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X He

Publications and source records attributed to X He.

At least 253 records · Page 14Linked to original sources
PubMed1999

[Research into the mechanism of fragile sealing on the composition packet].

The research into the fragility of the sealing on two composition films for ham packages by using Fourier infrared spectrometer, DTG and melting index detector is reported. The research shows that the cause of the fragility of the sealing is the differences in the materials and their softening points and melting indexes between the inner film and the outer film. The inner film is made of adhesive polypropylene, whose softening point is 148.8 degrees C and melting index (MI) is 6.049 g/10 min. However, the outer film is made of polyamide 610, whose softening point is 221 degrees C, 72.2 degrees C higher than that of inner film, and melting index is 3.09 g/10 min, almost half of the MI of inner film. The mechanism of the fragile sealing on the composition packet is also discussed.

Polypropylenes↗
PubMed1998

Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene.

Mutations of the gene Lps selectively impede lipopolysaccharide (LPS) signal transduction in C3H/HeJ and C57BL/10ScCr mice, rendering them resistant to endotoxin yet highly susceptible to Gram-negative infection. The codominant Lpsd allele of C3H/HeJ mice was shown to correspond to a missense mutation in the third exon of the Toll-like receptor-4 gene (Tlr4), predicted to replace proline with histidine at position 712 of the polypeptide chain. C57BL/10ScCr mice are homozygous for a null mutation of Tlr4. Thus, the mammalian Tlr4 protein has been adapted primarily to subserve the recognition of LPS and presumably transduces the LPS signal across the plasma membrane. Destructive mutations of Tlr4 predispose to the development of Gram-negative sepsis, leaving most aspects of immune function intact.

Amino Acid Sequence↗
PubMed1998

Amino acid residues in thrombin-sensitive region and first epidermal growth factor domain of vitamin K-dependent protein S determining specificity of the activated protein C cofactor function.

Human protein S (PS) potentiates the anticoagulant activity of human but not bovine activated protein C (APC), whereas bovine PS is a cofactor to APC from both species. The structural requirements for the specificity of the APC cofactor function of human PS are located in its thrombin-sensitive region (TSR) and the first epidermal growth factor (EGF1)-like module. To elucidate which residues in these two modules determine the specificity of the APC cofactor activity, 41 human PS mutants were expressed. All mutants were cofactors to human APC and some also to bovine APC. Residues in TSR (positions 49 and 52) and EGF1 (residues 97 and 106) together determined the specificity of the APC cofactor function, whereas substitution of individual residues did not change specificity. Bovine PS, and mutants expressing cofactor activity to bovine APC, stimulated phospholipid binding of bovine APC. In contrast, human PS and mutants lacking cofactor activity to bovine APC failed to support binding of bovine APC to phospholipids. These data indicate that residues in TSR and EGF1 cause the specificity of the APC cofactor activity and support the concept that key residues in these two modules interact with APC on the phospholipid surface.

Amino Acid Sequence↗
PubMed1998

Destabilization of beta-catenin by mutations in presenilin-1 potentiates neuronal apoptosis.

Mutations of the presenilin-1 gene are a major cause of familial early-onset Alzheimer's disease. Presenilin-1 can associate with members of the catenin family of signalling proteins, but the significance of this association is unknown. Here we show that presenilin-1 forms a complex with beta-catenin in vivo that increases beta-catenin stability. Pathogenic mutations in the presenilin-1 gene reduce the ability of presenilin-1 to stabilize beta-catenin, and lead to increased degradation of beta-catenin in the brains of transgenic mice. Moreover, beta-catenin levels are markedly reduced in the brains of Alzheimer's disease patients with presenilin-1 mutations. Loss of beta-catenin signalling increases neuronal vulnerability to apoptosis induced by amyloid-beta protein. Thus, mutations in presenilin-1 may increase neuronal apoptosis by altering the stability of beta-catenin, predisposing individuals to early-onset Alzheimer's disease.

Adenomatous Polyposis Coli Protein↗
PubMed1998

Integrins involved in the adhesion of megakaryocytes to fibronectin and fibrinogen.

