fetal trachea was studied in vascular casts viewed in a scanning electron microscope (SEM). The trachea is supplied by longitudinal vascular bundles running at both sides of the organ, including both longitudinal tracheoesophageal arteries and veins. They are the source of the segment vascularization of the trachea. Due to numerous arteriovenous anastomoses and anastomoses occurring within respective arterious and venous vascular systems, a constant blood flow within submucous capillary plexus and the tracheal wall is provided. A characteristic feature of tracheal vascularization is a very rich, dense network of vein.

Corrosion Casting↗
PubMed1994

Characteristics of aspartate aminotransferase binding immunoglobulin determined by the isotope method.

A woman who had no known underlying diseases showed a persistent elevation (about 300 U/L) of serum aspartate aminotransferase (AST) without other abnormal laboratory findings. Cellolose gel electrophoresis showed that the AST activity in the patient had an atypical band with slower mobility than normal AST. When the sera from the patient and from a patient with acute hepatitis were mixed, the atypical band increased in density and the band of normal size AST disappeared. When the serum was fractionated on Sephadex G-200 gel filtration medium, almost all AST activity was found between the void volume and the gamma-globulin fraction. However, the AST activity in this fraction was not retained on dissociation into small AST by acid treatment. This suggests the loss of enzyme activity in dissociated small AST. The patient's serum was then incubated with iodine 125-labeled porcine AST; when this was fractionated on gel filtration medium, the main radioactivity was eluted in the void volume fraction. The binding activity for 125I-porcine AST was found in the gamma-globulin fraction obtained by gel filtration. The affinity constant of 125I-porcine AST binding to the gamma-globulin fraction was 1.0 x 10(-8) mol/L by Scatchard analysis. The binding gamma-globulin appeared to be (polyclonal) IgG, and the binding site was located in F(ab')2 and Fab fragments. The IgG could be bound with both human and porcine AST but not with chick AST. Thus the IgG appears specific for AST of mammalian species.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

[A study on the difference of etiology between two types of hypertension in old people].

Basing on the prevalence survey, 94 cases were diagnosed as simple senile systolic hypertension and 67 cases as non simple senile systolic hypertension, and 136 persons with normal blood pressure were sampled as control. Two case-control studies were conducted, then the etiologic factors of two types of hypertension were compared. Among age, sex, smoking, drinking, mental incidence, family history of hypertension, body height, body weight, body weight index, blood sugar, TC, TG, HDL-c, etc., a total of 18 factors, mono variate unconditional logistic regression analysis showed that the occurrence of ISH associated with age, family history of hypertension, mental incidence and blood sugar, and that the risk factors of NISH were body weight index, body weight, smoking, drinking, mental incidence, and TC. Further multi-unconditional logistic regression turned out that mental incidence, family history of hypertension and blood sugar entered the model of ISH, and that the body weight index, smoking, mental incidence, blood and TC entered the model of ISH. The study showed that the etiologic factors of ISH differed from those of NISH, which was a syndrome differed from NISH.

Aged↗
PubMed1993

Transmembrane neural cell-adhesion molecule (NCAM), but not glycosyl-phosphatidylinositol-anchored NCAM, down-regulates secretion of matrix metalloproteinases.

During embryogenesis interactions between cells and extracellular matrix play a central role in the modulation of cell motility, growth, and differentiation. Modulation of matrix structure is therefore crucial during development; extracellular matrix ligands, their receptors, extracellular proteinases, and proteinase inhibitors all participate in the construction, maintenance, and remodeling of extracellular matrix by cells. The neural cell-adhesion molecule (NCAM)-negative rat glioma cell line BT4Cn secretes substantial amounts of metalloproteinases, as compared with its NCAM-positive mother cell line BT4C. We have transfected the BT4Cn cell line with cDNAs encoding the human NCAM-B and -C isoforms. We report here that the expression of transmembrane NCAM-B, but not of glycosyl-phosphatidylinositol-linked NCAM-C, induces a down-regulation of 92-kDa gelatinase (matrix metalloproteinase 9) and interstitial collagenase (matrix metalloproteinase 1), indicating that cellular expression of the recognition molecule NCAM regulates the metabolism of the surrounding matrix.

Animals↗
PubMed1993

NMR studies of 1H NOEs in glycogen.

