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Biomedical subjects

Jing Chen

Publications and source records attributed to Jing Chen.

At least 289 records · Page 16Linked to original sources
PubMed2003

Dynamin 3 is a component of the postsynapse, where it interacts with mGluR5 and Homer.

The dynamins comprise a large family of mechanoenzymes known to participate in membrane modeling events. All three conventional dynamin genes (Dyn1, Dyn2, Dyn3) are expressed in mammalian brain and produce more than 27 different dynamin proteins as a result of alternative splicing. Past studies have suggested that Dyn1 participates in specialized neuronal functions such as rapid synaptic vesicle recycling, while Dyn2 may mediate the conventional clathrin-mediated uptake of surface receptors. Currently, the distribution, expression, and function of Dyn3 in neurons, or in any other cell type, are completely undefined. Here, we demonstrate that Dyn1 and Dyn3 localize differentially in the synapse. Dyn1 concentrates within the presynaptic compartment, while Dyn3 localizes to dendritic spine tips. Within the postsynaptic density (PSD), we found Dyn3, but not Dyn1, to be part of a biochemically isolated complex comprised of Homer and metabotropic glutamate receptors. Finally, although dominant-negative Dyn3 did not seem to inhibit receptor endocytosis, overexpression of a specific Dyn3 spliced variant in mature neurons caused a marked remodeling of dendritic spines. These data suggest that Dyn3 is a postsynaptic dynamin and, like its binding partner Homer, plays a significant role in dendritic spine morphogenesis and remodeling.

Amino Acid Sequence↗
PubMed2003

Elimination of shrimp endogenous peroxidase background in immunodot blot assays to detect white spot syndrome virus (WSSV).

False positive results were obtained in immunodot blot assays to detect white spot syndrome virus when horseradish peroxidase-conjugated sheep anti-mouse immunoglobin (Ig) serum was used as a secondary antibody with 3-3'-diaminobenzine tetrahydrochloride dihydrate as the detection substrate. The cause was considered to be a reaction of shrimp endogenous peroxidase (POD) with the substrate. In experiments designed to inhibit POD activity, 9 different reagents were used at different concentrations and for different treatment times. EDTA, sodium azide, HEPES-Na, NaHSO3, H2O2 and phenylthiourea (PTU) were able to inhibit POD activity by 44, 60, 64, 67, 79, and 90%, respectively. Phenylmethylsulfonyl fluoride did not inhibit POD, and neither periodic acid nor H2O2 in methanol were appropriate due to the formation of flocculant precipitates when added to shrimp extracts. It was concluded that of the treatments tested, 10 mM PTU for 2 h yielded optimal inhibition and that such pretreatment of samples eliminates false positive results in immunodot blot assays.

Animals↗
PubMed2003

Calyculin A-induced actin phosphorylation and depolymerization in renal epithelial cells.

This study reports actin phosphorylation and coincident actin cytoskeleton alterations in renal epithelial cell line, LLC-PK1. Serine phosphorylation of actin was first observed in vitro after the cell lysate was incubated with phosphatase inhibitors and ATP. Both the phosphorylated actin and actin kinase activities were found in the cytoskeletal fraction. Actin phosphorylation was later detected in living LLC-PK1 cells after incubation with the phosphatase inhibitor calyculin A. Calyculin A-induced actin phosphorylation was associated with reorganization of the actin cytoskeleton, including net actin depolymerization, loss of cell-cell junction and stress fiber F-actin filaments, and redistribution of F-actin filaments in the periphery of the rounded cells. Actin phosphorylation was abolished by 3-h ATP depletion but not by the non-specific kinase inhibitor staurosporine. These results demonstrate that renal epithelial cells contain kinase/phosphatase activities and actin can be phosphorylated in LLC-PK1 cells. Actin phosphorylation may play an important role in regulating the organization of the actin cytoskeleton in renal epithelium.

Actin Cytoskeleton↗
PubMed2003

Molecular cloning, expression, purification, and mass spectrometric characterization of 3C-like protease of SARS coronavirus.

