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Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 253 records · Page 14Linked to original sources
PubMed2001

Nocardia beijingensis sp. nov., a novel isolate from soil.

The taxonomic status of a soil isolate, provisionally assigned to the genus Nocardia, was established following a polyphasic study. An almost complete sequence of the 16S rDNA of the strain was determined and aligned with available sequences for nocardiae and phylogenetic trees were inferred using four tree-making algorithms. The organism was associated consistently with the type strains of Nocardia brasiliensis and Nocardia farcinica in the neighbour-joining analysis, albeit with low bootstrap values. It was also found to have chemotaxonomic and morphological properties consistent with its assignment to the genus Nocardia. The organism was readily separated from representatives of other Nocardia species by a broad range of phenotypic properties. The name proposed for the novel species is Nocardia beijingensis sp. nov. The type strain is AS4.1521T (= IFO 16342T = JCM 10666T).

Base Composition↗
PubMed2001

Bullous pemphigoid: end of the century overview.

Bullous pemphigoid (BP) was first described by Lever in 1953 as a subepidermal blistering disease. Immunohistological features of BP include dermal-epidermal junction separation with an inflammatory cell infiltrate in the upper dermis, and autoantibodies in patients' circulation and bound to the basement membrane zone (BMZ). These autoantibodies show a linear staining at the dermal-epidermal junction (DEJ) and recognize two major hemidesmosomal proteins, the BP230 (BPAG1) and BP180 (BPAG2). An IgG passive transfer mouse model of BP was developed, that recapitulates the key features of human BP. Using this in vivo model system, key cellular and molecular events leading to BP disease phenotype are identified, including IgG binding to its target, complement activation, mast cell degranulation, neutrophil infiltration and activation. Proteinases and reactive oxygen species released by neutrophils work together to damage BMZ, causing DEJ separation. T cells from BP patients show a specific proliferative response to recombinant BP180 NC16A. These NC16A-responding T lymphocytes express alpha/beta T cell receptors and CD4 memory T cell surface markers and exhibited a Th1/Th2 mixed cytokine profile. After almost a half-century of studies, we have learned a great deal about IgG-mediated tissue injury and begin to understand the autoimmune responses leading to pathogenic IgG production in BP.

Animals↗
PubMed2001

Effects of the 20-kilodalton helper protein on Cry1Ac production and spore formation in Bacillus thuringiensis.

Bacillus thuringiensis produces large amounts of various pesticidal proteins during the stationary phase. In order to achieve a high yield and form crystals, some pesticidal proteins require the presence of other proteins. Helper protein P20 is required for efficient production of both the Cyt1A and Cry11A crystal proteins in B. thuringiensis subsp. israelensis. Although full-length Cry1 protoxins are usually independent in terms of expression and crystallization in B. thuringiensis, in this study P20 significantly enhanced production of Cry1Ac protoxin (133 kDa) in an acrystalliferous and plasmid-negative strain. In the presence of P20, the yield of Cry1Ac protoxin increased 2.5-fold, and on average the resulting crystals were 1.85 microm long and 0.85 microm wide, three times the size of the crystals formed in the control lacking P20. Correspondingly, the recombinant strain that coexpressed P20 and Cry1Ac exhibited higher toxicity against Heliothis armigera larvae than the control. Furthermore, serious degradation of Cry1Ac in vivo was observed, which has seldom been reported previously. Actually, most protein was completely degraded during synthesis, and after synthesis about one-third of the expressed protoxins were degraded further before crystallization. In this process, P20 protected only nascent Cry1Ac from degradation, indicating that it acted as a molecular chaperon. In addition, spores were smaller and rounder and had a thinner exosporium layer when they were produced in the presence of P20. In summary, Cry1Ac was severely degraded during synthesis; this degradation was effectively relieved by P20, which resulted in enhanced production. Our results indicated that P20 is an effective tool for optimizing protein production in vivo.

Animals↗
PubMed2001

ChvD, a chromosomally encoded ATP-binding cassette transporter-homologous protein involved in regulation of virulence gene expression in Agrobacterium tumefaciens.