We have examined the cross-relaxation behavior among the protons of oyster glycogen using nuclear Overhauser enhancement (NOE). Steady-state and transient NOEs were generated using low-power CW irradiation and frequency-selective inversions. In D2O, saturation of glycogen H2 and H4' at 3.64 ppm gave a strong negative NOE (eta = -0.74) at H1. The NOE was similar to the value predicted by the correlation time (tau c) calculated from the T1 and T2 of glycogen H1 in D2O assuming an isotropic rigid motor dipole-dipole model. Selective inversion of H2 and H4' gave a transient NOE at H1. In D2O, selective inversion of H1 also led to negative transient NOEs in the H2 + H4', H3, and H5 resonances. The magnitude and rates of appearance of the NOEs in H3 and H5 were too large to arise from direct H1-H3 and H1-H5 dipolar interactions, but were consistent with very efficient cross-relaxation leading to large second-order NOEs. The glycogen H1 NOE in H2O was also studied. Replacement of D2O with H2O as solvent significantly reduced the steady-state NOE at H1 following saturation of H2 + H4'. Saturation of the water resonance caused a large negative NOE at H1 (eta = -0.55) consistent with our earlier study which indicated that there was no direct dipolar interaction between H1 and free H2O.

Animals↗
PubMed1993

Localized 1H NMR measurement of glucose consumption in the human brain during visual stimulation.

Spatially localized 1H NMR spectroscopy has been applied to measure changes in brain glucose concentration during 8-Hz photic stimulation. NMR spectroscopic measurements were made in a 12-cm3 volume centered on the calcarine fissure and encompassing the primary visual cortex. The average maximum change in glucose levels was 0.34 mumol.g-1 (n = 5) at 15 min; glucose level had turned toward resting level at 25 min. The glucose change was used to calculate the increase of glucose cerebral metabolic rate in the visual cortex region for individual subjects by using the Michaelis-Menten model of glucose transport on the assumption of constant transport kinetics. The glucose cerebral metabolic rate was calculated to increase over the nonstimulated rate by 22% during the first 15 min of photic stimulation. A model in which the glucose metabolic rate gradually decreases during stimulation was proposed as a possible explanation for the recovery of brain glucose and previously measured lactate concentrations to prestimulus values after 15 min.

Blood Glucose↗
PubMed1993

Chromosomal rearrangement segregating with adrenoleukodystrophy: a molecular analysis.

The relationship between X chromosome-linked adrenoleukodystrophy and the red/green color pigment gene cluster on Xq28 was investigated in a large kindred. The DNA in a hemizygous male showed altered restriction fragment sizes compatible with at least a deletion extending from the 5' end of the color pigment genes. Segregation analysis using a DNA probe within the color pigment gene cluster showed significant linkage with adrenoleukodystrophy (logarithm of odds score of 3.19 at theta = 0.0). These data demonstrate linkage, rather than association, between a unique molecular rearrangement in the color pigment gene cluster and adrenoleukodystrophy. The DNA changes in this region are thus likely to be helpful for determining the location and identity of the responsible gene.

Adrenoleukodystrophy↗
PubMed1993

Nuclear magnetic resonance relaxation of glycogen H1 in solution.

The NMR relaxation properties of the H1 proton of oyster glycogen in D2O and H2O solutions have been studied using nonselective, semiselective, and selective inversion recovery and Hahn spin-echo pulse sequences. The data were analyzed in terms of an isotropic, rigid-rotor dipole-dipole model including cross-relaxation. At 8.4 T in D2O, p = 5.4 +/- 0.4 s-1 and sigma = -4.5 +/- 0.4 s-1. The large, negative sigma value is consistent with strong cross-relaxation and a long correlation time. The relaxation data can be explained by a single correlation time, tau c = 2.7 x 10(-9) s, indicating significant internal mobility. With this value of tau c, and assuming that the structure of the glucose moieties was the same as in alpha-D-glucose crystals, the dipole sum contributing to T1 relaxation was calculated. The intra-ring relaxation was dominated by dipole fields from the H2 proton, but these only accounted for approximately 18% of the total relaxation. Most of the relaxation comes from inter-glucose relaxation. From modeling, this is dominated by the H4' across the alpha-1,4-glycosidic bond. The H1 longitudinal relaxation rates were significantly enhanced in H2O compared with D2O. This enhancement is not due to direct dipolar interaction between H1 and bulk water. Transverse relaxation rates were not significantly enhanced in H2O.