Severe acute respiratory syndrome (SARS) is an acute respiratory illness, which has broken out in China. It has been known that SARS coronavirus (SARS_CoV) is a novel human coronavirus and is responsible for SARS infection. Belonging to one of the major proteins associated with SARS_CoV, SARS 3C-like protease (SARS_3CL(pro)) functions as a cysteine protease engaging in the proteolytic cleavage of the viral precursor polyprotein to a series of functional proteins required for coronavirus replication and is considered as an appealing target for designing anti-SARS agents. To facilitate the studies regarding the functions and structures of SARS_3CL(pro), in this report the synthetic genes encoding 3CL(pro) of SARS_CoV were assembled, and the plasmid was constructed using pQE30 as vector and expressed in Escherichia coli M15 cells. The highly yielded ( approximately 15mg/L) expressed protease was purified by use of NTA-Ni(2+) affinity chromatography and FPLC system, and its sequence was determined by LC/MS with the residue coverage of 46.4%.

Amino Acid Sequence↗
PubMed2003

Degradation of monomethylmercury chloride by hydroxyl radicals in simulated natural waters.

The degradation of methylmercury chloride by hydroxyl radicals (*OH) has been investigated using nitrate photolysis from 285 to 800 nm with a 450 W Xenon lamp as the (*OH source. The identified products are Hg(2+), Hg(0), CHCl(3) and formaldehyde. The second-order rate constant at pH of 5 at room temperature was determined to be 9.83(+-0.66)x10(9) M(-1) x s(-1)using benzoic acid as the *OH scavenger. The effects of chloride concentration and methylmercury speciation have also been investigated. A mechanism of the CH(3)HgCl-*OH reaction has been proposed. The calculated methylmercury degradation rates in natural waters using the above rate constant were comparable to the in situ photodegradation rates reported previously, indicating that degradation by (*)OH may be one of the important pathways of methylmercury degradation in sunlit surface waters.

Disinfectants↗
PubMed2003

Identification and characterization of a novel human testis-specific Golgi protein, NYD-SP12.

A novel human testis-specific gene, NYD-SP12, was identified by hybridizing human adult or fetal testes cDNA samples with a human cDNA microarray containing 9216 clones. mRNA expression level of NYD-SP12 was 30-fold higher in human adult testes than fetal testes. Similarly, semi-quantitative RT-PCR revealed a differential expression pattern of an NYD-SP12 homologous gene in mouse adult and infant testes. PCR and hybridization analysis of NYD-SP12 mRNA from multiple human tissues indicated the expression of NYD-SP12 exclusively in the testis. In-situ hybridization revealed that the expression of this gene was confined to spermatogenic epithelium and was not found in interstitial cells. NYD-SP12 transcript was not detected in patients with spermatogenic arrest and Sertoli cell-only syndrome. NYD-SP12 cDNA (GenBank accession number: AF345909) consisted of 2070 bp. The predicted 1707 bp open-reading fragment encoded a 569 amino acid protein that was 77% identical to a mouse homologue. Furthermore, computerized SMART and Motif analysis revealed that the protein contained a Structural Classification Of Proteins (SCOP) domain in the C-terminus and a cluster of phosphorylation sites for PKC, CK and cAMP/cGMP-dependent protein kinase. Interestingly, the EGFP-NYD-SP12 fusion protein was localized to the Golgi apparatus. In conclusion, the results suggest that NYD-SP12 is involved in spermatogenesis, and that NYD-SP12-encoded protein might function in the Golgi apparatus.

Amino Acid Sequence↗
PubMed2003

NYD-SP16, a novel gene associated with spermatogenesis of human testis.

By hybridizing human adult testis cDNA microarrays with human adult and embryo testis cDNA probes, a novel human testis gene NYD-SP16 was identified. NYD-SP16 expression was 6.44-fold higher in adult testis than in fetal testis. NYD-SP16 contains 1595 base pairs (bp) and a 762-bp open reading frame encoding a 254-amino acid protein with 73% amino acid sequence identity with the mouse testis homologous protein. The NYD-SP16 gene was localized to human chromosome 5q14. The deduced structure of the NYD-SP16 protein contains one transmembrane domain, which was confirmed by GFP/NYD-SP16 fusion protein expression in the cytomembrane of the transfected human choriocarcinoma JAR cells, suggesting that it is a transmembrane protein. Multiple tissue distribution indicated that NYD-SP16 mRNA is highly expressed in the testes and pancreas, with little or no expression elsewhere. Further analysis of abnormal expression in infertile male patients revealed complete absence of NYD-SP16 in the testes of patients with Sertoli-cell-only syndrome and variable expression in patients with spermatogenic arrest. Homologous gene expression in mouse testis was confirmed in spermatogenic cells by in situ hybridization. The results of cDNA microarray, in situ hybridization, and semiquantitative polymerase chain reaction in mouse testis of different stages indicated that NYD-SP16 expression is developmentally regulated. These results suggest that the putative NYD-SP16 protein may play an important role in testicular development/spermatogenesis and may be an important factor in male infertility.

