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Wen Liu

Publications and source records attributed to Wen Liu.

At least 73 records · Page 4Linked to original sources
PubMed2004

Biochemical characterization of the SgcA1 alpha-D-glucopyranosyl-1-phosphate thymidylyltransferase from the enediyne antitumor antibiotic C-1027 biosynthetic pathway and overexpression of sgcA1 in Streptomyces globisporus to improve C-1027 production.

Sequence analysis of the biosynthetic gene cluster for the enediyne antitumor antibiotic C-1027 from Streptomyces globisporus has previously suggested that the sgcA1 gene encodes a alpha-d-glucopyranosyl-1-phosphate thymidylyltransferase (Glc-1-P-TT) catalyzing the first step in the biosynthesis of the 4-deoxy-4-(dimethylamino)-5,5-dimethyl-d-ribopyranose moiety by activating alpha-d-glucopyranosyl-1-phosphate (Glc-1-P) into deoxythymidine diphosphate-alpha-d-glucose (dTDP-Glc). Here we report the overexpression of sgcA1 in E. coli, purification of the overproduced SgcA1 to homogenetity, biochemical and kinetic characterization of the purified SgcA1 as a Glc-1-P-TT, and yield improvement for C-1027 production by overexpression of sgcA1 and its flanking gene in S. globisporus. These findings provide biochemical evidence supporting the genetics-based hypothesis for C-1027 biosynthesis, set the stage for further investigation of the deoxysugar biosynthetic pathway, and demonstrate the utility of sugar biosynthesis genes in natural product yield improvement via combinatorial biosynthesis methods. In contrast to the homotetrameric quaternary structure known for Glc-1-P-TT enzymes from primary metabolic pathways, Glc-1-P-TT enzymes such as SgcA1 from secondary metabolic pathways are monomeric in solution. Sequence differences between the two subclasses of Glc-1-P-TT enzymes were noted. The monomeric structural feature of the latter enzymes could be exploited in engineering Glc-1-P-TT enzymes with broad substrate specificity for structural diversity via the glycorandomization strategy.

Amino Acid Sequence↗
PubMed2004

Bioptic significance of incarcerated contents at sclerotomy sites during vitrectomy.

PURPOSE: To study the clinical significance of incarcerated materials at sclerotomy sites during vitrectomy. METHODS: Fifty samples prolapsed from the entries to standard three-port pars plana vitrectomies were collected along the scleral surface. Samples from rhegmatogenous retinal detachments (RD) (n = 28), traumatic RD (n = 4), miscellaneous vitreous hemorrhages (n = 12), and intraocular foreign bodies (n = 6) were stained with hematoxylineosin and examined under light microscopy after being fixed in paraffin sections or smeared on slides. RESULTS: The specimens collected after sclerotomy contained vitreous tissue mixed with dispersive and sheet nonpigmented ciliary epithelia, scattered pigment granules, and small pigment gobbets. Specimens collected during vitrectomy contained pigment granules and various cells with a jellylike appearance. Fibrous tissue and remnants of ciliary body and retina were found in some specimens. The incarcerated tissues caused 12 cases of iatrogenic retinal breaks, among which RD recurred in six cases postoperatively due to anterior proliferative vitreoretinopathy. In the noniatrogenic retinal break group, only 4 RD recurred (6/12 versus 4/38, chi2 = 6.586, P = 0.01). CONCLUSION: The incarcerated contents at sclerotomy sites were mainly adjacent tissues and cells. Prolapsed and incarcerated ciliary body and retina fragments were common and might cause iatrogenic retinal breaks. Attention should be paid to this material intraoperatively.

Biopsy↗
PubMed2004

Retinoid X receptor regulates Nur77/TR3-dependent apoptosis [corrected] by modulating its nuclear export and mitochondrial targeting.

