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D X Liu

Publications and source records attributed to D X Liu.

At least 37 records · Page 2Linked to original sources
PubMed2001

The missing link in coronavirus assembly. Retention of the avian coronavirus infectious bronchitis virus envelope protein in the pre-Golgi compartments and physical interaction between the envelope and membrane proteins.

One missing link in the coronavirus assembly is the physical interaction between two crucial structural proteins, the membrane (M) and envelope (E) proteins. In this study, we demonstrate that the coronavirus infectious bronchitis virus E can physically interact, via a putative peripheral domain, with M. Deletion of this domain resulted in a drastic reduction in the incorporation of M into virus-like particles. Immunofluorescent staining of cells coexpressing M and E supports that E interacts with M and relocates M to the same subcellular compartments that E resides in. E was retained in the pre-Golgi membranes, prior to being translocated to the Golgi apparatus and the secretory vesicles; M was observed to exhibit similar localization and translocation profiles as E when coexpressed with E. Deletion studies identified the C-terminal 6-residue RDKLYS as the endoplasmic reticulum retention signal of E, and site-directed mutagenesis of the -4 lysine residue to glutamine resulted in the accumulation of E in the Golgi apparatus. The third domain of E that plays a crucial role in virus budding is a putative transmembrane domain present at the N-terminal region, because deletion of the domain resulted in a free distribution of the mutant protein and in dysfunctional viral assembly.

Amino Acid Sequence↗
PubMed2001

Characterization of a novel isoform of caspase-9 that inhibits apoptosis.

We have identified a novel isoform of rat caspase-9 in which the C terminus of full-length caspase-9 is replaced with an alternative peptide sequence. Casp-9-CTD (where CTD is carboxyl-terminal divergent) is expressed in multiple tissues, with the relative highest expression observed in ovary and heart. Casp-9-CTD was found primarily in the cytoplasm and was not detected in the nucleus. Structural predictions suggest that in contrast to full-length caspase-9, casp-9-CTD will not be processed. Our model is supported by reduced protease activity of casp-9-CTD preparations in vitro and by the lack of detectable processing of casp-9-CTD proenzyme or the induction of cell death following transfection into cells. Both neuronal and non-neuronal cell types transfected with casp-9-CTD were resistant to death evoked by trophic factor deprivation or DNA damage. In addition, cytosolic lysates prepared from cells permanently expressing exogenous casp-9-CTD were resistant to caspase induction by cytochrome c in reconstitution assays. Taken together, our observations indicate that casp-9-CTD acts as a dominant-negative variant. Its expression in various tissues indicates a physiological role in regulating cell death.

Amino Acid Sequence↗
PubMed2001

Neuronal apoptosis at the G1/S cell cycle checkpoint.

Apoptosis is a fundamental and essential process in development and tissue homeostasis of multicellular organisms. Roughly half of all the neurons produced during neurogenesis die apoptotically before the nervous system matures. Apoptosis is also involved in various neurodegenerative disorders such as Alzheimer's disease and neuronal trauma. Investigation of the mechanisms underlying neuronal apoptosis led to an unexpected discovery that in many cases revival of the quiescent and dormant cell cycle machinery is a common theme. Recent data suggest that uncoordinated expression of cell cycle molecules and the consequent breach of cell cycle checkpoints could be one of the primary mechanisms by which postmitotic neurons undergo apoptotic death. Evidence indicates that upregulation of cyclin-D-CDK4/6 activity and deregulation of E2F transcription factors mark key events in early stages of neuronal apoptosis. Active E2F repression by Rb family members is required for the survival of neurons. Apoptotic signals promote successive phosphorylation and dysfunction of Rb family members, resulting in sequential E2F derepression and expression of selective E2F-responsive genes. Thus, expression of derepressed E2F-responsive genes may be instrumental in propagating and amplifying the apoptotic signals instructing neuronal cells to carry out the apoptotic program.

Animals↗
PubMed2001

Comparison of the 5' leader sequences of North American isolates of reference and field strains of porcine reproductive and respiratory syndrome virus (PRRSV).

The 5' leader is documented to be an important regulatory element in many (+) ssRNAvirus genome. To understand the significance of the 5' leader RNA of PRRSV, we determined the complete leader sequences of fifteen different North American strains of PRRSV and predicted their secondary structures. Viruses analysed included three reference strains and nine field strains originating from different geographic locations. To further examine the leader region, one of the field strains was adapted to grow in tissue culture, and three clones were isolated. We also predicted the secondary structures of two European strains based on their published sequences. The predicted RNA secondary structures of the leader sequences suggested the existence of three conserved domains formed by the 5' region of the leader among the North American strains, two of which were conserved in the European strains. A variable structural domain was predicted from the 3' region of the leader sequences of the North American strains, where all tissue culture-adapted isolates were characterized by a stem-loop while field isolates were characterized by an internal bulge within the stem-loop.