Adult↗
PubMed2003

Estimate of annual average radon concentration in the normal living area from short-term tests.

Most residential radon guidelines refer to annual average radon concentration in the normal living area. However, decisions on whether a house needs mitigation are usually based on short term radon tests. Depending on where detectors are placed and when tests are performed, results of those measurements can differ significantly from the annual average radon concentration in the normal living area. We provide a practical method based on survey results in 5486 Canadian houses to estimate annual average radon levels from results of screening tests. The average ratio of radon concentration in the basement to that of the upper floors in a house is determined, and the average relative seasonal variations of radon levels in the basement and of the upper floors are identified. Based on these relative quantities, estimate factors are derived for four different combinations of detector location and the living area and tabulated for different calendar periods of radon testing. The annual average radon level can be estimated by multiplying the result of a short-term screening test with the appropriate estimate factor given in this study.

Air Pollutants, Radioactive↗
PubMed2003

Geographic variations in the prevalence, awareness, treatment and control of hypertension in China.

OBJECTIVE: To compare the prevalence, awareness, treatment and control of hypertension in north and south, and urban and rural residents of China. DESIGN: A cross-sectional survey conducted in 2000-2001. SETTING AND PARTICIPANTS: A multistage cluster sampling method was used to select a nationally representative sample of 15 540 men and women aged 35-74 years from the general Chinese population. MAIN OUTCOME MEASURES: Three blood pressure measurements were obtained by trained observers using a standardized mercury sphygmomanometer. Information on history of hypertension and use of antihypertensive medications was obtained by use of a standard questionnaire. Hypertension was defined as a mean systolic blood pressure >or= 140 mmHg and/or diastolic blood pressure >or= 90 mmHg and/or use of antihypertensive medications. RESULTS: The age-standardized prevalence of hypertension was significantly higher among residents living in north than in south China (33.8 versus 23.3%, P < 0.001), but similar in those living in urban and rural areas (29.0 versus 28.1%, P = 0.3). Average systolic and diastolic blood pressure levels were consistently higher in north than in south residents. Residents in north China had higher percentages of awareness but lower percentages of control compared with their counterparts in south China. Percentages of awareness, treatment and control of hypertension were significantly higher in urban than in rural residents. CONCLUSIONS: Our study documents a marked north-south gradient in the prevalence of hypertension in China. The previously reported urban-rural difference in the prevalence of hypertension was not noted, perhaps due to a rapid increase in the prevalence of hypertension in rural China.

Adult↗
PubMed2003

Insulin resistance and risk of chronic kidney disease in nondiabetic US adults.

This study examined the relationship of fasting serum glucose, insulin, C-peptide, glycosylated hemoglobin A (HbA1c), and Homeostasis Model Assessment (HOMA)-insulin resistance to risk of chronic kidney disease (CKD) among 6453 persons without diabetes (fasting glucose <126 mg/dl and not taking diabetes medication) who participated in the Third National Health and Nutrition Examination Survey and were aged 20 yr or older. CKD was defined as an estimated GFR <60 ml/min per 1.73 m(2). The prevalence of CKD was significantly and progressively higher with increasing levels of serum insulin, C-peptide, HbA1c, and HOMA-insulin resistance. After adjustment for potential confounding variables, the odds ratio of CKD for the highest compared with the lowest quartile was 4.03 (95% confidence interval [CI], 1.81 to 8.95; P = 0.001), 11.4 (95% CI, 4.07 to 32.1; P < 0.001), 2.67 (95% CI, 1.31 to 5.46; P = 0.002), and 2.65 (95% CI, 1.25 to 5.62; P = 0.008) for serum insulin, C-peptide, HbA1c levels, and HOMA-insulin resistance, respectively. For a one SD higher level of serum insulin (7.14 micro U/ml), C-peptide (0.45 Deltamol/ml), HbA1c (0.52%), and HOMA-insulin resistance (1.93), the odds ratio (95% CI) of CKD was 1.35 (1.16 to 1.57), 2.78 (2.25 to 3.42), 1.69 (1.28 to 2.23), and 1.30 (1.13 to 1.50), respectively. These findings combined with knowledge from previous studies suggest that the insulin resistance and concomitant hyperinsulinemia are presented in CKD patients without clinical diabetes. Further studies into the causality between insulin resistance and CKD are warranted.