Animals↗
PubMed1993

Construction and characterization of a novel cross-regulation system for regulating cloned gene expression in Escherichia coli.

A novel cross-regulation system employing two pairs of interacting promoter-repressor systems was constructed using the tac-lacI and lambda pL-cI promoter-operator-repressor systems. In particular, transcription of the cat gene and the fused cI gene is regulated by the tac promoter, while transcription of the lacI gene is controlled by the lambda pL promoter. In order to compare CAT production from this new system with a currently employed transcription control configuration, a control expression vector utilizing the constitutive repressor synthesis configuration was also constructed. In this construct, cat is under the control of the tac promoter, and lac repressor is provided from a single copy of the lacIq allele included in the plasmid. Induction results using different copy number vectors indicate that induced cat expression levels are at least twofold higher using the cross-regulation system which has very low basal expression. These results match well with previous mathematical modeling predictions indicating excellent control of basal expression and also higher cloned-gene expression post-induction over a broad range of copy numbers for a cross-regulation control configuration. Induction of the cross-regulation system both up-regulated the activation pathway and down-regulated the inhibition pathway, shifting the system steady-state from lac repressor expression to cat and cI expression. The control strategy presented here should be equally applicable to regulate transcription in diverse hosts.

Bacteriophage lambda↗
PubMed1993

T-cell immunity to oncogenic proteins including mutated ras and chimeric bcr-abl.

The process of malignant transformation can be ascribed to a series of characteristics and definable mutations of genes which encode proteins that control cell growth and differentiation. During the course of malignant transformation the cancer-related genes are altered by a variety of mechanisms including translocations, deletions, and point mutations which commonly result in the expression of aberrant proteins. Our laboratory has focused on determining the extent to which cancer-specific proteins expressed by aberrant cancer-related genes can function as tumor-specific antigens. The current paper reviews our studies with two prototype cancer-specific proteins, mutated p21ras protein and chimeric p210bcr-abl protein. Ras protooncogenes are activated by point mutation in approximately 20% of human malignancies. The mutations occur primarily at codons 12 or 61 and result in the expression of p21ras proteins with single substituted amino acids. Only a limited number of amino acid substitutions occur. Murine studies demonstrate that immunization with synthetic peptides corresponding to the mutated segment can elicit both class II restricted CD4+ helper/inducer T-cell responses and class I restricted CD8+ cytotoxic T-cell responses specific for mutated p21ras protein. In addition, the existence in vivo of tumors expressing mutated ras proteins can be detected by assaying for T-cell immunity to the mutated segment of ras protein. Preliminary human studies show that some patients with colon cancer have existent antibody responses to p21ras protein, implying the possible existence of autochthonous T-cell immunity to mutated ras proteins in those patients. In chronic myelogenous leukemia the human c-abl protooncogene from chromosome 9 is translocated to the specific breakpoint cluster (bcr) region on chromosome 22. The translocation results in the formation of a bcr-abl fusion gene that encodes at 210-kD chimeric protein. The joining region segment of chimeric bcr-abl protein is composed of a unique combination of c-abl and bcr amino acids and is expressed only by malignant cells. Studies demonstrate that immunization of mice with synthetic peptides corresponding to the joining region segment can elicit class II restricted CD4+ T-cell responses to p210bcr-abl proteins. Preliminary studies show that bcr-abl peptides can bind in the groove of both murine and human class I MHC molecules and can elicit bcr-abl peptide-specific cytotoxic T lymphocytes (CTL). Whether bcr-abl peptide-specific CTL can lyse cells expressing bcr-abl protein is a yet unknown. In summary, the results of the studies reviewed confirm that cancer-specific oncogenic proteins can serve as tumor-specific antigens.

Animals↗
PubMed1993

Stimulatory action of pituitary adenylate cyclase-activating polypeptide (PACAP) on thyroid gland.

PACAP 27 and 38 (27 and 38 amino acids, respectively) increased rapidly cAMP production in porcine thyroid cells in vitro. Both PACAPs also increased T4 production from mouse thyroid in vivo similar to TSH. Both PACAPs (especially 38) inhibited the binding of 125I-labeled TSH to thyroid membrane in the medium containing bovine serum albumin. This inhibitory action remarkably decreased in the medium containing normal human serum. Decrease of inhibition of TSH binding by serum containing PACAP could not be explained simply by proteolytic destruction of PACAP, although the labeled PACAP (especially 38) was destructed by proteases in thyroid membrane or human serum. These facts showed that PACAP had the thyroid stimulating action and the inhibitory action on the binding of TSH to thyroid receptor.