5' Untranslated Regions↗
PubMed2001

A new hypothesis of pathogenetic mechanism of viral hepatitis B and C.

The experimental data in recent years suggest apoptosis of liver cells plays a significant role in the pathogenesis of viral hepatitis. Firstly, the number of apoptotic hepatocytes in patients with hepatitis B or C is significantly higher than healthy objects. Secondly, the expression levels of Fas antigen in hepatocytes of patients with hepatitis B or C are closely correlated with inflammation activity. Thirdly, massive apoptosis of hepatocyte will result in fulminant hepatitis, while inhibition of apoptosis can prevent inflammation in experimental model of liver injury. And finally, the occurrence of hepatitis induced by CTL in transgenic mice is a process from hepatocyte apoptosis to liver necroinflammation. This paper will examine our current understanding of the possible relationship between hepatocellular apoptosis and the pathogenetic mechanism of hepatitis B and C.

Animals↗
PubMed2001

Induction of caspase-dependent apoptosis in cultured cells by the avian coronavirus infectious bronchitis virus.

Avian coronavirus infectious bronchitis virus (IBV) is the causative agent of chicken infectious bronchitis, an acute, highly contagious viral respiratory disease. Replication of IBV in Vero cells causes extensive cytopathic effects (CPE), leading to destruction of the entire monolayer and the death of infected cells. In this study, we investigated the cell death processes during acute IBV infection and the underlying mechanisms. The results show that both necrosis and apoptosis may contribute to the death of infected cells in lytic IBV infection. Caspase-dependent apoptosis, as characterized by chromosomal condensation, DNA fragmentation, caspase-3 activation, and poly(ADP-ribose) polymerase degradation, was detected in IBV-infected Vero cells. Addition of the general caspase inhibitor z-VAD-FMK to the culture media showed inhibition of the hallmarks of apoptosis and increase of the release of virus to the culture media at 16 h postinfection. However, neither the necrotic process nor the productive replication of IBV in Vero cells was severely affected by the inhibition of apoptosis. Screening of 11 IBV-encoded proteins suggested that a 58-kDa mature cleavage product could induce apoptotic changes in cells transiently expressing the protein. This study adds one more example to the growing list of animal viruses that induce apoptosis during their replication cycles.

Amino Acid Chloromethyl Ketones↗
PubMed2001

[Inhibitory effect of aminoglycoside antibiotics on rabbit carotid baroreceptor activity in vitro].

The present study was to investigate the effects of aminoglycoside antibiotics, changes in extracellular Ca2+ concentration and antagonists of L-type Ca-channels on the activity of rabbit carotid sinus baroreceptors (CS-BRA) in isolated and superperfused carotid sinus-carotid sinus nerve (CS-CNS) preparations, using extracellular recording technique. The results are as follows. (1) Streptomycin (0.25-0.75 mmol/L) and gentamycin (0.43-1.29 mmol/L) inhibited CS-BRA in a dose-dependent manner, which recovered after the drugs were washed out. (2) Perfusion with high Ca2+ (3.3 mmol/L) solution inhibited CS-BRA, while perfusate with trace Ca2+ (in the order of 10(-5) mol/L) increased it. (3) Verapamil and diltiazem had no effect on CS-BRA at a concentration of 10(-7) mol/L, but inhibited it at higher concentrations (> 10(-6) mol/L). These results suggest: (1) aminoglycoside antibiotics can inhibit CS-BRA specifically, thus providing a new tool for the study of baroreceptors; (2) calcium ions are not necessary for producing generator potentials of baroreceptors, and the L-type calcium channel does not seem to be involved in CS-BRA per se; and (3) the inhibitory effects of aminoglycoside antibiotics on CS-BRA may not be related to the blocking of L-type calcium channels.

Aminoglycosides↗
PubMed2001

Effect of sodium dimercaptopropanesulfonate on antagonism of tetramethylenedisulphotetramine to GABA receptor.

