Biomedical subjects

C Xu

Publications and source records attributed to C Xu.

At least 19 recordsLinked to original sources

PubMed2000

Molecular basis of voltage-dependent delayed rectifier K+ channels in smooth muscle cells from rat tail artery.

The molecular basis of voltage-dependent K+ (Kv) current in smooth muscle cells (SMCs) from rat tail artery was investigated by screening transcriptional expression of 15 Kv channel alpha-subunits and 3 Kv beta-subunits using RT-PCR technique. Among Kv genes that encode delayed rectifier Kv currents, mRNAs of Kv1.2, Kv1.3, Kv1.5, Kv2.1, Kv2.2, and Kv3.2 were expressed, but those of Kv1.1, Kv1.6, and Kv3.1 were not detected. The transient outward Kv current-encoding genes Kv1.4, Kv3.3, Kv3.4, Kv4.1- Kv4.3 as well as Kvbeta1, Kvbeta2, and Kvbeta3 were also expressed at mRNA level. Western blot study demonstrated the presence of Kv1.2, Kv1.3, Kv1.5, and Kv2.1, but not Kv3.2 proteins, in tail artery tissue. Immunocytochemistry study confirmed the presence of Kv1.2, Kv1.3, Kv1.5, and Kv2.1 channel proteins in primary cultured single SMCs. Our results represent the first systematic characterization of Kv gene expression in rat tail artery SMCs.

Animals↗

PubMed2000

A critical role for murine complement regulator crry in fetomaternal tolerance.

Complement is a component of natural immunity. Its regulation is needed to protect tissues from inflammation, but mice with a disrupted gene for the complement regulator decay accelerating factor were normal. Mice that were deficient in another murine complement regulator, Crry, were generated to investigate its role in vivo. Survival of Crry-/- embryos was compromised because of complement deposition and concomitant placenta inflammation. Complement activation at the fetomaternal interface caused the fetal loss because breeding to C3-/- mice rescued Crry-/- mice from lethality. Thus, the regulation of complement is critical in fetal control of maternal processes that mediate tissue damage.

Animals↗

PubMed2000

Patterns of gene expression associated with BMP-2-induced osteoblast and adipocyte differentiation of mesenchymal progenitor cell 3T3-F442A.

The pluripotent mesenchymal stem cells give rise to osteoblasts, adipocytes, chondrocytes, and myoblasts. The differentiation of these stem cells into each of the mature functional cells may be controlled by a distinctive master gene(s) and is associated with temporal and spatial expression of diverse genes. Identification of genes that are expressed during the differentiation of the mesenchymal cells to osteoblasts is, therefore, important to obtain insights into the molecular mechanisms of osteogenesis. The murine undifferentiated mesenchymal cell 3T3-F442A, when treated with the bone morphogenetic protein 2 (BMP-2), a well-characterized inducer of mesenchymal cell differentiation, exhibited both osteoblastic and adipocytic differentiation. Using the SAGE (serial analysis of gene expression) technique, which has been shown to enable quantitative analysis of large numbers of genes in a simple and quick manner, we obtained 1600 sequence tags representing 2107 individual nucleotide sequences from control and BMP-2-treated 3T3-F442A cells, respectively. By comparing the frequency of tag occurrence, we found profiles of up- or downregulated genes associated with osteoblast or adipocyte phenotype such as type I collagen, osteonectin and OSF-2, or C/EBPbeta, aP2, fatty acid synthase, and lipoprotein lipase, respectively, in BMP-2-treated 3T3-F442A cells. Our data show that BMP-2 induces not only osteoblastic but also adipocytic differentiation in the 3T3-F442A cells. They also show that the 3T3-F442A cells have bipotentials of differentiating toward osteoblasts and adipocytes. The results, therefore, might explain the inverse correlation between trabecular bone volume and fat volume in the bone marrow cavity. The results also suggest that the SAGE may be a useful technique that allows us a fast and efficient way to generate global and local views of gene expression associated with cellular differentiation of the mesenchymal stem cells.

3T3 Cells↗

PubMed2000

Antibodies eluted from acutely rejected renal allografts bind to and activate human endothelial cells.

