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S Liu

Publications and source records attributed to S Liu.

At least 235 records · Page 13Linked to original sources
PubMed2000

Interaction of MyoD family proteins with enhancers of acetylcholine receptor subunit genes in vivo.

The myogenic determination factors (MDFs) are transcriptional activators that target E boxes in many muscle-specific promoters, including those of the genes coding for the subunits of the acetylcholine receptor. It is not known, however, if in vivo a given E box in a transcriptionally active gene is occupied, either uniquely by one MDF or randomly by all MDFs. We have analyzed expression of MDF and acetylcholine receptor subunits in cultured mouse muscle cells and, using chromatin immunoprecipitation, have determined which individual MDFs reside at promoters of several receptor subunit genes. We find that before fusion, C2C12 cells express myf-5, MyoD, and myogenin, all of which take up residence at promoters of all subunits except epsilon. At this stage, herculin is present in limited amounts and is detected mainly at the gamma and delta subunit genes. On myotube formation, herculin reaches high levels; concomitantly, the epsilon subunit gene becomes a common MDF target and begins to be expressed. In general, any MDF protein that is expressed also is present on transcriptionally active receptor genes; transcriptional activity of target genes correlates with occupancy by MDF, in particular, herculin.

Animals↗
PubMed2000

Reduction of inner sulfonium salts, thioethers, and sulfones derived from closo-[B12H12]2- by lithium in methylamine: a new route to mercaptododecaborates.

Anions [Me2SB12H11]- (2) and [MeSB12H11]2- (3) can be reduced by excess lithium in methylamine at -15 degrees C to yield [HSB12H11]2- (1) after workup. Such behavior toward this reducing system is similar to that of alkyl aryl sulfides. The sulfone [MeSO2B12H11]2- (12) also yields 1 as a major boron product upon reduction, while alkyl aryl sulfones produce the corresponding arenes under the same conditions. Similarly, isomers of (Me2S)2B12H10 (4-6) are reduced by lithium in methylamine yielding dithiols [(HS)2B12H10]2- (7-9). The tetrabutylammonium salts of 1 and 7-9 are obtained in 80-90% yields and characterized by multinuclear NMR and mass spectrometry, the latter three compounds being isolated and characterized for the first time. The reduction reaction provides access to dithiols 7-9 for biological evaluation and use in synthesis. Thus, 2 and 4-6 can be easily converted to [R2SB12H11]- and (R2S)2B12H10 in a two-step reduction-alkylation procedure. 1,2-(Bn2S)2B12H10 (13) obtained by alkylation of the reduction product of 4 by benzyl chloride was characterized by single-crystal X-ray diffraction analysis. Crystal data for 1,2-(Bn2S)2B12H10.CD3CN: C2/c (No. 15), a = 13.666(1) A, b = 16.978(1) A, c = 14.667(1) A, beta = 91.08(1) degrees, Z = 4.

Journal Article↗
PubMed2000

Cloning and heterologous expression of a sulfur oxygenase/reductase gene from the thermoacidophilic archaeon Acidianus sp. S5 in Escherichia coli.

A thermoacidophilic, obligately chemolithotrophic, facultatively aerobic archaebacterium, Acidianus sp. S5, was isolated from acidothermal springs in southwest China. The sulfur oxygenase/reductase (SOR) gene of Acidianus sp. S5 was cloned and expressed in Escherichia coli. Several primers were designed and successfully applied for detection and cloning of the sor gene. A 3.7-kb EcoRI fragment containing the sor gene and three neighboring open reading frames was sequenced. Sequence analysis indicated that the sor gene of Acidianus sp. S5 showed 81% identity to the sor gene of Acidianus ambivalens. E. coli cells carrying the sor gene on pBV220SOR were able to overproduce SOR upon a temperature shift from 30 to 42 degrees C. SOR produced in E. coli catalyzes the oxidation of elemental sulfur and concomitant production of sulfite, thiosulfate and hydrogen sulfide. The recombinant enzyme exhibits the same catalytic properties as the one from Acidianus S5.

Amino Acid Sequence↗
PubMed2000

Docosahexaenoic acid, a ligand for the retinoid X receptor in mouse brain.

