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921.
Most research on the study of associations among paired failuretimes has either assumed time invariance or been based on complexmeasures or estimators. Little has accommodated competing risks.This paper targets the conditional cause-specific hazard ratio,henceforth called the cause-specific cross ratio, a recent modificationof the conditional hazard ratio designed to accommodate competingrisks data. Estimation is accomplished by an intuitive, nonparametricmethod that localizes Kendall's tau. Time variance is accommodatedthrough a partitioning of space into bins betweenwhich the strength of association may differ. Inferential proceduresare developed, small-sample performance is evaluated, and themethods are applied to the investigation of familial associationin dementia onset. 相似文献
922.
表达HIV壳体蛋白转基因枸杞悬浮细胞的培养与鉴定 总被引:3,自引:0,他引:3
枸杞是我国珍贵的中药材,利用枸杞作为转基因材料具有易于遗传操作,生物性状稳定的优点。将携有人类免疫缺陷病毒I型(HIV-1)壳体蛋白基因的植物表达载体导入根瘤农杆菌EHA105中,并通过农杆菌侵染枸杞叶片,诱导产生抗性愈伤组织,利用抗性愈伤组织作为材料进行悬浮细胞的培养并对转基因枸杞悬浮细胞鉴定。PCR结果表明已获得遗传转化的转基因枸杞悬浮细胞系。免疫组织化学检测结果表明HIV壳体蛋白已在转基因枸杞悬浮细胞中表达。 相似文献
923.
Forced dissociation of selectin-ligand bonds is crucial to such biological processes as leukocyte recruitment, thrombosis formation, and tumor metastasis. Although the bond rupture has been well known at high loading rate rf (≥102 pN/s), defined as the product of spring constant k and retract velocity v, how the low rf (<102 pN/s) or the low k regulates the bond dissociation remains unclear. Here an optical trap assay was used to quantify the bond rupture at rf ≤ 20 pN/s with low k (∼10−3-10−2 pN/nm) when P-selectin and P-selectin glycoprotein ligand 1 (PSGL-1) were respectively coupled onto two glass microbeads. Our data indicated that the bond rupture force f retained the similar values when rf increased up to 20 pN/s. It was also found that f varied with different combinations of k and v even at the same rf. The most probable force, f*, was enhanced with the spring constant when k < 47.0 × 10−3 pN/nm, indicating that the bond dissociation at low rf was spring constant dependent and that bond rupture force depended on both the loading rate and the mechanical compliance of force transducer. These results provide new insights into understanding the P-selectin glycoprotein ligand 1 bond dissociation at low rf or k. 相似文献
924.
Tan TL Fang N Neo TL Singh P Zhang J Zhou R Koh CG Chan V Lim SG Chen WN 《Biochimica et biophysica acta》2008,1783(3):360-374
Hepatitis B virus (HBV) is a causative agent for liver diseases including hepatocellular carcinoma. Understanding its interactions with cellular proteins is critical in the elucidation of the mechanisms of disease progression. Using a cell-based HBV replication system, we showed that HBV replication in HepG2 cells resulted in a cellular morphological changes displaying membrane rufflings and lamellipodia like structures reminiscent of cells expressing constitutively activated Rac1. We also showed that activated Rac1 resulted in increased viral replication. HBV replication specifically activated wild type Rac1, but not Cdc42. The Rac1 activation by HBV replication also resulted in the phosphorylation of ERK1/2 and AKT, the downstream targets of Rac1 signaling cascade. The smallest HBV viral protein, HBX, was able to activate the endogenous Rac1 and induce membrane ruffling when transfected into cells. Significantly, HBX was found to directly interact with a Rac1 nucleotide exchange factor (betaPIX) through a SH3 binding motif. Taken together, we have shown the interaction of HBV with the Rho GTPase, affecting cell morphology through the Rac1 activation pathway. HBV may possibly make use of an activated Rac1 signaling pathway for increased replication and resultant metastatic effects. 相似文献
925.
Adhesion of lactobacilli to the host gastrointestinal (GI) tract is considered an important factor in health-promoting effects. However, studies addressing the molecular mechanisms of the adhesion of lactobacilli to the host GI tract have not yet been performed. The aim of this work was to identify Lactobacillus reuteri surface molecules mediating adhesion to intestinal epithelial cells and mucins. Nine strains of lactobacilli were tested for their ability to adhere to human enterocyte-like HT-29 cells. The cell surface proteins involved in the adhesion of Lactobacillus to HT-29 cells and gastric mucin were extracted. The active fractions were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting with horseradish peroxidase-labeled mucin and NHS-Biotin-labeled HT-29 cells. Furthermore, tandem mass spectrometry analysis was performed to identify the surface protein that participates in adhesion. It was shown that the ability of lactobacilli to adhere to HT-29 cells in vitro varied considerably among different strains. The most adhesive strain was the chicken intestinal tract isolate Lactobacillus reuteri JCM1081 (495.07 +/- 80.03 bacterial cells/100 HT-29 cells). The adhesion of L. reuteri JCM1081 to HT-29 cells appeared to be mediated by a cell surface protein, with an approximate molecular mass of 29 kDa. The peptides generated from the 29-kDa protein significantly matched the Lr0793 protein sequence of L. reuteri strain ATCC55730 (~71.1% identity) and displayed significant sequence similarity to the putative ATP-binding cassette transporter protein CnBP. 相似文献
926.
