Search PubMed⌕ Search

Biomedical subjects

Y Yang

Publications and source records attributed to Y Yang.

At least 1,117 records · Page 62Linked to original sources
PubMed1995

Upregulation of class I major histocompatibility complex antigens by interferon gamma is necessary for T-cell-mediated elimination of recombinant adenovirus-infected hepatocytes in vivo.

Recombinant adenoviruses are attractive vehicles for liver-directed gene therapy because of the high efficiency with which they transfer genes to hepatocytes in vivo. First generation recombinant adenoviruses deleted of E1 sequences also express recombinant and early and late viral genes, which lead to development of destructive cellular immune responses. Previous studies indicated that class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTLs) play a major role in eliminating virus-infected cells. The present studies utilize mouse models to evaluate the role of T-helper cells in the primary response to adenovirus-mediated gene transfer to the liver. In vivo ablation of CD4+ cells or interferon gamma (IFN-gamma) was sufficient to prevent the elimination of adenovirus-transduced hepatocytes, despite the induction of a measurable CTL response. Mobilization of an effective TH1 response as measured by in vitro proliferation assays was associated with substantial upregulation of MHC class I expression, an effect that was prevented in IFN-gamma-deficient animals. These results suggest that elimination of virus-infected hepatocytes in a primary exposure to recombinant adenovirus requires both induction of antigen-specific CTLs as well as sensitization of the target cell by TH1-mediated activation of MHC class I expression.

Adenoviruses, Human↗
PubMed1995

Interaction of the cobalt complex of a bleomycin functional model with d(CGCAATTGCG)2: evidence of minor groove binding by 2D NMR methods.

The interaction between the cobalt complex of a bleomycin functional model and d(CGCAATTGCG)2 was determined by 2D NMR methods. The intermolecular NOE cross peaks between ligand protons and the DNA minor groove protons suggest that the cobalt complex of AMPHIS-NET binds in the minor groove of DNA at the central AATT site. Also, the NOEs interactions of H8 pyridine proton and H2 imidazole proton in the metal-binding domain with H4' sugar proton of C9 and H4' sugar proton of A15 demonstrate that the sixth ligand site of cobalt complex, which is occupied by a solvent molecule, faces towards the minor groove of DNA. This binding model is in accord with the observed non-diffusion DNA cleavage by the metal-complexes of the bleomycin functional model compounds.

Base Sequence↗
PubMed1995

Male-specific lethal 2, a dosage compensation gene of Drosophila, undergoes sex-specific regulation and encodes a protein with a RING finger and a metallothionein-like cysteine cluster.

In Drosophila the equalization of X-linked gene products between males and females, i.e. dosage compensation, is the result of a 2-fold hypertranscription of most of these genes in males. At least four regulatory genes are required for this process. Three of these genes, maleless (mle), male-specific lethal 1 (msl-1) and male-specific lethal 3 (msl-3), have been cloned and their products have been shown to interact and to bind to numerous sites on the X chromosome of males, but not of females. Although binding to the X chromosome is negatively correlated with the function of the master regulatory gene Sex lethal (Sxl), the mechanisms that restrict this binding to males and to the X chromosome are not yet understood. We have cloned the last of the known autosomal genes involved in dosage compensation, male-specific lethal 2 (msl-2), and characterized its product. The encoded protein (MSL-2) consists of 769 amino acid residues and has a RING finger (C3HC4 zinc finger) and a metallothionein-like domain with eight conserved and two non-conserved cysteines. In addition, it contains a positively and a negatively charged amino acid residue cluster and a coiled coil domain that may be involved in protein-protein interactions. Males produce a msl-2 transcript that is shorter than in females, due to differential splicing of an intron of 132 bases in the untranslated leader. Using an antiserum against MSL-2 we have shown that the protein is expressed at a detectable level only in males, where it is physically associated with the X chromosome. Our observations suggest that MSL-2 may be the target of the master regulatory gene Sxl and provide the basic elements of a working hypothesis on the function of MSL-2 in mediating the 2-fold increase in transcription that is characteristic of dosage compensation.

Amino Acid Sequence↗
PubMed1995

A viral inhibitor of peptide transporters for antigen presentation.