A yeast two-hybrid screen searching for chromosomally encoded proteins that interact with the Agrobacterium tumefaciens VirB8 protein was carried out. This screen identified an interaction candidate homologous to the partial sequence of a gene that had previously been identified in a transposon screen as a potential regulator of virG expression, chvD. In this report, the cloning of the entire chvD gene is described and the gene is sequenced and characterized. Insertion of a promoterless lacZ gene into the chvD locus greatly attenuated virulence and vir gene expression. Compared to that of the wild-type strain, growth of the chvD mutant was reduced in rich, but not minimal, medium. Expression of chvD, as monitored by expression of beta-galactosidase activity from the chvD-lacZ fusion, occurred in both rich and minimal media as well as under conditions that induce virulence gene expression. The ChvD protein is highly homologous to a family of ATP-binding cassette transporters involved in antibiotic export from bacteria and has two complete Walker box motifs. Molecular genetic analysis demonstrated that disruption of either Walker A box, singly, does not inactivate this protein's effect on virulence but that mutations in both Walker A boxes renders it incapable of complementing a chvD mutant strain. Constitutive expression of virG in the chvD mutant strain restored virulence, supporting the hypothesis that ChvD controls virulence through effects on virG expression.

ATP-Binding Cassette Transporters↗
PubMed2001

Identification and antimicrobial susceptibility of Alcaligenes xylosoxidans isolated from patients with cystic fibrosis.

In the past decade, potential pathogens, including Alcaligenes species, have been increasingly recovered from cystic fibrosis (CF) patients. Accurate identification of multiply antibiotic-resistant gram-negative bacilli is critical to understanding the epidemiology and clinical implications of emerging pathogens in CF. We examined the frequency of correct identification of Alcaligenes spp. by microbiology laboratories affiliated with American CF patient care centers. Selective media, an exotoxin A probe for Pseudomonas aeruginosa, and a commercial identification assay, API 20 NE, were used for identification. The activity of antimicrobial agents against these clinical isolates was determined. A total of 106 strains from 78 patients from 49 CF centers in 22 states were studied. Most (89%) were correctly identified by the referring laboratories as Alcaligenes xylosoxidans. However, 12 (11%) strains were misidentified; these were found to be P. aeruginosa (n = 10), Stenotrophomonas maltophilia (n = 1), and Burkholderia cepacia (n = 1). Minocycline, imipenem, meropenem, piperacillin, and piperacillin-tazobactam were the most active since 51, 59, 51, 50, and 55% of strains, respectively, were inhibited. High concentrations of colistin (100 and 200 microg/ml) inhibited 92% of strains. Chloramphenicol paired with minocycline and ciprofloxacin paired with either imipenem or meropenem were the most active combinations and inhibited 40 and 32%, respectively, of strains. Selective media and biochemical identification proved to be useful strategies for distinguishing A. xylosoxidans from other CF pathogens. Standards for processing CF specimens should be developed, and the optimal method for antimicrobial susceptibility testing of A. xylosoxidans should be determined.

Alcaligenes↗
PubMed2001

Cdc25B functions as a novel coactivator for the steroid receptors.

We have previously demonstrated that overexpression of Cdc25B in transgenic mice resulted in mammary gland hyperplasia and increased steroid hormone responsiveness. To address how Cdc25B enhances the hormone responsiveness in mammary glands, we showed that Cdc25B stimulates steroid receptor-dependent transcription in transient transfection assays and in a cell-free assay with chromatin templates. Surprisingly, the effect of Cdc25B on steroid receptors is independent of its protein phosphatase activity in vitro. The direct interactions of Cdc25B with steroid receptors, on the other hand, were evidenced in in vivo and in vitro assays, suggesting the potential direct contribution of Cdc25B on the steroid receptor-mediated transcription. In addition, p300/CBP-associated factor and CREB binding protein were shown to interact and synergize with Cdc25B and further enhance its coactivation activity. Thus, we have uncovered a novel function of Cdc25B that serves as a steroid receptor coactivator in addition to its role as a regulator for cell cycle progression. This dual function might likely contribute to its oncogenic action in breast cancer.

