Biomedical subjects

Z Li

Publications and source records attributed to Z Li.

At least 883 records · Page 49Linked to original sources

PubMed1998

Novel 5-(3-aryl-2-propynyl)-5-(arylsulfonyl)thiazolidine-2,4-diones as antihyperglycemic agents.

Novel 5-(3-aryl-2-propynyl)-5-(arylsulfonyl)thiazolidine-2,4-diones and 5-(3-aryl-2-propynyl)-5-(arylsulfanyl)thiazolidine-2,4-diones were prepared and evaluated as oral antihyperglycemic agents in the obese, insulin resistant db/db mouse model at 100 mg/kg and, if the analogue had sufficient potency, 20 mg/kg. The sulfonylthiazolidinediones, 2, were more potent than the corresponding sulfanylthiazolidinedione congeners, 1. With regard to substituent effects on the 3-propynyl phenyl ring (Ar') of 2, 4-halogen substitution generally resulted in the more potent analogues. Substituent effects on the phenylsulfonyl moiety (Ar) of 2 were less clear, although para-halogen substitution on Ar generally was preferable. 2-Pyridinesulfonyl derivatives (Ar = 2-pyridine in 2) also had good potency. Several compounds from series 2 were effective at lowering glucose and insulin in the obese, insulin resistant ob/ob mouse at the 50 mg/kg oral dose. Compound 20 significantly improved the glucose tolerance of obese, insulin resistant Zucker rats at the 20 mg/kg dose level and had no effect on plasma glucose or on glucose tolerance in normal rats fasted for 18 h at the 100 mg/kg level.

Animals↗

PubMed1998

The ice-binding site of Atlantic herring antifreeze protein corresponds to the carbohydrate-binding site of C-type lectins.

The type II antifreeze proteins (AFPs) of smelt and Atlantic herring are homologous to the carbohydrate-recognition domains (CRDs) of Ca2+-dependent (C-type) animal lectins and, like these lectins, acquire a stable and active structure upon binding Ca2+ ions. In the C-type lectin CRD, the carbohydrate-binding site is located at a Ca2+-binding site. Site-directed mutagenesis was used to test the hypothesis that the ice-binding site of the type II AFP corresponds to the carbohydrate-binding site of the lectins. To disrupt this site in the herring AFP without perturbing the Ca2+-dependent protein fold, a double mutant was constructed that changed the Ca2+- and carbohydrate-binding motif from the galactose-type of wild-type AFP containing the sequence Gln-Pro-Asp to a mannose-type that has the sequence Glu-Pro-Asn and is also known to bind Ca2+. The mutant AFP exhibited proper Ca2+ binding, folding, and stability as demonstrated by ruthenium red staining, proteolysis protection assays, and CD spectroscopy. However, it showed no antifreeze activity (thermal hysteresis) and did not alter ice crystal morphology to form bipyramidal crystals as does the active wild-type AFP. These results demonstrate that the ice-binding site of the herring type II AFP corresponds to the carbohydrate-binding site of the C-type lectin CRDs and further suggest that this ice-binding function evolved from the carbohydrate-binding site of a preexisting C-type lectin.

Amino Acid Sequence↗

PubMed1998

3' exoribonucleolytic trimming is a common feature of the maturation of small, stable RNAs in Escherichia coli.

In addition to tRNA and 5S RNA, Escherichia coli contains several other small, stable RNA species; these are M1, 10Sa, 6S, and 4.5S RNA. Although these RNAs are initially synthesized as precursor molecules, relatively little is known about their maturation. The data presented here show that 3' exoribonucleolytic trimming is required for the final maturation of each of these molecules. As found previously with tRNA, but not 5S RNA, any one of a number of exoribonucleases can carry out the trimming reaction in vivo, although RNases T and PH are most effective. In their absence, large amounts of immature molecules accumulate for most of the RNAs, and these can be converted to the mature forms in vitro by the purified RNases. A model is proposed that identifies a structural feature present in all the small, stable RNAs of E. coli, and describes how this structure together with the RNases influences the common mechanism for 3' maturation.

Endoribonucleases↗

PubMed1998

Functional expression of recombinant N-methyl-D-aspartate receptors in the yeast Saccharomyces cerevisiae--localization and pharmacological characterization.