Cytotoxic T lymphocytes lyse target cells after T-cell-receptor-mediated recognition of class I major histocompatibility complex molecules presenting peptides. Antigenic peptides are generated in the cytoplasm by proteasomes and translocated into the lumen of the endoplasmic reticulum (ER) by peptide transporters (TAP). Herpes simplex virus (HSV) expresses a cytoplasmic protein, ICP47, which seems to interfere with such immune surveillance by mediating retention of 'empty' class I molecules in the ER. By expressing ICP47 in HeLa cells under an inducible promoter, we show that ICP47 efficiently inhibits peptide transport across the ER membrane such that nascent class I molecules fail to acquire antigenic peptides. This inhibition was overcome by transfecting murine TAP. Further, we demonstrate that ICP47 colocalizes and physically associates with TAP within the cell. Inhibition of peptide translocation by a viral protein indicates a previously undocumented potential mechanism for viral immune evasion.

ATP-Binding Cassette Transporters↗
PubMed1995

Fas and activation-induced Fas ligand mediate apoptosis of T cell hybridomas: inhibition of Fas ligand expression by retinoic acid and glucocorticoids.

Activation of T cell hybridomas induces a G1/S cell cycle block and apoptosis. We isolated a variant of the 2B4.11 T cell hybridoma that, when activated via the TCR, produced IL-2 and underwent growth inhibition but did not die. Analysis of a variety of cell surface molecules revealed that the variant cell line, termed VD1, expressed very low levels of Fas compared to the wild type cells. Unlike 2B4.11 cells, VD1 cells were not killed by Fas ligand (FasL)-bearing effector cells. To determine if Fas is involved in activation-induced apoptosis, two different reagents that specifically bind Fas without killing the T cell hybridomas, a monoclonal antibody and a soluble Fas:Fc chimeric molecule, were added to activated T cell hybridomas. Both treatments prevented activation-induced apoptosis in a dose-dependent manner, but had no effect on IL-2 production or growth inhibition. Northern blot analysis revealed that unactivated 2B4.11 cells expressed negligible levels of FasL mRNA, but transcripts were detectable as early as 2 h after activation and continued to increase up to 4-6 h after activation. Anti-TCR induced activation of 2B4.11 cells in the presence of a TCR- 2B4.11 variant resulted in death of the unactivated "bystander" cells, which was inhibited by anti-Fas antibodies. Finally, treatment of T hybridoma cells with 9-cis retinoic acid or glucocorticoids, which are known to prevent activation-induced T cell apoptosis, inhibited the up-regulation of FasL. We conclude that up-regulated expression of FasL and its subsequent interaction with Fas accounts for the apoptotic response of T cell hybridomas to activation, and that retinoic acid and corticosteroids inhibit activation-induced apoptosis by preventing up-regulation of FasL.

Animals↗
PubMed1995

Cytotoxicity, metabolism, and mechanisms of action of 2',2'-difluorodeoxyguanosine in Chinese hamster ovary cells.

The emerging clinical success of gemcitabine (2',2'-difluorodeoxycytidine) stimulated interest in the synthesis and evaluation of purine congeners. The cytotoxicity, metabolism, and mechanisms of action of the lead candidate, 2',2'-difluorodeoxyguanosine (dFdGuo), were studied in Chinese hamster ovary cells. Unlike the natural nucleoside deoxyguanosine (dGuo), dFdGuo was not a substrate for purine nucleoside phosphorylase. Wild-type Chinese hamster ovary cells and a mutant line deficient in deoxycytidine (dCyd) kinase were similarly affected by dFdGuo (50% inhibitory concentration, 7.5 and 6.5 microM, respectively), suggesting that unlike gemcitabine, dCyd kinase was not responsible for activation of dFdGuo. This was further confirmed by separation of nucleoside kinases (adenosine kinase, dGuo kinase, and dCyd kinase) of Chinese hamster ovary cells on DEAE-cellulose column chromatography. The kinase activity that phosphorylated dGuo also converted dFdGuo to its monophosphate, suggesting that dGuo kinase activated dFdGuo. Consistent with this result, coincubation with dGuo spared the dFdGuo-mediated toxicity; however, addition of up to 10 mM dCyd did not reverse the toxicity of dFdGuo. Intracellularly, dFdGuo was phosphorylated to its mono-, di-, and triphosphates; dFdGuo triphosphate (dFdGTP) was the major metabolite and accumulated to 45 microM after a 6-h incubation with 30 microM dFdGuo. The elimination of dFdGTP was monophasic with a t1/2 of about 6 h. Deoxynucleotides were decreased in cells incubated with dFdGuo, suggesting that ribonucleotide reductase was inhibited. dATP, which decreased 78% after a 4-h incubation with 30 microM dFdGuo, was most affected. dFdGuo was a potent inhibitor of DNA synthesis. Extension of a DNA primer over a defined template in the presence of dFdGTP revealed that dFdGTP was a good substrate for incorporation opposite C sites of the template by DNA polymerase alpha. dFdGTP incorporation caused DNA polymerase alpha to pause after the polymerization of one additional deoxynucleotide. This pattern of inhibition, which is shared by gemcitabine, distinguishes 2',2'-difluoronucleosides from arabinosylnucleosides which halt primer extension at the incorporation site. dGTP competed effectively with dFdGTP for incorporation by DNA polymerase alpha. The unique activation requirements and patterns of inhibition of DNA synthesis distinguish this promising new antimetabolite from other nucleoside analogues.