Acetyltransferases↗
PubMed2001

Mast cells play a key role in neutrophil recruitment in experimental bullous pemphigoid.

Bullous pemphigoid (BP) is an inflammatory subepidermal blistering disease associated with an IgG autoimmune response to the hemidesmosomal protein BP180. Passive transfer of antibodies to the murine BP180 (mBP180) ectodomain triggers a blistering skin disease in mice that depends on complement activation and neutrophil infiltration and closely mimics human BP. In the present study, we show that mast cells (MCs) play a crucial role in experimental BP. Wild-type mice injected intradermally with pathogenic anti-mBP180 IgG exhibited extensive MC degranulation in skin, which preceded neutrophil infiltration and subsequent subepidermal blistering. In contrast, mice genetically deficient in MCs or MC-sufficient mice pretreated with an inhibitor of MC degranulation failed to develop BP. Further, MC-deficient mice reconstituted in skin with MCs became susceptible to experimental BP. Despite the activation of complement to yield C3a and C5a, in the absence of MCs, accumulation of neutrophils at the injection site was blunted. The lack of response due to MC deficiency was overcome by intradermal administration of a neutrophil chemoattractant, IL-8, or by reconstitution of the injection sites with neutrophils. These findings provide the first direct evidence to our knowledge that MCs play an essential role in neutrophil recruitment during subepidermal blister formation in experimental BP.

Animals↗
PubMed2001

Isolation of mature spinal motor neurons and single-cell analysis using the comet assay of early low-level DNA damage induced in vitro and in vivo.

We developed an isolation technique for motor neurons from adult rat spinal cord. Spinal cord enlargements were discretely microdissected into ventral horn tissue columns that were trypsin-digested and subjected to differential low-speed centrifugation to fractionate ventral horn cell types. A fraction enriched in alpha-motor neurons was isolated. Motor neuron enrichment was verified by immunofluorescence for choline acetyltransferase and prelabeling axon projections to skeletal muscle. Adult motor neurons were isolated from naïve rats and were exposed to oxidative agents or were isolated from rats with sciatic nerve lesions (avulsions). We tested the hypothesis, using single-cell gel electrophoresis (comet assay), that hydrogen peroxide, nitric oxide, and peroxynitrite exposure in vitro and axotomy in vivo induce DNA damage in adult motor neurons early during their degeneration. This study contributes three important developments in the study of motor neurons. It demonstrates that mature spinal motor neurons can be isolated and used for in vitro models of motor neuron degeneration. It shows that adult motor neurons can be isolated from in vivo models of motor neuron degeneration and evaluated on a single-cell basis. This study also demonstrates that the comet assay is a feasible method for measuring DNA damage in individual motor neurons. Using these methods, we conclude that motor neurons undergoing oxidative stress from reactive oxygen species and axotomy accumulate DNA damage early in their degeneration.

Animals↗
PubMed2001

Branched chain amino acids activate messenger ribonucleic acid translation regulatory proteins in human skeletal muscle, and glucocorticoids blunt this action.

Branched chain amino acids (BCAA) are particularly effective anabolic agents. Recent in vitro studies suggest that amino acids, particularly leucine, activate a signaling pathway that enhances messenger ribonucleic acid translation and protein synthesis. The physiological relevance of these findings to normal human physiology is uncertain. We examined the effects of BCAA on the phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (eIF4E-BP1) and ribosomal protein S6 kinase (p70(S6K)) in skeletal muscle of seven healthy volunteers. We simultaneously examined whether BCAA affect urinary nitrogen excretion and forearm skeletal muscle protein turnover and whether the catabolic action of glucocorticoids could be mediated in part by inhibition of the action of BCAA on the protein synthetic apparatus. BCAA infusion decreased urinary nitrogen excretion (P < 0.02), whole body phenylalanine flux (P < 0.02), plasma phenylalanine concentration (P < 0.001), and improved forearm phenylalanine balance (P = 0.03). BCAA also increased the phosphorylation of both eIF4E-BP1 (P < 0.02) and p70(S6K) (P < 0.03), consistent with an action to activate the protein synthetic apparatus. Dexamethasone increased plasma phenylalanine concentration (P < 0.001), prevented the BCAA-induced anabolic shift in forearm protein balance, and inhibited their action on the phosphorylation of p70(S6K). We conclude that in human skeletal muscle BCAA act directly as nutrient signals to activate messenger ribonucleic acid translation and potentiate protein synthesis. Glucocorticoids interfere with this action, and that may be part of the mechanism by which they promote net protein catabolism in muscle.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Heat shock interferes with steroidogenesis by reducing transcription of the steroidogenic acute regulatory protein gene.

