Search PubMed⌕ Search

Biomedical subjects

Z Yang

Publications and source records attributed to Z Yang.

At least 775 records · Page 43Linked to original sources
PubMed1994

Biochemical characterization of the developmental stage- and tissue-specific erythroid transcription factor, NF-E4.

Analysis of the nuclear factors responsible for erythroid gene regulation has led to the cloning of several transcriptional regulatory proteins with clear lines of evidence suggesting or demonstrating their roles in tissue-specific gene expression. However, the erythroid cell lineage-restricted proteins that have been characterized to date do not differ significantly in activity during the distinct developmental stages of erythropoiesis, a characteristic that might be expected for a nuclear factor that actively participates in the differential regulation of various alpha- or beta-type globin genes (called globin gene switching) at distinct stages of embryonic development. We reported previously the identification of such a differentially expressed DNA binding activity, which appeared to be present in mature definitive (adult) erythroid cells but absent in immature definitive or primitive (embryonic) erythroid cells. Here we detail the biochemical properties of this erythroid tissue- and developmental stage-specific DNA binding activity (called nuclear factor-erythroid 4; NF-E4), which contains characteristics of a molecule that may be intimately involved in globin gene switching.

Animals↗
PubMed1994

Total synthesis of taxol.

Taxol, a substance originally isolated from the Pacific yew tree (Taxus brevifolia) more than two decades ago, has recently been approved for the clinical treatment of cancer patients. Hailed as having provided one of the most significant advances in cancer therapy, this molecule exerts its anticancer activity by inhibiting mitosis through enhancement of the polymerization of tubulin and consequent stabilization of microtubules. The scarcity of taxol and the ecological impact of harvesting it have prompted extension searches for alternative sources including semisynthesis, cellular culture production and chemical synthesis. The latter has been attempted for almost two decades, but these attempts have been thwarted by the magnitude of the synthetic challenge. Here we report the total synthesis of taxol by a convergent strategy, which opens a chemical pathway for the production of both the natural product itself and a variety of designed taxoids.

Models, Molecular↗
PubMed1994

Charge replacement near the phosphorylatable serine of the myosin regulatory light chain mimics aspects of phosphorylation.

Phosphorylation of the myosin regulatory light chains (RLCs) activates contraction in smooth muscle and modulates force production in striated muscle. RLC phosphorylation changes the net charge in a critical region of the N terminus and thereby may alter interactions between the RLC and myosin heavy chain. A series of N-terminal charge mutations in the human smooth muscle RLC has been engineered, and the mutants have been evaluated for their ability to mimic the phosphorylated form of the RLC when reconstituted into scallop striated muscle bundles or into isolated smooth muscle myosin. Changing the net charge in the region from Arg-13 to Ser-19 potentiates force in scallop striated muscle and maintains smooth muscle myosin in an unfolded filamentous state without affecting ATPase activity or motility of smooth muscle myosin. Thus, the effect of RLC phosphorylation in striated muscle and its ability to regulate the folded-to-extended conformational transition in smooth muscle may be due to a simple reduction of net charge at the N terminus of the light chain. The ability of phosphorylation to regulate smooth muscle myosin's ATPase activity and motility involves a more complex mechanism.

Amino Acid Sequence↗
PubMed1994

Renaturation and tumor necrosis factor-alpha stimulation of a 97-kDa ceramide-activated protein kinase.

