Biomedical subjects

Li Tan

Publications and source records attributed to Li Tan.

At least 37 records · Page 2Linked to original sources

PubMed2005

[Studies on lignan glycosides from the roots of Bupleurum scorzonerifolium].

AIM: To study the lignan glycosides from the roots of Bupleurum scorzonerifolium. Chromatography methods was used to isolate compounds and chemical and spectral methods were used to identify the structures of isolated compounds. RESULTS: Two lignan glycosides were isolated from the roots of B. scorzonerifolium and their structures were identified as 2, 3-E-2,3-dihydro-2-(3'-methoxy-4'-O-beta-D-glucopyranosyl-phenyl)-3-hydroxymethyl-5-(3"-hydroxypropenyl )-7-methoxy-1-benzo [b] furan (1) and 2, 3-E-2, 3-dihydro-2-( 3'-methoxy-4'-hydroxy-phenyl)-3-hydroxymethyl-5-( 3"-hydroxypropenyl)-7-O-beta-D-glucopyranosyl-1-benzo[b]furan (2), both of them which were the mixture of (+)2S,3R- and (-)2R,3S-type diastereoisomer and in both of them the amount of (+)2S,3R-type was a little more than that of the (-)2R,3S-type. CONCLUSION: Compounds 1 and 2 were isolated from B. scorzonerifolium for the first time. (+)2S, 3R-2, 3-Dihydro-2-(3'-methoxy-4'-hydroxy-phenyl)-3-hydroxymethyl-5-(3"-hydroxypropenyl)-7-O-beta-D-glucopyranosyl-1-benzo[b] furan is a new compound.

Bupleurum↗

PubMed2004

A hybrid protein of the amino-terminal fragment of urokinase and mutant plasminogen activator inhibitor-2 efficiently inhibits tumor cell invasion and metastasis.

The urokinase plasminogen activator(uPA) system plays important roles in tumor cell invasion and metastasis. In the present study, we evaluated the effects of ATF-PAI2CD, a hybrid protein of the amino-terminal fragment of urokinase and mutant plasminogen activator inhibitor-2, on 95D cells in vitro and in vivo. Furthermore, our results support a current hypothesis that fusion protein blocks tumor invasion and motility by inhibiting localized pericellular proteolysis. Treatment of 95D cells with ATF-PAI2CD resulted in a dose-dependent decrease in tumor-cell invasion through matrigel, and ATF-PAI2CD was much more effective than PAI-2CD. In addition, extracellular regular protein kinase (ERK1/2) expression was downregulated and the adhesion ability to fibronectin was increased in 95D cells treated with the fusion protein, which was confirmed by cell adhesion assay. A high-concentration of ATF-PAI2CD caused a significant reduction in tumor volume and weight in BALB/c (nu/nu) mice female inoculated with human 95D cells (5 x 10(6)); the antitumor effects were significant, which demonstrated a 67.9+/-4.2% reduction in tumor growth compared with control mice. The number of lymphatic metastasis was significantly reduced in mice treated with high- and middle- concentrations of ATF-PAI2CD, whereas a low-concentration of ATF-PAI2CD failed to exhibit any antimetastatic effects. In conclusion, the results suggested that the hybrid protein has therapeutic potential for lung carcinoma and other tumors to inhibit tumor invasion and metastasis.

Animals↗

PubMed2004

Di-isodityrosine is the intermolecular cross-link of isodityrosine-rich extensin analogs cross-linked in vitro.

