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Biomedical subjects

Yan Liu

Publications and source records attributed to Yan Liu.

At least 343 records · Page 19Linked to original sources
PubMed2003

Catalytically active MAP KAP kinase 2 structures in complex with staurosporine and ADP reveal differences with the autoinhibited enzyme.

MAP KAP kinase 2 (MK2), a Ser/Thr kinase, plays a crucial role in the inflammatory process. We have determined the crystal structures of a catalytically active C-terminal deletion form of human MK2, residues 41-364, in complex with staurosporine at 2.7 A and with ADP at 3.2 A, revealing overall structural similarity with other Ser/Thr kinases. Kinetic analysis reveals that the K(m) for ATP is very similar for MK2 41-364 and p38-activated MK2 41-400. Conversely, the catalytic rate and binding for peptide substrate are dramatically reduced in MK2 41-364. However, phosphorylation of MK2 41-364 by p38 restores the V(max) and K(m) for peptide substrate to values comparable to those seen in p38-activated MK2 41-400, suggesting a mechanism for regulation of enzyme activity.

Adenosine Diphosphate↗
PubMed2003

Application of statistically-based experimental designs for the optimization of nisin production from whey.

Statistically-based experimental designs were applied for the optimization of nisin production by Lactococcus lactis in a whey-based medium. Yeast extract, KH2PO4, and MgSO4 were identified to have significant effects on nisin biosynthesis by a Plackett-Burman design. These three significant factors were subsequently optimized using central composite design, and the optimal conditions were determined to be 12.067 g l(-1) for yeast extract, 0.569 g l(-1) for KH2PO4, and 0.572 g l(-1) for MgSO4. The validity of the optimal conditions was verified by a separate experiment.

Animals↗
PubMed2003

The effect of preparation procedures on the morphology of melanin from the ink sac of Sepia officinalis.

The structure of melanin extracted from the ink sac of the cuttlefish Sepia officinalis was examined for different methods of isolation and purification of the pigment. Scanning electron microscopy (SEM) images of Sepia eumelanin prepared by different procedures establish that multi-microm-sized aggregates reported by previous workers are generated by their sample preparation, and that the dominant constituents of Sepia melanin are approximately 150 nm spherical granules. Brunauer-Emmett-Teller (BET) measurements reveal that Sepia eumelanin from Sigma (prepared by spray drying the pigment) has a surface area of 14.3 m2/g. Pigment extracted directly from the fresh ink sac and then freeze-dried has a surface area of 21.5 m2/g, while CO2-supercritically dried has a surface area of 37.5 m2/g. This is consistent with SEM images showing that the process of freeze-drying produces aggregates, but to a lesser extent than spray drying. Supercritical drying of the sample produces suspensions of the individual approximately 150 nm granule, which is more reflective of the natural pigment. Brunauer-Emmett-Teller surface area analysis and Barrett-Joyner-Halenda (BJH) pore volume analysis indicate that the surface of the granules is not smooth and the interior of the granules is not porous, but rather the aggregates of granules are porous. Ultra-high resolution SEM and atomic force microscopy (AFM) images show the granules are easily deformed and are comprised of smaller constituents. De-aggregation of the granules by sonication and ultra-filtration reveal a range of structures depending on the pore size of the membrane used. The implications of these results on quantifying photochemical properties and kinetic reaction rate constants of melanin are discussed.

Animals↗
PubMed2003

Comparison of the structural and physical properties of human hair eumelanin following enzymatic or acid/base extraction.

Eumelanin was isolated from a sample of black, Indonesian human hair using three different published procedures: two different acid/base extractions and an enzymatic extraction. The morphology and spectroscopic properties of the isolated pigments differ significantly. The acid/base procedures both yield an amorphous material, while enzymatic extraction yields ellipsoidal melanosomes. Amino acid analysis shows that there is protein associated with the isolated pigments, accounting for 52, 40 and 14% of the total mass for the two acid/base extractions and the enzymatic extraction, respectively. The amino acid compositions do not correlate with those of keratin or tyrosinase. Metal elemental analysis shows that the acid/base extraction removes a majority of many metal ions bound to the pigment. Chemical degradation analysis by KMnO4/H+ and H2O2/OH- indicates significant differences between the pigments isolated by acid/base and enzymatic extraction. After correction for the protein mass in the two pigments, the lower yields of both pyrrole-2,3,5-tricarboxylic acid and pyrrole-2,3-dicarboxylic acid, eumelanin degradation products, indicate acid/base extraction modifies the chemical structure of the melanin, consistent with the result of Soluene solubilization assay. While the optical absorption spectra of the bulk pigments are similar, the spectra of the molecular weight less than 1000 mass fractions differ significantly. The data clearly indicate that pigment obtained from human hair by acid/base extraction contains significant protein, exhibits destruction of the melanosome, and possesses altered molecular structure. The acid/base extracted hair melanin is not representative of the natural material and is a poor model system for studying the physical and biological properties of melanins. The enzymatically extracted hair melanin, on the contrary, retains the morphology of intact melanosomes and is an excellent source of human melanin.

