Biomedical subjects

J Xu

Publications and source records attributed to J Xu.

At least 361 records · Page 20Linked to original sources

PubMed2000

[Effects of glycidyl methacrylate on gap junctional intercellular communication].

In order to probe into the mechanism of glycidyl methacrylate (GMA)-induced cell transformation, the effects of GMA on gap junctional intercellular communication (GJIC) in human lung, embryonic fibroblasts(HLEF) were studied by using scrape-loading and dye transfer(SLDT) technique. HLEF cells were treated with GMA at concentrations of 0.5, 2.5 and 5.0 mg/L for 12 hours and Lucifer Yellow was introduced by scrape-loading after exposure. The GJIC in exposed cells and that of control were determined directly as the diffusion extent of fluorescent dye into adjacent cells. The results indicated that GMA could inhibit the GJIC in exposed cells in a dose-dependent manner. Significantly decreased GJIC was found in 2.5 and 5.0 mg/L dose groups. It was suggested that the inhibition of GJIC might be one of the mechanisms responsible for GMA-induced cell transformation.

Cell Communication↗

PubMed2000

New functions for non-collagenous domains of human collagen type IV. Novel integrin ligands inhibiting angiogenesis and tumor growth in vivo.

Collagen type IV is a major component of the basal lamina of blood vessels. Six genetically distinct collagen type IV chains have been identified and are distributed in a tissue-specific manner. Here we define a novel function for soluble non-collagenous (NC1) domains of the alpha2(IV), alpha3(IV), and alpha6(IV) chains of human collagen type IV in the regulation of angiogenesis and tumor growth. These NC1 domains were shown to regulate endothelial cell adhesion and migration by distinct alpha(v) and beta(1) integrin-dependent mechanisms. Systemic administration of recombinant alpha2(IV), alpha3(IV), and alpha6(IV) NC1 domains potently inhibit angiogenesis and tumor growth, whereas alpha1(IV), alpha4(IV), and alpha5(IV) showed little if any effect. These findings suggest that specific NC1 domains of collagen type IV may represent an important new class of angiogenesis inhibitors.

Amino Acid Sequence↗

PubMed2000

Identification of differentially expressed genes in human prostate cancer using subtraction and microarray.

We have identified human prostate cancer- and tissue-specific genes using cDNA library subtraction in conjunction with high throughput microarray screening. Subtracted cDNA libraries of prostate tumors and normal prostate tissue were generated. Characterization of subtracted libraries showed enrichment of both cancer- and tissue-specific genes. Highly redundant clones were eliminated by colony hybridization. The remaining clones were selected for microarray to determine gene expression levels in a variety of tumor and normal tissues. Clones showing overexpression in prostate tumors and/or normal prostate tissues were selected and sequenced. Here we report the identification of two genes, P503S and P504S, from subtracted libraries and a third gene, P510S, by subtraction followed by microarray screening. Their expression profiles were further confirmed by Northern blot, real-time PCR (TaqMan), and immunohistochemistry to be overexpressed in prostate tissues and/or prostate tumors. Full-length cDNA sequences were cloned, and their subcellular locations were predicted by a bioinformatic algorithm, PSORT, to be plasma membrane proteins. The genes identified through these approaches are potential candidates for cancer diagnosis and therapy.

Blotting, Northern↗

PubMed2000

Pramipexole inhibits lipid peroxidation and reduces injury in the substantia nigra induced by the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in C57BL/6 mice.

Pramipexole has been showed to protect cultured dopaminergic (DAergic) cells against free radical-induced cytotoxicity. To test if pramipexole is protective against 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-mediated nigral DAergic injury in vivo and if such protection is related to inhibition of lipid peroxidation, DAergic function and lipid peroxidation were determined in MPTP-treated C57BL/6 mice. We reported that MPTP administration induced a 38.1% increase of lipid peroxidation product thiobarbituric acid reactive substance (TBARS) in nigra, a 46.7% decrease of tyrosine hydroxylase -positive nigral DAergic neurons and a 59.4% reduction of striatal DA levels. However, pramipexole treatment significantly inhibited the TBARS production by 76%, and attenuated the MPTP-induced decreases in nigral DAergic neurons and striatal DA levels by about 50%. This study suggests that pramipexole can inhibit free radical-mediated lipid peroxidation and protect MPTP-induced nigral injury.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2000

Analysis and significance of anti-latent membrane protein-1 antibodies in the sera of patients with EBV-associated diseases.