This study was designed to investigate how antiendothelial antibodies (EAbs) are involved in acute irreversible renal graft rejection. Eluates from 25 renal allografts, lost by irreversible rejection (n = 22) and by renal vein thrombosis (controls n = 3), were tested against a panel of cultured human umbilical vein endothelial cells (HUVEC). All patients were under immunosuppression at the time of nephrectomy. EAbs binding and membrane expression of adhesion molecules ELAM-1 and VCAM-1 were analyzed by flow cytometry (FACS) and by semiquantitative RT-PCR for mRNAs coding for those molecules. The absence of anti-HLA antibodies against the donor was ascertained at transplant, and before and after nephrectomy by the negativity of specific crossmatches performed using the most sensitive techniques. EAbs eluted from eight rejected kidneys bound to HUVEC. They did not induce any cytotoxicity, but their incubation with HUVEC (4 h at 37 degrees C; 2.5 mg/ml) led to upregulation of mRNAs coding for VCAM-1 (35- to 60-fold increases) and ICAM-1 (8- to 12-fold increases) as compared with control EAbs. Membrane expression of adhesion molecules was also strikingly increased, with 80% of the cells expressing VCAM-1 and 65% expressing ELAM-1 upon incubation. EAbs were detected in eight out of nine (88.8%) eluates from kidneys lost from acute vascular rejection, but in none of the 13 (0.0%) kidneys lost from other types of rejection (p < 0.0001). We conclude that EAbs, capable of activating human endothelial cells, can be recovered from acutely rejected kidneys and may play a direct role in the pathogenesis of acute rejection.

Acute Disease↗

PubMed2000

An efficient and stereoselective synthesis of xerulin via Pd-catalyzed cross coupling and lactonization featuring (E)-lodobromoethylene as a novel two-carbon synthon.

[structure: see text] Xerulin, an inhibitor of cholesterol biosynthesis, has been synthesized from commercially available (E)-1-bromopropene, acetylene, and propynoic acid in five steps (longest linear sequence) in 30% overall yield and >96% stereoselectivity. The preparation of (E)-iodobromoethylene and its use in the Pd-catalyzed cross coupling are two of the novel aspects of the synthesis reported herein.

Anticholesteremic Agents↗

PubMed2000

Genital tract human immunodeficiency virus type 1 (HIV-1) shedding and inflammation and HIV-1 env diversity in perinatal HIV-1 transmission.

This study sought to identify genital tract characteristics associated with vertical transmission of human immunodeficiency virus type 1 (HIV-1). HIV-1 DNA and RNA, HIV-1 env diversity, and inflammatory cells were quantified in cervicovaginal lavages (CVLs) of 24 women enrolled in the Women and Infants Transmission Study; 7 women transmitted HIV-1 perinatally. Vaginal candidiasis, HIV-1 culture positivity, levels of HIV-1 DNA and cell-free RNA, and HIV-1 env diversity were significantly higher in the CVLs of transmitters. CVL HIV-1 DNA levels correlated with higher levels of inflammatory cells and cell-free HIV-1 RNA. Of subjects with paired blood and CVL specimens, there was more HIV-1 env heterogeneity between blood and CVLs in transmitters than in nontransmitters. In summary, increased HIV-1 shedding is correlated with a more complex population of HIV-1 quasispecies in the genital tracts of parturient women, which may increase the probability that a fetotropic strain is transmitted.

Cervix Uteri↗

PubMed2000

Purification, characterization, and molecular cloning of the gene of a seed-specific antimicrobial protein from pokeweed.

A small cysteine-rich protein with antimicrobial activity was isolated from pokeweed (Phytolacca americana) seeds and purified to homogeneity. The protein inhibits the growth of several filamentous fungi and gram-positive bacteria. The protein was highly basic, with a pI higher than 10. The entire amino acid sequence of the protein was determined to be homologous to antimicrobial protein (AMP) from Mirabilis jalapa. The cDNA encoding the P. americana AMP (Pa-AMP-1) and chromosomal DNA containing the gene were cloned and sequenced. The deduced amino acid sequence shows the presence of a signal peptide at the amino terminus, suggesting that the protein is synthesized as a preprotein and secreted outside the cells. The chromosomal gene shows the presence of an intron located within the region encoding the signal peptide. Southern hybridization showed that there was small gene family encoding Pa-AMP. Immunoblotting showed that Pa-AMP-1 was only present in seeds, and was absent in roots, leaves, and stems. The Pa-AMP-1 protein was secreted into the environment of the seeds during germination, and may create an inhibitory zone against soil-borne microorganisms. The disulfide bridges of Pa-AMP-1 were identified. The three-dimensional modeling of Pa-AMP-1 indicates that the protein has a small cystine-knot folding, a positive patch, and a hydrophobic patch.