Acids↗
PubMed2003

Measurement of enthalpy and volume changes in photoinitiated reactions on the ms timescale with a novel pressure cell.

Time-resolved photoacoustics is an excellent method with which to measure enthalpy and volume changes of photochemical and photobiological reactions. However, it fails at times longer than approximately 10 micros. The design principles of a pressure or volume cell covering the time range of 20 micros to several seconds is presented. The sensitivity of the cell has been verified and its application to the photocycle of bacteriorhodopsin is presented. Because of the similar cell structure and data analysis it is now possible to determine enthalpy and volume changes in photo-initiated reactions over the timescale of nanoseconds to seconds with the same solution.

Acoustics↗
PubMed2003

Isolation and biophysical studies of natural eumelanins: applications of imaging technologies and ultrafast spectroscopy.

The major pigments found in the skin, hair, and eyes of humans and other animals are melanins. Despite significant research efforts, the current understanding of the molecular structure of melanins, the assembly of the pigment within its organelle, and the structural consequences of the association of melanins with protein and metal cations is limited. Likewise, a detailed understanding of the photochemical and photophysical properties of melanins has remained elusive. Many types of melanins have been studied to date, including natural and synthetic model pigments. Such studies are often contradictory and to some extent the diversity of systems studied may have detracted from the development of a basic understanding of the structure and function of the natural pigment. Advances in the understanding of the structure and function of melanins require careful characterization of the pigments examined so as to assure the data obtained may be relevant to the properties of the pigment in vivo. To address this issue, herein the influence of isolation procedures on the resulting structure of the pigment is examined. Sections describing the applications of new technologies to the study of melanins follow this. Advanced imaging technologies such as scanning probe microscopies are providing new insights into the morphology of the pigment assembly. Recent photochemical studies on photoreduction of cytochrome c by different mass fraction of sonicated natural melanins reveal that the photogeneration of reactive oxygen species (ROS) depends upon aggregation of melanin. Specifically, aggregation mitigates ROS photoproduction by UV-excitation, suggesting the integrity of melanosomes in tissue may play an important role in the balance between the photoprotective and photodamaging behaviors attributed to melanins. Ultrafast laser spectroscopy studies of melanins are providing insights into the time scales and mechanisms by which melanin dissipates absorbed light energy.

Animals↗
PubMed2003

Cytotoxic alkaloids from Boehmeria siamensis.

Two new phenanthroquinolizidine alkaloids, boehmeriasins A and B, were isolated from the aqueous ethanolic extract of Boehmeria siamensis Craib (Urticaceae) by bioassay-guided fractionation. Their structures were elucidated on the basis of spectral evidence. Boehmeriasin A possesses cytotoxic activity against 12 cell lines from 6 panels of cancer including lung cancer, colon cancer, breast cancer, prostate cancer, kidney cancer and leukemia with GI (50) between 0.2 and 100 ng/mL, whereas boehmeriasin B showed lower activity.

Alkaloids↗
PubMed2003

Enteric disposition and recycling of flavonoids and ginkgo flavonoids.

OBJECTIVE: The objective of this study was to determine the intestinal and microbial disposition of flavonoids and how these disposition processes affect their enteric recycling. DESIGN: Studies were performed using a perfused rat intestinal model or using enrichment cultures and a pure isolate of Enterococcus avium (LY1). RESULTS: In the rat intestine, aglycones, such as quercetin and apigenin, were as permeable (P*(eff) > or = 2) as compounds such as propranolol (100% absorption). However, a significant portion of the absorbed aglycones was conjugated and the metabolites were excreted into the lumen. Flavonoid glycosides, such as isoquercitrin and apigenin-7-O-glucoside, also had high apparent P*(eff) values (> or = 2) in the upper small intestine because of rapid hydrolysis. However, isoquercitrin was absorbed much slower (P*(eff) < or = 0.7, p < 0.05) when hydrolysis was absent or inhibited by 20 mmol gluconolactone. Absorption of other intact glycosides was similar to intact isoquercitrin and was much slower than the corresponding aglycones (P*(eff) < or = 0.7, p < 0.05). Intestinal bacteria, such as LY1, hydrolyzed the flavonoid glycosides used in the study. Excreted glycosidases were involved in the hydrolysis of glycosides because glycosides were poorly taken up by LY1. In conclusion, glycosidase-catalyzed hydrolysis is a critical first step in the intestinal and microbial disposition of flavonoid glycosides. Aglycones were not only rapidly absorbed, but also rapidly metabolized into phase II conjugates, which were then excreted back into the lumen. Therefore, intestinal and microbial glycosidases and intestinal phase II enzymes make a significant contribution to the disposition of flavonoids via the proposed enteric and enterohepatic recycling scheme.