The yeast Saccharomyces cerevisiae was used for expressing the genes encoding the ionotropic N-methyl-D-aspartate (NMDA) receptor subunits from rats (NR1a, NR2A, NR2C) and mice (NR2B). Four plasmids were constructed by cloning the different NMDA receptor genes in the two multi-copy yeast-Escherichia coli shuttle vectors pMB01 (--> NR1a gene) and pMB02 (--> NR2A-2C genes). The protease-deficient S. cerevisiae strain cI3-ABYS-86 (leu-, ura-) was transformed or co-transformed with the resulting plasmids pMBNR1a (leu+) or pMBNR1a/pMBNR2A-C (ura+) respectively. Western blotting analysis with antibodies raised against amino acid sequences at the C-termini of the respective subunits revealed that the recombinant receptor proteins were differently expressed and only partially glycosylated in the cell membranes of the recombinant yeast strains. The expression and localization of the recombinant NMDA receptor proteins were also proved by immunofluorescence microscopy which indicated a distinct expression of the different NMDA receptor subunits in the plasma membrane of the transformed yeast cells. Pharmacological characterization of crude membrane preparations of the recombinant yeast cells showed saturable binding of the glycine antagonist [3H]MDL105,519 with Kd values of 56.9 +/- 6.19 nM (NR1a/NR2A), 26.72 +/- 2.13 nM (NR1a/NR2B), and 21.22 +/- 1.64 nM (NR1a/NR2C), and bound capacities of 17.94 +/- 1.24 pmol/mg membrane protein (NR1a/NR2A), 11.45 +/- 0.67 pmol/mg (NR1a/NR2B), and 16.15 +/- 0.86 (NR1a/NR2C) pmol/mg. The [3H]MDL105,519 binding was inhibited by the glycine antagonist 5,7-dichlorokynurenate, ethyl-2-carboxy-4,6-dichloro-3-indoleacetate, and itself, but not by glycine, D-serine or 1-amino-cyclopropanecarboxylic acid. Specific binding of [3H]glycine or the NMDA channel blocker [3H]dizolcipine were not observed.

Animals↗

PubMed1998

A novel site, Mt, in the human desmin enhancer is necessary for maximal expression in skeletal muscle.

Previous investigations have shown that expression of the muscle-specific intermediate filament desmin gene in skeletal muscle is controlled in part by a 5' muscle-specific enhancer. This enhancer activity can be divided into myoblast-specific and myotube-specific activation domains. The myotube-specific region contains a MyoD and MEF2 sites, whereas the myoblast-specific region contains Sp1, Krox, and Mb sites. In the present study, we designed mutations in the conserved portion of the myotube-specific region; transfection analysis of these mutations showed that a novel site located between the MyoD and MEF2 sites, named Mt (GGTATTT), is required for full transcriptional activity of the desmin enhancer in skeletal muscle. Although gel mobility shift assays demonstrate that myotube, myoblast, fibroblast, and HeLa nuclear extracts contain a nuclear factor that binds specifically to Mt, four copies of the Mt site function as the native enhancer only in myotubes. Functional synergism among the MyoD, MEF2, and Mt sites in myotubes has been demonstrated. These results show that the novel Mt site cooperates with MyoD and MEF2 to give maximal expression of the desmin gene.

Base Sequence↗

PubMed1998

Inhibitors of farnesyl protein transferase. 4-Amido, 4-carbamoyl, and 4-carboxamido derivatives of 1-(8-chloro-6,11-dihydro-5H-benzo[5,6]- cyclohepta[1,2-b]pyridin-11-yl)piperazine and 1-(3-bromo-8-chloro-6,11- dihydro-5H-benzo[5,6]cyclohepta[1,2-b]pyridin-11-yl)piperazine.