Retinoid X receptor (RXR) plays a central role in the regulation of intracellular receptor signaling pathways by acting as a ubiquitous heterodimerization partner of many nuclear receptors, including the orphan receptor Nur77 (also known as TR3 [corrected] or NGFI-B), which translocates from the nucleus to mitochondria, where it interacts with Bcl-2 to induce apoptosis. Here, we report that RXRalpha is required for nuclear export and mitochondrial targeting of Nur77 through their unique heterodimerization that is mediated by dimerization interfaces located in their DNA-binding domain. The effects of RXRalpha are attributed to a putative nuclear export sequence (NES) present in its carboxyl-terminal region. RXRalpha ligands suppress NES activity by inducing RXRalpha homodimerization or altering RXRalpha/Nur77 heterodimerization. The RXRalpha NES is also silenced by RXRalpha heterodimerization with retinoic acid receptor or vitamin D receptor. Consistently, we were able to show that the mitochondrial targeting of the RXRalpha/Nur77 heterodimer and its induction of apoptosis are potently inhibited by RXR ligands. Together, our results reveal a novel nongenotropic function of RXRalpha and its involvement in the regulation of the Nur77-dependent apoptotic pathway [corrected]

Active Transport, Cell Nucleus↗
PubMed2004

Effects of antipsychotics on fat deposition and changes in leptin and insulin levels. Magnetic resonance imaging study of previously untreated people with schizophrenia.

BACKGROUND: Weight gain is a common consequence of antipsychotic drug treatment and can lead to further morbidity. AIMS: To assess the effects of antipsychotic drug therapy on abdominal fat deposition, on insulin and leptin secretion, and on circulating glucose and lipids. METHOD: Abdominal body fat was determined by magnetic resonance imaging in a group of previously untreated patients with schizophrenia, before and after 10 weeks' antipsychotic drug treatment. Body mass and blood concentrations of glucose, insulin, leptin and lipids were also measured. RESULTS: Significant increases in both subcutaneous and intra-abdominal fat were identified after antipsychotic drug treatment. A three-fold increase in leptin secretion as well as significant increases in levels of circulating lipids and non-fasting glucose were also identified. CONCLUSIONS: Patients first receiving antipsychotic drugs experience substantial deposition of both subcutaneous and intra-abdominal fat, reflecting a loss of the normal inhibitory control of leptin on body mass. Along with fat deposition, the increase in levels of fasting lipids and in non-fasting glucose may provide early signs of drug-induced progression towards the metabolic syndrome.

Abdomen↗
PubMed2004

[Adjuvant treatment of anisodamine to acute serous otitis media].

OBJECTIVE: To evaluate the adjuvant treatment of anisodamine to acute serous otitis media. METHOD: Sixty-one acute otitis media patients were divided randomly into two groups. Group A with 30 patients were treated with 1% ephedrine nosedrop, antibiotic and antihistamine. Group B with 30 patients were treated with 1% ephedrine nose drops, antibiotic, antihistamine and anisodamine. They took anisodamine 10 mg twice a day. Then the treating efficiency of group A was compared with that of group B in 5 days and 10 days respectively. RESULT: The symptoms including hearing loss, tinnitus, hydrotympanum and eustachian tube function of group B recover more guickly than that of group A. CONCLUSION: Anisodamine adjuvant treatment of acute serous otitis media by improving the function of eustachian tube and microcirculation.

Acute Disease↗
PubMed2003

[Association of -2548G/A functional polymorphism in the promoter region of leptin gene with antipsychotic agent-induced weight gain].

OBJECTIVE: To investigate whether the -2548G/A functional polymorphism in promoter region of leptin gene influencing weight gain following antipsychotic agents (APS) acute treatment in schizophrenic patients. METHODS: 128 Chinese Han untreated patients with schizophrenia (male 61, female 67) with an age and gender matched health controls (n = 38) were recruited. The polymorphism of leptin gene was determined with PCR-RFLP technique. MRI determined abdominal body fat in 22 controls and 30 patients on admission and after 10 weeks treatment with risperidone or chlorpromazine. Body mass index (BMI) was measured on admission and every week subsequently (for patients). RESULTS: There were average increases in (6.2 +/- 5.7)% of baseline weight and in (38.5 +/- 42)% of baseline abdominal subcutaneous fat (SUB) and in (40.0 +/- 41.2)% of baseline intra-abdominal fat (IAF) 10 weeks after treatment. There were no significant differences in the distribution of allele and genotypes either between the patients and controls or between gender groups. It was found significantly increased weight gain in the patient with the -2548AA genotype (chi(2) = 7.529, df = 1, P = 0.006; OR = 1.941; 95% CI: 1.175 - 3.207); The genotypes had no influence on the baseline weight indicators both in patients and controls. However, as compared with the patients with G allele, the patients with AA genotype had significant increase in BMI (P = 0.003) and SUB (P = 0.009). CONCLUSION: The finding identify that the -2548G/A polymorphism in promoter region of leptin gene associated with APS-induced weight gain and abdominal fat deposition and distribution. -2548AA may be a genetic risk factor for the development of weight gain and body fat deposition in Chinese Han schizophrenic patients during APS acute treatment.