Anti-latent membrane protein-1 (LMP-1) is an EBV-encoded type III integral membrane protein with oncogenic potential that is expressed most consistently in various EBV-associated malignancies. Unlike many other EBV proteins, LMP-1 Abs have rarely been demonstrated in EBV-associated disease conditions. We established a high level LMP-1-expressing cell clone and used it for the detection, quantitation, and characterization of these Abs in various human sera in immunoblots and ELISA. Our results demonstrate that, in contrast to the commonly held notion, LMP-1 induces significant humoral immune responses in EBV-associated malignant conditions especially in nasopharyngeal carcinoma (NPC) patients in whom >70% sera are positive for these Abs, and their titers correlate with the clinical condition of the tumors. Interestingly, anti-LMP-1 Abs of IgA isotype were found only in NPC patients. These Abs were absent from the sera of infectious mononucleosis and chronic EBV infection patients, whereas a small fraction ( approximately 5%) of the healthy, EBV-seropositive individuals were positive for them; however, their OD values were much lower than those of NPC patients. These studies demonstrate, for the first time, the potential significance of LMP-1-specific Abs for the diagnosis and prognosis of EBV-associated malignancies, especially of NPC.

Antibodies, Viral↗

PubMed2000

Metalloproteolytic release of endothelial cell protein C receptor.

Previous studies observed that there is about 100 ng/ml soluble endothelial cell protein C receptor (EPCR) in human plasma and that the levels increase in inflammatory diseases. In this study we examine the potential mechanisms involved in release of EPCR from cells. We find that EPCR is released from the surface of endothelium and transfected 293 cells by a metalloprotease in a constitutive fashion. The mass of soluble EPCR is 4 kDa less than intact EPCR. Release is blocked by either the hydroxamic acid based inhibitor, KD-IX-73-4 or by 1,10-phenanthroline, but not by matrix metalloprotease inhibitors. Release is stimulated by phorbol 12-myristate 13-acetate, thrombin, interleukin-1beta, and hydrogen peroxide. Stimulation with these agents reduces EPCR expression levels sufficiently to decrease the rate of protein C activation to a limited extent. The influence of phorbol 12-myristate 13-acetate on both EPCR release and inhibition of protein C activation are enhanced by microtubule disruption with nocodazole. EPCR release is augmented by transfection of EPCR expressing 293 cells with caveolin, suggesting that release is caveolae dependent. These studies indicate that metalloproteolytic release of EPCR is a highly regulated process that is sensitive to both coagulation factors and inflammatory mediators.

Blood Coagulation Factors↗

PubMed2000

Multistep expression and assembly of neuronal nicotinic receptors is both host-cell- and receptor-subtype-dependent.

We tested the hypothesis that the folding, assembly and insertion of neuronal nicotinic receptors are critically dependent on the host cell line. We used recombinant adenoviruses encoding either the rat alpha7, alpha4 or beta2 subunits in which expression of the subunit is controlled by a tetracycline-dependent promoter to screen five cell lines (GH4C1, SH-EP1, CV1, SN-56, and CHO-CAR). All five lines do not express detectable nicotinic receptor but do express receptor for human adenovirus, and all expressed mRNA for alpha7, alpha4 and beta2 subunits when infected with viruses. Each cell line expressed varying levels of alpha4beta2 receptors that bound [3H]cytisine, but only the GH4C1 and SH-EP1 cell lines expressed either surface or internal alpha7 receptors that bound [125I]alpha-bungarotoxin ([125I]alpha-BGT). All five cell lines expressed a 60 kDa protein immunoblotted by anti-alpha7 antibodies when infected with the alpha7 virus, presumably representing unassembled alpha7 subunits. In addition, GH4C1 cells expressed over 10-fold more surface alpha7 receptor than SH-EP1 cells, even though the total alpha7 receptor in the two cell lines was similar. Sedimentation experiments indicate that SH-EP1 cells only partially assemble alpha7 receptors compared with GH4C1 cells and control alpha7 from rat brain. These data suggest that not only is surface alpha7 receptor expression a multistep process, but that each step may involve cell-specific assembly factors.

Adenoviridae↗

PubMed2000

MSY2: a slowly evolving minisatellite on the human Y chromosome which provides a useful polymorphic marker in Chinese populations.

