Biomedical subjects

Z Yang

Publications and source records attributed to Z Yang.

At least 145 records · Page 8Linked to original sources

PubMed2001

Crystal structure studies on fibrinogen and fibrin.

X-ray crystallography studies on fragments D and double-D from human fibrinogen and fibrin have revealed the details of knob-hole interactions between fibrin units, as well as the nature of the association at their ends. More recently, a lower-resolution structure of native chicken fibrinogen has provided details about the structure of the central domain, and particularly the arrangement of disulfide bonds. Parts of the fibrinogen molecule are so flexible that they have not been visualized in electron density maps. The elusive regions include the alpha C domain, the amino-terminal segments of the alpha and beta chains, and the carboxyl-terminal segments of the gamma chains. Nonetheless, when all the structural data are considered together, it is possible to construct a realistic model not only of a fibrinogen molecule but also of a fibrin protofibril.

Crystallography, X-Ray↗

PubMed2001

Functional analysis of mouse kinesin motor Kif3C.

Members of the kinesin II family are thought to play essential roles in many types of intracellular transport. One distinguishing feature of kinesin II is that it generally contains two different motor subunits from the Kif3 family. Three Kif3 family members (Kif3A, Kif3B, and Kif3C) have been identified and characterized in mice. Intracellular localization and biochemical studies previously suggested that Kif3C is an anterograde motor involved in anterograde axonal transport. To understand the in vivo function of the Kif3C gene, we used homologous recombination in embryonic stem cells to construct two different knockout mouse strains for the Kif3C gene. Both homozygous Kif3C mutants are viable, reproduce normally, and apparently develop normally. These results suggest that Kif3C is dispensable for normal neural development and behavior in the mouse.

Animals↗

PubMed2001

Arsenic trioxide is a potent inhibitor of the interaction of SMRT corepressor with Its transcription factor partners, including the PML-retinoic acid receptor alpha oncoprotein found in human acute promyelocytic leukemia.

The SMRT corepressor complex participates in transcriptional repression by a diverse array of vertebrate transcription factors. The ability to recruit SMRT appears to play a crucial role in leukemogenesis by the PML-retinoic acid receptor alpha (RARalpha) oncoprotein, an aberrant nuclear hormone receptor implicated in human acute promyelocytic leukemia (APL). Arsenite induces clinical remission of APL through a incompletely understood mechanism. We report here that arsenite is a potent inhibitor of the interaction of SMRT with its transcription factor partners, including PML-RARalpha. Arsenite operates, in part, through a mitogen-activated protein (MAP) kinase cascade culminating in phosphorylation of the SMRT protein, dissociation of SMRT from its nuclear receptor partners, and a relocalization of SMRT out of the nucleus into the cytoplasm of the cell. Conversely, inhibition of this MAP kinase cascade attenuates the effects of arsenite on APL cells. Our results implicate SMRT as an important biological target for the actions of arsenite in both normal and neoplastic cells.

Animals↗

PubMed2001

Molecular cloning and functional analysis of mouse C-terminal kinesin motor KifC3.

Proteins of the kinesin superfamily define a class of microtubule-dependent motors that play crucial roles in cell division and intracellular transport. To study the molecular mechanism of intracellular transport involving microtubule-dependent motors, a cDNA encoding a new kinesin-like protein called KifC3 was cloned from a mouse brain cDNA library. Sequence and secondary structure analysis revealed that KifC3 is a member of the C-terminal motor family. In contrast to other mouse C-terminal motors, KifC3 is apparently ubiquitous and may have a general role in intracellular transport. To understand the in vivo function of the KifC3 gene, we used homologous recombination in embryonic stem cells to construct knockout mouse strains for the KifC3 gene. Homozygous mutants of the KifC3 gene are viable, reproduce normally, and apparently develop normally. These results suggest that KifC3 is dispensable for normal development and reproduction in the mouse.

Amino Acid Sequence↗

PubMed2001

Functional analysis of mouse C-terminal kinesin motor KifC2.

Proteins of the kinesin superfamily define a class of microtubule-dependent motors that play crucial roles in cell division and intracellular transport. In the mouse, several kinesin motors have been characterized and are suggested to play roles in axonal and/or dendritic transport. One such kinesin is KifC2. Sequence and secondary structure analysis revealed that KifC2 is a member of the C-terminal motor family. Northern and Western blot analyses indicated that KifC2 is specifically expressed in both the central and peripheral nervous systems. The cellular locations of the KifC2 proteins were found to be mainly in neural cell bodies and dendrites but also in axons. To understand the in vivo function of the KifC2 gene, we used homologous recombination in embryonic stem cells to construct knockout mouse strains for the KifC2 gene. Homozygous KifC2 mutants were viable and reproduced normally, and their development was apparently normal. These results suggest that KifC2 is dispensable for normal neural development and behavior in the mouse.