Adipose Tissue↗
PubMed2003

Ascorbic acid antagonizes the inhibitory effect of acute ethanol on nitrite levels in the striatum of freely moving mice.

The effect of exogenous ascorbic acid (AA) on acute ethanol-induced decrease in extracellular nitrites contents in striatum of freely moving mice was investigated by using microdialysis coupled to high performance liquid chromatography with electrochemical detection. The results showed that exogenous AA had no effect on basal extracellular levels of nitrites, but significantly increased striatal extracellular contents of AA in a dose-depended manner. Co-administration of AA with ethanol significantly antagonized the ethanol-induced decrease in extracellular nitrites contents, but did not affect ethanol-induced release of AA. These data provided the first evidence of an antagonistic action of AA on ethanol-induced decrease in extracellular nitrites contents in striatum of freely moving mice.

Animals↗
PubMed2003

Role of nitric oxide in ethanol-induced ascorbic acid release in striatum of freely moving mice.

In the present study, in vivo brain microdialysis coupled with high performance liquid chromatography (HPLC) and electrochemical detection were used to evaluate the effects of either L-arginine (L-Arg), the substrate of nitric oxide synthase (NOS), Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME), a non-selective NOS inhibitor, or sodium nitroprusside (SNP), a donor of NO, on the ethanol-induced release of ascorbic acid (AA) in the striatum of freely moving mice. Drugs were administered intrastriatally via the microdialysis probe and ethanol (2-4 g/kg) was administered intraperitoneally. The results showed that L-arginine (1-10 mg/ml) had no effect on either the basal AA contents in striatal extracellular fluid or the ethanol-induced release of AA. L-NAME (10(-4) to 10(-3) mg/ml) and SNP (10(-4) to 10(-3) mg/ml) both reduced the basal AA concentrations in striatal extracellular fluid. L-NAME significantly inhibited ethanol-induced release of AA, while SNP only had a transient inhibitory effect on the ethanol-induced release of AA. SNP significantly increased dehydroascorbic acid (DHAA) contents and DHAA/AA ratio but had no effect on the total AA contents (AA and DHAA contents) in striatal extracellular fluid, while L-NAME had no effect on DHAA contents but decreased the total AA contents in striatal extracellular fluid. Only high concentration L-NAME induced a transient increase in DHAA/AA ratio. Our results suggest that nitric oxide (NO) might not directly be involved in the mechanism of ethanol-induced release of AA in mouse striatum.

Animals↗
PubMed2003

Isolation of temperature-sensitive p53 mutations from a comprehensive missense mutation library.

Temperature-sensitive (ts) mutations have been used as a genetic and molecular tool to study the functions of many gene products. Each ts mutant protein may contain a temperature-dependent intramolecular mechanism such as ts conformational change. To identify key ts structural elements controlling the protein function, we screened ts p53 mutants from a comprehensive mutation library consisting of 2,314 p53 missense mutations for their sequence-specific transactivity through p53-binding sequences in Saccharomyces cerevisiae. We isolated 142 ts p53 mutants, including 131 unreported ts mutants. These mutants clustered in beta-strands in the DNA-binding domain, particularly in one of the two beta-sheets of the protein, and 15 residues (Thr155, Arg158, Met160, Ala161, Val172, His214, Ser215, Pro223, Thr231, Thr253, Ile254, Thr256, Ser269, Glu271, and Glu285) were ts hot spots. Among the 142 mutants, 54 were examined further in human osteosarcoma Saos-2 cells, and it was confirmed that 89% of the mutants were also ts in mammalian cells. The ts mutants represented distinct ts transactivities for the p53 binding sequences and a distinct epitope expression pattern for conformation-specific anti-p53 antibodies. These results indicated that the intramolecular beta-sheet in the core DNA-binding domain of p53 was a key structural element controlling the protein function and provided a clue for finding a molecular mechanism that enables the rescue of the mutant p53 function.