We present the second human Y-specific minisatellite, MSY2 (DYS440). It consists of three or four copies of a 99-110bp repeat unit and is located about 1kb upstream of the DBY gene. The most common allele contains four units, but a three-unit allele has arisen on at least four occasions; in chimpanzees and orangutans, MSY2 contains only two units. It is therefore evolving slowly and provides a particularly useful polymorphic marker for Chinese populations.

Alleles↗

PubMed2000

Isolation and expression of a novel alternatively spliced mu opioid receptor isoform, MOR-1F.

The MOR-1 gene is large, with a recent study reporting nine exons spanning 250 kb which combine to yield six different mu opioid receptor splice variants. We now report the isolation of exon 10, which is contained within yet another splice variant, MOR-1F, which is composed of exons 1, 2, 3, 10, 6, 7, 8 and 9. Exon 10 comprises 186 bp which predict a unique 58 amino acid sequence extending beyond exon 3. It has been mapped between exons 4 and 6 and has flanking consensus splice sequences. On Northern blot analysis, the MOR-1F mRNA is smaller than the other MOR-1 mRNAs. When expressed in CHO cells, MOR-1F binds the mu opioid radioligand [3H]DAMGO with high affinity (K(D) = 1.04+/-0.03 nM). Competition studies demonstrated the selectivity of the variant for mu opioid ligands, supporting its classification within the mu opioid receptor family.

Alternative Splicing↗

PubMed2000

Altered binding of mutated presenilin with cytoskeleton-interacting proteins.

The majority of familial Alzheimer's disease (AD) cases are linked to mutations on presenilin 1 and 2 genes (PS1 and PS2). The normal function of the proteins and the mechanisms underlying early-onset AD are currently unknown. To address this, we screened an expression library for proteins that bind differentially to the wild-type PS1 and mutant in the large cytoplasmic loop (PS1L). Thus we isolated the C-terminal tail of the 170 kDa cytoplasmic linker protein (CLIP-170) and Reed-Sternberg cells of Hodgkin's disease-expressed intermediate filament-associated protein (Restin), cytoplasmic proteins linking vesicles to the cytoskeleton. PS1L binding to CLIP-170/restin requires Ca(2+). Treating cells with thapsigargin or ionomycin increased the mutated PS1 in CLIP-170 immunoprecipitates. Further, PS1 and CLIP-170 co-localize in transfected cells and neuronal cultures.

Alzheimer Disease↗

PubMed2000

Caspase-12 mediates endoplasmic-reticulum-specific apoptosis and cytotoxicity by amyloid-beta.

Apoptosis, or cellular suicide, is important for normal development and tissue homeostasis, but too much or too little apoptosis can also cause disease. The family of cysteine proteases, the so- called caspases, are critical mediators of programmed cell death, and thus far 14 family members have been identified. Some of these, such as caspase-8, mediate signal transduction downstream of death receptors located on the plasma membrane. Others, such as caspase-9, mediate apoptotic signals after mitochondrial damage. Stress in the endoplasmic reticulum (ER) can also result in apoptosis. Here we show that caspase-12 is localized to the ER and activated by ER stress, including disruption of ER calcium homeostasis and accumulation of excess proteins in ER, but not by membrane- or mitochondrial-targeted apoptotic signals. Mice that are deficient in caspase-12 are resistant to ER stress-induced apoptosis, but their cells undergo apoptosis in response to other death stimuli. Furthermore, we show that caspase-12-deficient cortical neurons are defective in apoptosis induced by amyloid-beta protein but not by staurosporine or trophic factor deprivation. Thus, caspase-12 mediates an ER-specific apoptosis pathway and may contribute to amyloid-beta neurotoxicity.

Alzheimer Disease↗

PubMed2000

Electron impact mass spectral fragmentation patterns of 2a,4-disubstituted 5-benzoyl-2-chloro-2a,3,4,5-tetrahydroazeto[1,2-a][1,5]benzodiazepin-1( 2H)-ones.