The retinoid X receptor (RXR) is a nuclear receptor that functions as a ligand-activated transcription factor. Little is known about the ligands that activate RXR in vivo. Here, we identified a factor in brain tissue from adult mice that activates RXR in cell-based assays. Purification and analysis of the factor by mass spectrometry revealed that it is docosahexaenoic acid (DHA), a long-chain polyunsaturated fatty acid that is highly enriched in the adult mammalian brain. Previous work has shown that DHA is essential for brain maturation, and deficiency of DHA in both rodents and humans leads to impaired spatial learning and other abnormalities. These data suggest that DHA may influence neural function through activation of an RXR signaling pathway.

Animals↗
PubMed2000

Cloning of differentially expressed sequence tags from nickel-transformed human embryonic lung cells.

Differential display polymerase chain reaction (DD-PCR) was used to analyze the differentially expressed genes from nickel-transformed human embryonic lung (HEL) cells (MRC-9 and IMR-90) and their control counterparts (non-treated). Two genes, MS515 and IC82, were confirmed by Northern blot analysis. MS515 was detected in control and nickel oxide (NiO)-transformed MRC-9 cells, as well as in non-small cell lung cancer (NSCLC) EBC-1 cells, while very weak expression was observed in nickel subsulfide (Ni(3)S(2))-transformed MRC-9 cells and small cell lung cancer (SCLC) SBC-2 cells. IC82 could not be detected in control IMR-90 cells, while it was expressed in EBC-1 cells and NiO- and Ni(3)S(2)-transformed IMR-90 cells. These findings indicate that individual nickel compounds have their own target gene(s) in inducing lung cancer. Sequencing analyses showed that the MS515 gene shared a high degree of homology (over 80%) with the gene Mena, which is involved in actin polymerization. IC82 showed 99% homology with human chromosome 4 clone C0440E08 and a coding sequence in the brain. The roles of these two genes in nickel carcinogenesis will be discussed.

Base Sequence↗
PubMed2000

Impact of prenatal glucose screening on the diagnosis of gestational diabetes and on pregnancy outcomes.

The authors examined the impact of universal screening on the diagnosis of gestational diabetes and its complications. All mothers and newborns registered by the Canadian Institute for Health Information from 1984 to 1996 (even-numbered fiscal years only) were included in the analysis. Over this time period, the proportion of women with gestational diabetes increased ninefold (from 0.3% to 2.7%) while the proportion with prepregnancy diabetes fell from 0.7% to 0.4%. As rates of gestational diabetes increased, a corresponding reduction in the risks of complications (polyhydramnios, amniotic cavity infection, cesarean delivery, and preeclampsia) occurred for women with gestational diabetes. The incidence of gestational diabetes fell in Metro-Hamilton (where screening was discontinued in 1989) but remained high in the rest of Ontario (where screening continued in most areas). No related temporal trends for fetal macrosomia, cesarean delivery, or other diabetes-related complications were observed, regardless of screening policy. The authors concluded that the substantial increase in gestational diabetes in Canada is an artifact caused by universal screening, with no evidence of beneficial effects on pregnancy outcomes.

Blood Glucose↗
PubMed2000

Molecular cloning of a regulatory protein for membrane-bound guanylate cyclase GC-A.

Activation of membrane-bound guanylate cyclase GC-A by atrial natriuretic factor (ANF) may require the involvement of accessory proteins. To identify these postulated proteins, we isolated a 1. 0-kb cDNA clone from a rat brain expression library using a polyclonal antiserum against mastoparan. The 1.0-kb cDNA encodes a protein of 111 amino acids. Expression of this cDNA in COS-7 cells potentiated ANF-stimulated GC-A activity. Therefore, the 1.0-kb gene encodes a guanylate cyclase regulatory protein (GCRP). Fluorescence microscopy studies using the fusion protein of GCRP with green fluorescence protein (GFP) indicated that GCRP was present in the cytosol in PC12 cells, but translocated toward the plasma membrane in the presence of ANF. Coimmunoprecipitation experiments indicate that GCRP associates with GC-A in the presence of ANF. These results suggest that ANF induces the association of GCRP with GC-A and this association contributes to the activation of GC-A.

Amino Acid Sequence↗
PubMed2000

Neural stem cells display extensive tropism for pathology in adult brain: evidence from intracranial gliomas.