Amino Acid Sequence↗
PubMed2003

Rapid PCR amplification of minimal enediyne polyketide synthase cassettes leads to a predictive familial classification model.

A universal PCR method for the rapid amplification of minimal enediyne polyketide synthase (PKS) genes and the application of this methodology to clone remaining prototypical genes from producers of structurally determined enediynes in both family types are presented. A phylogenetic analysis of the new pool of bona fide enediyne PKS genes, consisting of three from 9-membered producers (neocarzinostatin, C1027, and maduropeptin) and three from 10-membered producers (calicheamicin, dynemicin, and esperamicin), reveals a clear genotypic distinction between the two structural families from which to form a predictive model. The results from this study support the postulation that the minimal enediyne PKS helps define the structural divergence of the enediyne core and provides the key tools for generating enediyne hybrid genes/molecular scaffolds; by using the model, a classification is also provided for the unknown enediyne PKS genes previously identified via genome scanning.

Actinomycetales↗
PubMed2003

Effect of flow and stretch on the [Ca2+]i response of principal and intercalated cells in cortical collecting duct.

An acute increase in tubular fluid flow rate in the microperfused cortical collecting duct (CCD), associated with a approximately 20% increase in tubular diameter, leads to an increase in intracellular Ca2+ concentration ([Ca2+]i)in both principal and intercalated cells (Woda CB, Leite M Jr, Rohatgi R, and Satlin LM. Am J Physiol Renal Physiol 283: F437-F446, 2002). The apical cilium present in principal but not intercalated cells has been proposed to be a flow sensor. To determine whether flow across the cilium and/or epithelial stretch mediates the [Ca2+]i response, CCDs from New Zealand White rabbits were microperfused in vitro, split-open (to isolate the effect of flow across cilia), or occluded (to examine the effect of stretch and duration/magnitude of the flow impulse), and [Ca2+]i was measured using fura 2. In perfused and occluded CCDs, a rapid (<1 s) but not slow (>3 min) increase in luminal flow rate and/or circumferential stretch led to an approximately threefold increase in [Ca2+]i in both principal and intercalated cells within approximately 10 s. This response was mediated by external Ca2+ entry and inositol 1,4,5-trisphosphate-mediated release of cell Ca2+ stores. In split-open CCDs, an increase in superfusate flow led to an approximately twofold increase in [Ca2+]i in both cell types within approximately 30 s. These experimental findings are interpreted using mathematical models to predict the fluid stress on the apical membranes of the CCD and the forces and torques on and deformation of the cilia. We conclude that rapid increases in luminal flow rate and circumferential stretch, leading to shear or hydrodynamic impulses at the cilium or apical membrane, lead to increases in [Ca2+]i in both principal and intercalated cells.

Animals↗
PubMed2003

Understanding the function-structure and function-mutation relationships of p53 tumor suppressor protein by high-resolution missense mutation analysis.

Inactivation of the tumor suppressor p53 by missense mutations is the most frequent genetic alteration in human cancers. The common missense mutations in the TP53 gene disrupt the ability of p53 to bind to DNA and consequently to transactivate downstream genes. However, it is still not fully understood how a large number of the remaining mutations affect p53 structure and function. Here, we used a comprehensive site-directed mutagenesis technique and a yeast-based functional assay to construct, express, and evaluate 2,314 p53 mutants representing all possible amino acid substitutions caused by a point mutation throughout the protein (5.9 substitutions per residue), and correlated p53 function with structure- and tumor-derived mutations. This high-resolution mutation analysis allows evaluation of previous predictions and hypotheses through interrelation of function, structure and mutation.

Amino Acid Substitution↗
PubMed2003

A novel 4-methylideneimidazole-5-one-containing tyrosine aminomutase in enediyne antitumor antibiotic C-1027 biosynthesis.