Adenosine Triphosphate↗
PubMed1995

Retinoic acid inhibition of ex vivo human immunodeficiency virus-associated apoptosis of peripheral blood cells.

T cells from human immunodeficiency virus (HIV)-infected individuals undergo spontaneous and activation-induced ex vivo apoptosis. Here we report that peripheral blood mononuclear cells (PBMCs) obtained from six HIV-infected individuals exhibited reduced ex vivo DNA fragmentation and cell death after ingestion of all-trans-retinoic acid (tRA). These effects were attenuated with continued daily RA administration, which correlated with a > 5-fold decrease in serum peak RA concentrations. Incubation of PBMCs from HIV+ individuals with tRA in vitro resulted in decreased DNA fragmentation in a subset of patients, especially those having < 500 CD4+ T cells per mm3. tRA also inhibited apoptosis of preactivated normal PBMCs induced to die by restimulation, which raises the possibility of a common mechanism between activation-induced apoptosis of activated normal PBMCs and apoptosis associated with HIV infection. Whether HIV-associated apoptosis of PBMCs, and its prevention by RA, has an impact on T-cell survival or the course of disease in patients infected with HIV will require further evaluation.

Administration, Oral↗
PubMed1995

Interaction between the signaling molecules WNT7a and SHH during vertebrate limb development: dorsal signals regulate anteroposterior patterning.

Growth and patterning of the vertebrate limb are controlled by the ridge, posterior mesenchyme, and non-ridge ectoderm. Fibroblast growth factor 4 (FGF4) and Sonic hedgehog (SHH) can mediate signaling from the ridge and posterior mesenchyme, respectively. Here we show that dorsal ectoderm is required together with FGF4 to maintain Shh expression. Removal of dorsal ectoderm results in loss of posterior skeletal elements, which can be rescued by exogenous SHH. Wnt7a, which is expressed in dorsal ectoderm, provides the signal required for Shh expression and formation of posterior structures. These results provide evidence that all three axes (dorsoventral, proximodistal, and anteroposterior) are intimately linked by the respective signals WNT7a, FGF4, and SHH during limb out-growth and patterning.

Animals↗
PubMed1995

Polyanion-induced alpha-helical structure of a synthetic 23-residue peptide representing the lysine-rich segment of the N-terminal extension of yeast cytoplasmic aspartyl-tRNA synthetase.

Conformational studies were performed on the synthetic tricosapeptide N-acetyl-SKKALKKLQKEQEKQRKKEERAL-amide, representing the highly basic segment (residues 30-52) of the N-terminal extension of yeast cytoplasmic aspartyl-tRNA synthetase. Circular dichroism experiments show that, in aqueous solution at neutral pH, the peptide adopts a random conformation. The effects of pH, temperature, addition of trifluoroethanol (TFE), and titration with polyanions on the conformation of the peptide were studied. In TFE or in the presence of an equimolar concentration of (phosphate)18, the peptide adopts a 100% alpha-helical conformation. A partially alpha-helical conformation is induced by (phosphate)4 or d(pT)8 (respectively 40% and 35% helical content). Raising the pH in aqueous solution promotes 75% alpha-helicity, with a transition pK of 9.9 reflecting deprotonation of lysine residues. On the basis of these results, nuclear magnetic resonance studies were carried out in TFE as well as in aqueous solution in the presence of (phosphate)18, to determine the structure of the molecule. Complete 1H resonance assignments were obtained by conventional two-dimensional NMR techniques. A total of 138 interproton constraints derived from NOESY experiments were used to calculate the three-dimensional structure by a two-stage distance geometry/simulated annealing procedure. The two deduced structures were highly similar and show that nine cationic residues are segregated on one face of a helical structure, providing an ideal polycationic interface for binding to polyanionic surfaces.

Amino Acid Sequence↗
PubMed1995

Intrafamilial transmission of hepatitis C virus in hemodialysis patients.