Animals↗
PubMed1993

The CDC42 homologue from Caenorhabditis elegans. Complementation of yeast mutation.

A Caenorhabditis elegans cDNA encoding a homologue of the p21 ras-related CDC42, designated as CDC42Ce, was isolated from a nematode mixed stage cDNA library. The encoded protein of 188 amino acid residues has 85% identity to both human G25K and CDC42Hs and 79 and 76% identity to the yeast CDC42Sp and CDC42Sc proteins, respectively. The CDC42Ce cDNA maps to a position on C. elegans chromosome II in close proximity to lin-26, a cell lineage gene. The CDC42Ce cDNA hybridizes to 2- and 1.5-kilobase mRNAs. Their expression is developmentally regulated with highest levels at the embryonic stage, decreasing progressively during development except for an increase of the more abundant 1.5-kilobase mRNA at the L3 stage. The glutathione S-transferase/CDC42Ce fusion protein expressed in Escherichia coli displays both GTP binding and intrinsic GTPase activities. The GTPase activity of CDC42Ce is moderately stimulated by human n-chimaerin, a GTPase-activating protein for the related p21 rac1. The CDC42Ce protein complements the temperature-sensitive lethal mutation cdc42-1 in yeast Saccharomyces cerevisiae. These data suggest that CDC42Ce is the C. elegans homologue of the yeast CDC42. The developmental expression pattern of mRNA and is biochemical properties of its encoded protein which are closely related to CErac1 suggest that the two p21s might be involved in related biological processes.

Amino Acid Sequence↗
PubMed1993

Electroporation and commercial liposomes efficiently deliver soluble protein into the MHC class I presentation pathway. Priming in vitro and in vivo for class I-restricted recognition of soluble antigen.

Class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocyte responses to ovalbumin (OVA) were evaluated following delivery of soluble antigen mixed with commercial liposomes or by electroporation of soluble protein into target cells. Splenic antigen presenting cells (APC) and transfected L cell lines were sensitised for recognition by OVA-specific, class I-restricted T hybridomas when antigen was introduced by either method into live cells. Delivery of soluble OVA by both electroporation and commercial liposomes proved more efficient than osmotic loading in sensitising for class I presentation. OVA-specific cytotoxic T lymphocytes (CTL) were effectively primed in naive mice following reinjection of spleen cells pulsed with soluble OVA encapsulated by liposomes or electroporated in vitro. These CTL recognised the well defined OVA257-264 determinant in association with H-2Kb and were derived under conditions where CTL activity obtained from cross priming by soluble OVA alone was undetectable. In addition, using electroporation and commercial liposomes, the loading of APC for OVA recognition required intact MHC-linked antigen presentation genes deleted in the T2-Kb cell line. Antigen delivery to APC by electroporation and commercial liposomes provides a simple and efficient way of studying class I-restricted T cell recognition of soluble protein antigens.

Animals↗
PubMed1993

Changes at peptide residues buried in the major histocompatibility complex (MHC) class I binding cleft influence T cell recognition: a possible role for indirect conformational alterations in the MHC class I or bound peptide in determining T cell recognition.

Recent crystallographic studies on two peptide complexes with the mouse Kb molecule have shown that peptide binding appears to alter the conformation of the class I alpha-helical regions that flank the antigen binding cleft. Given that this study also showed that much of the foreign peptide is buried within the class I binding cleft with only a small portion accessible for direct interaction with the components of the T cell receptor, this finding suggests that at least some component of T cell specificity may arise as a consequence of peptide-induced conformational changes in the class I structure. To assess this possibility, we have made systematic substitutions at residues within the Kb-restricted determinant from ovalbumin (OVA257-264) that are thought to be buried on binding to the class I molecule. We have found that changes in this determinant at the completely buried second residue (P2) can influence T cell recognition without affecting binding to Kb, suggesting that the substitutions may indirectly determine T cell recognition by altering the conformation of the class I molecule or the bound peptide.

Amino Acids↗