Recent investigations identified a new signal transduction pathway, termed the sphingomyelin pathway, which may mediate the action of tumor necrosis factor (TNF) alpha and interleukin-1 beta (Mathias, S., Younes, A., Kan, C., Orlow, I., Joseph, C., and Kolesnick, R. N. (1993) Science 259, 519-522). This pathway is initiated by hydrolysis of sphingomyelin to ceramide by a neutral sphingomyelinase and stimulation of a ceramide-activated Ser/Thr protein kinase. Recent investigations demonstrated that kinase activity is proline-directed, recognizing substrates in which the phosphoacceptor site is followed by a proline residue. Until now, the kinase has been defined only as a membrane-bound activity capable of phosphorylating a peptide derived from the sequence surrounding Thr669 of the epidermal growth factor receptor. In the present studies, the kinase was quantitatively extracted from membrane with detergent and separated from protein kinase C by anion-exchange chromatography and isoelectric focusing. Ceramide-activated protein kinase was resolved as an exclusively membrane-bound, 97-kDa protein with a pI of 7.05. Kinase activity toward the epidermal growth factor receptor peptide co-purified with activity toward a generic proline-directed substrate, myelin basic protein. Kinase activity was reconstituted by a denaturation-renaturation procedure and demonstrated activity toward self (autophosphorylation) and exogenous substrate (myelin basic protein). Autophosphorylation occurred exclusively on serine residues. These activities were enhanced to 7-fold of control by ceramide and TNF alpha. These investigations provide additional evidence for a role for ceramide-activated protein kinase in signal transduction for TNF alpha.

Cell Line↗
PubMed1994

Serum components enhance bacterial lipopolysaccharide-induced tissue factor expression and tumor necrosis factor-alpha secretion by bovine alveolar macrophages in vitro.

We have compared the effect of bacterial lipopolysaccharide (LPS) in combination with normal adult bovine serum (NBS), fetal bovine serum (FBS), or a bovine serum fraction on tissue factor expression and tumor necrosis factor alpha (TNF-alpha) secretion by bovine alveolar macrophages. At a concentration of 1 ng/ml, bacterial LPS alone failed to induce measurable tissue factor expression by the macrophages, but the presence of FBS, NBS, or a fraction of normal pooled bovine serum isolated by ion-exchange chromatography (fraction 2) markedly potentiated the effect of LPS. A protein concentration of 64 micrograms/ml NBS, 192 micrograms/ml FBS, and only 640 ng/ml fraction 2 was required to induce maximal tissue factor expression on the macrophages in combination with 1 ng/ml LPS. Comparison of quantities of added serum protein required to induce maximal potentiating effects indicated that fraction 2 was 100 times more potent than whole NBS and 300 times more potent than whole FBS. We similarly found that TNF-alpha secretion by macrophages exposed to LPS was responsive to serum and was highly responsive to fraction 2. LPS alone (1 ng/ml) induced a relatively low level of TNF-alpha secretion by the macrophages, and the presence of FBS, NBS, or fraction 2 potentiated the effect of LPS. A concentration of 64.0 micrograms/ml NBS, 320.0 micrograms/ml FBS, and 3.2 micrograms/ml fraction 2 serum protein induced near-maximal TNF-alpha secretion by the macrophages. Comparison of the concentration of serum protein required to induce these potentiating effects indicated that fraction 2 was approximately 20 times more potent than whole NBS and 100 times more potent than whole FBS. The stimulatory effect of LPS plus fraction 2 serum proteins was dependent on the CD14 receptor, as monoclonal antibodies directed against CD14 (My4, 60bd; 10 micrograms/ml) inhibited tissue factor expression and TNF-alpha secretion by the macrophages.

Animals↗
PubMed1994

Identification and characterization of a bovine lipopolysaccharide-binding protein.

Endogenous regulatory mechanisms exist in mammals that enable a rapid response to lipopolysaccharide (LPS, endotoxin) stemming from gram-negative bacterial infections. Serum proteins and cell surface receptors exist that bind LPS, and this interaction may either aid in nonpathogenic removal of LPS from the body or potentiate the effects of LPS. We have used a photoreactive, thiol-cleavable, radiolabeled derivative of E. coli 0111:B4 LPS [LPS-(p-azidosalicylamido)-1,3'-dithiopropionamide; 125I-ASD-LPS], to identify the presence of LPS-binding proteins (LBPs) in bovine serum. Ion exchange chromatography was used to fractionate bovine serum, and eluted protein was subsequently photoaffinity labeled using 125I-ASD-LPS. LBPs were identified by autoradiography of sodium dodecyl sulfate-polyacrylamide gels. Several LBPs including three with apparent molecular masses of 65, 60, and 50 kDa were variably present within the chromatography pools. A 22-residue NH2-terminal amino acid sequence of the 60-kDa protein showed 77% homology with human LBP and 68% with rabbit LBP within this region. Further purification utilizing high-performance liquid chromatography yielded a protein fraction that contained the 60-kDa protein and was distinctly more active than whole bovine serum in LPS-dependent macrophage activation assays (up to 1600-fold on a weight/volume basis). The LPS-mediated macrophage activation in concert with chromatographically purified serum protein in tissue factor assays was inhibitable using anti-CD14 monoclonal antibodies. The results indicate that an LPS-binding protein exists in samples of pooled bovine serum and that this protein has features in common with human and rabbit LBP.