One of the impediments to the treatment of brain tumors (e.g., gliomas) has been the degree to which they expand, infiltrate surrounding tissue, and migrate widely into normal brain, usually rendering them "elusive" to effective resection, irradiation, chemotherapy, or gene therapy. We demonstrate that neural stem cells (NSCs), when implanted into experimental intracranial gliomas in vivo in adult rodents, distribute themselves quickly and extensively throughout the tumor bed and migrate uniquely in juxtaposition to widely expanding and aggressively advancing tumor cells, while continuing to stably express a foreign gene. The NSCs "surround" the invading tumor border while "chasing down" infiltrating tumor cells. When implanted intracranially at distant sites from the tumor (e.g., into normal tissue, into the contralateral hemisphere, or into the cerebral ventricles), the donor cells migrate through normal tissue targeting the tumor cells (including human glioblastomas). When implanted outside the CNS intravascularly, NSCs will target an intracranial tumor. NSCs can deliver a therapeutically relevant molecule-cytosine deaminase-such that quantifiable reduction in tumor burden results. These data suggest the adjunctive use of inherently migratory NSCs as a delivery vehicle for targeting therapeutic genes and vectors to refractory, migratory, invasive brain tumors. More broadly, they suggest that NSC migration can be extensive, even in the adult brain and along nonstereotypical routes, if pathology (as modeled here by tumor) is present.

Animals↗
PubMed2000

A phase I/II trial of iodine-131-tositumomab (anti-CD20), etoposide, cyclophosphamide, and autologous stem cell transplantation for relapsed B-cell lymphomas.

Relapsed B-cell lymphomas are incurable with conventional chemotherapy and radiation therapy, although a fraction of patients can be cured with high-dose chemoradiotherapy and autologous stem-cell transplantation (ASCT). We conducted a phase I/II trial to estimate the maximum tolerated dose (MTD) of iodine 131 ((131)I)-tositumomab (anti-CD20 antibody) that could be combined with etoposide and cyclophosphamide followed by ASCT in patients with relapsed B-cell lymphomas. Fifty-two patients received a trace-labeled infusion of 1.7 mg/kg (131)I-tositumomab (185-370 MBq) followed by serial quantitative gamma-camera imaging and estimation of absorbed doses of radiation to tumor sites and normal organs. Ten days later, patients received a therapeutic infusion of 1.7 mg/kg tositumomab labeled with an amount of (131)I calculated to deliver the target dose of radiation (20-27 Gy) to critical normal organs (liver, kidneys, and lungs). Patients were maintained in radiation isolation until their total-body radioactivity was less than 0.07 mSv/h at 1 m. They were then given etoposide and cyclophosphamide followed by ASCT. The MTD of (131)I-tositumomab that could be safely combined with 60 mg/kg etoposide and 100 mg/kg cyclophosphamide delivered 25 Gy to critical normal organs. The estimated overall survival (OS) and progression-free survival (PFS) of all treated patients at 2 years was 83% and 68%, respectively. These findings compare favorably with those in a nonrandomized control group of patients who underwent transplantation, external-beam total-body irradiation, and etoposide and cyclophosphamide therapy during the same period (OS of 53% and PFS of 36% at 2 years), even after adjustment for confounding variables in a multivariable analysis.

Adult↗
PubMed2000

Tumor cell-selective cytotoxicity of matrix metalloproteinase-activated anthrax toxin.

Matrix metalloproteinases (MMPs) are overexpressed in a variety of tumor tissues and cell lines, and their expression is highly correlated to tumor invasion and metastasis. To exploit these characteristics in the design of tumor cell-selective cytotoxins, we constructed two mutated anthrax toxin protective antigen (PA) proteins in which the furin protease cleavage site is replaced by sequences selectively cleaved by MMPs. These MMP-targeted PA proteins were activated rapidly and selectively on the surface of MMP-overexpressing tumor cells. The activated PA proteins caused internalization of a recombinant cytotoxin, FP59, consisting of anthrax toxin lethal factor residues 1-254 fused to the ADP-ribosylation domain of Pseudomonas exotoxin A. The toxicity of the mutated PA proteins for MMP-overexpressing cells was blocked by hydroxamate inhibitors of MMPs, including BB94, and by a tissue inhibitor of matrix metalloproteinases (TIMP-2). The mutated PA proteins killed MMP-overexpressing tumor cells while sparing nontumorigenic normal cells when these were grown together in a coculture model, indicating that PA activation occurred on the tumor cell surface and not in the supernatant. This method of achieving cell-type specificity is conceptually distinct from, and potentially synergistic with, the more common strategy of retargeting a protein toxin by fusion to a growth factor, cytokine, or antibody.