We studied integrins involved in the adhesion of resting and activated megakaryocytes (MK) to fibronectin (FN) and fibrinogen (FGN). Guinea pig MK were isolated and in some experiments were activated by thrombin. MK adhering to FN or FGN coated on coverslips were quantitated by a computerized image analysis program. The binding of soluble human FN to MK was detected by Western blotting. Anti-integrin antibodies, disintegrins, and cyclic RGD peptides were used to identify integrins involved in the adhesion of MK to FN or FGN. Resting MK adhered to coverslips with immobilized FN. The adhesion of MK to FN was primarily inhibited by an anti-alpha5 antibody and EMF-10, a distintegrin highly specific for alpha5 beta1. However, the adhesion of MK to FN was not blocked by agents that inhibit alphaIIb beta3, alphav beta3 or alpha4 beta1. A beta1 activating antibody increased the number of MK bound to FN due to the activation of alpha5 beta1. The binding of soluble FN was also primarily inhibited by agents that block alpha5 beta1. Resting MK did not adhere to FGN. However, MK activated by thrombin did adhere to FGN. This binding was mediated by alphaIIb beta3, because binding was inhibited by bitistatin, a disintegrin, and a cyclic RGD peptide that are known to block this integrin. The binding of thrombin-activated MK to FN was mediated by both alpha5 beta1 and alphaIIb beta3 based on the additive effect of agents that inhibit these integrins. The study indicates that resting MK bind to FN but not to FGN and that alpha5 beta1 is the major integrin involved in the binding of MK to FN. Activated MK bind to FGN primarily by alphaIIb beta3. However, the binding of activated MK to FN is due to both alpha5 beta1 and alphaIIb beta3. The demonstration that alpha5 beta1 and that alphaIIb beta3 are involved in MK adhesion indicates that these integrins may have a role in MK maturation and platelet production.

Animals↗
PubMed1998

Predictive models for GABAA/benzodiazepine receptor subtypes: studies of quantitative structure-activity relationships for imidazobenzodiazepines at five recombinant GABAA/benzodiazepine receptor subtypes [alphaxbeta3gamma2 (x = 1-3, 5, and 6)] via comparative molecular field analysis.

Affinities of a series of substituted imidazobenzodiazepines at recombinant alpha1beta3gamma2, alpha2beta3gamma2, alpha3beta3gamma2, alpha5beta3gamma2, and alpha6beta3gamma2 GABAA/benzodiazepine receptor subtypes are reported. Many of these ligands displayed high affinities (low-nanomolar to subnanomolar scale) at all five receptor subtypes. Furthermore, a number of imidazobenzodiazepines exhibited relatively good selectivity at the alpha5-containing receptor isoform. For example, ligand 27 (RY-023) demonstrated a 55-fold higher selectivity at alpha5beta3gamma2 isoforms in comparison to other receptor subtypes. The affinity ratio of alpha1 (the most prevalent subtype in the brain) to alpha5 of this series of ligands ranged from 60- to 75-fold for the most selective ligands. Studies of quantitative structure-activity relationships (QSAR) by means of comparative molecular field analysis (CoMFA) were carried out. As a result, examination of CoMFA models for all five receptor subtypes demonstrated their predictability for affinities of imidazobenzodiazepines at the five receptor subtypes. Regions of molecular fields which would favor or disfavor the binding affinity of a ligand at a specific receptor subtype were examined via CoMFA for alpha1, alpha2, alpha3, alpha5, and alpha6 subtypes. A CoMFA regression analysis was applied to predict the ratio of Ki alpha1/Ki alpha5, an index for the selectivity of a ligand at the alpha5 subtype. All of the CoMFA models offered good cross-validated correlations for the ligands in the test set as well as the ratios of Ki alpha1/Ki alpha5, which demonstrated their potential for prediction.

Animals↗
PubMed1998

cDNA cloning and expression of a novel serine protease, TLSP.

A cDNA for a putative novel serine protease, TLSP, was cloned from human hippocampus cDNA with polymerase chain reaction based strategies. The putative amino acid sequence of TLSP is similar to the trypsin-type serine proteases. TLSP mRNA is expressed in keratinocytes. Overexpressed TLSP protein in neuro2a cells was detected in culture medium.