Acute-Phase Proteins↗
PubMed1994

Tumor cell-enhanced sensitivity of vascular endothelial cells to photodynamic therapy.

Effective antitumor photodynamic therapy (PDT) may be related to damage of vasculature within the tumor. The purpose of this study was to determine if tumor cells secrete factors that stimulate proliferation of human umbilical vein endothelial cells (HUVEC) and result in enhanced sensitivity of HUVEC to aluminum-sulfonated phthalocyanine (AlSPc)-PDT. Three human tumor cell lines--pharyngeal squamous carcinoma, colonic carcinoma, and mammary carcinoma--were used in this study. Co-culture of HUVEC and either squamous carcinoma or colonic carcinoma, but not mammary carcinoma, significantly increased HUVEC proliferation and AlSPc-PDT mediated cell damage. In addition, supernatant from squamous carcinoma and colonic carcinoma cultures also stimulated HUVEC proliferation and sensitivity to AlSPc-PDT. Both supernatant and cell lysate from squamous carcinoma cells contained angiogenic factors consistent with basic and acidic fibroblast growth factors, as evidenced by Western blot analysis and BALB/c 3T3 fibroblast cell proliferation assays. Collectively, these results suggest that selected tumor cell lines produce angiogenic factors that induce HUVEC proliferation and subsequently enhance sensitivity to AlSPc-PDT.

3T3 Cells↗
PubMed1994

Maximum likelihood phylogenetic estimation from DNA sequences with variable rates over sites: approximate methods.

Two approximate methods are proposed for maximum likelihood phylogenetic estimation, which allow variable rates of substitution across nucleotide sites. Three data sets with quite different characteristics were analyzed to examine empirically the performance of these methods. The first, called the "discrete gamma model," uses several categories of rates to approximate the gamma distribution, with equal probability for each category. The mean of each category is used to represent all the rates falling in the category. The performance of this method is found to be quite good, and four such categories appear to be sufficient to produce both an optimum, or near-optimum fit by the model to the data, and also an acceptable approximation to the continuous distribution. The second method, called "fixed-rates model", classifies sites into several classes according to their rates predicted assuming the star tree. Sites in different classes are then assumed to be evolving at these fixed rates when other tree topologies are evaluated. Analyses of the data sets suggest that this method can produce reasonable results, but it seems to share some properties of a least-squares pairwise comparison; for example, interior branch lengths in nonbest trees are often found to be zero. The computational requirements of the two methods are comparable to that of Felsenstein's (1981, J Mol Evol 17:368-376) model, which assumes a single rate for all the sites.

Animals↗
PubMed1994

Estimating the pattern of nucleotide substitution.

Knowledge of the pattern of nucleotide substitution is important both to our understanding of molecular sequence evolution and to reliable estimation of phylogenetic relationships. The method of parsimony analysis, which has been used to estimate substitution patterns in real sequences, has serious drawbacks and leads to results difficult to interpret. In this paper a model-based maximum likelihood approach is proposed for estimating substitution patterns in real sequences. Nucleotide substitution is assumed to follow a homogeneous Markov process, and the general reversible process model (REV) and the unrestricted model without the reversibility assumption are used. These models are also applied to examine the adequacy of the model of Hasegawa et al. (J. Mol. Evol. 1985;22:160-174) (HKY85). Two data sets are analyzed. For the psi eta-globin pseudogenes of six primate species, the REV models fits the data much better than HKY85, while, for a segment of mtDNA sequences from nine primates, REV cannot provide a significantly better fit than HKY85 when rate variation over sites is taken into account in the models. It is concluded that the use of the REV model in phylogenetic analysis can be recommended, especially for large data sets or for sequences with extreme substitution patterns, while HKY85 may be expected to provide a good approximation. The use of the unrestricted model does not appear to be worthwhile.