Animals↗

PubMed2001

Absence of endogenous interleukin 10 enhances early stress response during post-ischaemic injury in mice intestine.

BACKGROUND: Interleukin 10 (IL-10) exerts a wide spectrum of regulatory activities in immune and inflammatory responses. AIMS: The aim of this study was to investigate the role of endogenous IL-10 on modulation of the early inflammatory response after splanchnic ischaemia and reperfusion. METHODS: Intestinal damage was induced by clamping the superior mesenteric artery and the coeliac trunk for 45 minutes followed by reperfusion in IL-10 deficient mice (IL-10(-/-)) and wild-type controls. RESULTS: IL-10(-/-) mice experienced a higher rate of mortality and more severe tissue injury compared with wild-type mice subjected to ischaemia and reperfusion. Splanchnic injury was characterised by massive epithelial haemorrhagic necrosis, upregulation of P-selectin and intercellular adhesion molecule 1, and neutrophil infiltration. The degree of oxidative and nitrosative damage was significantly higher in IL-10(-/-) mice than in wild-type littermates, as indicated by elevated malondialdehyde levels and formation of nitrotyrosine. Plasma levels of the proinflammatory cytokines tumour necrosis factor alpha and interleukin 6 were also greatly enhanced in comparison with wild-type mice. These events were preceded by increased immunostaining and activity of the stress regulated c-Jun NH(2) terminal kinase and activation of the transcription factor activator protein 1 in the cellular nuclei of damaged tissue. CONCLUSIONS: These data demonstrate that endogenous IL-10 exerts an anti-inflammatory role during reperfusion injury, possibly by regulating early stress related genetic response, adhesion molecule expression, neutrophil recruitment, and subsequent cytokine and oxidant generation.

Acute-Phase Reaction↗

PubMed2001

Targeted deletion of A(3) adenosine receptors improves tolerance to ischemia-reperfusion injury in mouse myocardium.

A(3) adenosine receptors (A(3)ARs) have been implicated in regulating mast cell function and in cardioprotection during ischemia-reperfusion injury. The physiological role of A(3)ARs is unclear due to the lack of widely available selective antagonists. Therefore, we examined mice with targeted gene deletion of the A(3)AR together with pharmacological studies to determine the role of A(3)ARs in myocardial ischemia-reperfusion injury. We evaluated the functional response to 15-min global ischemia and 30-min reperfusion in isovolumic Langendorff hearts from A(3)AR(-/-) and wild-type (A(3)AR(+/+)) mice. Loss of contractile function during ischemia was unchanged, but recovery of developed pressure in hearts after reperfusion was improved in A(3)AR(-/-) compared with wild-type hearts (80 +/- 3 vs. 51 +/- 3% at 30 min). Tissue viability assessed by efflux of lactate dehydrogenase was also improved in A(3)AR(-/-) hearts (4.5 +/- 1 vs. 7.5 +/- 1 U/g). The adenosine receptor antagonist BW-A1433 (50 microM) decreased functional recovery following ischemia in A(3)AR(-/-) but not in wild-type hearts. We also examined myocardial infarct size using an intact model with 30-min left anterior descending coronary artery occlusion and 24-h reperfusion. Infarct size was reduced by over 60% in A(3)AR(-/-) hearts. In summary, targeted deletion of the A(3)AR improved functional recovery and tissue viability during reperfusion following ischemia. These data suggest that activation of A(3)ARs contributes to myocardial injury in this setting in the rodent. Since A(3)ARs are thought to be present on resident mast cells in the rodent myocardium, we speculate that A(3)ARs may have proinflammatory actions that mediate the deleterious effects of A(3)AR activation during ischemia-reperfusion injury.

Adaptation, Physiological↗

PubMed2001

Adrenergic and endothelin B receptor-dependent hypertension in dopamine receptor type-2 knockout mice.