AIM: To study effects of sodium dimercaptopropanesulfonate (DMPS) on the antagonism of tetramethylenedisulphotetramine (TETS) to gamma-aminobutyric acid (GABA) receptor. METHODS: Acute toxicity experiments were conducted to observe the effects of DMPS and TETS on mice. Contents of free amino acids in mouse brain were determined with automatic analyzer for amino acids. Autoradiography was used to observe the [3H]GABA bindings in the rat brain slices under different conditions. RESULTS: After icv and ip DMPS, the number of mice experiencing convulsions reduced from 20 in control group to 4 and 2 respectively in TETS poisoned mice. The content of GABA was altered in DMPS control group and TETS control group compared with DMPS protection group and NS control group [micromol/g: (2.09 +/- 0.05) and (2.67 +/- 0.15) vs (2.40 +/- 0.10 (micromol/g)) and (2.41 +/- 0.21)]; the content of glutamic acid was (12.3 +/- 1.2), (12.0 +/- 0.8), (10.2 +/- 0.6), and (11.8 +/- 1.0) micromol/g in NS control group, DMPS control group, TETS control group, and DMPS protection group, respectively. The OD value of autoradiograms decreased in TETS group compared with buffer control group in cortex, hippocampus, diencephalon, and brainstem [(0.084 +/- 0.008), (0.081 +/- 0.009), (0.094 +/- 0.006) and (0.081 +/- 0.006), vs (0.102 +/- 0.003), (0.109 +/- 0.005), (0.128 +/- 0.007), and (0.125 +/- 0.008), respectively]. OD value was maintained or higher than the normal level in DMPS+TETS group in the four brain areas [(0.116 +/- 0.008), (0.125 +/- 0.011), (0.129 +/- 0.005), and (0.128 +/- 0.010) vs (0.102 +/- 0.003), (0.109 +/- 0.005), (0.128 +/- 0.007), and (0.125 +/- 0.008), respectively]. CONCLUSION: The inhibitory effects of DMPS on the antagonism of TETS to GABA receptor are due to the increase in the GABA binding to its receptors in brain caused by DMPS

Animals↗
PubMed2000

Further characterization of the coronavirus infectious bronchitis virus 3C-like proteinase and determination of a new cleavage site.

Coronavirus infectious bronchitis virus (IBV) encodes a trypsin-like proteinase (3C-like proteinase) by ORF 1a, which has been demonstrated to play a pivotal role in proteolytic processing of gene 1-encoded polyproteins. In our previous studies, the proteinase was identified as a 33-kDa protein in IBV-infected cells, and its catalytic center was shown to consist of H(2820) and C(2922) residues. It is released from the 1a and 1a/1b polyproteins by autoprocessing at two Q-S dipeptide bonds (Q(2779)-S(2780) and Q(3086)-S(3087)). In this report, further characterization of the two cleavage sites demonstrates that the N-terminal Q(2779)-S(2780) site is tolerant to mutations at the P1 position. Deletion of the C-terminal region of the proteinase shows that a significant amount of the enzymatic activity is maintained upon deletion of up to 67 amino acids, suggesting that the extreme C-terminal region may be dispensable for the proteolytic activity of the proteinase. Analysis of the autoprocessing kinetics in vitro reveals that proteolysis at the Q(2779)-S(2780) site is the first cleavage event mediated by this proteinase. This is followed by cleavage at the Q(3086)-S(3087) site. The occurrence of both cleavage events in intact cells is potentially rapid and efficient, as no intermediate cleavage products covering the proteinase were detected in either IBV-infected or transfected cells. Immunofluorescence microscopy and subcellular fractionation studies further show differential subcellular localization of the proteinase in IBV-infected cells and in cells expressing the 3C-like proteinase alone, indicating that additional roles in viral replication might be played by this protein. Finally, a Q-A (Q(3379)-A(3380)) dipeptide bond encoded by nucleotides 10,663 to 10,668 was demonstrated to be a cleavage site of the proteinase.

Amino Acid Sequence↗
PubMed2000

Determination of the complete nucleotide sequence of a vaccine strain of porcine reproductive and respiratory syndrome virus and identification of the Nsp2 gene with a unique insertion.

The complete nucleotide sequence of the genomic RNA of a vaccine strain (SP) of porcine reproductive and respiratory syndrome virus (PRRSV) was determined. It shares approximately 94% identity of nucleotide sequence with two recently reported North American strains, 16244B and VR2332, but only 78% with a European strain, Lelystad virus (LV). Its genome is the longest among the four published complete sequences of PRRSV, due to an insertion in the Nsp2-encoding region. Compared to Nsp2 of the North American strains and the European strain, the predicted Nsp2 of strain SP contains 36 and 155 amino acid insertions, respectively, near the C-terminus, in addition to several highly variable regions. The insertion shows no homology with any equivalent arterivirus proteins. This high sequence disparity of Nsp2 among different PRRSV isolates suggested that it could be used as a marker to differentiate PRRSV genotypes. The 5' RACE and primer extension analysis of three North American strains demonstrated that the utmost 5'-end nucleotides are conserved among PRRSV strains isolated from two continents. The predicted polyprotein 1 a/b contains conserved proteinase, polymerase and helicase domains responsible for polyprotein processing, RNA transcription and replication.