A key regulatory point in fine tuning of steroidogenesis is the synthesis of steroidogenic acute regulatory protein, which transfers cholesterol into mitochondria. Heat shock and toxic insults reduce steroidogenic acute regulatory protein, severely compromising steroid synthesis. As the molecular mechanisms for this reduction remain elusive, we tested the hypothesis that heat shock directly interferes with transcription of the steroidogenic acute regulatory protein gene. We show that, in mouse MA-10 Leydig tumor cells, heat shock caused drastic declines in (Bu)(2)cAMP-induced progesterone accumulation and steroidogenic acute regulatory protein transcript abundance. A proximal steroidogenic acute regulatory protein promoter fragment (-85 to +39) is sufficient to direct both cAMP inducibility and heat shock inhibition. Nuclear extracts from MA-10 cells displayed binding to this proximal promoter fragment as a low mobility complex in gel shift experiments. This complex disappeared in nuclear extracts taken at 5 and 10 min after initiation of heat shock and reappeared in extracts taken at 2 and 8 h. Similar low- mobility complexes formed on oligonucleotides representing the overlapping subfragments of the minimal steroidogenic acute regulatory protein promoter fragment sensitive to the heat shock effect. Extracts from heat-shocked MA-10 cells displayed reduced complex formation to each of the subfragments. We conclude that heat shock reduces progesterone synthesis, steroidogenic acute regulatory protein mRNA abundance, and steroidogenic acute regulatory protein promoter activity and disrupts binding of nuclear proteins to the proximal region of the steroidogenic acute regulatory protein promoter. Together these observations provide strong evidence for a mechanism of transcriptional inhibition in the down-regulation of steroidogenic acute regulatory protein expression by heat shock.

Animals↗
PubMed2001

Triton-X-100-modified polymer and microspheres for reversal of multidrug resistance.

Triton X-100 is a non-ionic detergent capable of reversing multidrug resistance (MDR) due to its interaction with cell membranes. However, it interacts with cells in a non-specific way, causing cytotoxicity. This work aimed to develop polymeric chemosensitizers that possess the ability to reverse MDR and lower toxic side effects. When being delivered to tumours, the polymeric chemosensitizers may also have longer retention times in tumours than the free detergent. Triton-X-100-immobilized dextran microspheres (T-MS) and inulin (T-IN) were prepared and characterized. Their cytotoxicity against multidrug-resistant Chinese hamster ovary cells (CH(R)C5) was compared with that of free Triton X-100 solutions. The in-vitro effect of the products on 3H-vinblastine accumulation by CH(R)C5 cells was determined. Both T-MS and T-IN showed a marked decrease in the cytotoxicity, as compared with free Triton solutions at equivalent concentrations. Drug accumulation by CH(R)C5 cells was increased over two fold in the presence of T-MS or T-IN. These results suggest that polymeric drug carriers with MDR-reversing capability and lower cytotoxicity may be prepared by immobilization of chemosensitizers.

Animals↗
PubMed2001

Slit proteins are not dominant chemorepellents for olfactory tract and spinal motor axons.

