Biomedical subjects

Li Chen

Publications and source records attributed to Li Chen.

At least 235 records · Page 13Linked to original sources

PubMed2003

Overexpression of the ASN1 gene enhances nitrogen status in seeds of Arabidopsis.

In wild-type Arabidopsis, levels of ASN1 mRNA and asparagine (Asn) are tightly regulated by environmental factors and metabolites. Because Asn serves as an important nitrogen storage and transport compound used to allocate nitrogen resources between source and sink organs, we tested whether overexpression of the major expressed gene for Asn synthetase, ASN1, would lead to changes in nitrogen status in the ultimate storage organ for metabolites-seeds. Transgenic Arabidopsis constitutively overexpressing ASN1 under the cauliflower mosaic virus 35S promoter were constructed (35S-ASN1). In seeds of the 35S-ASN1 lines, three observations support the notion that the nitrogen status was enhanced: (a) elevations of soluble seed protein contents, (b) elevations of total protein contents from acid-hydrolyzed seeds, and (c) higher tolerance of young seedlings when grown on nitrogen-limiting media. Besides quantitative differences, changes in the relative composition of the seed amino acid were also observed. The change in seed nitrogen status was accompanied by an increase of total free amino acids (mainly Asn) allocated to flowers and developing siliques. In 35S-ASN1 lines, sink tissues such as flowers and developing siliques exhibit a higher level of free Asn than source tissues such as leaves and stems, despite significantly higher levels of ASN1 mRNA observed in the source tissues. This was at least partially due to an enhanced transport of Asn from source to sink via the phloem, as demonstrated by the increased levels of Asn in phloem exudates of the 35S-ASN1 plants.

Amino Acids↗

PubMed2003

Structure-activity relationship of cyclic peptide penta-c[Asp-His(6)-DPhe(7)-Arg(8)-Trp(9)-Lys]-NH(2) at the human melanocortin-1 and -4 receptors: His(6) substitution.

A series of MT-II related cyclic peptides, based on potent but non-selective hMC4R agonist (Penta-c[Asp-His(6)-DPhe(7)-Arg(8)-Trp(9)-Lys]-NH(2)) was prepared in which His(6) residue was systematically substituted. Two of the most interesting peptides identified in this study are Penta-c[Asp-5-ClAtc-DPhe-Arg-Trp-Lys]-NH(2) and Penta-c[Asp-5-ClAtc-DPhe-Cit-Trp-Lys]-NH(2) which are potent hMC4R agonists and are either inactive or weak partial agonists (not tested for their antagonist activities) in hMC1R, hMC3R and hMC5R agonist assays.

Amino Acid Substitution↗

PubMed2003

Interleukin-6 family of cytokines mediates isoproterenol-induced delayed STAT3 activation in mouse heart.

This study was aimed to determine whether beta-adrenergic receptor (beta-AR) stimulated by isoproterenol (ISO) activates signal transducers and activators of transcription (STAT) in mouse heart and, if so, to examine the underlying mechanism. We found that treatment of adult male mice by ISO (15 mg/kg body weight, intraperitoneal) caused a delayed STAT3 activation (at 60-120 min), which was fully abolished by beta-AR antagonist, propranolol. ISO-induced phosphorylation of STAT3 was markedly enhanced by phosphodiesterase inhibitor amrinone, indicating that cAMP is critically involved in beta-AR-mediated STAT3 activation. In addition, beta-AR stimulation significantly increased gene expression of interleukin-6 (IL-6) family of cytokines (IL-6, leukemia inhibitory factor, ciliary neurotrophic factor, and cardiotrophin-1). IL-6 protein levels in serum and mouse myocardium were also significantly increased in response to ISO treatment. In cultured cardiac fibroblasts, IL-6 level was enhanced significantly after ISO (10-6 mol/liter) stimulation for 2 h and then peaked at 12 h, whereas the response of IL-6 in cultured cardiomyocytes to ISO stimulation was not significant, suggesting that ISO-induced increase in IL-6 is primarily from cardiac fibroblasts rather than cardiomyocytes. Most importantly, IL-6 could activate STAT3 in a time-dependent manner in cultured cardiomyocytes, and inhibition of IL-6 level by anti-IL-6-neutralizing antibody clearly attenuated ISO-induced phosphorylation of STAT3 in myocardium. Taken together, these results indicate that beta-AR stimulation leads to a delayed STAT3 activation via an IL-6 family of cytokine-mediated pathway and that cardiac fibroblasts, but not cardiomyocytes, is probably the predominant source of IL-6 in response to ISO stimulation in mouse myocardium.