Animals↗
PubMed1994

Signal transduction pathways of bacterial lipopolysaccharide-stimulated bovine vascular endothelial cells.

Increased procoagulant activity of vascular endothelial cells may be an important component in the pathogenesis of intravascular coagulation associated with gram-negative bacterial diseases. Two bovine endothelial cell (BEC) lines isolated from pulmonary arteries (ENS-2 and ENT-18) were used in this study to investigate procoagulant signal transduction pathways of endotoxin (lipopolysaccharide, LPS)--stimulated BECs. The endothelial cell line ENS-2 was sensitive to LPS as demonstrated by tissue factor (TF) expression, but in contrast, the ENT-18 endothelial cell line was unusually resistant to the effects of LPS. No remarkable quantitative difference in binding of radiolabeled LPS was detected between the two endothelial cell lines. A protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate, PMA) failed to induce TF expression in either cell line at concentrations ranging from 0.05 to 1.00 microM when used as a sole stimulus for the endothelial cells. However, when PMA was used in combination with LPS, PMA enhanced the stimulatory effect of LPS on the endothelial cells. In parallel experiments, PKC inhibitors (H-7 and GF 109203X) interfered with the stimulatory effect of LPS on the cells by decreasing tissue factor expression. We also found that an activator of adenylate cyclase, forskolin, similarly inhibited LPS-induced tissue factor activity. In contrast, protein tyrosine kinase inhibitors (genistein, lavendustin A) had no inhibitory effect on LPS-induced endothelial cell tissue factor expression. Our results collectively suggest that activation of PKC is an important step in stimulation of endothelial cells by LPS, and that LPS and phorbol esters may synergize to produce an enhanced stimulatory effect. Our results also suggest participation of cAMP in controlling LPS-mediated stimulation of endothelial cells, but fail to demonstrate a role for protein tyrosine kinase activity.

Adenylyl Cyclases↗
PubMed1994

Cross-cultural validity of a parent's version of the Dental Fear Survey Schedule for children in Chinese.

The cross-cultural validity of a parent's version of the Dental Fear Survey Schedule (DFSS) for children was assessed by examining the relationship between the parent's report of child fear in Chinese (DFSS) and actual child behavior (CB) in the dental environment for two samples: 70 Chinese children ages 5-15 yr, residing in Canada, and 99 mainland Chinese children ages 2.5-7.0 yr residing in Kunming, Yunnan, PRC Canadian DFSS score M = 31.9 (SD = 9.5) with no differences by age or sex. PRC DFSS score M = 35.7 (SD = 8.9) with girls reported more fearful than boys. No age difference was detected. Higher DFSS scores were associated with more CB in both samples. Factor analyses yielded similar solutions and internal consistency was high. Control and potential victimization were identified as important constructs. The results suggest the Chinese version of the DFSS is a reliable and valid parental measure of child dental fear.

Adult↗
PubMed1994

Serum interleukin-6 concentration in schizophrenia: elevation associated with duration of illness.

Using an enzyme immunoassay (ELISA), we measured serum interleukin-6 (IL-6) concentration in 128 schizophrenic patients (24 of whom were never medicated) and in 110 normal control subjects. Mean serum IL-6 concentration was significantly higher in the schizophrenic patients as compared with the control subjects (p = 0.009). Comparisons within the patient group revealed that serum IL-6 was significantly correlated with duration of illness (r = 0.32, p = 0.0004). After covariation for duration of illness, there was no relationship between IL-6 levels and the production of autoantibodies, clinical state, or medication status. Thus, elevated serum IL-6 levels in schizophrenia develop during the course of illness and may be related to treatment or to disease progression.

Adult↗
PubMed1994

Colocalization of atrial natriuretic factor and beta-endorphin in rat thymic macrophages.