Animals↗
PubMed2003

Gab3-deficient mice exhibit normal development and hematopoiesis and are immunocompetent.

Gab proteins are intracellular scaffolding and docking molecules involved in signaling pathways mediated by various growth factor, cytokine, or antigen receptors. Gab3 has been shown to act downstream of the macrophage colony-stimulating factor receptor, c-Fms, and to be important for macrophage differentiation. To analyze the physiological role of Gab3, we used homologous recombination to generate mice deficient in Gab3. Gab3(-/-) mice develop normally, are visually indistinguishable from their wild-type littermates, and are healthy and fertile. To obtain a detailed expression pattern of Gab3, we generated Gab3-specific monoclonal antibodies. Immunoblotting revealed a predominant expression of Gab3 in lymphocytes and bone marrow-derived macrophages. However, detailed analysis demonstrated that hematopoiesis in mice lacking Gab3 is not impaired and that macrophages develop in normal numbers and exhibit normal function. The lack of Gab3 expression during macrophage differentiation is not compensated for by increased levels of Gab1 or Gab2 mRNA. Furthermore, Gab3-deficient mice have no major immune deficiency in T- and B-lymphocyte responses to protein antigens or during viral infection. In addition, allergic responses in Gab3-deficient mice appeared to be normal. Together, these data demonstrate that loss of Gab3 does not result in detectable defects in normal mouse development, hematopoiesis, or immune system function.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Interaction between hepatitis C virus core protein and translin protein--a possible molecular mechanism for hepatocellular carcinoma and lymphoma caused by hepatitis C virus.

AIM: To investigate the interaction between hepatitis C virus core protein and translin protein and its role in the pathogenensis of hepatocellular carcinoma and lymphoma. METHODS: With the components of the yeast two hybrid system 3, "bait" plasmids of HCV core the gene was constructed. After proving that hepatitis C virus core protein could be firmly expressed in AH109 yeast strains, yeast two- hybrid screening was performed by mating AH109 with Y187 that transformed with liver cDNA library plasmids-pACT2 and then plated on quadruple dropout (QDO) medium and then assayed for alpha-gal activity. Sequencing analysis of the genes of library plasmids in yeast colonies that could grow on QDO with alpha-gal activity was performed. The interaction between HCV core protein and the protein we obtained from positive colony was further confirmed by repeating yeast two - hybrid analysis and coimmunoprecipitation in vitro. RESULTS: A gene from a positive colony was the gene of translin, a recombination hotspot binding protein. The interaction between HCV core protein and translin protein could be proved not only in yeast, but also in vitro. CONCLUSION: The core protein of HCV can interact with translin protein. This can partly explain the molecular mechanism for hepatocellular carcinoma and lymphoma caused by HCV.

Carcinoma, Hepatocellular↗
PubMed2003

[Cloning of genes transactivated by hepatitis B virus X protein].

OBJECTIVE: To construct a subtractive cDNA library of genes transactivated by hepatitis B virus X protein (HBX) using suppression subtractive hybridization (SSH) technique and to clone genes associated with HBX transactivating function. METHODS: The mRNA was isolated from HepG2 cells transfected with pcDNA3.1(-)-X and pcDNA3.1(-) empty vector respectively, then cDNA was synthesized. After restriction enzyme RsaI digestion, a number of small size cDNA was obtained. Then tester cDNA was subdivided into two portions and each was ligated with different cDNA adaptor. After tester cDNA was hybridized with driver cDNA twice and underwent nested polymerase chain reaction (PCR) twice the production was subcloned into T/A plasmid vectors to set up the subtractive cDNA library. Amplification of the library was carried out with E. coli strain JM109, some cDNA was sequenced and analyzed in GenBank with Blast. RESULTS: The subtractive cDNA library of genes transactivated by HBX was constructed. The amplified library contained 85 positive clones, and colony PCR showed that these clones contained 200-1000 bp inserts. 65 clones were analyzed by sequencing and bioinformatics, which suggested nineteen known genes and fifteen genes with unknown function. CONCLUSION: A subtractive cDNA library of genes transactivated by HBX using SSH technique has been constructed successfully, which may bring some new clues for studying the biological functions of HBX and the pathogenesis of hepatoma.