Amino Acid Sequence↗

PubMed2000

Structure of xylose isomerase from Streptomyces diastaticus no. 7 strain M1033 at 1.85 A resolution.

The structure of xylose isomerase (XyI) from Streptomyces diastaticus No. 7 strain M1033 (SDXyI) has been refined at 1.85 A resolution to conventional and free R factors of 0.166 and 0.219, respectively. SDXyI was crystallized in space group P2(1)2(1)2, with unit-cell parameters a = 87.976, b = 98.836, c = 93.927 A. One dimer of the tetrametric molecule is found in each asymmetric unit. Each monomer consists of two domains: a large N-terminal domain (residues 1-320), containing a parallel eight-stranded alpha/beta barrel, and a small C-terminal loop (residues 321-387), containing five helices linked by random coil. The four monomers are essentially identical in the tetramer, possessing non-crystallographic 222 symmetry with one twofold axis essentially coincident with the crystallographic twofold axis in the space group P2(1)2(1)2, which may explain why the diffraction pattern has strong pseudo-I222 symmetry even at medium resolution. The crystal structures of XyIs from different bacterial strains, especially from Streptomyces, are similar. The alpha2 helix of the alpha/beta barrel has a different position in the structures of different XyIs. The conformation of C-terminal fragment 357-364 in the SDXyI structure has a small number of differences to that of other XyIs. Two Co(2+) ions rather than Mg(2+) ions exist in the active site of the SDXyI structure; SDXyI seems to prefer to bind Co(2+) ions rather than Mg(2+) ions.

Aldose-Ketose Isomerases↗

PubMed2000

The effects of recombinant RA538 and antisense c-myc adenovirus on tumor cells and the molecular mechanism concerned.

OBJECTIVE: Compare the biological effects of recombinant RA538 and antisense c-myc adenovirus on human gastric cancer cell line (SGC7901) and explore the molecular mechanism in vitro and in vivo. METHODS: SGC7901 cells were treated with Ad-RA538, Ad-AS c-myc or Ad-LacZ. MTT, DNA ladder, TUNEL and FCM, RT-PCR, Western blot analysis, the tumorigenicity in nude mice and experimental therapy of the nude mice were used. RESULTS: Ad-RA538 and Ad-ASc-myc could strongly inhibit cell growth and induce apoptosis of SGC7901 cells. The growth of the Ad-RA538- and Ad-ASc-myc-infected SGC7901 cells were inhibited by 76.3% and 44.1% respectively. The over expression of RA538 and ASc-myc could down-regulate expression of c-myc, bcl-2 and cyclinD1 gene and up-regulate expression of bax gene, but it could not regulate expression of p53, p16, TGase, and ras gene. The tumorigenicity of Ad-RA538 or Ad-ASc-myc in nude mice showed that three of three mice failed to form tumor, compared with Ad-LacZ and parent SGC7901 cells from 7 to 30 days. Experimental therapy of the nude mice bearing subcutaneous tumor of SGC7901 cells showed that intratumor instillation of Ad-RA538 and Ad-ASc-myc inhibited the growth of the tumors. Ad-RA538- and Ad-ASc-myc-treated tumors were inhibited by 60.7% or 68.9% respectively, compared with the tumor injected with Ad-LacZ and mock. CONCLUSION: The expression of Ad-RA538 and Ad-ASc-myc can inhibit growth and induce apoptosis of gastric cancer cell in vitro and in vivo. RA538 and ASc-myc relate to c-myc, bcl-2, cyclinD1 and bax gene closely and have noticeable biologic effects on gastric cancer cells.

Adenoviridae↗

PubMed1999

The CTLA-4 gene is associated with multiple sclerosis.