Recent demonstration of immunoreactive (IR) atrial natriuretic factor (ANF) and beta-endorphin (beta-EP) in the thymus prompted a reexamination of the distribution and cellular localization of the two peptides within that tissue. Double labeling immunohistochemistry was carried out on gelatin-embedded cryostat thymic sections of adult male Sprague-Dawley rats. Cells stained positive with antiserum (S118), raised against rANF(1-28), were colocalized in > 95% of cases with immunofluorescent staining of IR-beta-EP(1-31). The cells were found sparsely distributed along the corticomedullary junction and in subcapsular regions. In 1- or 5-day monolayer cultures of adherent thymic cells, 15-20% of the cells stained positive for either IR-ANF or IR-beta-EP. Under these conditions, > 95% of IR-ANF or IR-beta-EP positive cells were also fluorescence stained for the rat macrophage marker ED-1. Thus, taken together with previous reports, our present findings suggest that, in the rat thymus, both ANF and beta-EP are produced by the same population of macrophages. To further investigate their presence in the thymus, the contents and molecular species of the two peptides were compared over the developmental period of the animal using well-characterized radioimmunoassays (RIA). Both peptides significantly increased their contents between day 2 and day 60. However, in terms of concentration, IR-ANF at day 2 was approximately 50% higher than day 16 and five times greater that at day 60; in comparison the concentration of IR-beta-EP remained relatively constant and the only significant difference from day 2 being a slight increase in the day 16 animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

ANP(5-28) is the major molecular species in hypophysial portal blood of the rat.

We have previously demonstrated that the concentrations of immunoreactive atrial natriuretic peptide (IR-ANP) are significantly higher in hypophysial portal compared with peripheral blood of the rat, and that ANP suppresses the pituitary release of ACTH and beta-endorphin in vitro and in vivo. Using HPLC, we have now shown that the predominant species of IR-ANP in extracts of portal blood from adult male and female rats is ANP(5-28), whereas in peripheral blood, ANP(1-28) predominates. The ratio of ANP(5-28) in portal compared with peripheral blood was 4.2 in male and 4.8 in female animals.

Animals↗
PubMed1994

DNurbs: DNA modeled with NURBS.

DNurbs (dee-in-urbs) are a small number of bicubic patches wrapping each base pair in complementary DNA. NURBS, the nonuniform rational B-spline surfaces now popular in computer graphics, are employed for the patches. Control points for the surface patches are generated from the molecular surface based on canonical base pairs.

Base Sequence↗
PubMed1994

Immunotoxicity of particulate lead: in vitro exposure alters pulmonary macrophage tumor necrosis factor production and activity.

Rabbit pulmonary macrophages were exposed in vitro to particulate lead oxide (PbO) for periods of up to 72 h and then assayed for the activity of tumor necrosis factor-alpha (TNF alpha) released after stimulation with lipopolysaccharide (LPS). The levels of TNF alpha obtained from PbO-treated cells were decreased in a dose-dependent manner as compared with metal-free control cells for each time point examined. Cells treated simultaneously with both LPS and PbO yielded less monokine than did cells receiving LPS alone. In addition, incubation of cell-free TNF alpha with PbO resulted in a diminution of cytotoxicity directed against TNF alpha-sensitive tumor target cells. Macrophage burdens of PbO particles increased with both the length of incubation and concentration of PbO used; increases in cellular lead burdens were paralleled by reductions in cell viability. Thus, under in vitro conditions, PbO affects the levels of the immunoregulatory monokine TNF alpha and also disrupts its cytotoxic properties after release from activated macrophages.

Animals↗
PubMed1994

Safety and toxicity of catheter gene delivery to the pulmonary vasculature in a patient with metastatic melanoma.

One approach to gene therapy for human cancer is transcatheter injection of DNA liposomes into tumor masses. To determine the feasibility of selective delivery of recombinant genes by a catheter to the pulmonary vasculature in humans, a patient with melanoma received two treatments of HLA-B7 plasmid DNA complexed to cationic liposomes into a right posterior basal pulmonary artery associated with a mass lesion. The treatments were well tolerated. No adverse respiratory, cardiac, immunologic, or other organ toxicities were detected. The delivery of recombinant genes by catheter may be a useful modality to treat human malignancy and other diseases.

Adenocarcinoma↗