Polymorphism of the dopamine receptor type-2 (D(2)) gene is associated with essential hypertension. To assess whether D(2) receptors participate in regulation of blood pressure (BP), we studied mice in which the D(2) receptor was disrupted. In anesthetized mice, systolic and diastolic BPs (in millimeters of mercury) were higher in D(2) homozygous and heterozygous mutant mice than in D(2)+/+ littermates. BP after alpha-adrenergic blockade decreased to a greater extent in D(2)-/- mice than in D(2)+/+ mice. Epinephrine excretion was greater in D(2)-/- mice than in D(2)+/+ mice, and acute adrenalectomy decreased BP to a similar level in D(2)-/- and D(2)+/+ mice. An endothelin B (ET[B]) receptor blocker for both ET(B1) and ET(B2) receptors decreased, whereas a selective ET(B1) blocker increased, BP in D(2)-/- mice but not D(2)+/+ mice. ET(B) receptor expression was greater in D(2)-/- mice than in D(2)+/+ mice. In contrast, blockade of ET(A) and V(1) vasopressin receptors had no effect on BP in either D(2)-/- or D(2)+/+ mice. The hypotensive effect of an AT(1) antagonist was also similar in D(2)-/- and D(2)+/+ mice. Basal Na(+),K(+)-ATPase activities in renal cortex and medulla were higher in D(2)+/+ mice than in D(2)-/- mice. Urine flow and sodium excretion were higher in D(2)-/- mice than in D(2)+/+ mice before and after acute saline loading. Thus, complete loss of the D(2) receptor results in hypertension that is not due to impairment of sodium excretion. Instead, enhanced vascular reactivity in the D(2) mutant mice may be caused by increased sympathetic and ET(B) receptor activities.

Adrenergic alpha-Antagonists↗

PubMed2001

Rat osteoblast functions on the o-carboxymethyl chitosan-modified poly(D,L-lactic acid) surface.

In this study, the functions of rat osteoblasts on o-carboxymethyl chitosan-modified poly(D,L-lactic acid) (PDLLA) films were investigated in vitro. The surface characterization was measured by contact angle and electron spectroscopy for chemical analysis (ESCA). Cell adhesion and proliferation were used to assess cell behavior on the modified surface and control. The MTT assay was used to determined cell viability and alkaline phosphatase (ALP) activity was performed to evaluate differentiated cell function. Compared to the control films, cell adhesion of osteoblasts on o-carboxymethyl chitosan-modified PDLLA films was significantly higher (p < 0.05) after 6 and 8 h culture, and osteoblast proliferation was also significantly higher (p < 0.01) between 4 and 7 days. The MTT assay suggested cell viability of osteoblasts cultured on o-carboxymethyl chitosan modified PDLLA films was significantly greater (p < 0.05) than that seeded on control one, and the ALP activity of cells cultured on modified PDLLA films was significantly higher (p < 0.01) than that found on control. These results give the first evidence that o-carboxymethyl chitosan could be used to modify PDLLA surface for improving biocompatibility.

Alkaline Phosphatase↗

PubMed2001

Low molecular weight protamine (LMWP) as nontoxic heparin/low molecular weight heparin antidote (I): preparation and characterization.

Low molecular weight protamine (LMWP) appears to be a promising solution for heparin neutralization without the protamine-associated catastrophic toxic effects. The feasibility of this hypothesis was proven previously by using a peptide mixture produced from proteolytic digestion of protamine. To further examine the utility of this compound as an ultimate nontoxic protamine substitute, detailed studies on the purification and characterization of LMWP including the precise amino acid sequence, structure-function relationship, and possible mechanism were conducted. A number of LWMP fragments, composed of highly cationic peptides with molecular weights ranging from 700 to 1900 d, were prepared by digestion of native protamine with the protease thermolysin. These fragments were fractionated using a heparin affinity chromatography, and their relative binding strengths toward heparin were elucidated. Five distinct fractions were eluted at NaCl concentration ranging from 0.4 to 1.0 M and were denoted as TDSP1 to TDSP5, in increasing order of eluting ionic strength. Among these 5 fractions, TDSP4 and TDSP5 contained 3 LMWP peptide fragments, and they were found to retain the complete heparin-neutralizing function of protamine. By using a peptide mass spectrometry (MS) fingerprint mapping technique, the amino acid sequences of the microheterogeneous LMWP fragments in all these 5 elution fractions were readily identified. A typical structural scaffold made by arginine clusters in the middle and nonarginine residues at the N-terminal of the peptide sequence was observed for all these LMWP fragments. By aligning the sequences with the potency in heparin neutralization of these LMWP fragments, it was found that retention of potency similar to that of protamine required the presence of at least 2 arginine clusters in the LMWP fragments; such as the sequence of VSRRRRRRGGRRRR seen in the most potent LMWP fraction-TDSP5. The above finding was further validated by using a synthetic LMWP analogue-CRRRRRRR-and it was found that its heparin-neutralizing ability was increased by changing from a monomeric to a dimeric structure of this analogue peptide. Based on these results, the structural requirement for a compound to function as an effective heparin antidote and the possible mechanism involved in heparin neutralization were established.