Adrenergic beta-Agonists↗

PubMed2003

Structure-activity relationship of linear peptide Bu-His6-DPhe7-Arg8-Trp9-Gly10-NH2 at the human melanocortin-1 and -4 receptors: DPhe7 and Trp9 substitution.

A series of pentapeptides, based on hMC4R pentapeptide agonist (Bu-His(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2)), was prepared in which either DPhe(7) or Trp(9) residue was systematically substituted. A number of interesting DPhe surrogates (D-Thi, D-3-CF(3)Phe, D-2-Nal and D-3,4-diClPhe) as well as Trp surrogates (2-Nal and Bta) were identified in this study.

Amino Acid Substitution↗

PubMed2003

Cyclicity of mosquito vitellogenic ecdysteroid-mediated signaling is modulated by alternative dimerization of the RXR homologue Ultraspiracle.

In anautogenous mosquitoes, egg maturation requires a blood meal. As a consequence, mosquitoes are vectors of numerous devastating human diseases. Blood feeding triggers a 20-hydroxyecdysone (20E) hormonal cascade, which activates yolk protein precursor (YPP) genes in the female fat body, an insect metabolic tissue. An important adaptation for anautogeny is the previtellogenic arrest preventing activation of YPP genes. Equally essential is termination of their expression, so that another arrest is achieved after a batch of eggs is laid. Here, we report that mosquito Seven-up (AaSvp), a chicken ovalbumin upstream promoter-transcription factor homologue, is involved in regulating the cyclicity of vitellogenic ecdysteroid-mediated signaling through heterodimerization with a retinoid X receptor homologue Ultraspiracle (USP), the obligatory functional ecdysteroid receptor (EcR) partner. AaSvp inhibits 20E-dependent activation of the vitellogenin (Vg) gene in transfection assays. Two-hybrid and GST pull-down analyses demonstrate that in vitro AaSvp interacts with both AaUSP and AaEcR. However, the coimmunoprecipitation using fat body nuclear extracts reveals that at 33-36 h postblood meal, when the 20E titer sharply declines and YPP gene expression ceases, AaSvp replaces AaEcR in USP heterodimers. The chromatin immunoprecipitation assay indicates that protein-protein interaction rather than binding competition for the Vg ecdysteroid response element accounts for the inhibition of Vg expression by AaSvp.

Animals↗

PubMed2003

Structure-activity relationship of linear peptide Bu-His-DPhe-Arg-Trp-Gly-NH(2) at the human melanocortin-1 and -4 receptors: histidine substitution.

Systematic substitution of His(6) residue using non-selective hMC4R pentapeptide agonist (Bu-His(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2)) as the template led to the identification of Bu-Atc(6)(2-aminotetraline-2-carboxylic acid)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2) which showed moderate selectivity towards hMC4R over hMC1R. Further SAR studies resulted in the discovery of Penta-5-BrAtc(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2) and Penta-5-Me(2)NAtc(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2) which are potent hMC4R agonists and are inactive in hMC1R, hMC3R and hMC5R agonist assays.

Amino Acid Sequence↗

PubMed2003

The Protein Data Bank and structural genomics.