McAllister SE Ashrafpour H Cahoon N Huang N Moses MA Neligan PC Forrest CR Lipa JE Pang CY 《American journal of physiology. Regulatory, integrative and comparative physiology》2008,295(2):R681-R689
We tested our hypothesis that postischemic conditioning (PostC) is effective in salvage of ischemic skeletal muscle from reperfusion injury and the mechanism involves inhibition of opening of the mitochondrial permeability transition pore (mPTP). In bilateral 8x13 cm pig latissimus dorsi muscle flaps subjected to 4 h ischemia, muscle infarction increased from 22+/-4 to 41+/-1% between 2 and 24 h reperfusion and remained unchanged at 48 (38+/-6%) and 72 (40+/-1%) h reperfusion (P<0.05; n=4 pigs). PostC induced by four cycles of 30-s reperfusion/reocclusion at the onset of reperfusion after 4 h ischemia reduced muscle infarction from 44+/-2 to 22+/-2% at 48 h reperfusion. This infarct protective effect of PostC was mimicked by intravenous injection of the mPTP opening inhibitor cyclosporin A or NIM-811 (10 mg/kg) at 5 min before the end of 4 h ischemia and was abolished by intravenous injection of the mPTP opener atractyloside (10 mg/kg) at 5 min before PostC (P<0.05; n=4-5 pigs). PostC or intravenous cyclosporin A injection at 5 min before reperfusion caused a decrease in muscle myeloperoxidase activity and mitochondrial free Ca2+ concentration and an increase in muscle ATP content after 4 h ischemia and 2 h reperfusion compared with the time-matched controls. These effects of PostC were abolished by intravenous injection of atractyloside at 5 min before PostC (P<0.05; n=6 pigs). These observations support our hypothesis that PostC is effective in salvage of ischemic skeletal muscle from reperfusion injury and the mechanism involves inhibition of opening of the mPTP. 相似文献
927.
The dynamics of nitric oxide (NO) and peroxynitrite concentration changes during brain ischemia/reperfusion are poorly understood.
In this paper, a NO-selective sensor was used to measure NO concentration changes in the rat brain hippocampus during global
brain ischemia/reperfusion. Four-vessel occlusion model of transient global brain ischemia was used. Global cerebral ischemia
was induced by occluding both common carotid arteries with artery nips (for 20 min) and reperfusion was induced by loosening
the artery nips. Results showed that the changes of NO concentration during global brain ischemia/reperfusion could be divided
into different stages. Together with the effects of O2 tension changes and NO synthase (NOS) on nitric oxide levels, we determined five stages in the NO concentration profile:
(1) acute O2-limited decrease stage; (2) O2-limited steady stage; (3) neuronal NOS activation stage; (4) acute O2-recovery elevation stage; and (5) O2-recovery steady stage. In addition, a chemical reaction network model was constructed to simulate the dynamics of peroxynitrite
during the reperfusion stage, and the effects of a change in the NO formation rate on the dynamics of peroxynitrite were investigated
specifically. Results show the rate of NO formation has a great influence on peroxynitrite dynamics. 相似文献
928.
Commercial trade in wildlife is the major cause of species endangerment and a main threat to animal welfare in China and its
neighboring countries. Driven by consumptive use for food and traditional medicine, the large volume of both legal and illegal
trade in wildlife has caused great destruction to ecosystems and pushed many species to the brink of extinction. Data gathered
from trading hubs at ports, boundary markets, city markets and stores, indicates the large amount of wildlife traded in the
region of Guangxi, Yunnan and Qinghai provinces, a direct result of the numerous wildlife markets available. In a survey distributed
in various trading places, while about half of the respondents agreed that wildlife should be protected, 60% of them had consumed
wildlife at some point in the last 2 years. The results also indicated that law and regulation on wildlife trade control is
insufficient. Wildlife trade controls are very limited because of bias on the utilization of wildlife as a natural resource
to be exploited by the government agencies. The survey also shows that the current situation of wildlife consumption in key
cities in China is serious, especially the consumption for food. The main consumption groups in China are male and young people
with high education levels and good incomes. The key in public awareness publicity and education is to give them more information
on the negative impacts of wildlife consumption and knowledge of protection. 相似文献
929.
930.
Jian-Feng LI Robert QI Liang-Hu QU Autar K Mattoo Ning LI 《植物学报(英文版)》2005,47(11):1352-1363
1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) is the principal enzyme in phytohormone ethylene biosynthesis. Previous studies have shown that the hypervariable C-terminus of ACS is proteolytically processed in vivo. However, the protease responsible for this has not yet been identified. In the present study, we investigated the processing of the 55-kDa full-length tomato ACS (LeACS2) into 52-, 50- and 49-kDa truncated isoforms in ripening tomato (Lycopersicon esculentum Mill. cv. Cooperation 903) fruit using the sodium dodecyl sulfate-boiling method. Meanwhile, an LeACS2-processing protease was purified via multi-step column chromatography from tomato fruit. Subsequent biochemical analysis of the 64-kDa purified protease revealed that it is a metalloprotease active at multiple cleavage sites within the hypervariable C-terminus of LeACS2. N-terminal sequencing and matrix-assisted laser desorption/ionization time-of-flight analysis indicated that the LeACS2-processing metalloprotease cleaves at the C-terminal sites Lys^438, Glu^447, Lys^448, Asn^456, Ser^460, Ser^462, Lys^463, and Leu^474, but does not cleave the N- terminus of LeACS2. Four C-terminus-deleted (26-50 amino acids) LeACS2 fusion proteins were overproduced and subjected to proteolysis by this metalloprotease to identify the multiple cleavage sites located on the N-terminal side of the phosphorylation site Ser^460. The results indisputably confirmed the presence of cleavage sites within the region between the α-helix domain (H14) and Ser^460 for this metalloprotease. Furthermore, the resulting C-terminally truncated LeACS2 isoforms were active enzymatically. Because this protease could produce LeACS2 isoforms in vitro similar to those detected in vivo, it is proposed that this metalloprotease may be involved in the proteolysis of LeACS2 in vivo. 相似文献