Amino Acid Sequence↗
PubMed2000

Cucumber mosaic virus mutants with altered physical properties and defective in aphid vector transmission.

Two mutant strains of cucumber mosaic virus (CMV) were investigated with respect to virion stability and molecular determinants of aphid vector transmission. The mutant 2A1-MT-60x, derived from the mechanically passaged wild type 2A1-AT, is poorly transmissible by the aphid Aphis gossypii and not transmissible by the aphid Myzus persicae, whereas the wild type virus is transmissible by both aphid species. The mutant phenotype was shown to be conferred by a single encoded amino acid change of alanine to threonine at position 162 of the coat protein (CP). Modifying the mutant CP gene to encode the wild type sequence (alanine) at position 162 restored aphid transmission. To test for a correspondence between changes in the physical stability of virions and defects in aphid transmission, a urea disruption assay was developed. Virions of aphid-transmissible strains 2A1-AT and CMV-Fny were stable with treatments of up to between 3 and 4 M urea. In this assay mutant viruses 2A1-MT-60x and CMV-M were less stable, as they were completely disrupted at urea concentrations of 2 and 1 M urea, respectively. The mutant 2A1-MT-60x also accumulated at a reduced level in infected squash relative to the wild type virus. These studies suggest that a primary factor in the loss of aphid transmissibility of some strains of CMV is a reduction in virion stability.

Amino Acid Substitution↗
PubMed2000

The upstream region of the Rpe65 gene confers retinal pigment epithelium-specific expression in vivo and in vitro and contains critical octamer and E-box binding sites.

RPE65 is essential for all-trans- to 11-cis-retinoid isomerization, the hallmark reaction of the retinal pigment epithelium (RPE). Here, we identify regulatory elements in the Rpe65 gene and demonstrate their functional relevance to Rpe65 gene expression. We show that the 5' flanking region of the mouse Rpe65 gene, like the human gene, lacks a canonical TATA box and consensus GC and CAAT boxes. The mouse and human genes do share several cis-acting elements, including an octamer, a nuclear factor one (NFI) site, and two E-box sites, suggesting a conserved mode of regulation. A mouse Rpe65 promoter/beta-galactosidase transgene containing bases -655 to +52 (TR4) of the mouse 5' flanking region was sufficient to direct high RPE-specific expression in transgenic mice, whereas shorter fragments (-297 to +52 or -188 to +52) generated only background activity. Furthermore, transient transfection of analogous TR4/luciferase constructs also directed high reporter activity in the human RPE cell line D407 but weak activity in the non-RPE cell lines HeLa, HepG2, and HS27. Functional binding of potential transcription factors to the octamer sequence, AP-4, and NFI sites was demonstrated by directed mutagenesis, electrophoretic mobility shift assay, and cross-linking. Mutations of these sites abolished binding and corresponding transcriptional activity and indicated that octamer and E-box transcription factors synergistically regulate the RPE65 promoter function. Thus, we have identified the regulatory region in the Rpe65 gene that accounts for tissue-specific expression in the RPE and found that octamer and E-box transcription factors play a critical role in the transcriptional regulation of the Rpe65 gene.

5' Untranslated Regions↗
PubMed2000

Non-replicating Epstein-Barr virus-based plasmids extend gene expression and can improve gene therapy in vivo.