The Protein Data Bank (PDB; http://www.pdb.org/) continues to be actively involved in various aspects of the informatics of structural genomics projects--developing and maintaining the Target Registration Database (TargetDB), organizing data dictionaries that will define the specification for the exchange and deposition of data with the structural genomics centers and creating software tools to capture data from standard structure determination applications.

Animals↗

PubMed2003

Are nurses prepared to manage cancer pain? A national survey of nurses' knowledge about pain control in Taiwan.

Nurses play a crucial role in cancer pain control, but little is known about how well-prepared nurses are to manage cancer pain in Taiwan. The purpose of this study was to examine the level of knowledge about pain management among Taiwanese nurses with different background characteristics and to determine the predictor(s) of nurses' pain management knowledge. Nurse subjects were recruited by a cross-sectional nationwide survey with stratified sampling from nine hospitals distributed in the four major geographic regions of Taiwan. The Nurses' Knowledge and Attitudes Survey-Taiwanese version (NKAS-T) and a background information form were used to collect the data. Of 1900 surveys distributed, 1797 valid questionnaires (94.5%) were analyzed. The average correct response rate was 50.5%, with rates ranging from 7-86% for each survey question. Results from stepwise regression showed that nurses with higher mean correct answer scores had BS or higher degrees, had received pain education at professional conferences, had more prior hours of pain education, had longer clinical care experiences, and always worked with cancer patients. Nurses who worked in intensive care units, however, had significantly lower mean correct scores. The results strongly suggest an urgent need to strengthen pain education in Taiwan. The results also provide the direction for developing pain education.

Data Collection↗

PubMed2003

Effects of prenatal alcohol exposure on glucose tolerance in the rat offspring.

Low birth weight in humans predisposes to obesity, cardiovascular diseases, and type 2 diabetes in adult life. Alcohol exposure during pregnancy has been associated with fetal growth restriction. We investigated the effects of prenatal exposure to alcohol on glucose metabolism later in the offspring. Female Sprague Dawley rats were given ethanol (ETOH), 4 g/kg/day by gavage throughout pregnancy. Compared with controls, newborn ETOH rats had decreased body size (5.1 +/- 0.1 v 6.3 +/- 0.1 g, P <.001), plasma insulin (0.44 +/- 0.4 v 0.67 +/- 0.1 ng/mL, P <.05), and leptin mRNA (P <.05), but they had normal beta-cell mass and elevated adipose resistin mRNA and plasma glucose (5.0 +/- 0.5 v 3.6 +/- 0.3 mmol/L, P <.01). Food intake was decreased in ETOH rats during the fourth week of life, and body weight remained decreased compared with controls until a catch-up growth occurred by 7 weeks of life. At 13 weeks of age, body weight and beta-cell mass of ETOH offspring were normal, but plasma glucose and insulin after a glucose challenge were increased compared with controls (P <.05). Adipose leptin and hypothalamic Ob-R mRNA were not different from controls, but resistin was increased (P <.05), and muscle GLUT4 content was decreased (P <.05) in ETOH offspring compared with controls. The data suggest that prenatal alcohol exposure impairs glucose tolerance in the offspring by both inducing insulin resistance and beta-cell dysfunction. The prevailing mechanism in 3-month-old rat offspring appears to be insulin resistance, manifested by glucose intolerance and decreased GLUT4 despite hyperinsulinemia.

Animals↗

PubMed2003

Isolation, expression pattern of a novel human RAB gene RAB41 and characterization of its intronless homolog RAB41P.

Small GTPases form a big family including Ras, Rho, Rac, Rab, Sar1/Arf subfamilies and Ran homologs, playing important roles in diverse cellular processes. Through data mining, a novel human RAB41 gene was predicted and subsequently isolated from human testis. The open reading frame of RAB41 is 636bp in length. RAB41 was composed of three exons, and it was mapped to chromosome 3q21.3 by comparing with the human genomic data. RAB41 protein contains a RAB domain. Similarity analysis indicated that RAB41 is closely similar to RAB19. The results of PCR amplification indicated that human RAB41 is widely expressed in brain, testis, lung, heart, ovary, colon, kidney, uterus and spleen but not in liver. By genomic searching, an intronless pseudogene homologous to RAB41 at chromosome 16--RAB41P was identified at human chromosome 16q11.2. Flanking the pseudogene RAB41P in human genome, there exist some transposable elements LINEs--L1, whose contribution in the generation of this intronless homolog is discussed.