The prevalence of hepatitis C virus (HCV) infection in chronic hemodialysis patients ranges from 20 to 50% and these patients may serve as a reservoir of infection for their household contacts. The aim of this study was to investigate the prevalence of anti-HCV in hemodialysis patients and their families, and to evaluate possible routes of infection. One hundred eighty-six family members of 84 hemodialysis patients and 529 healthy adults were enrolled. The family members consisted of 50 spouses, 96 children, 11 parents, 29 siblings, and other relatives living together with the patients. Serum samples were collected for testing anti-HCV. Exposure to risk factors was obtained by a questionnaire and an interview. The results showed that prevalence of anti-HCV in hemodialysis patients was 44%, whereas in family members it was 5.4%, not significantly different from that of age-matched healthy adults (standardized morbidity rate = 1.51, P = 0.390). The anti-HCV rate in family members tended to increase with age, and a spouse of an infected hemodialysis patient had a higher risk of HCV infection than other family members (15% vs. 2.6%, odds ratio 6.6, P = 0.058). Except for the age factor, no difference was found between seropositive and seronegative family members with respect to risk factors such as blood transfusion, surgery, frequent injections, dental procedures, or acupuncture. It was concluded that, although the anti-HCV positivity of hemodialysis patients is high, the risk of HCV infection for their family members is not higher than that of the general population. Among family members, spouses of seropositive hemodialysis patients have the highest risk of HCV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Isolation and characterization of two major degradation products of dyclonine hydrochloride.

Dyclonine hydrochloride, a local anesthetic, is known to degrade in aqueous media. In this paper, the isolation and characterization of two major degradation products, formed by heating of an aqueous solution of dyclonine hydrochloride for 2 weeks at 50 degrees C, are presented. The proton and carbon-13 nuclear magnetic resonance, infrared, and mass spectral data reported conclusively show the two products to be 1-(4-butoxyphenyl)-2-propen-1-one and 1-(4-butoxyphenyl)-3-hydroxy-1-propanone. The proton and carbon-13 nuclear magnetic resonance spectral data of the free dyclonine base are also included.

Anesthetics, Local↗
PubMed1995

Molecular interactions between fibronectin and integrins during mouse blastocyst outgrowth.

To investigate the mechanism of trophoblast adhesion to fibronectin, we cultured blastocysts in serum-free medium on proteolytic fibronectin fragments containing its major functional domains, and localized fibronectin-binding integrins in outgrowing trophoblast cells by immunofluorescent staining. Outgrowth comparable to that obtained with intact fibronectin was observed using a 120 kD chymotryptic fragment containing the central cell-binding domain (FN-120) and the Arg-Gly-Asp (RGD) recognition sequence. A 40 kD COOH-terminal chymotryptic fragment of fibronectin containing both a heparin-binding region and an alternate (non-RGD) cell-binding site was inactive in supporting trophoblast adhesion. Three synthetic peptides derived from the heparin-binding domain, including the CS1 alternate cell-binding site, were also unable to promote trophoblast cell adhesion. A 75 kD recombinant protein, ProNectin F, containing 13 copies of the cell recognition epitope of fibronectin, Val-Thr-Gly-Arg-Gly-Asp-Ser-Pro-Ala-Ser, vigorously supported blastocyst outgrowth. Blastocyst outgrowth was not significantly different when surfaces were precoated with cellular fibronectin, which contains an alternatively spliced type III repeat and is the form actually encountered in vivo. Several putative fibronectin receptors were localized in trophoblast outgrowths by immunofluorescent labeling. Antibodies reactive with integrin subunits alpha 3, alpha 5, alpha IIb, alpha v, beta 1 and beta 3, but not alpha 4, all bound to trophoblast cells. Antibodies raised against either the beta 1 or beta 3 integrin subunits significantly inhibited fibronectin-mediated outgrowth. These findings demonstrate the key role of the central cell-binding domain of fibronectin in trophoblast adhesion, and suggest four RGD-binding integrins, alpha 3 beta 1, alpha 5 beta 1, alpha IIb beta 3, and alpha v beta 3, that could mediate trophoblast adhesion in vitro and may play an important role during implantation.

Amino Acid Sequence↗
PubMed1995

Measurement of water diffusion in hormone-treated rat uteri by diffusion-weighted magnetic resonance imaging.

In this study, apparent water diffusion coefficients in hormone-treated rat uteri were measured by diffusion-weighted NMR imaging. Four groups of ovariectomized, mature young rats were treated with estrogen, progesterone, estrogen plus progesterone, or saline (as control). It was found that water diffusion is anisotropic in the myometrium, but not in the endometrium, and that it depends on hormonal conditions in the endometrium, but not in the myometrium. The anisotropy of water diffusion can be exploited to improve image contrast among the various uterine tissue types. The hormonal response suggests that diffusion imaging of human uterus may be useful in detecting endometrial pathology.

Animals↗