Extensins are cell wall hydroxyproline-rich glycoproteins that form covalent networks putatively involving tyrosyl and lysyl residues in cross-links catalyzed by one or more extensin peroxidases. The precise cross-links remain to be chemically identified both as network components in muro and as enzymic products generated in vitro with native extensin monomers as substrates. However, some extensin monomers contain variations within their putative cross-linking motifs that complicate cross-link identification. Other simpler extensins are recalcitrant to isolation including the ubiquitous P3-type extensin whose major repetitive motif, Hyp)(4)-Ser-Hyp-Ser-(Hyp)(4)-Tyr-Tyr-Tyr-Lys, is of particular interest, not least because its Tyr-Tyr-Tyr intramolecular isodityrosine cross-link motifs are also putative candidates for further intermolecular cross-linking to form di-isodityrosine. Therefore, we designed a set of extensin analogs encoding tandem repeats of the P3 motif, including Tyr --> Phe and Lys --> Leu variations. Expression of these P3 analogs in Nicotiana tabacum cells yielded glycoproteins with virtually all Pro residues hydroxylated and subsequently arabinosylated and with likely galactosylated Ser residues. This was consistent with earlier analyses of P3 glycopeptides isolated from cell wall digests and the predictions of the Hyp contiguity hypothesis. The tyrosine-rich P3 analogs also contained isodityrosine, formed in vivo. Significantly, these isodityrosine-containing analogs were further cross-linked in vitro by an extensin peroxidase to form the tetra-tyrosine intermolecular cross-link amino acid di-isodityrosine. This is the first identification of an inter-molecular cross-link amino acid in an extensin module and corroborates earlier suggestions that di-isodityrosine represents one mechanism for cross-linking extensins in muro.

Agrobacterium tumefaciens↗

PubMed2004

Intestinal barrier damage caused by trauma and lipopolysaccharide.

AIM: To investigate the intestinal barrier function damage induced by trauma and infection in rats. METHODS: Experimental models of surgical trauma and infection were established in rats. Adult Sprague-Dawley rats were divided into 4 groups: control group (n = 8), EN group (n = 10), PN group (n = 9) and Sep group (n = 8). The rats in PN and Sep groups were made into PN models that received isonitrogenous, isocaloric and isovolumic TPN solution during the 7-d period. Rats in EN and Sep groups received laparotomy and cervical catheterization on day 1 and received lipopolysaccharide injection intraperitoneally on d 7. On the 7(th) day all the animals were gavaged with lactulose and mannitol to test the intestinal permeability. Twenty-four hours later samples were collected and examined. RESULTS: The inflammatory responses became gradually aggravated from EN group to Sep group. The mucosal structure of small intestine was markedly impaired in PN and Sep groups. There was a low response in IgA level in Sep group when compared with that of EN group. Lipopolysaccharide injection also increased the nitric oxide levels in the plasma of the rats. The intestinal permeability and bacterial translocation increased significantly in Sep group compared with that of control group. CONCLUSION: One wk of parenteral nutrition causes an atrophy of the intestinal mucosa and results in a moderate inflammatory reaction in the rats. Endotoxemia aggravates the inflammatory responses that caused by laparotomy plus TPN, increases the production of nitric oxide in the body, and damages the intestinal barrier function.

Animals↗

PubMed2004

Structure of a hydroxyproline (Hyp)-arabinogalactan polysaccharide from repetitive Ala-Hyp expressed in transgenic Nicotiana tabacum.

A synthetic gene encoding the fusion protein (Ala-Hyp)(51)-enhanced green fluorescent protein expressed in Nicotiana tabacum cells produced a fusion glycoprotein with all proline residues hydroxylated and substituted with an arabinogalactan polysaccharide. Alkaline hydrolysis of the fusion glycoprotein yielded a population of hydroxyproline (Hyp)-arabinogalactan polysaccharides ranging in size from 13 to 26 saccharide residues/Hyp, with a median size of 15-17 residues. We isolated a 15-residue Hyp-arabinogalactan for structure determination by sugar analyses and one- and two-dimensional nuclear magnetic resonance techniques that provided the assignment of proton and carbon signals of a small polysaccharide O-linked to the hydroxyl group of Hyp. The polysaccharide consisted of a 1,3-linked beta-D-Galp backbone with a single 1,6-linked beta-D-Galp "kink." The backbone had two side chains of Galp substituted at position 3 with an arabinose di- or trisaccharide and at position 6 with glucuronic acid or rhamnosyl glucuronic acid. Energy-minimized space-filling molecular models showed hydrogen bonding within polysaccharides attached to repetitive Ala-Hyp and also between polysaccharides and the peptide backbone. Polysaccharides distorted the peptide Ramachandran angles consistent with the circular dichroic spectra of isolated (Ala-Hyp)(51) and its reversion to a polyproline II-like helix after deglycosylation. This first complete structure of a Hyp-arabinogalactan polysaccharide shows that computer-based molecular modeling of Hyp-rich glycoproteins is now feasible and supports the suggestion that small repetitive subunits comprise larger arabinogalactan polysaccharides.