Amino Acid Sequence↗

PubMed2003

Decreased CD154 expression by neonatal CD4+ T cells is due to limitations in both proximal and distal events of T cell activation.

Neonatal CD4(+) T cells express less CD154 protein and mRNA than adult CD4(+) T cells after activation by calcium ionophore and phorbol ester, but the mechanism for this reduced expression and its relevance to the primary immune response remain unclear. We compared expression of CD154 protein and mRNA and CD154 gene promoter activity by purified naive (CD45RA(high)CD45RO(low)) neonatal and adult CD4(+) T cells after activation by calcium ionophore (ionomycin) and phorbol myristate acetate (PMA) treatment or by engagement of alphabeta TCR-CD3 complex. Substantial and consistent reductions in expression by neonatal cells were found in all cases and were paralleled by decreased CD154-dependent activation of a B cell line. CD69 expression by neonatal CD4(+) T cells after alphabeta TCR-CD3 engagement was also reduced compared to adult cells, which suggested that limitations in activation-induced signaling by neonatal CD4(+) T cells occurred at a point upstream of where the signaling pathways leading to CD154 and CD69 expression diverge. Decreased CD154 expression by neonatal cells after alphabeta TCR-CD3 engagement was paralleled by a lower free intracellular calcium concentration, a key event for CD154 gene transcription. Reduced CD154 promoter activity by neonatal cells persisted when proximal signaling events were bypassed using ionomycin and PMA, suggesting an additional and more distal mechanism for decreased transcription. In contrast, CD154 mRNA stability was similar in neonatal and adult cells after either ionomycin and PMA stimulation or engagement of the alphabeta TCR-CD3 complex. We conclude that decreased CD154 production by neonatal CD4(+) T cells is due to limitations in both proximal and distal activation events, which together ultimately limit CD154 gene transcription.

Adult↗

PubMed2003

Transcriptional activation of immediate-early gene ETR101 by human T-cell leukaemia virus type I Tax.

Human T-cell leukaemia virus type I (HTLV-I) Tax regulates viral and cellular gene expression through interactions with multiple cellular transcription pathways. This study describes the finding of immediate-early gene ETR101 expression in HTLV-I-infected cells and its regulation by Tax. ETR101 was persistently expressed in HTLV-I-infected cells but not in HTLV-I uninfected cells. Expression of ETR101 was dependent upon Tax expression in the inducible Tax-expressing cell line JPX-9 and also in Jurkat cells transiently transfected with Tax-expressing vectors. Tax transactivated the ETR101 gene promoter in a transient transfection assay. A series of deletion and mutation analyses of the ETR101 gene promoter indicated that a 35 bp region immediately upstream of the TATA-box sequence, which contains a consensus cAMP response element (CRE) and a G+C-rich sequence, is the critical responsive element for Tax activation. Site-directed mutagenesis analysis of the 35 bp region suggested that both the consensus CRE motif and its upstream G+C-rich sequence were critical for Tax transactivation. Electrophoretic mobility shift analysis (EMSA) using the 35 bp sequence as probe showed the formation of a specific protein-DNA complex in HTLV-I-infected cell lines. EMSA with specific antibodies confirmed that the CREB transcription factor was responsible for formation of this specific protein-DNA complex. These results suggested that Tax directly transactivated ETR101 gene expression, mainly through a CRE sequence via the CREB transcription pathway.

Animals↗

PubMed2003

NMR characterization of interleukin-2 in complexes with the IL-2Ralpha receptor component, and with low molecular weight compounds that inhibit the IL-2/IL-Ralpha interaction.