Animals↗
PubMed2000

Endogenous fatty acid synthesis in squamous cell carcinomas of the oral cavity.

We measured the synthesis of endogenous fatty acids in oral squamous cell carcinoma, its adjacent tissue, and normal oral tissues that were collected fresh from surgical specimens. The tissues were minced in Roswell Park Memorial Institute Medium 1640 (RPMI 1640) and incubated in [1(2)-(14)C] acetic acid, sodium salt ((14)CH(3)(14)CO(2)Na). Total lipids were then extracted and(14)C was measured by scintillation counter. We found that incorporation of(14)C in the total lipids of squamous cell carcinoma was significantly higher than in the other tissues.

Carbon Radioisotopes↗
PubMed2000

Identification of a novel cleavage activity of the first papain-like proteinase domain encoded by open reading frame 1a of the coronavirus Avian infectious bronchitis virus and characterization of the cleavage products.

The coronavirus Avian infectious bronchitis virus (IBV) employs polyprotein processing as a strategy to express its gene products. Previously we identified the first cleavage event as proteolysis at the Gly(673)-Gly(674) dipeptide bond mediated by the first papain-like proteinase domain (PLPD-1) to release an 87-kDa mature protein. In this report, we demonstrate a novel cleavage activity of PLPD-1. Expression, deletion, and mutagenesis studies showed that the product encoded between nucleotides 2548 and 8865 was further cleaved by PLPD-1 at the Gly(2265)-Gly(2266) dipeptide bond to release an N-terminal 195-kDa and a C-terminal 41-kDa cleavage product. Characterization of the cleavage activity revealed that the proteinase is active on this scissile bond when expressed in vitro in rabbit reticulocyte lysates and can act on the same substrate in trans when expressed in intact cells. Both the N- and C-terminal cleavage products were detected in virus-infected cells and were found to be physically associated. Glycosidase digestion and site-directed mutagenesis studies of the 41-kDa protein demonstrated that it is modified by N-linked glycosylation at the Asn(2313) residue encoded by nucleotides 7465 to 7467. By using a region-specific antiserum raised against the IBV sequence encoded by nucleotides 8865 to 9786, we also demonstrated that a 33-kDa protein, representing the 3C-like proteinase (3CLP), was specifically immunoprecipitated from the virus-infected cells. Site-directed mutagenesis and expression studies showed that a previously predicted cleavage site (Q(2583)-G(2584)) located within the 41-kDa protein-encoding region was not utilized by 3CLP, supporting the conclusion that the 41-kDa protein is a mature viral product.

3C Viral Proteases↗
PubMed2000

[Study of bracket placement with the preadjusted appliance for extraction cases].

OBJECTIVE: To determine the bracket placement with the preadjusted appliance for extraction cases. METHODS: Sixty finishing occlusions were chosen as Andrews stated at debonding. The placement of the incisor teeth bracket was in the middle of the clinical crown, and retention arch wire was straight wire without step bends. The measurement from the incisal or occlusal edges to the bracket center was the height of the placement of the bracket. In order to produce bracket placement chart, the values of measurements +0.5 mm and +1.0 mm were added for larger teeth, and -0.5 mm and -1.0 mm for smaller teeth. RESULTS: The placement in the second bicuspid and first molar was different between extraction cases and nonextraction cases. CONCLUSION: The bracket placement chart improves the accuracy of bracket placement with the preadjusted appliance for extraction cases.

English Abstract↗
PubMed1999

An outbreak of enterically transmitted non-A, non-E viral hepatitis.

Patients with isolated serum transaminase elevations of unknown cause are common in China. An outbreak of such disease took place in a technicians' school during 1996. To define the epidemic and determine the etiology, a study was carried out, which included investigation of epidemiological, clinical and histological features. The symptoms of this disease were mild. The major clinical feature was transaminase elevation, and all serum markers of known hepatitis viruses were negative. Although the course of disease in most patients was self-limiting, in a few it was prolonged and relapsed. Histological findings were mild portal hepatitis or non-specific reactive hepatitis. The disease first appeared in 1994, and this outbreak occurred after October 1996. A total of 381 people were affected and the prevalence was as high as 60.7%. Casual contact and small-scale food transmission were considered to be risk factors for infection and the epidemic was under control 2 months later following the introduction of preventive measures for gastroenteric infection. Viral genomic fragments from the so-called transfusion-transmitted virus (TTV) were detected in acute-phase sera and stool samples collected 2 weeks before onset. Therefore, this disease outbreak might be another form of enterically transmitted viral hepatitis, not related to hepatitis A and E.

Adult↗