Cloning, Molecular↗
PubMed2003

[Screening of the genes of hepatitis B virus PreS2 interacting proteins].

OBJECTIVE: To screen and clone the genes of proteins in hepatocytes interacting with hepatitis B virus (HBV) PreS2 by yeast-two hybridization technique. METHODS: The HBV PreS2 gene was amplified by polymerase chain reaction (PCR) and HBV PreS2 bait plasmid was constructed by using yeast-two hybridization system 3, then transformed into yeast AH109, followed by mating with yeast Y187 containing liver cDNA library plasmid in 2 YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-Ade-His) and synthetic dropout nutrient medium (SD/-Trp-Leu-Ade-His) containing X-alpha-gal for selecting positive blue clones, then amplified by PCR, sequenced, and performed bioinformatics analysis. RESULTS: HBV PreS2 gene was cloned successfully and expressed in yeast AH109.Twenty-six positive colonies were selected, among them, twelve containing metallothionein 2A, one cytochrome C oxidase II, two cytochrome P450 subfamily IV4F, two cytochrome c oxidase subunit 4 isoform 1, three albumin (ALB), one Na(+)K(+) transporting ATPase beta-1 polypeptide, two prealbumin, one lectin galactoside-binding subunit, and Two new genes with unknown function. CONCLUSION: Genes of HBV PreS2 interacting proteins have been successfully cloned, which brings some new clues for studying the biological functions of HBV PreS2 and related proteins.

Cloning, Molecular↗
PubMed2003

Nutritional predictors of insulin-like growth factor I and their relationships to cancer in men.

The insulin-like growth factor (IGF) axis may play opposing roles in health and disease. The age-related declines in growth hormone and IGF-I may be associated with potentially deleterious changes in body composition and functioning, but recent studies suggest that IGF-I levels may be related to risk of prostate, colorectal, premenopausal breast, and possibly other cancers. Thus, we studied dietary influences on plasma IGF-I and IGF-I:IGF-binding protein-3 ratio in 753 men in the Health Professionals Follow-Up Study who completed a food frequency questionnaire. In this generally well-nourished population of middle-aged to elderly men, plasma IGF-I and IGF-I:IGF-binding protein-3 molar ratio tended to increase with higher intake of protein and minerals, including potassium, zinc, magnesium, calcium, and phosphorus. Men with relatively high intakes of total protein (top quintile) and minerals (top quintile of the five minerals combined) had a 25% higher mean plasma level of IGF-I compared with those in the low quintiles simultaneously. The major sources of animal protein, including milk, fish, and poultry, but not red meat, as well as total vegetable protein, were associated with an increase in IGF-I levels. Energy intake was positively related to plasma IGF-I level but only in men with body mass index <25 kg/m(2). The age-related decline in plasma IGF-I may be exacerbated by low intakes of protein and minerals. The potential role of these dietary factors on cancer risk through altering IGF-I levels requires study.

Aged↗
PubMed2003

[Synergetic transactivating effect of HCV core and HBV X proteins on SV40 early promoter/enhancer].

BACKGROUND: To investigate the synergetic transactivating effects of HCV core and HBV X proteins. METHODS: HCV core and HBV X protein-expressing plasmids were constructed with the vector pcDNA3.1(-). The plasmids were transfected into HepG2 cells and cotransfected Hep2 cells with reporter plasmid Psv-lacZ by lipofectamine plus reagents. The virus proteins produced in transient expression system were detected at the transcription and translation levels. The activity of b-galactosidase was detected, which reflected the transactivating function of the proteins. RESULTS: The expression of plasmids were detected in soluble protein cell extracts of transiently transfected HepG2 cells. HCV core protein activated the b-galactosidase expression at a value 4.9 times higher than the control, while HBV X protein activated at a value 3.5 times. It arrived at 9 times transfected with the plasmids simultaneously. The activating effect increased in relation to the amount of plasmids. CONCLUSIONS: The results suggested that the two kinds of virus proteins have transactivating effect on SV40 early promoter/enhancer, and they acted synergistically. These contribute to explain the mechanisms of liver injury or tumorigenesis induced by HCV or/and HBV infection.

Animals↗
PubMed2003

[Temocapril treatment upregulated cardiomyocyte thioredoxin expression and improved autoimmune myocarditis].