Anticoagulants↗

PubMed2001

Isoform-specific transcriptional regulation by thyroid hormone receptors: hormone-independent activation operates through a steroid receptor mode of co-activator interaction.

Thyroid hormone receptors (T3Rs) are hormone-regulated transcription factors that play important roles in vertebrate homeostasis, differentiation, and development. T3Rs are synthesized as multiple isoforms that display tissue-specific expression patterns and distinct transcriptional properties. Most T3R isoforms associate with co-activator proteins and mediate transcriptional activation only in the presence of thyroid hormone. The pituitary-specific T3Rbeta-2 isoform departs from this general rule and is able to interact with p160 co-activators, and to mediate transcriptional activation in both the absence and presence of hormone. We report here that this hormone-independent activation is mediated by contacts between the unique N terminus of T3Rbeta-2 and an internal interaction domain in the SRC-1 (steroid receptor co-activator-1) and GRIP-1 (glucocorticoid receptor interacting protein 1) co-activators. These hormone-independent contacts between T3Rbeta-2 and the p160 co-activators are distinct in sequence and function from the LXXLL motifs that mediate hormone-dependent transcriptional activation and resemble instead a mode of co-activator recruitment previously observed only for the steroid hormone receptors and only in the presence of steroid hormone. Our results suggest that the transcriptional properties of the different T3R isoforms represent a combinatorial mixture of repression, antirepression, and hormone-independent and hormone-dependent activation functions that operate in conjunction to determine the ultimate transcriptional outcome.

Amino Acid Sequence↗

PubMed2001

The problems and strategy relevant to the quality management of clinical laboratories.

AIM: This study is aimed to discuss the present situation, existing problems, and relevant measures concerning the management of clinical laboratories in China. METHODS: This study was carried out through the analysis of the problems relevant to the quality management of the laboratory medicine, based on the advanced experiences of ISO and developed countries in the management of clinical laboratories. RESULTS: Many problems still remain unsolved concerning the quality management of clinical laboratories. CONCLUSION: Only legalized and standardized management guarantees the quality of clinical inspection.

Accreditation↗

PubMed2001

Culture condition-dependent senescence-like growth arrest and immortalization in rodent embryo cells.

Culture Condition-Dependent Senescence-Like Growth Arrest and Immortalization in Rodent Embryo Cells. We investigated the telomerase activity, telomere length, and replicative life span of cells from human embryos and rodent embryos (mouse, rat and Syrian hamster). We used two culture conditions for rodent embryo cells whereby the cells were plated at a density of 2 x 10(5) into a 25-cm(2) flask and subcultured every 3 days or every 10 days. We found that nearly 100% of the cultures of rodent embryo cells become immortal when they are subcultured using the 10-day culture protocol. These rodent embryo cells retain telomerase activity and long telomeres (19-50 kb) in the long-term cultures, whereas human embryo cells rapidly deplete telomerase activity associated with significant shortening of telomeres, and then they senesce. In contrast to the results from 10-day cultures, we found that some mouse cell cultures and most Syrian hamster cell cultures arrest cell growth after 13 and 29 population doublings, respectively, while retaining substantial levels of telomerase activity and experiencing no significant loss of telomeres when the cells were subcultured using the 3-day culture protocol. This growth arrest is phenotypically indistinguishable from cellular senescence. The present results suggest that in rodent cells the onset of senescence-like arrest can be activated without repression of telomerase, and that this activation pathway can be bypassed easily under certain culture conditions, such as the 10-day culture protocol.

Animals↗

PubMed2001

The effect of changes in laboratory practices on the rate of false-positive cultures for Mycobacterium tuberculosis.