The synthesis of a variety of novel 4-amido, 4-carbamoyl and 4-carboxamido derivatives of 1-(8-chloro-6,11-dihydro-5H-benzo[5,6]cyclohepta[1,2-b]pyridin-11-yl) piperazine to explore the SAR of this series of FPT inhibitors is described. This resulted in the synthesis of the 4- and 3-pyridylacetyl analogues 45a and 50a, respectively, both of which were orally active but were found to be rapidly metabolized in vivo. Identification of the principal metabolites led to the synthesis of a variety of new compounds that would be less readily metabolized, the most interesting of which were the 3- and 4-pyridylacetyl N-oxides 80a and 83a. Novel replacements for the pyridylacetyl moiety were also sought, and this resulted in the discovery of the 4-N-methyl and 4-N-carboxamidopiperidinylacetyl derivatives 135a and 160a, respectively. All of these derivatives exhibited greatly improved pharmacokinetics. The synthesis of the corresponding 3-bromo analogues resulted in the discovery of the 4-pyridylacetyl N-oxides 83b (+/-) and 85b [11S(-)] and the 4-carboxamidopiperidinylacetamido derivative 160b (+/-), all of which exhibited potent FPT inhibition in vitro. All three showed excellent oral bioavailability in vivo in nude mice and cynomolgus monkeys and exhibited excellent antitumor efficacy against a series of tumor cell lines when dosed orally in nude mice.

3T3 Cells↗

PubMed1998

The beta protein of phage lambda promotes strand exchange.

Bacteriophage lambda encodes a 28 kDa protein called beta that binds to single-stranded DNA and promotes the renaturation of complementary single strands. beta Protein fails to bind directly to duplex DNA but remains bound to the DNA product of renaturation that beta itself catalyzes. These observations led to an examination of the ability of beta protein to promote strand exchange. beta Protein caused the replacement of a 43-mer oligonucleotide annealed to M13 circular single-stranded DNA by a homologous 63-mer whose 20 extra nucleotide residues were complementary to the adjacent 3' region of M13 DNA. The role of beta protein in this reaction was manifested in several ways: beta protein pushed the exchange through four to eight mismatches, which blocked exchange mediated by spontaneous renaturation and branch migration; beta imposed a polarity on the strand exchange that was lacking in the spontaneous reaction; and beta remained bound to the heteroduplex product of strand exchange. These observations reveal a mechanism by which a protein can drive strand exchange in one direction without using ATP or any other exogenous source of energy.

Bacteriophage M13↗

PubMed1998

The beta protein of phage lambda binds preferentially to an intermediate in DNA renaturation.

Phage lambda encodes two recombination proteins that are required for homologous recombination in a recA- host strain. Of these two recombination proteins, one is an exonuclease whose action on double-stranded DNA produces 3' single-stranded ends; the other, called beta protein, is a DNA binding protein that promotes the renaturation of complementary single strands. The enzymes of phage lambda provide a model for understanding a recombination pathway called "single-strand annealing". Further investigation of the binding of beta protein to DNA has revealed a new mechanism of renaturation. As reported before, beta protein binds directly to single-stranded DNA, but not to double-stranded DNA. However, in the experiments reported here, we observed that beta protein bound more strongly to a presumed intermediate in the renaturation reaction that beta itself catalyzed, and beta thereby protected all of a renatured duplex 83-mer oligonucleotide from nuclease digestion.

Bacteriophage lambda↗

PubMed1998

Effects of adenovirus-mediated p16INK4A expression on cell cycle arrest are determined by endogenous p16 and Rb status in human cancer cells.

We constructed an adenoviral vector containing human p16 cDNA in order to evaluate the cytotoxic effects of exogenous p16 expression on cancer cell proliferation and to explore the potential use of p16 in cancer gene therapy. Following infection of human breast (MCF-7, MDA-MB-231, and BT549), osteosarcoma (U-2 OS and Saos-2), cervical (C33a), and lung cancer (H358) cell lines with the recombinant adenovirus Adp16, high levels of p16 expression were observed in all cell lines. Cancer cell lines which were mutant or null for p16 but wild-type for the retinoblastoma gene product (pRb) (MCF-7, MDA-MB-231, BT549 and U-2 OS) were 7-22-fold more sensitive to the cytotoxic effects of Adp16 than to a control virus. In contrast, cancer cell lines which were wild-type for p16 but mutant or null for pRb (Saos-2, C33a and H358) were <threefold more sensitive to Adp16 when compared to a control virus. Analysis of 5-bromodeoxyuridine incorporation into DNA following infection with Adp16 showed a loss of S phase in those cell lines which were null or mutant for p16 but expressed a functional pRb. This cell cycle arrest was associated with binding of the p16 protein to cyclin-dependent kinase 4 and dephosphorylation of pRb. In contrast, human cancer cell lines expressing a wild-type p16 and a mutant pRb or no pRb showed no substantial loss of S phase following Adp16 infection. Based on these studies, we conclude that p16-mediated cytotoxicity is tightly associated with the presence of functional pRb in human cancer cells, and that tumor cells which are mutant or null for p16 are candidates for Adp16 mediated cancer gene therapy.