Blood Glucose↗
PubMed2003

Gene cloning and characterization of VcrM, a Na+-coupled multidrug efflux pump, from Vibrio cholerae non-O1.

We cloned a DNA fragment responsible for drug resistance from chromosome of Vibrio cholerae non-O1. Nucleotide sequence analysis of this fragment revealed the presence of a single open reading frame encoding a protein consisting of 445 amino acid residues. We designated the gene as vcrM. Hydropathy analysis of the deduced amino acid sequence of VcrM suggests the presence of 12 trans-membrane segments. A dendrogram showed that VcrM is a member of the DinF-subfamily within the MATE family of multidrug efflux pumps. Expression of the cloned vcrM gene in drug-hypersensitive Escherichia coli KAM32 cells made them resistant to acriflavine, 4', 6-diamidino-2-phenylindole, Hoechst 33342, rhodamine 6G, tetraphenylphosphonium chloride (TPPCl) and ethidium bromide. Efflux of acriflavine due to VcrM was dependent on Na+ or Li+. Moreover, Na+ efflux was observed with VcrM when TPPCl was added to Na+-loaded cells. Therefore, we conclude that VcrM is a Na+/drug antiporter-type multidrug efflux pump.

Acriflavine↗
PubMed2003

Molecular cloning and characterization of an ABC multidrug efflux pump, VcaM, in Non-O1 Vibrio cholerae.

A gene responsible for multidrug resistance was cloned from the chromosomal DNA of non-O1 Vibrio cholerae NCTC 4716 by using as a host drug-hypersensitive Escherichia coli strain KAM32, which lacks major multidrug efflux pumps. E. coli cells transformed with the gene showed elevated levels of resistance to a number of structurally dissimilar drugs, such as tetracycline, norfloxacin, ciprofloxacin, doxorubicin, daunomycin, 4',6-diamidino-2-phenylindole, and Hoechst 33342. We determined the nucleotide sequence and found one open reading frame. We designated the gene vcaM. The deduced product, VcaM, seems to be a polypeptide with 619 amino acid residues (69 kDa) that has a putative topology of six transmembrane segments in the N-terminal hydrophobic domain, followed by an ATP binding domain in the C-terminal hydrophilic region. The sequence of VcaM was shown to be similar to those of human multidrug resistance proteins P-glycoprotein MDR1 and lactococcal LmrA, which are driven by ATP. The efflux of Hoechst 33342 and doxorubicin from cells possessing VcaM was detected. The efflux activity was inhibited by reserpine and sodium o-vanadate, which are potent inhibitors of MDR1 and LmrA. Thus, we conclude that VcaM is a member of the family of multidrug efflux pumps of the ATP binding cassette type and the first experimentally proven example of a multidrug efflux pump of this family in gram-negative bacteria.

ATP-Binding Cassette Transporters↗
PubMed2003

Cortactin is a component of clathrin-coated pits and participates in receptor-mediated endocytosis.

The actin cytoskeleton is believed to contribute to the formation of clathrin-coated pits, although the specific components that connect actin filaments with the endocytic machinery are unclear. Cortactin is an F-actin-associated protein, localizes within membrane ruffles in cultured cells, and is a direct binding partner of the large GTPase dynamin. This direct interaction with a component of the endocytic machinery suggests that cortactin may participate in one or several endocytic processes. Therefore, the goal of this study was to test whether cortactin associates with clathrin-coated pits and participates in receptor-mediated endocytosis. Morphological experiments with either anti-cortactin antibodies or expressed red fluorescence protein-tagged cortactin revealed a striking colocalization of cortactin and clathrin puncta at the ventral plasma membrane. Consistent with these observations, cells microinjected with these antibodies exhibited a marked decrease in the uptake of labeled transferrin and low-density lipoprotein while internalization of the fluid marker dextran was unchanged. Cells expressing the cortactin Src homology three domain also exhibited markedly reduced endocytosis. These findings suggest that cortactin is an important component of the receptor-mediated endocytic machinery, where, together with actin and dynamin, it regulates the scission of clathrin pits from the plasma membrane. Thus, cortactin provides a direct link between the dynamic actin cytoskeleton and the membrane pinchase dynamin that supports vesicle formation during receptor-mediated endocytosis.