Nuclear magnetic resonance (NMR) methods were employed to study the interaction of the cytokine Interleukin-2 (IL-2) with the alpha-subunit of its receptor (IL-2Ralpha), and to help understand the behavior of small molecule inhibitors of this interaction. Heteronuclear (1)H-(15)N HSQC experiments were used to identify the interaction surface of (15)N-enriched Interleukin-2 ((15)N-IL-2) in complex with human IL-2Ralpha. In these experiments, chemical shift and line width changes in the heteronuclear single-quantum coherence (HSQC) spectra upon binding of (15)N-IL-2 enabled classification of NH atoms as either near to, or far from, the IL-2Ralpha interaction surface. These data were complemented by hydrogen/deuterium (H/D) exchange measurements, which illustrated enhanced protection of slowly-exchanging IL-2 NH protons near the site of interaction with IL-2Ralpha. The interaction surface defined by NMR compared well with the IL-2Ralpha binding site identified previously using mutagenesis of human and murine IL-2. Two low molecular weight inhibitors of the IL-2/IL-2Ralpha interaction were studied: one (a cyclic peptide derivative) was found to mimic a part of the cytokine and bind to IL-2Ralpha; the other (an acylphenylalanine derivative) was found to bind to IL-2. For the interaction between IL-2 and the acylphenylalanine, chemical shift perturbations of (15)N and (15)NH backbone resonances were tracked as a function of ligand concentration. The perturbation pattern observed for this complex revealed that the acylphenylalanine is a competitive inhibitor-it binds to the same site on IL-2 that interacts with IL-2Ralpha.

Interleukin-2↗

PubMed2003

Glucose intolerance and resistin expression in rat offspring exposed to ethanol in utero: modulation by postnatal high-fat diet.

High-fat diet and intrauterine growth retardation may predispose to obesity, insulin resistance, and type 2 diabetes. Because prenatal ethanol (ETOH) exposure causes intrauterine growth retardation, we investigated its interactions with postnatal high-fat diet on glucose tolerance and adipocyte-derived hormones in the rat offspring. High-fat-fed offspring had increased adiposity, serum leptin, and muscle uncoupling protein-3, but decreased adiponectin mRNA, compared with corresponding chow-fed groups. ETOH-exposed offspring had normal adiponectin, but increased resistin mRNA and protein, compared with controls, regardless of postnatal diet. Skeletal muscle glucose transporter-4 content was decreased after both ETOH exposure and high-fat feeding. Glycemic and insulin responses to an ip glucose challenge were equally increased in non-ETOH-exposed high-fat-fed offspring and in ETOH-exposed chow-fed offspring, with additive effects of ETOH and high-fat diet. Pancreatic insulin content was elevated only in non-ETOH-exposed high-fat-fed offspring. The data suggest that high-fat diet worsens glucose intolerance in offspring of rats exposed to ETOH. Prenatal ETOH exposure and postnatal high-fat diet might cause insulin resistance through separate mechanisms, involving resistin and adiponectin, respectively.

Adiponectin↗

PubMed2003

Band centers and track finding for large two-dimensional infrared spectroscopic arrays.

An efficient two-dimensional (2D) peak-finding algorithm is proposed to find peak maps that specify the peak centers of all bands in two-dimensional arrays of time-series infrared spectral data. The algorithm combines the second-derivative method with the intrinsic characteristics of 2D infrared reaction spectral data. Initially, the second-derivative method is used to detect all possible peak center positions, and then three criteria drawn from characteristics of 2D continuous spectral data are employed to filter peak positions. Four 2D peak maps are generated in a sequential order, with better and better approximations to the peak center positions being obtained in each. The 2D peak-finding algorithm has been successfully applied to both simulated spectra (to initially evaluate the algorithm) and then real 2D experimental spectra. The resulting peak maps exhibit very good estimates of the peak center positions. An ordering from the most significant to the least significant bands is obtained. The final peak maps can be used as starting parameters for various applications including the computationally intensive curve-fitting of time-series data.