OBJECTIVE: Thioredoxin (TRX) is a redox regulatory protein that protects cells from various stresses. Angiotensin-converting enzyme (ACE) inhibitor was reported to enhance endogenous antioxidant enzyme activities. This study was carried out to investigate whether temocapril, a novel non-sulfhydryl containing ACE inhibitor, reduces the severity of myocarditis via redox regulation mechanisms involving TRX. METHODS: The up-regulation of TRX by temocapril treatment was checked by Western blot in normal rat myocytes in vitro and in vivo, as well as in rats with experimental autoimmune myocarditis (EAM). RESULTS: Temocapril enhanced cytosolic redox regulatory protein TRX expression, but neither mitochondrial TRX2 nor antioxidant enzymes, such as copper-zinc superoxide dismutase (Cu/Zn-SOD) or manganese superoxide dismutase (Mn-SOD) expression, was up-regulated by the preconditioning treatment. In rats with EAM, the severity of myocarditis and the protein carbonyl contents were less increased in temocapril treatment (10 mg x kg(-1) x d(-1), orally) from day 1 to day 21, but not in temocapril treatment from day 15 to day 21. If the characteristics of this model that myocardial inflammation begins around day 15 and keeps on until day 21 is considered, temocapril treatment for 3 weeks might be thought as a preconditioning treatment. CONCLUSIONS: TRX and the redox state modified by TRX may play a crucial role in the pathophysiology of EAM. Temocapril ameliorates myocarditis with inducing TRX up-regulation in a preconditioning manner, although the mechanism of TRX up-regulation by temocapril remains to be elucidated.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2003

[Epidemiological characteristics of 403 patients with severe acute respiratory syndrome in Haidian district, Beijing].

OBJECTIVE: To analyze epidemiological features of severe acute respiratory syndrome (SARS) in Haidian district, Beijing. METHODS: Each SARS case was interviewed by trained investigator using standardized questionnaire followed a descriptive analysis. RESULTS: Four hundred and three SARS cases were identified and 27 of them died from March 18 and May 31, 2003. The incidence rate of SARS was 18.0/100,000 with case fatality rate as 6.7% in Haidian district, Beijing. Seventy-four percent of patients were adults with higher risk in age group of 20 - 29 year. SARS patients were scattered around in 32 out of 33 streets and villages in this district. The disease appeared to be sporadic but the case of outbreaks in family or university only seen in three streets. The course of SARS epidemic in this district could be divided into three phases: initial-which last for days, peak-21 days and then rapid decline-for 26 days. Number of patients having had a history of close contact to other SARS were gradually decreasing along with the process of the epidemics (trend chi(2) = 8.800, P = 0.003). Seventy-two point seven percent of the SARS cases had been exposed to the injection in the hospital settings. When the epidemics came to a rapid decline, 85.7% of the patients diagnosed during that period could be traced down to have had the history of contacting SARS cases within their own families. The distribution of occupation was also showed significantly different in the three respective stages (chi(2) = 36.41, P < 0.01). Among the patients who could not be identified as having confirmed contact history, 26.6% having had outward activities and 47.6% of them visited hospitals, especially during the peak stage. CONCLUSION: The intensity of SARS epidemic among the residents of Haidian district was recognized as similar to the other parts of Beijing. Nosocomial infection in hospital settings was most important cause responsible for the transmission of SARS in this district.

Adolescent↗
PubMed2003

[Research on expression and control of p16 and p21 by wild-type p53 gene in two lung adenocarcinoma cell lines].

OBJECTIVE: To evaluate the potential of p53 gene therapy for lung cancer in nude mice. METHODS: Two lung adenocarcinoma cell lines L-18 and 95D were infected with adenovirus encoding wild-type p53 gene pAdCMV -p53 (Ad-p53 ) in vitro and in vivo. The antitumor effect of wild type p53 gene was assessed by cell growth curve, reverse transcriptase polymerase chain reaction (RT-PCR) analysis and TUNEL staining methods. RESULTS: The p53-specific growth inhibition and apoptosis of tumor cells were observed in both cell lines in vitro. By RT-PCR analysis, the increasing expression of p21 gene but not of p16 gene after p53 gene infection suggested that p21 gene played an important role in p53 gene induced cell apoptosis. The in vivo study revealed that celiac injection of p53 gene significantly inhibited the tumorigenesis in 95D and L-18 cells in nude mice. However, no obvious inhibition of tumorigenesis was observed after subcutaneous injection of p53 gene in L-18 cell line, compared with the inhibition noted in 95D cell line. CONCLUSION: The results showed the adenovirus-mediated antitumor therapy by means of p53 gene infection might be a potential way to inhibit cancer growth and induce tumor cell apoptosis.

Adenocarcinoma↗