Amino Acid Sequence↗
PubMed1998

Cloning and characterization of the full-length cDNA and genomic sequences encoding murine acid ceramidase.

The full-length cDNA and genomic sequences encoding murine acid ceramidase (AC; E.C. 3.5.1.23) have been isolated and characterized. The 2176-bp cDNA was approximately 80% identical to the human cDNA (Koch et al., 1996) and predicted a 394-amino-acid polypeptide that was approximately 90% identical to the human protein. A fluorescence-based assay system was developed to determine AC enzymatic activity, and transfection of COS-1 cells with the full-length mouse cDNA led to increased AC activity, demonstrating its functionality. The murine AC gene, which spanned approximately 38 kb, consisted of 14 exons separated by 13 introns. The exons ranged in size from 46 to 1038 bp and were flanked by exon/intron junctions that adhered closely to known donor and acceptor splice site consensus sequences. Exon 1 encoded the putative translation start site and the signal peptide region, while exon 14 encoded the carboxy end of the AC polypeptide and all of the 3' untranslated region. Sequence analysis of a 497-bp region upstream from the first in-frame ATG revealed several features of a housekeeping promoter, as well as several tissue-specific and/or hormone-inducible regulatory sites. Insertion of this sequence into a chloramphenicol acyltransferase (CAT) expression vector led an approximately fivefold increase in CAT activity after transfection into NIH3T3 cells. Northern blot analysis and enzymatic assays also were carried out on various murine tissues to examine AC expression. Of the tissues studied, the highest AC activity and mRNA levels were found in the kidney, followed by the brain; almost no AC activity or mRNA was found in the testis or skeletal muscle. These latter studies provided clear evidence that despite the housekeeping function of AC, its expression was tissue-specific.

Acid Ceramidase↗
PubMed1998

Genetic evaluation of suspected cases of transient HIV-1 infection of infants.

Detection of human immunodeficiency virus-type 1 (HIV-1) on only one or a few occasions in infants born to infected mothers has been interpreted to indicate that infection may be transient rather than persistent. Forty-two cases of suspected transient HIV-1 viremia among 1562 perinatally exposed seroreverting infants and one mother were reanalyzed. HIV-1 env sequences were not found in specimens from 20; in specimens from 6, somatic genetic analysis revealed that specimens were mistakenly attributed to an infant; and in specimens from 17, phylogenetic analysis failed to demonstrate the expected linkage between the infant's and the mother's virus. These findings argue that transient HIV-1 infection, if it exists, will only rarely be satisfactorily documented.

DNA, Viral↗
PubMed1998

Exogenously provided peptides of a self-antigen can be processed into forms that are recognized by self-T cells.

Major histocompatibility complex (MHC) class II molecules can present peptides derived from two different sources. The predominant source of peptide in uninfected antigen presenting cells (APCs) is from self-proteins that are synthesized within the cell and traffic through the MHC class II compartment. The other source of antigen is endocytosed proteins, which includes both self- and foreign proteins. Foreign protein antigens generate adaptive immune responses, whereas self-peptides stabilize the MHC class II heterodimer on the cell surface, allowing positive and negative selection of thymocytes. Therefore, self-antigens play an important normal role in shaping the T cell receptor repertoire as well as a pathological role in autoimmunity. To determine whether processing and presentation of self-antigens by MHC class II molecules differs depending on whether the antigen is supplied through synthesis within the cell or by endocytosis, we used a T cell clone against an Ealpha peptide presented by I-Ab to show that processing through these two routes can differ. We also show that mice can be tolerant to the epitope formed through the endogenous route, but responsive to the epitope that can be formed through endocytosis. This suggests that negative selection occurs primarily against antigens that are synthesized within the APC, and that endocytosed self-antigens could serve as autoantigens. Finally, we also demonstrate that lipopolysaccharide-activated B cells are defective for uptake, processing, and presentation of this self-antigen, and that this correlates with the increased expression of the costimulatory molecules B7.1 and B7.2. This may provide a model for studying the onset of an autoimmune response.