Members of the Slit family are large extracellular glycoproteins that may function as chemorepellents in axon guidance and neuronal cell migration. Their actions are mediated through members of the Robo family that act as their receptors. In vertebrates, Slit causes chemorepulsion of embryonic olfactory tract, spinal motor, hippocampal and retinal ganglion cell axons. Since Slits are expressed in the septum and floor plate during the period when these tissues cause chemorepulsion of olfactory tract and spinal motor axons respectively, it has been proposed that Slits function as guidance cues. We have tested this hypothesis in collagen gel co-cultures using soluble Robo/Fc chimeras, as competitive inhibitors, to disrupt Slit interactions. We find that the addition of soluble Robo/Fc has no effect on chemorepulsion of olfactory tract and spinal motor axons when co-cultured with septum or floor plate respectively. Thus, we conclude that although Slits are expressed in the septum and floor plate, their proteins do not contribute to the major chemorepulsive activities emanating from these tissues which cause repulsion of olfactory tract and spinal motor axons.

Animals↗
PubMed2001

High fat diet enhances colonic cell proliferation and carcinogenesis in rats by elevating serum leptin.

We postulated that high fat diet enhances colon cell proliferation and carcinogenesis by elevating serum leptin. To examine this possibility, the present study was conducted to investigate the effect of leptin on the growth of human colon cancer cells (HT29) and the relationship between serum leptin and colon cell proliferation and aberrant crypt foci (ACF) in the 1,2-dimethylhydrazine-treated rats fed graded levels of dietary fat for 28 days. In cell culture experiments, leptin stimulated the growth and proliferation (BrdU incorporation) of colon cancer cells and the expression of c-fos protein. In the in vivo experiments, an elevation of dietary fat caused higher serum leptin and adipose-tissue weight. Colonic cell proliferation (BrdU incorporation), c-fos protein expression and ACF were elevated with increasing dietary fat. There was a significant correlation between serum concentration of leptin and colon cell proliferation and ACF. The results suggest that the enhancement of colon cell proliferation and carcinogenesis by high fat diet is mediated through elevating serum leptin.

1,2-Dimethylhydrazine↗
PubMed2001

Primary gastric choriocarcinoma: a case report and review of the literature.

Choriocarcinoma is a rapidly invasive, widely metastatic human chorionic gonadotropin (HCG)-producing neoplasm, usually intrauterine and gestational. Primary gastric choriocarcinoma is very rare, and its pathogenesis is still uncertain. We report a case of primary gastric choriocarcinoma associated with adenocarcinoma in a 36-year-old woman. The patient presented with gastrointestinal bleeding and a gastric mass clinically suspicious of gastric adenocarcinoma. Histopathologic evaluation proved the tumor to be a choriocarcinoma, with a minor component of a poorly differentiated adenocarcinoma. The patient was treated with a standard nongestational choriocarcinoma chemotherapy regimen. An impressive initial response was evidenced by clinical reduction of the tumor volume and drop of the serum beta-HCG levels after the first cycle. However, the tumor rapidly recurred in the abdomen and disseminated to the lungs, which were documented by new elevation of serum beta-HCG levels and computed tomographic scans despite continuing with 3 more cycles of chemotherapy. The patient died 6 months after diagnosis.

Adenocarcinoma↗
PubMed2001

[Mannose-binding protein gene polymorphism influences the patterns of glomerular immune deposition in IgA nephropathy].