To date, no gene transfer vector has produced prolonged gene expression following a single intravenous injection and then efficiently re-expressed the delivered gene following repeated systemic injection into immunocompetent hosts. To overcome these limitations, a gene therapy regimen using non-replicating Epstein-Barr virus (EBV)-based expression plasmids was developed. One plasmid contains the FR (EBV family of repeats) sequence and the expressed gene. The other encodes Epstein-Barr nuclear antigen 1 (EBNA-1), but lacks FR. Although unable to replicate in mice, intravenous co-injection of EBV-based plasmids in cationic liposome-DNA complexes (CLDCs) substantially prolonged luciferase gene expression. The use of a two-vector system limited host exposure to the EBNA-1 gene product. Furthermore, this EBV-based vector system could be intravenously re-injected multiple times into immunocompetent mice without loss of transfection efficiency. Use of this vector system significantly improved the therapeutic efficacy of the biologically important human granulocyte colony-stimulating factor gene. Delivery of the human granulocyte colony-stimulating factor gene in EBV-based plasmids increased circulating white blood counts for at least 2 months following a single CLDC-based intravenous co-injection. Conversely, white blood counts were never elevated following injection of CLDCs lacking EBV-derived elements. Thus, this EBV-based plasmid vector system both markedly prolongs gene expression at therapeutic levels and efficiently and repeatedly re-transfects immunocompetent hosts. These properties of EBV-based plasmid vectors appear to be due, at least in part, to the documented abilities of the EBNA-1 protein both to retain FR-containing DNA intracellularly and within the nucleus and to block anti-EBNA-1 cytotoxic T cell responses.

Animals↗
PubMed2000

Whole grain consumption and risk of ischemic stroke in women: A prospective study.

CONTEXT: Although increased intake of grain products has been recommended to prevent cardiovascular disease (CVD), prospective data examining the relation of whole grain intake to risk of ischemic stroke are sparse, especially among women. OBJECTIVE: To examine the hypothesis that higher whole grain intake reduces the risk of ischemic stroke in women. DESIGN, SETTING, AND PARTICIPANTS: A prospective cohort of 75,521 US women aged 38 to 63 years without previous diagnosis of diabetes mellitus, coronary heart disease, stroke, or other CVDs in 1984, who completed detailed food frequency questionnaires (FFQs) in 1984, 1986, 1990, and 1994, and were followed up for 12 years as part of the Nurses' Health Study. MAIN OUTCOME MEASURE: Incidence of ischemic stroke, confirmed by medical records, by quintile of whole grain intake according to FFQ responses. RESULTS: During 861,900 person-years of follow-up, 352 confirmed incident cases of ischemic stroke occurred. We observed an inverse association between whole grain intake and ischemic stroke risk. The age-adjusted relative risks (RRs) from the lowest to highest quintiles of whole grain intake were 1.00 (referent), 0.68 (95% confidence interval [CI], 0.49-0.94), 0.69 (95% CI, 0.51-0.95), 0.49 (95% CI, 0.35-0.69), and 0.57 (95% CI, 0.42-0.78; P =.003 for trend). Adjustment for smoking modestly attenuated this association (RR comparing extreme quintiles, 0.64; 95% CI, 0.47-0.89). This inverse association remained essentially unchanged with further adjustment for known CVD risk factors, including saturated fat and transfatty acid intake (multivariate-adjusted RR comparing extreme quintiles, 0.69; 95% CI, 0.50-0.98). The inverse relation between whole grain intake and risk of ischemic stroke was also consistently observed among subgroups of women who never smoked, did not drink alcohol, did not exercise regularly, or who did not use postmenopausal hormones. No significant association was observed between total grain intake and risk of ischemic stroke. CONCLUSIONS: In this cohort, higher intake of whole grain foods was associated with a lower risk of ischemic stroke among women, independent of known CVD risk factors. These prospective data support the notion that higher intake of whole grains may reduce the risk of ischemic stroke.

Adult↗
PubMed2000

Activation (tyrosine phosphorylation) of ErbB-2 (HER-2/neu): a study of incidence and correlation with outcome in breast cancer.