Algorithms↗

PubMed2003

Computationally efficient curve-fitting procedure for large two-dimensional experimental infrared spectroscopic arrays using the Pearson VII model.

Extraction of quantitative information from large sets of sequential time-series spectra (two-dimensional, 2D, data) using a curve-fitting procedure is investigated. The difference between any experimental spectrum and any curve-fitted spectrum is constructed in a least-squares manner and the Pearson VII model is selected as the general band-shape function for the infrared absorbance spectra. The starting point for the curve-fitting procedure is a 2D peak map. Next, an interior spectrum from the 2D array is chosen, initial guesses of the band parameters are provided by an initialization scheme, and curve fitting is performed. Once optimal values of the Pearson VII model band parameters are obtained from the starting spectrum in the 2D array, these are then used as reasonable and judicious initial guesses for subsequent curve fitting of the neighboring spectra in the time series. This increases computational efficiency enormously. By adjusting the band center positions for moving bands, and re-optimizing each subsequent curve-fitting calculation to account for changing band shapes, the entire 2D array is rapidly and efficiently modeled. A 2D experimental spectroscopic time-series array from a homogeneous rhodium-catalyzed hydroformylation reaction was successfully curve fitted in this manner. The procedure holds considerable promise for the curve fitting of massive time-series spectroscopic data, such as that arising from on-line process monitoring of expensive value-added specialty chemical and pharmaceutical syntheses.

Algorithms↗

PubMed2003

Spectral pattern recognition of in situ FT-IR spectroscopic reaction data using minimization of entropy and spectral similarity (MESS): application to the homogeneous rhodium catalyzed hydroformylation of isoprene.

An improved algorithm using minimization of entropy and spectral similarity (MESS) was tested to recover pure component spectra from in situ experimental Fourier transform infrared (FT-IR) reaction spectral data, which were collected from a homogeneous rhodium catalyzed hydroformylation of isoprene. The experimental spectra are complicated and highly overlapping because of the presence of multiple intermediate products in this reaction system. The traditional entropy minimization method fails to resolve real reaction mixture spectra, but MESS can successfully reconstruct pure component spectra of unknown intermediate products for real reaction systems by the addition of minimization of spectral similarity. The quantitative measure of spectral similarity between two spectra was given by their inner products. The results indicate that MESS is a stable and useful algorithm for spectral pattern recognition of highly overlapped experimental reaction spectra. Comparison is also made between MESS, entropy minimization, simple-to-use interactive self-modeling mixture analysis (SIMPLISMA), interactive principle component analysis (IPCA), and orthogonal projection approach-alternating least squares (OPA-ALS).

Algorithms↗

PubMed2003

Determination of enantiomeric excess using the ultraviolet-circular dichroism and the high-performance liquid chromatography-circular dichroism methods.

Two useful numerical methods using ultraviolet (UV) and circular dichroism (CD) spectroscopies are proposed to determine enantiomeric excess (e.e). An algorithm is also proposed to generate self-consistent pure R and S enantiomer reference spectra. After all pure reference spectra are generated, a simulated annealing algorithm is applied to minimize the mismatch between the experimental spectra and the spectra after a least-squares fit. Optimal factors for R and S enantiomers are then used to determine e.e. The ultraviolet-circular dichroism (UV-CD) method uses the combined UV and CD spectra in a composite form, while the high-performance liquid chromatography (HPLC)-CD method only employs the CD spectra with the total concentrations of R plus S enantiomers provided by HPLC using a non-chiral stationary phase. Both methods were successfully tested on mixtures with known composition and then applied to real experimental data (unknown compositions). Compared with the UV-CD method, the results show that excellent results are more readily obtained using the HPLC-CD method. With the systems studied, the latter usually provided outstanding estimations of e.e with low error percentages.

Algorithms↗