CONTEXT: False-positive cultures for Mycobacterium tuberculosis have been found in nearly all DNA fingerprinting studies, but the effectiveness of interventions to reduce cross-contamination has not been evaluated. OBJECTIVE: To evaluate whether changes in laboratory policies and procedures reduced the rate of false-positive cultures. DESIGN: Retrospective study of isolates with matching DNA fingerprints. SETTING: A mycobacteriology laboratory serving an urban tuberculosis control program and public hospital system. PATIENTS: All M tuberculosis isolates processed from July 1994 to December 1999. METHODS: Isolates were fingerprinted using IS6110; pTBN12 was used to fingerprint isolates having fewer than 6 copies of IS6110. We further evaluated all patients having only one positive culture whose DNA fingerprint matched that of another isolate processed in the laboratory within 42 days. INTERVENTIONS: We changed laboratory policy to reduce the number of smear-positive specimens processed and changed laboratory procedures to minimize the risk of cross-contamination during batch processing. MAIN OUTCOME MEASURE: The rate of false-positive cultures. RESULTS: Of 13 940 specimens processed during the study period, 630 (4.5%) from 184 patients and 48 laboratory proficiency specimens grew M tuberculosis. There were no cases (0/184) of probable or definite cross-contamination, compared with the 4% rate (8/199) identified in our previous study (P =.008). We also fingerprinted a convenience sample of isolates from other laboratories in Denver; 13.6% (3/22) of these were false-positive, a rate similar to the 11.9% rate (5/42) identified for other laboratories in our previous study (P =.84). CONCLUSIONS: Laboratory cross-contamination decreased significantly after relatively simple, inexpensive changes in laboratory policies and practices. Cross-contamination continued to occur in other laboratories in Denver.

Colorado↗

PubMed2001

The effect of attenuated varicella-zoster virus on replication of HBV.

OBJECTIVE: To observe the effect of attenuated varicella-zoster virus (VZV) on replication of HBV in vitro and vivo. METHODS: The attenuated VZV were inoculated into the ducks infected with DHBV and into the cultural HepG(2) 2.2.15 cells, respectively. DHBV DNA, HBsAg and HBeAg were detected from the duck serum and cell cultural fluid by dot-blot hybridization and EIA. RESULTS: The decline of DHBV DNA in duck serum was found in two dosage groups. Compared with pre-treatment, the level of AD value in 200 pfu/kg group was significantly decreased from 1.17+/-0.29 to 0.59+/-0.45 (10 day after VZV treatment) and 0.21+/-0.21 (5 day after withdrawal of VZV)(t =3.51, 7.54, P<0.001). The level in 400 pfu/kg group was from 0.70+/-0.25 to 0.32+/-0.17 on the 5th day of withdrawal of VZV (t =3.58, P<0.01), respectively after treatment. The inhibitory rates of HBeAg and HBsAg were 61% and 33%, respectively. The effect on HBeAg seems to be more obvious than on HBsAg. CONCLUSIONS: Attenuated VZV could significantly decrease serum DHBV DNA in DHBV-infected ducks and directly inhibit the HBeAg and HBsAg secreted by 2.2.15 cells, suggesting that VZV seems to interfere or inhibit the replication of DHBV.

Animals↗

PubMed2001

Maximum likelihood analysis of adaptive evolution in HIV-1 gp120 env gene.

Every functional protein appears to have some conserved amino acids which are critically important to the basic structure and function of the protein and thus under purifying selection. Some proteins also have variable amino acids which, when changed, offer a selective advantage, and thus undergo adaptive evolution. These amino acids are also important to the structure and function of the protein, although in a different way. It seems that the selective pressure in every protein varies among sites. Maximum likelihood models developed recently for comparison of silent and replacement nucleotide substitution rates allow for variable selective pressures among amino acid sites, and provide a powerful approach to studying the evolutionary process of protein-coding genes. This paper applies the likelihood models to analyze a data set of 186 HIV-1 gp120 env gene sequences for comparison with a previous analysis of the same data set. The maximum likelihood analysis identified a number of sites under positive selection, some in the conserved regions of the protein.

Adaptation, Physiological↗

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↗

PubMed2001

[Effect of cholesterol deficiency on the membrane fluidity of Jurkat T lymphocytes].

The mechanism of cholesterol deficiency on inhibiting the proliferation of T lymphocytes was investigated on cell membrane fluidity by using fluorescence polarization measurement, 3H-TdR incorporation test and flow cytometer analysis in Jurkat cells, in order to clarify the importance of cholesterol in maintaining the normal function of lymphocytes. The results showed that cell membrane fluidity was increased, cell proliferation was inhibited and blocked on G0/G1 phase in Jurkat cells after being cultured with lovastatin (an inhibitor of rate limiting enzyme for cholesterol synthesis) for 3 days. When the cells were treated with LDL. The changes could be partially buffered. These results suggest that the change of membrane fluidity may be caused by cholesterol deficiency on the proliferation of Jurkat cells.

Anticholesteremic Agents↗