The mass spectrometric behaviour of six 2a,4-disubstituted 5-benzoyl-2-chloro-2a,3,4,5-tetrahydroazeto[1,2-a][1,5]benzodia zepin-1(2H)-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a chlorine atom, a chlorine atom plus benzaldehyde, benzoyl radical, chloroketene or chlorine atom plus CO and H2O molecules to yield, respectively, [M-Cl]+ ions, 2a,4-disubstituted 2a,3-dihydroazeto[1,2-a][1,5]benzodiazepin-1(2H)-one ions, [M-PhCO]+ ions, 2,4-disubstituted 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions, or 1,2,4-trisubstituted 1H-1,7-benzodiazonine ions, which could also be formed from [M-Cl]+ ions by loss of CO and H2O molecules simultaneously. The [M-Cl]+ ions could further lose benzoyl radical to form [M-Cl-PhCO]+ ions, or lose benzoyl amide and undergo a rearrangement to form 4,6-disubstituted 1-benzoazocine-2(1H)-one ions. The [M-PhCO]+ ions could eliminate NH to produce 2a,4-disubstituted 2,2a,3,4-tetrahydroazeto[1,2,-a]quinolin-1-one ions, which could further eliminate chloroketene, CO and/or HCl to produce some important ions, respectively. 2,4-Disubstituted 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions could lose benzoyl radical to yield 2,4-disubstituted 2,3-dihydro-1H-1,5-benzodiazepine ions, which could further yield other small fragment ions by loss of propene/styrene or small fragments.

Benzodiazepinones↗

PubMed2000

Electron impact mass spectral fragmentation of 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]benzothia zepin-1-ones.

The mass spectrometric behaviour of nine 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]b enzothiazepin-1-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a neutral chlorine atom, or a chloroketene, or neutral propene, or styrene or substituted styrene molecule, plus Cl and/or H (or Cl) atom(s), to yield [M-Cl]+ ions, 2,3-dihydro-1,5-benzothiazepine derivative ions, 4,5-dihydro-5H-1,5-benzothiazepin-4-one ions which can further lose CO to give 1,4-benzothiazine ions. Both molecular ions and [M-Cl]+ ions show a tendency to eliminate an ethyl or benzyl/substituted benzyl radical to produce 2,2a-dihydro-1H-azeto[2,1-c][1,4]benzothiazin-1-one ions. The [M-Cl]+ ions could undergo rearrangement to yield 2,2a-dihydro-1H-azeto[2,1-d][1,5]benzothiazepin-1-one ions, 2,2a,3,4-tetrahydro-1H-azeto[1,2-a]quinoline ions or 1,1a,2,3-tetrahydro-azirino[2,1-d][1,5]benzothiazepine ions by loss of an ethane or a benzene/substituted benzene, a SH radical or a CO molecule. The molecular ions could also undergo rearrangement reactions to form other small fragment ions.

Benzodiazepinones↗

PubMed2000

Cloning the full-length cDNA for rat connective tissue growth factor: implications for skeletal development.

The mammalian osteopetroses represent a pathogenetically diverse group of skeletal disorders characterized by excess bone mass resulting from reduced osteoclastic bone resorption. Abnormalities involving osteoblast function and skeletal development have also been reported in many forms of the disease. In this study, we used the rat mutation, osteopetrosis (op), to examine differences in skeletal gene expression between op mutants and their normal littermates. RNA isolated from calvaria and long bones was used as a template for mRNA-differential display. Sequence information for one of the many cDNA that were selectively expressed in either normal or mutant bone suggested that it is the rat homologue of connective tissue growth factor (CTGF) previously cloned in the human, mouse, and other species. A consensus sequence was assembled from overlapping 5'-RACE clones and used to confirm the rat CTGF cDNA protein coding region. Northern blot analysis confirmed that this message was highly (8- to 10-fold) over-expressed in op versus normal bone; it was also upregulated in op kidney but none of the other tissues (brain, liver, spleen, thymus) examined. In primary rat osteoblast cultures, the CTGF message exhibits a temporal pattern of expression dependent on their state of differentiation. Furthermore, CTGF expression is regulated by prostaglandin E(2), a factor known to modulate osteoblast differentiation. Since members of the CTGF family regulate the expression of specific genes, such as collagen and fibronectin, we propose that CTGF may play a previously unreported role in normal skeletal modeling/remodeling. Its dramatic over-expression in the op mutant skeleton may be secondary to the uncoupling of bone resorption and bone formation resulting in dysregulation of osteoblast gene expression and function.

Amino Acid Sequence↗

PubMed2000

The hexadentate hydroxypyridinonate TREN-(Me-3,2-HOPO) is a more orally active iron chelator than its bidentate analogue.