Carbon↗

PubMed2004

Interaction of plasminogen activator inhibitor-2 and proteasome subunit, beta type 1.

The apoptosis protection by plasminogen activator inhibitor -2(PAI-2) is dependent on a 33 amino acids fragment between helix C and D of PAI-2 which is probably may be due to the interaction of PAI-2 with unknown intracellular proteins. In this study we used the fragment between helix C and D of PAI-2 as bait to screen a HeLa cells cDNA library constructed during apoptosis in a yeast two-hybrid system and retrieved a clone that encodes 241 amino acids of proteasome (prosome, macropain) subunit, beta type 1(PSMbeta1) which plays important roles in NF-kappaB activation. GST-pulldown experiments confirmed the interaction between PAI-2 and PSMB1 in vitro. These data suggest that the antiapoptosis activity of PAI-2 is probably related to its interaction with PSMbeta1.

Amino Acid Sequence↗

PubMed2004

Transcriptional regulation of urokinase receptor in high- (95D) and low-metastatic (95C) human lung cancer cells.

To study the transcriptional regulation of urokinase receptor (uPAR) in high- (95D) and low-metastatic (95C) human lung cancer cells, we performed PCR to amplify 2238 bp uPAR promoter from 95C and 95D cells. According to the results of sequencing, five different bases are found in uPAR promoter between 95C and 95D cells. The results of luciferase activity assay showed that these differences have no significant effect on the uPAR promoter activity. Based on a normal uPAR promoter, progressive truncated mutants were constructed. The transient transfection/reporter assay showed that the promoter region from -136 to +9 may interact with relevant nuclear factors, which result in different levels of uPAR expression between 95C and 95D cells.

Base Sequence↗

PubMed2004

A novel gene delivery system targeting urokinase receptor.

Recombinant proteins that combine different functions required for cell targeting and intra-cellular delivery of DNA present an attractive approach for the development of nonviral gene delivery vectors. Here, we described a novel protein termed ATF-lys10 which facilitated cell-specific gene transfer via receptor-mediated endocytosis. ATF-lys10 was composed of the amino-terminal fragment of urokinase and ten lysines at the carboxyl terminus. Bacterially expressed ATF-lys10 protein existed in soluble form, and had antigenicity of human urokinase. Purified ATF-lys10 specifically bound to uPAR-expressing cells and formed protein-DNA complexes with plasmid pGL3-control. After neutralization of excess negative charge with poly-L-lysine, these complexes served as a specific gene delivery vector for uPAR-expressing cells. Lyso-somotropic compounds, such as chloroquine, drastically increased the ATF-lys10 mediated gene delivery efficiency. Our results suggest that the recombinant protein ATF-lys10 with the properties of DNA binding and tumor cell targeting represents a promising method for gene transfer and expression in tumor cells.

Base Sequence↗

PubMed2004

Antisense Tiam1 down-regulates the invasiveness of 95D cells in vitro.

As a specific guanine nucleotide exchange factor of Rac1, Tiam1 (T-lymphoma invasion and metastasis inducing protein 1) is involved in a number of cellular events, such as cytoskeleton reorganization, cell adhesion, and cell migration. Since Tiam1 was implicated in the invasion and metastasis of T-lymphoma cells and breast tumor cells, we compared the expression level of Tiam1 in two human giant-cell lung carcinoma cell strains with high or low metastasis potential, and found that Tiam1 expression level in high-metastatic 95D cells was higher than that in low-metastatic 95C cells. To further confirm the role of Tiam1 in invasion and metastasis, we constructed the antisense Tiam1 expression plasmid (pcDNA3-anti-Tiam1), which was transfected into 95D cells. A stable transfected clone with decreased Tiam1 expression was screened and selected for further research. Transwell assay showed that down-regulation of endogenous Tiam1 by anti-Tiam1 can reduce the in vitro invasiveness of 95D cells. Our results suggested that Tiam1 signaling contributed to the invasion and metastasis of the human giant-cell lung carcinoma cells.