The C-1027 enediyne antibiotic contains an unusual 3-chloro-4,5-dihydroxy-beta-phenylalanine moiety that is thought to be derived from tyrosine by an aminomutase reaction. However, none of the genes identified within the C-1027 gene cluster encode proteins with strong homology to known aminomutases. The sgcC4 gene encodes a protein with strong homology to dehydroalanine-dependent histidine/phenylalanine ammonia lyases. The sgcC4 gene was expressed in E. coli, and overproduced SgcC4 was purified as a His6-tagged fusion protein. Biochemical characterization of the purified SgcC4 establishes that SgcC4 is an aminomutase that catalyzes the conversion of l-tyrosine to (S)-beta-tyrosine and employs 4-methylideneimidazole-5-one (MIO) at its active site. The latter was supported by borohydride and cyanide inhibition studies and confirmed by site-directed mutagenesis. The S153A mutant exhibited a 340-fold decrease in kcat/KM. SgcC4 represents a novel type of aminomutase, extending the known MIO chemistry from ammonia lyases into aminomutases.

Alanine↗
PubMed2003

The selective inhibition of phosphatases by natural toxins: the anhydride domain of tautomycin is not a primary factor in controlling PP1/PP2A selectivity.

Analogues of the potent and moderately selective PP1/PP2A inhibitor tautomycin (TM) were prepared with modifications in the C1'-C7' anhydride moiety. While all retain varying degrees of activity within a 3000-fold range of potencies, they also show remarkable constancy in their IC(50) ratios, suggesting that the anhydride moiety is not critical in controlling the selectivity of inhibition.

Anhydrides↗
PubMed2003

A new model of the tautomycin-PP1 complex that is not analogous to the corresponding okadaic acid structure.

A revised model of PP1-tautomycin (TM) complex suggests that this toxin does not bind in a conformation analogous to its structural cousin okadaic acid (OA), as has been assumed, but instead more resembles the mode of binding adopted by calyculin. This model rationalizes the unexpected potency of a truncated TM analogue lacking the bicyclic ketal common to TM and OA.

Enzyme Inhibitors↗
PubMed2003

Sequence and structure of the extrachromosomal palindrome encoding the ribosomal RNA genes in Dictyostelium.

Ribosomal RNAs (rRNAs) are encoded by multicopy families of identical genes. In Dictyostelium and other protists, the rDNA is carried on extrachromosomal palindromic elements that comprise up to 20% of the nuclear DNA. We present the sequence of the 88 kb Dictyostelium rDNA element, noting that the rRNA genes are likely to be the only transcribed regions. By interrogating a library of ordered YAC clones, we provide evidence for a chromosomal copy of the rDNA on chromosome 4. This locus may provide master copies for the stable transmission of the extrachromosomal elements. The extrachromosomal elements were also found to form chromosome-sized clusters of DNA within nuclei of nocodazole-treated cells arrested in mitosis. These clusters resemble true chromosomes and may allow the efficient segregation of the rDNA during mitosis. These rDNA clusters may also explain the cytological observations of a seventh chromosome in this organism.

Animals↗
PubMed2003

A genomics-guided approach for discovering and expressing cryptic metabolic pathways.

Genome analysis of actinomycetes has revealed the presence of numerous cryptic gene clusters encoding putative natural products. These loci remain dormant until appropriate chemical or physical signals induce their expression. Here we demonstrate the use of a high-throughput genome scanning method to detect and analyze gene clusters involved in natural-product biosynthesis. This method was applied to uncover biosynthetic pathways encoding enediyne antitumor antibiotics in a variety of actinomycetes. Comparative analysis of five biosynthetic loci representative of the major structural classes of enediynes reveals the presence of a conserved cassette of five genes that includes a novel family of polyketide synthase (PKS). The enediyne PKS (PKSE) is proposed to be involved in the formation of the highly reactive chromophore ring structure (or "warhead") found in all enediynes. Genome scanning analysis indicates that the enediyne warhead cassette is widely dispersed among actinomycetes. We show that selective growth conditions can induce the expression of these loci, suggesting that the range of enediyne natural products may be much greater than previously thought. This technology can be used to increase the scope and diversity of natural-product discovery.

Actinobacteria↗