Bidentate hydroxypyridinone chelators effectively complex and facilitate excretion of trivalent iron. To test the hypothesis that hexadentate chelators are more effective than bidentate chelators at low concentrations, urinary and biliary Fe excretions were determined in Fe-loaded rats before and after administration of a bidentate chelator, Pr-(Me-3,2-HOPO), or its hexadentate analogue, TREN-(Me-3,2-HOPO). The bidentate chelator slightly increased biliary Fe excretion in Fe-loaded rats after IV (90 micromol/kg) and PO (90 or 270 micromol/kg) administration, but chelation efficiency did not exceed 1%. The hexadentate chelator markedly increased biliary Fe excretion, achieving overall chelation efficiencies of 14% after IV administration of 30 micromol/kg and 8 or 3% after PO (30 or 90 micromol/kg) administration. The hexadentate chelator was significantly more effective than the bidentate chelator after IV injection and oral dosing. In chelator-treated Fe-loaded or saline-injected rats, >90% of the excreted Fe was in the bile. Oral TREN-(Me-3,2-HOPO), given to non-Fe-loaded rats, did not appreciably change Fe output, indicating that there was little Fe depletion in the absence of Fe overload. These results support the hypothesis that greater Fe chelation efficiency can be achieved with hexadentate than with bidentate chelators at lower, and presumably safer, concentrations. The results also demonstrate that TREN-(Me-3, 2-HOPO) is a promising, orally effective, Fe chelator.

Animals↗

PubMed2000

Regioselective synthesis and electron impact mass spectral fragmentation differentiation of 2- or 3-isopropylthio, phenylthiosuccinic acid 4-methyl/isopropyl ethers.

2- and 3-isopropylthio/phenylthiosuccinic acid 4-methyl/isopropyl esters were synthesized regioselectively by Michael additions of isopropylthiol/thiophenol to maleic anhydride, followed by alcoholysis with methanol/isopropanol. Their mass spectrometric behavior has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate an alkoxy group, an alcohol, or an alkoxycarbonyl group from the respective molecular ion. Some molecular ions also show a tendency to eliminate a molecule of water, propene or CO(2). The [M - MeCH = CH(2)](+) ions could further lose H(2)O to form substituted succinic anhydride ions, or lose CO(2) to form 3-substituted propionic acid ions. Both of these ions could further yield other small fragment ions by loss of CO(2)H, CO or other small fragments. It has been found that 2-isopropylthio- and 3-phenylthiosuccinic acid 4-esters show more abundant [M - H(2)O](+) peaks than their 3-isopropylthio and 2-phenylthio isomers in their mass spectra.

Carboxypeptidases↗

PubMed2000

Electron impact mass spectral fragmentation of 3a,5-disubstituted 1, 3-diphenyl-3a,4,5,6-tetra-hydro-3H-1,2,4-triazolo[4,3-a][1, 5]benzo-diazepines.

The mass spectrometric behaviour of six 3a,5-disubstituted 1, 3-diphenyl-3a,4,5,6-tetrahydro-3H-1,2,4-triazolo[4,3-a][1, 5]benzodiazepines has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate (substituted) styrene molecules, aryl radicals, arylmethyl radicals or phenylnitrene (PhN:). All of the resulting fragment ions, except [M - PhN:](+.), could further undergo a reverse [2 + 3] cycloaddition. The [M - PhN:](+.) ions could further lose styrene derivatives and undergo a ring enlargement rearrangement. The molecular ions also show a tendency to eliminate a phenyl radical, and the [M - Ph](+) ions could eliminate styrene derivatives. The [M - R(1)CH = CH(2)](+.) ions could further lose NH(2) to yield stable tetracyclic 1,3-diphenyl-1,2,4-triazolo[4,3-d]phenanthridine ions, which could further lose benzonitrile, or undergo a reverse [2 + 3] cycloaddition. The molecular ions could also undergo a reverse [2 + 3] cycloaddition to produce N-phenylbenzonitrile imine ions and 2, 4-disubstituted 2,3-dihydro-1H-1,5-benzodiazepine ions, whose further fragmentations were also investigated.

Anti-Anxiety Agents↗

PubMed2000

Electron impact mass spectral studies of 2a,4-disubstituted 2-phthalimido-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1, 5]benzothiazepin-1-ones.

The mass spectrometric behaviour of seven 2a,4-disubstituted 2-phthalimido-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1, 5]benzothiazepin-1-ones has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a CO molecule, a phthalimido (PhthN) radical, or a phthalimide (PhthNH) molecule. All of the resulting fragment ions could further lose a propene or (substituted) styrene molecule. The molecular ions could also undergo a reverse [2 + 2] cycloaddition reaction.

Carbon Dioxide↗