Base Sequence↗

PubMed2004

Interaction between plasminogen activator inhibitor type-2 and pre-mRNA processing factor 8.

The plasminogen activator inhibitor type-2 (PAI-2) dependent apoptosis protection is due to the 33 amino acids fragment located between helix C and D of PAI-2, this fragment may interact with some unknown intracellular proteins. In this study we used the fragment between helix C and D of PAI-2 as a bait to perform a yeast two-hybrid screen using a cDNA library constructed with HeLa cells during apoptosis, and retrieved a clone encoding 94 amino acid residues of C-terminus of pre-mRNA processing factor 8 (PRPF8). Co-immunoprecipitation experiments confirmed that PAI-2 could interact with PRPF8 in vivo. PAI-2 could bind PRPF8 C-terminal in both the inside and outside of nuclear. These results suggested that the interaction between these two proteins might not be involved in the apoptosis process.

Amino Acid Sequence↗

PubMed2004

A movable surface: formation of Yersinia sp. biofilms on motile Caenorhabditis elegans.

Bubonic plague is transmitted by fleas whose feeding is blocked by a mass of Yersinia pestis in the digestive tract. Y. pestis and the closely related Y. pseudotuberculosis also block the feeding of Caenorhabditis elegans by forming a biofilm on the nematode head. C. elegans mutants with severe motility defects acquire almost no biofilm, indicating that normal animals accumulate the biofilm matrix as they move through a Yersinia lawn. Using the lectin wheat germ agglutinin as a probe, we show that the matrix on C. elegans contains carbohydrate produced by Yersinia. The carbohydrate is present in bacterial lawns prior to addition of nematodes, indicating that biofilm formation does not involve signaling between the two organisms. Furthermore, biofilm accumulation depends on continuous C. elegans exposure to a lawn of Yersinia bacteria.

Animals↗

PubMed2004

Prophylactic treatment with growth hormone improves intestinal barrier function and alleviates bacterial translocation in stressed rats.

BACKGROUND: Damage to the gut barrier often occurs during critical illnesses. In such cases, it is very important to alleviate impairment of the intestinal barrier and protect intestinal barrier function. This study investigated the protective effect of growth hormone on intestinal barrier function in rats under stress. METHODS: This study consisted of prospective, randomized, and controlled animal experiments. Twenty-five Sprague-Dawley rats served as total parenteral nutrition (TPN) models and were divided into three groups: TPN group, sepsis (Sep) group, and growth hormone (GH) group. Another 8 rats served as normal controls. Each group received different stress stimuli. Rats were fed for 7 days, and samples were taken for examination 24 hours after gavaging with dual saccharides. RESULTS: The architecture of the small intestinal mucosa in the Sep group showed the most severe damage among all groups. Nitric oxide levels in blood plasma and immunoglobulin A levels in the intestinal mucosa of the GH group were significantly lower than in the Sep group (P < 0.02). There were no significant changes in CD3 counts and in the CD4/CD8 ratio between the four groups. Dual sugar tests and bacteriological examinations revealed that intestinal permeability and rate of bacterial translocation in the GH group were lower than in the Sep group (P < 0.01, respectively). CONCLUSION: Prophylactic treatment with growth hormone can alleviate damage to intestinal barrier function caused by trauma and endotoxemia in rats under stress.

Animals↗

PubMed2004

[Determination of gamma-aminobutyric acid and glutamate in human gastric mucosa by high performance liquid chromatography].