OBJECTIVE: To investigate the relationship between mannose-binding protein(MBP) gene codon 54 (GGC/GAC) polymorphism and the patterns of glomerular immune deposition in IgA nephropathy (IgAN) and explore its functional significance. METHODS: IgAN patients were divided into two groups according to the pattern of glomerular immune deposition. Group A included 77 patients with glomerular IgA and C3 deposits. Group AGM consisted of 70 patients with glomerular IgA, IgG, IgM, C3 and Clq deposits. One hundred and forty healthy adults were used as normal controls. MBP genotypes were investigated by PCR-RFLP. Serum MBP levels of some subjects with different genotypes were also assayed by ELISA simultaneously. RESULTS: The genotype frequency of GAC heterozygotes was significantly higher in group AGM than in group A (41.4% vs. 19.5%, P<0.01) or normal subjects (41.4% vs. 26.4%, P<0.05), while no difference was found in the distribution of MBP genotypes between group A and normal subjects. The allele frequency of GAC mutation was also higher in group AGM than in group A (0.236 vs. 0.136, P<0.05) or normal subjects (0.236 vs. 0.146, P<0.05). The variant allele (GAC) was markedly associated with group AGM (OR=1.95, 95%CI: 1.06-3.58). In both group A and group AGM, more patients carrying the variant allele had episodes of upper respiratory or gastrointestinal infections prior to the onset or exacerbation of IgAN than wild homozygotes. In addition, a significant difference in serum MBP level was also observed among the three genotypes (GGC/GGC>GGC/GAC>GAC/GAC) (P<0.0001) for all groups, while there were no differences in serum MBP levels for subjects with the same genotypes among the three groups (P>0.05). CONCLUSION: The above findings provide evidence that IgAN patients with abundant immune deposits in glomeruli show a higher frequency of MBP gene variation which is associated with a high frequency of infection and a low serum MBP level. This genetic deficiency may lead to an impaired first-line defense and a less effective clearance of immune complex than those without this mutation and thereafter accelerate glomerular immune deposition during the process of disease.

Adolescent↗
PubMed2001

[Polymorphism of MAO-B gene and NAD(P)H: quinone oxidoreductase gene in Parkinson's disease].

OBJECTIVE: To investigate whether Parkinson's disease(PD) is associated with genetic polymorphism of intron 13 of monoamine oxidase B(MAO-B) and NAD(P)H: quinone oxidoreductase(NQO1) gene cDNA 609C to T. METHODS: Association study was performed in 126 PD patients and 136 healthy control subjects matched for age, sex and origin. The NQO1 gene polymorphism was analyzed with the polymerase chain reaction-restriction fragment length polymorphism, the polymorphism of intron 13 of MAO-B was analyzed by allele- specific PCR. RESULTS: The allelic frequency of the mutant T allele of NQO1 gene was significantly higher in the PD patients as compared to the controls(P<0.05). The relative risk of suffering from PD increased (OR=3.8) in the individuals with T allelic genotype of NQO1 gene, and the odds ratio was as high as 5.7 when the individuals with A or AA genotype of MAO-B gene coexisted with the T allele genotype of NQO1 gene. CONCLUSION: The cDNA 609T allele of NQO1 gene might be a risk factor of PD, which could be associated with the genetic susceptibility of PD. The high activity A or AA genotype of MAO-B and the low activity genotype of NQO1 gene might have synergistic effect. When both genotypes coexist, the risk of suffering PD will be increased greatly.

Aged↗
PubMed2001

[Estrogenicity of black cohosh (Cimicifuga racemosa) and its effect on estrogen receptor level in human breast cancer MCF-7 cells].

The estrogenicity of Black Cohosh (Cimicifuga racemosa, CR) was tested in vivo and in vitro and its effect on estrogen receptor (ER) level of human breast cancer MCF-7 cells were investigated. Based on the body weight of animals, 75, 150 and 300 mg/kg of CR were administered by tube feeding to immature female mice for 14 days. Estrus was observed and the uterine and ovary weights of mice were measured. The optimal dose of CR for the growth of MCF-7 cells was screened by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay. Subsequently, Growth curves of MCF-7 cells in blank control, 4.75 micrograms/L of CR and 0.3 nmol/L of 17 beta-estradiol groups were observed for 5 days. ER level in MCF-7 cells was analyzed by indirect immunofluorescence assay in flow cytometry. The results showed that uterine weight increased with the increasing dosage of CR and the days of estrus was significantly prolonged in the 300 mg/kg group (P < 0.05). The concentration of CR at 4.75 micrograms/L showed the strongest enhancement effects (64.7%). The doubling time (TD) of cell growth in CR group and 17 beta-estradiol group were 32.1 h and 31.7 h respectively, which were shorter than that of blank control (TD = 35.3 h). Additionally, 4.75 micrograms/L of CR significantly increased ER levels compared with the blank control (P < 0.01). Taking all the results together, CR has an estrogen-like action. The enhancing effect of CR on ER level is one of the potential mechanisms involved with its therapeutic role in climacteric syndrome.

Animals↗