We have investigated whether three intragenic polymorphisms of the CTLA-4 gene, a C/T base exchange in the promoter (p.-318), an A/G substitution in exon 1 (p.49) and a dinucleotide repeat polymorphism in exon 4 (p.642), were associated with genetic susceptibility to multiple sclerosis (MS). We observed a significant association (p < 0.05) for homozygosity for the G49 allele in a case-control analysis of 378 MS patients and 237 controls, and a transmission disequilibrium (p < 0.02) for the G49 allele in 31 MS families. This was further corroborated by evidence for linkage by the affected pedigree member (APM) analysis (p < 0.0002) and a transmission distortion (p < 0.05) of the exon 4(642) polymorphism. Sequencing of the promoter, the first and second exons and the parts of the first intron revealed no further polymorphisms. Our results suggest that a dysregulation of CTLA-4-driven downregulation of T-cell activation could be involved in the pathogenesis of MS.

Abatacept↗

PubMed1999

Characterization of peroxidase:anti-peroxidase immune complexes by capillary zone electrophoresis and high-performance size-exclusion chromatography.

Determination of the molecular constituents of commercial peroxidase:anti-peroxidase (PAP) preparations is necessary for the proper interpretation of PAP applications based on competitive binding assay. Capillary zone electrophoresis with field 300 V/cm, 40 cm capillary length (20 cm effective length), and high-performance size exclusion chromatography equipped with Superose 12 HR10/30 column revealed that a PAP preparation used for Fc gamma receptor studies contained multiple sizes of immune complexes, an excess amount of free peroxidase, and little or no free anti-peroxidase antibody. The antibody:antigen ratios of the three major immune complex components were 2:2, 1:2, and 1:1. These techniques provide useful methods of qualitative, as well as quantitative analysis of PAP preparations.

Antigen-Antibody Complex↗

PubMed1999

Dielectrophoresis of human red cells in microchips.

The dielectric properties of human red cells are strongly affected by the applied electric field, especially the frequency. Under the high frequency, the cells are acted on by positive dielectrophoresis (DEP) force and move to the tip region of the interdigitated electrode where the electric field is strongest. The cells are acted on by negative DEP force and aggregated in the "bay" zone between the neighboring electrode castellation tips and the surface of the electrodes. The patterns formed by DEP force are identical with the distribution of the electric field.

Electrodes↗

PubMed1999

Immune complex size and complement regulate cytokine production by peripheral blood mononuclear cells.

We have previously shown that immune complexes isolated from children with juvenile rheumatoid arthritis are heterogeneous in their size, composition, and proinflammatory capacities. The experiments described here were undertaken to clarify further the roles of size and composition in determining the proinflammatory effects of immune complexes. We incubated peripheral blood mononuclear cells (PBMCs) with different soluble immune complex preparations: opsonized complexes, which were formed in the presence of serum, unopsonized complexes, which were formed in the absence of serum, and immune precipitates solubilized by complement after their formation. ELISA assays showed that immune complexes formed in the presence of complement were less efficient than unopsonized complexes in inducing IL-1beta and IL-8 secretion from leukocytes. Solubilized immune precipitates showed intermediate capacity to stimulate the release of both cytokines. Complexes formed in heat-inactivated serum were as efficient as unopsonized complexes in eliciting cytokine secretion from the cells. The capacity of complement to regulate cytokine secretion from leukocytes was related, at least in part, to immune complex size. Sucrose density gradients showed unopsonized complexes and solubilized immune precipitates were larger than opsonized immune complexes. In contrast, fluid-phase binding of C4 to immune complexes, which did not appreciably change immune complex size, substantially increased IL-1beta secretion from PBMC.

Antigen-Antibody Complex↗

PubMed1999

Tropomyosin positions in regulated thin filaments revealed by cryoelectron microscopy.

Past attempts to detect tropomyosin in electron micrograph images of frozen-hydrated troponin-regulated thin filaments under relaxing conditions have not been successful. This raised the possibility that tropomyosin may be disordered on filaments in the off-state, a possibility at odds with the steric blocking model of muscle regulation. By using cryoelectron microscopy and helical image reconstruction we have now resolved the location of tropomyosin in both relaxing and activating conditions. In the off-state, tropomyosin adopts a position on the outer domain of actin with a binding site virtually identical to that determined previously by negative staining, although at a radius of 3.8 nm, slightly higher than found in stained filaments. Molecular fitting to the atomic model of F-actin shows that tropomyosin is localized over sites on actin subdomain 1 required for myosin binding. Restricting access to these sites would inhibit the myosin-cross-bridge cycle, and hence contraction. Under high Ca(2+) activating conditions, tropomyosin moved azimuthally, away from its blocking position to the same site on the inner domain of actin previously determined by negative staining, also at 3.8 nm radius. These results provide strong support for operation of the steric mechanism of muscle regulation under near-native solution conditions and also validate the use of negative staining in investigations of muscle thin filament structure.