A method for analysis of gamma-aminobutyric acid (GABA) and glutamate (Glu) in human gastric mucosa by high performance liquid chromatography (HPLC) was developed. A gradient elution was used for the separation and quantification of GABA and Glu after pre-column derivatization with phenylisothiocyanate (PITC). The column was Pico x Tag for free amino acids. GABA and Glu were determined with UV detector at 254 nm. Good linearities were observed within the ranges from 0.125 to 6.25 micromol/L for GABA and from 0.025 to 2.5 mmol/L for Glu. The average recoveries were 95.4% for GABA and 93.5% for Glu. The intra- and inter-precision values were within 3.56% and 7.47% for GABA, and 1.12% and 5.98% for Glu, respectively. The method is sensitive, specific and accurate. It can be used in the determination of GABA and Glu in human gastric mucosa tissue. The concentrations of GABA and Glu in cancer tissues are significantly higher than those in normal tissue.

Chromatography, High Pressure Liquid↗

PubMed2003

Glycosylation motifs that direct arabinogalactan addition to arabinogalactan-proteins.

Hydroxyproline (Hyp)-rich glycoproteins (HRGPs) participate in all aspects of plant growth and development. HRGPs are generally highly O-glycosylated through the Hyp residues, which means carbohydrates help define the interactive molecular surface and, hence, HRGP function. The Hyp contiguity hypothesis predicts that contiguous Hyp residues are sites of HRGP arabinosylation, whereas clustered noncontiguous Hyp residues are sites of galactosylation, giving rise to the arabinogalactan heteropolysaccharides that characterize the arabinogalactan-proteins. Early tests of the hypothesis using synthetic genes encoding only clustered noncontiguous Hyp in the sequence (serine [Ser]-Hyp-Ser-Hyp)(n) or contiguous Hyp in the series (Ser-Hyp-Hyp)(n) and (Ser-Hyp-Hyp-Hyp-Hyp)(n) confirmed that arabinogalactan polysaccharide was added only to noncontiguous Hyp, whereas arabinosylation occurred on contiguous Hyp. Here, we extended our tests of the codes that direct arabinogalactan polysaccharide addition to Hyp by building genes encoding the repetitive sequences (alanine [Ala]-proline [Pro]-Ala-Pro)(n), (threonine [Thr]-Pro-Thr-Pro)(n), and (valine [Val]-Pro-Val-Pro)(n), and expressing them in tobacco (Nicotiana tabacum) Bright-Yellow 2 cells as fusion proteins with green fluorescent protein. All of the Pro residues in the (Ala-Pro-Ala-Pro)(n) fusion protein were hydroxylated and consistent with the hypothesis that every Hyp residue was glycosylated with arabinogalactan polysaccharide. In contrast, 20% to 30% of Pro residues remained non-hydroxylated in the (Thr-Pro-Thr-Pro)(n), and (Val-Pro-Val-Pro)(n) fusion proteins. Furthermore, although 50% to 60% of the Hyp residues were glycosylated with arabinogalactan polysaccharide, some remained non-glycosylated or were arabinosylated. These results suggest that the amino acid side chains of flanking residues influence the extent of Pro hydroxylation and Hyp glycosylation and may explain why isolated noncontiguous Hyp in extensins do not acquire an arabinogalactan polysaccharide but are arabinosylated or remain non-glycosylated.

Amino Acid Motifs↗

PubMed2003

Characterization of the first molluscicidal lipopolysaccharide from Moraxella osloensis.

Moraxella osloensis is a bacterium that is mutualistically associated with Phasmarhabditis hermaphrodita, a nematode that has potential for the biocontrol of mollusk pests, especially the slug Deroceras reticulatum. We discovered that purified M. osloensis lipopolysaccharide (LPS) possesses a lethal toxicity to D. reticulatum when administered by injection but no contact or oral toxicity to this slug. The toxicity of the LPS resides in the lipid A moiety. M. osloensis LPS was semiquantitated at 6 x 10(7) endotoxin units per mg. The LPS is a rough-type LPS with an estimated molecular weight of 5,300. Coinjection of galactosamine with the LPS increased the LPS's toxicity to the slug two- to four-fold. The galactosamine-induced sensitization of the slug to the LPS was reversed completely by uridine.