Actins↗
PubMed2003

Functional cloning and expression of emeA, and characterization of EmeA, a multidrug efflux pump from Enterococcus faecalis.

A fragment of chromosomal DNA from Enterococcus faecalis ATCC 29212 was cloned using Escherichia coli KAM32 host cells lacking major multidrug efflux pumps. E. coli KAM32 cells were sensitive to many antimicrobial agents, and the transformed cells harboring a recombinant plasmid became resistant to several structurally unrelated antimicrobial agents such as tetraphenylphosphonium chloride, 4',6-diamidino-2-phenylindole (DAPI), Hoechst 33342, acriflavine, benzalkonium chloride, norfloxacin and ethidium bromide. This suggests that the cloned DNA fragment carries a gene(s) encoding a multidrug efflux pump. Determination of the nucleotide sequence of the cloned DNA revealed a gene designated as emeA. The transformed E. coli cells showed efflux activity of several antimicrobial agents such as DAPI, Hoechst 33342 and acriflavine. Efflux of DAPI via EmeA was strongly inhibited by reserpine.

Bacterial Proteins↗
PubMed2003

Multidrug resistance in Serratia marcescens and cloning of genes responsible for the resistance.

Six clinically isolated strains of Serratia marcescens were tested for their drug resistance. All showed fairly high resistance to many antimicrobial agents tested including norfloxacin, streptomycin, ampicillin, erythromycin, tetracycline, chloramphenicol, and antimicrobial dyes. Using the drug-hypersensitive strain of Escherichia coli KAM32 as the host, we cloned the genes responsible for multidrug resistance from chromosomal DNA of one of the strains of S. marcescens, NUSM8906. We obtained 28 hybrid plasmids that made host cells resistant to several antimicrobial agents. Many of the transformants harboring each of the plasmids showed multidrug resistance, and some showed resistance to specific drugs. The hybrid plasmids were classified into several groups based on their drug specificity. It appears that each class of plasmid carries different types of drug resistance genes. Analysis of such genes will reveal the multiple mechanisms involved in multidrug resistance in S. marcescens.

Anti-Bacterial Agents↗
PubMed2003

Comparative microdosimetry of photoelectrons and Compton electrons: an analysis in terms of generalized proximity functions.

A current discussion on mammography screening is focused on claims of high relative biological effectiveness (RBE) of mammography X rays compared to conventional 200 kV X rays. An earlier assessment in terms of the electron spectra of these radiations has led to the conclusion that the RBE is bound to be less than 2, regardless of specific model assumptions and the microdosimetric properties of electrons. The present study extends this result in terms of the microdosimetric proximity function, t(x), for electrons, which is essentially the spatial auto-correlation function of energy within particle tracks. If pairs of DNA lesions, e.g. chromosome breaks or deletions, bring about the observed damage, the value t(x) determines for a specified radiation the relative frequency of pairs of lesions a distance x apart. The effectiveness of the radiation is thus proportional to an average of the values of t(x) over the distances, x, for which lesions can combine. The analysis suggests that 15 keV electrons can have a low-dose relative biological effectiveness (RBE(M)) of 1.6 relative to 40 keV electrons if the interaction distances do not exceed about 1 micro m. An extension of the concept, the reduced proximity function, t(delta)(x), permits the inclusion of models with an energy threshold, such as delta = 100 eV, 500 eV or 2 keV, for the formation of each of the DNA lesions. This makes it possible to assess the potential impact of the Auger electrons which accompany most photoelectrons, but only a minority of the Compton electrons. It is found that the Auger electrons could make photoelectrons substantially more effective than Compton electrons at energies below 10 keV but not at energies above 15 keV. The conclusions obtained for the RBE of 15 keV electrons relative to 40 keV electrons will be roughly representative of the RBE of mammography X rays relative to conventional 200 kV X rays.

Biophysics↗