Animals↗
PubMed1998

Thrombomodulin increases the rate of thrombin inhibition by BPTI.

Thrombin undergoes allosteric modulation by thrombomodulin (TM) that results in a shift in macromolecular specificity, blocking fibrinogen clotting while enhancing protein C activation. The TM enhancement of protein C activation involves both an 8-fold decrease in Km and a 200-fold increase in kcat. Although TM-mediated conformational changes in thrombin have been detected by many techniques, the nature of these changes remains obscure. Access to the active center of thrombin is relatively restricted due to the presence of a large insertion loop at residue 60 (chymotrypsin numbering) that has been implicated in modeling studies as being responsible for poor inhibition by BPTI. Thrombin and the E192Q mutant, which binds BPTI much more tightly than thrombin, are both inhibited very slowly by BPTI. TM increases the rate of thrombin or thrombin E192Q inhibition by BPTI approximately 10-fold. When analyzed as slow tight binding inhibition, the TM effect on thrombin E192Q inhibition by BPTI is primarily on the first, reversible step in the reaction. Structural studies of the thrombin E192Q-BPTI complex have previously shown that the 60 loop lies over the BPTI, a position which requires 8 A movement at the apex of the 60 loop, and that BPTI is found in the same canonical orientation as in the trypsin complex. It follows that TM enhancement of the initial interaction of thrombin results in a conformation that favors interactions with BPTI, probably involving motion of the 60 loop.

Allosteric Regulation↗
PubMed1998

Genetic and physical mapping of the Lps locus: identification of the toll-4 receptor as a candidate gene in the critical region.

On the basis of 2093 meioses analyzed in two separate intraspecific backcrosses, the location of the mouse Lpsd mutation was circumscribed to a genetic interval 0.9 cM in size. A total of 19 genetic markers that lie in close proximity to the mutation were examined in mapping. Most of these were previously unpublished polymorphic microsatellites, identified by fragmentation of YAC and BAC clones spanning the region of interest. Lpsd was found to be inseparable from the microsatellite marker D4MIT178, and from three novel polymorphic microsatellites identified near D4MIT178. The mutation was confined between two novel microsatellite markers, herein designated "B" and "83.3." B lies centromeric to the mutation, and was separated by four crossovers in a panel of 1600 mice; 83.3 lies distal to the mutation and was separated by three crossovers in a panel of 493 mice. 66 BAC clones and one YAC clone were assembled to cover > 95% of the critical region. Estimates based on pulsed field gel electrophoresis and fluorescence in situ hybridization indicate that the The B-->83.3 interval is about 3.2 Mb in length. A minimal area of zero recombinational distance from Lpsd was also assigned, and found to occupy approximately 1.2 Mb of physical size. To identify gene candidates, nearly 40,000 sequencing runs were performed across the critical region. Selective hybridization and exon trapping were also employed to identify genes throughout the "zero" region. Only a single intact gene was identified within the entire critical region. This gene encodes the Toll-4 receptor, a member of the IL-1 receptor family.

Animals↗
PubMed1998

A polarized salivary cell monolayer useful for studying transepithelial fluid movement in vitro.

There are no reported, convenient in vitro models for studying polarized functions in salivary epithelial cells. Accordingly, we examined three often-used salivary cell lines for their ability to form a polarized monolayer on permeable, collagen-coated polycarbonate filters. Only the SMIE line, derived from rat submandibular gland, had this ability. The SMIE cell monolayer exhibited junctional complexes, with a tight-junction-associated protein, ZO-1, localized to cell-cell contact areas. The Na+/K+-ATPase alpha1-subunit was detected predominantly in the basolateral membranes, while the Na+/H+ exchanger isoform 2 appeared primarily in the apical membranes. Using adenovirus-mediated cDNA transfer, SMIE cells were shown to be capable of routing marker proteins (beta-galactosidase +/- a nuclear targeting signal, alpha1-antitrypsin, aquaporin-1) to appropriate locations. Furthermore, this salivary cell monolayer provided a convenient tool for studying aquaporin-1-mediated, osmotically directed, transepithelial fluid movement in vitro. Thus, SMIE cells appear to be a useful experimental model with which to study some polarized functions in a salivary epithelial cell line.