Animals↗

PubMed2003

[Screening of proteins interacting with tTG in HeLa cells].

Tissue transglutaminase(tTG) belongs to a class of transglutaminase family which is up-regulated in almost all cells apoptosis and is thought to be closely related to cell apoptosis. To investigate the mechanism of tTG in cell apoptosis, yeast two hybrid system was used to screen HeLa cDNA library. One of the 17 positive clones we have obtained encoded the glutamine-rich carboxyl terminus of TIAR, and this interaction between tTG and TIAR, which was finely regulated by Ca(2+), was proved in vitro by GST pull-down. These findings suggest that tTG might affect the function of TIAR by a calcium-dependent posttranslational modification and the interaction might possibly be involved in the regulation of cell apoptosis.

Amino Acid Sequence↗

PubMed2003

[The effects of weight reduction in reversing fatty liver changes in overweight and obese patients].

OBJECTIVE: To study the effects of weight loss on nonalcoholic steatohepatitis (NASH) in obese patients. METHODS: It is a prospective study. Blood biochemical parameters were examined in 220 overweight or obese patients without alcoholic consumption and without detectable HBsAg. Ultrasonographic examination was performed by a fixed doctor. 45 obese patients followed a program of weight loss, including diet restriction, exercise or drug for a trial period of one year. Weight, blood biochemical tests and ultrasonic examination of liver were compared before and after the trial in all the patients. RESULTS: 75.9% of the patients were diagnosed as NASH. Logistic regression analysis revealed that the risk factors of NASH were body mass index (BMI, beta = 0.926, P = 0.021), age (beta = 0.973, P = 0.021), 2-hour postprandial glucose (beta = 0.987, P = 0.012), 1-hour postprandial net insulin in serum (beta = 1.027, P = 0.032), waist circumference (beta = 1.091, P = 0.038)and low density lipoprotein cholesterol (beta = 0.980, P = 0.041). After the treatment, 65.7% of the patients with NASH improved. The level of ALT in these patients decreased significantly (P = 0.040). The improvement of NASH correlated positively with the reduction of BMI (beta = 3.032, P = 0.010), triglycerides (TG, beta = 1.041, P = 0.025) and waist circumference (beta = 1.115, P = 0.029). The decrease of ALT level correlated with the decrease of BMI (beta = 1.165, P = 0.002), TG (beta = 0.986, P = 0.005), waist circumference (beta = 0.736, P = 0.041), and the increase of high density lipoprotein cholesterol (beta = -0.772, P = 0.016). CONCLUSION: NASH is one of the most important complications of obesity. Weight loss is the mainstay of treatment for obese patients.

Adolescent↗

PubMed2003

[Biological function of fusion protein ATF-PAI2CD].

To express the fusion protein ATF-PAI2CD (urokinase-type plasminogen activator amino terminal fragment-plasminogen activator inhibitor type 2 with the region inter C and D helices deleted ) gene in E.coli and determine the biological characterization of fusion protein ATF-PAI2CD, the cDNA fragment encoding ATF-PAI2CD was cloned into the expression vector pLY-4 and transformed into E.coli JF1125. After temperature induction, the expression amount of ATF-PAI2CD account for 15% of total bacterial protein. The result was confirmed by Western blot. ATF-PAI2CD protein was isolated and purified by washing and solubilization of inclusion body, renaturation and ion exchange chromatography. The final product displayed a single band with a corresponding molecular weight 62 kD in SDS-PAGE. The purity was over 90%, the protein yield was 50% and the specific activity was 12 000 IU/mg. The PAI activity was measured by chromogenic assay. The purified fusion protein inhibited urokinase-type plasminogen activator as measured by milk-agarose plate assay, and bound to human lung cancer cells via uPA receptor (uPAR), which was confirmed by radio competition experiments. The results indicate that the biological characteristics of ATF-PAI2CD were very similar to those of the wide type PAI-2 (or mutants PAI-2, PAI-2CD) and to pro-uPA in binding to uPAR-bearing cells.

Escherichia coli↗