Actins↗

PubMed1999

Experimental analysis of distortion of magnetoencephalography signals by the skull.

OBJECTIVES: Magnetoencephalography (MEG) signals are, on theoretical grounds, thought to be relatively undistorted by the skull in contrast to electroencephalographic (EEG) signals. This assumption was experimentally tested in an animal preparation with a brain similar to the human brain in many respects. METHODS: Possible skull effects on MEG were evaluated directly using an in vivo porcine preparation, by measuring the somatic evoked magnetic field (SEF) above the skull with and without the skull under, otherwise, the same condition. RESULTS: The SEF was virtually undistorted by the skull with no obvious visible change in its waveform and amplitude under these two conditions. However, there was some small, but significant attenuation when the skull was removed, the distortion being greater for deeper sources. CONCLUSION: Our results are consistent with a theoretical expectation that the skull should be virtually 'transparent' to the magnetic fields for shallow sources, but less so for fields generated by deeper sources.

Animals↗

PubMed1999

Comparison of MEG and EEG on the basis of somatic evoked responses elicited by stimulation of the snout in the juvenile swine.

OBJECTIVE: Some basic characteristics of magnetoencephalographic (MEG) and electroencephalographic (EEG) signals were studied by comparing somatic evoked fields (SEFs) and potentials (SEPs) elicited by electrical stimulations of different areas of the snout in piglets. METHODS: SEFs were measured with and without an intact skull, whereas SEPs were measured on the skull and cortex (Electrocorticograms - ECoG) and within the cortex of the same animal. RESULTS: The SEFs above the skull and dura were very similar to each other in temporal waveform and spatial topography, indicating small effects of the skull. They both revealed very similar somatotopic projections of the snout. The SEPs on the skull and cortex were, in contrast, clearly different in their amplitudes as well as temporal and spatial morphologies, indicating significant effects of the skull. However, an early component of the SEP on the skull revealed a somatotopic representation of the snout, indicating that EEG can be also useful for inferring cortical projection areas. Discrepancies in their maps were due to predominance of the potentials produced by currents in the gyral cortex. The projection sites inferred from SEFs were quite accurate in comparison to those inferred from ECoGs and intracortical SEPs. CONCLUSION: The similarities and differences clearly point out the complementary nature of MEG and EEG.

Animals↗

PubMed1999

Microscopic evidence against HIV-1 infection of germ cells or attachment to sperm.

For a number of years we have intensively investigated the localization of HIV-1 in male genital tract tissues and secretions using a variety of microscopy techniques including immunocytochemistry, in situ hybridization, in situ PCR and electron microscopy. Our studies have failed to demonstrate an association between HIV-1 and either testicular germ cells or spermatozoa. In this article we present our results in the context of other related studies, and discuss the strengths and weaknesses of the techniques that have been used to address this important research question.

HIV Infections↗

PubMed1999

The up-regulation of endosomal-lysosomal components in amyloid beta-resistant cells.

The abundance of amyloid beta peptide (A beta) and the selective loss of neurons are characteristics of Alzheimer's disease. However, subpopulations of brain cells survive, including neurons near A beta-rich plaques. The surviving neurons may have gene expression profiles that allow them to be resistant to A beta toxicity. Here we use the differential display technique to compare the profiles of gene expression in an A beta-resistant cell line with its parental cells. Prominent among the changes are two components of the endosomal-lysosomal system, insulin growth factor II receptor/mannose-6-phosphate receptor and arylsulfatase B. Both are more highly expressed in the A beta-resistant clone, and arylsulfatase is inducible by A beta and hydrogen peroxide. Another lysosomal enzyme, beta-glucuronidase, is also up-regulated in A beta-resistant cells. These results are consistent with the observation that the endosomal-lysosomal system is highly activated in Alzheimer's disease brains, and they raise the possibility that the high expression of endosomal-lysosomal components is important for neuronal survival in the presence of A beta.

Amyloid beta-Peptides↗