Adenoviridae↗
PubMed1998

Serological characterization of the 3'-proximal encoded proteins of beet yellows closterovirus.

The 3'-proximal open reading frames (ORFs) of beet yellows closterovirus, California isolate (BYV-CA), were sequenced and the expression of the corresponding proteins analyzed. The nucleotide sequence of ORF 5 (coding for p24) was most conserved compared with ORF 7 (coding for p20) and ORF 8 (coding for p21) among the isolates analyzed. Polyclonal antisera were produced to GST fusion proteins of p24, p20, and p21. Accumulation of p24, CP, p20 and p21 was studied in infected Tetragonia expansa plants and Chenopodium quinoa protoplasts. All four proteins were expressed in all tissues (old leaves, young leaves and stems), and most abundantly in young leaves. The subcellular localization of each protein in different tissues showed that compared with p24, CP and p21, p20 accumulated less in transfected protoplasts. Immunogold labeling in sugarbeet with p24 and CP antisera demonstrated co-localization of p24 and CP in vascular petiole tissues. In infectivity neutralization tests, antisera against p24 and CP greatly reduced transmission of BYV by viruliferous aphids compared with viruliferous aphids fed on preimmune serum or antiserum to p21.

Amino Acid Sequence↗
PubMed1998

Extending the range of rate constants available from BIACORE: interpreting mass transport-influenced binding data.

Surface-based binding assays are often influenced by the transport of analyte to the sensor surface. Using simulated data sets, we test a simple two-compartment model to see if its description of transport and binding is sufficient to accurately analyze BIACORE data. First we present a computer model that can generate realistic BIACORE data. This model calculates the laminar flow of analyte within the flow cell, its diffusion both perpendicular and parallel to the sensor surface, and the reversible chemical reaction between analyte and immobilized reactant. We use this computer model to generate binding data under a variety of conditions. An analysis of these data sets with the two-compartment model demonstrates that good estimates of the intrinsic reaction rate constants are recovered even when mass transport influences the binding reaction. We also discuss the conditions under which the two-compartment model can be used to determine the diffusion coefficient of the analyte. Our results illustrate that this model can significantly extend the range of association rate constants that can be accurately determined from BIACORE.

Binding Sites↗
PubMed1998

Position 120-123, a potential active site of trichosanthin.

Trichosanthin (TCS) is a type-I ribosome-inactivating protein (RIP) with wide spectrum of biological and pharmacological activities. In the present study, a potential site on the TCS molecule (position 120-123) is identified which may be important for the biological activities of TCS. By using site-directed mutagenesis, position 120-123 of TCS was either deleted or changed from Lys-Ile-Arg-Glu (hydrophilic) to Ser-Ala-Gly-Gly (hydrophobic). Deletion of these residues rendered a TCS molecule completely deprived of ribosome inactivating activity, while hydrophobic replacement caused 4000-fold decrease in ribosome inactivating activity. The abortifacient activity of these two mutants was retained with decreased potency. This implies that position 120-123 of the native TCS molecule plays a critical role in maintaining its biological activity.

Abortifacient Agents, Nonsteroidal↗
PubMed1998

Systemic action of human growth hormone following adenovirus-mediated gene transfer to rat submandibular glands.

We have previously suggested that although salivary glands function in an exocrine manner they might none the less offer a useful way to deliver therapeutic proteins systemically. As a direct functional test of this hypothesis, we constructed a recombinant adenovirus (AdCMVhGH) encoding human growth hormone (hGH) and then studied the biological action of hGH produced following transfer of the hGH gene to rat submandibular glands. At 48 h following infusion of AdCMVhGH into these glands via cannulation of the main excretory duct, serum levels of hGH were approximately 16 ng/ml and rat insulin-like growth factor-1 was elevated approximately 25%. Moreover, serum chemistry profiles of rats subjected to in vivo gene transfer displayed alterations in the BUN:creatinine ratio and triglyceride levels presumably reflecting the anabolic actions of the hGH. These results provide the first demonstration of systemic biological action from a transgene product secreted in an endocrine fashion from the salivary glands.

Adenoviridae↗