PURPOSE: We hypothesize that phosphorylated ErbB-2 (P-ErbB-2, identified by a novel antibody PN2A) may provide either more significant or additional prognostic marker data for breast cancer patients. This study was designed to compare the incidence and prognostic value of ErbB-2 (HER-2/neu) and P-ErbB-2 immunoexpression in archival breast cancer samples. MATERIALS AND METHODS: Eight hundred sixteen invasive breast cancers with a median of 16.3 years of follow-up were immunostained for ErbB-2 (using antibody CB11) and P-ErbB-2 (using antibody PN2A). ErbB-2 and P-ErbB-2 data were compared with clinical, histologic, immunohistochemical, and outcome variables. RESULTS: Of 816 primary breast cancers, 307 (38%) were positive for ErbB-2 and 37 (12% of ErbB-2 positive and 5% of the study population) expressed P-ErbB-2. P-ErbB-2 was not detected in ErbB-2-negative cases (n = 509). ErbB-2 immunohistochemical data were bimodal; patients with > or = 80% cellular expression had the shortest disease-free and disease-specific survival. P-ErbB-2 was associated with a higher percentage of ErbB-2-positive cells, a higher number of positive lymph nodes, and cellular proliferation. ErbB-2 and P-ErbB-2 were indicators of poor prognosis in node-positive patients in both univariate and multivariate analyses. We found that either P-ErbB-2 expression or high (> or = 80%) ErbB-2 expression provided the most significant prognostic value in node-positive cases by multivariate analyses. There were too few P-ErbB-2-positive cases and events in the node-negative patient group to allow statistical analysis of P-ErbB-2 in that subgroup. CONCLUSION: PN2A immunostaining identified a subset (approximately 12% of ErbB-2-positive breast cancers) with activation (phosphorylation) of the receptor ErbB-2. P-ErbB-2 expression was strongly associated with higher levels of ErbB-2 expression (> or = 80%), although it was not a surrogate. Identification of cases with a high percentage of invasive breast cancer cells expressing ErbB-2 or determination of receptor activation via P-ErbB-2 may provide additional prognostic value in node-positive breast cancers.

Adult↗
PubMed2000

B cells of HIV-1-infected patients bind virions through CD21-complement interactions and transmit infectious virus to activated T cells.

The impact of HIV-associated immunopathogenesis on B cells has been largely associated with indirect consequences of viral replication. This study demonstrates that HIV interacts directly with B cells in both lymphoid tissues and peripheral blood. B cells isolated from lymph node and peripheral blood mononuclear cells (PBMCs) of 4 and 23 chronically infected patients, respectively, demonstrated similar capacities to pass virus to activated HIV-negative PBMCs when compared with CD4(+) cells from the same patients. However, in contrast to T cells, virus associated with B cells was surface bound, as shown by its sensitivity to pronase and the staining pattern revealed by in situ amplification of HIV-1 RNA. Cell sorting and ligand displacing approaches established that CD21 was the HIV-binding receptor on B cells, and that this association was mediated through complement-opsonized virus. These B cells were also found to express significantly lower levels of CD21 compared with HIV-negative individuals, suggesting a direct perturbing effect of HIV on B cells. These findings suggest that B cells, although they themselves are not readily infected by HIV, are similar to follicular dendritic cells in their capacity to serve as extracellular reservoirs for HIV-1. Furthermore, B cells possess the added capability of circulating in peripheral blood and migrating through tissues where they can potentially interact with and pass virus to T cells.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Cyclopamine inhibition of Sonic hedgehog signal transduction is not mediated through effects on cholesterol transport.

Cyclopamine is a teratogenic steroidal alkaloid that causes cyclopia by blocking Sonic hedgehog (Shh) signal transduction. We have tested whether this activity of cyclopamine is related to disruption of cellular cholesterol transport and putative secondary effects on the Shh receptor, Patched (Ptc). First, we report that the potent antagonism of Shh signaling by cyclopamine is not a general property of steroidal alkaloids with similar structure. The structural features of steroidal alkaloids previously associated with the induction of holoprosencephaly in whole animals are also associated with inhibition of Shh signaling in vitro. Second, by comparing the effects of cyclopamine on Shh signaling with those of compounds known to block cholesterol transport, we show that the action of cyclopamine cannot be explained by inhibition of intracellular cholesterol transport. However, compounds that block cholesterol transport by affecting the vesicular trafficking of the Niemann-Pick C1 protein (NPC1), which is structurally similar to Ptc, are weak Shh antagonists. Rather than supporting a direct link between cholesterol homeostasis and Shh signaling, our findings suggest that the functions of both NPC1 and Ptc involve a common vesicular transport pathway. Consistent with this model, we find that Ptc and NPC1 colocalize extensively in a vesicular compartment in cotransfected cells.

Androstenes↗