Adenoviridae↗

PubMed1998

Depletion of a Drosophila homolog of yeast Sup35p disrupts spindle assembly, chromosome segregation, and cytokinesis during male meiosis.

In the course of a genetic screen for male-sterile mutations in Drosophila affecting chromosome segregation during the meiotic divisions in spermatocytes, we identified the mutation dsup35(63D). Examination of mutant testes showed that chromosome misbehavior was a consequence of major disruptions in meiotic spindle assembly. These perturbations included problems in aster formation, separation, and migration around the nuclear envelope; aberrations in spindle organization and integrity; and disappearance of the ana/telophase central spindle, which in turn disrupts cytokinesis. The dsup35(63D) mutation is caused by a P element insertion that affects, specifically in the testis, the expression of a gene (dsup35) encoding the Drosophila homolog of the yeast Sup35p and Xenopus eRF3 proteins. These proteins are involved in the termination of polypeptide synthesis on ribosomes, but previous studies have suggested that Sup35p and closely related proteins of the same family also interact directly with microtubules. An affinity-purified antibody directed against the product of the dsup35 gene was prepared; interestingly, this antibody specifically labels primary spermatocytes in one or two discrete foci of unknown structure within the nucleoplasm. We discuss how depletion of the dsup35 gene product in spermatocytes might lead to the global disruptions in meiotic spindle assembly seen in mutant spermatocytes.

Amino Acid Sequence↗

PubMed1998

Plakoglobin induces desmosome formation and epidermoid phenotype in N-cadherin-expressing squamous carcinoma cells deficient in plakoglobin and E-cadherin.

Pg is a homologue of beta-catenin and Armadillo, the product of the Drosophila segment polarity gene and has been shown to have both adhesive and signaling functions. It interacts with both classic and desmosomal cadherins. Pg interaction with the desmosomal cadherins is essential for desmosome assembly. Its precise role in the classic cadherin complexes is unclear, although Pg-E-cadherin interaction appears to be necessary for the formation of desmosomes. In addition to cadherins in adhesion complexes, Pg interacts with a number of proteins involved in regulation of cell differentiation and proliferation such as Lef-1/Tcf-1 transcription factors and the tumor suppressor protein APC. In this study, we have introduced Pg cDNA into SCC9 cells, a Pg- and E-cadherin-deficient squamous cell carcinoma line, which also lacks desmosomes. These cells have both alpha-catenin and beta-catenin, display unusual expression of N-cadherin, and have the typical fibroblastic phenotype of transformed cells. Pg-expressing SCC9 cells (SCC9P) formed desmosomes. Desmosome formation coincided with the appearance of an epidermoid phenotype, with increased adhesiveness and a contact-dependent decrease in growth. Biochemical characterization of SCC9P cells showed an increase in the expression and stability of N-cadherin and a decrease in level and stability of beta-catenin, without any apparent effects on alpha-catenin. These results show that, in the absence of E-cadherin, Pg can efficiently use N-cadherin to induce desmosome formation and epidermoid phenotype. They also suggest a role for Pg as one of the regulators of the intracellular beta-catenin levels and underscore the pivotal role of this protein in regulating cell adhesion and differentiation.

Cadherins↗

PubMed1998

Testing causal hypotheses in multivariate linkage analysis of quantitative traits: general formulation and application to sibpair data.

We provide a general framework for the development of model-free methods for the linkage analysis of multivariate phenotypic data. It is possible within this framework to test both for linkage of a set of phenotypes to one or more markers and for the presence of structural relations among the phenotypes themselves. This report presents the general model, paying special attention to the assumptions that enter its formulation, and outlines the estimation procedures that may be used.

Chromosome Mapping↗

PubMed1998

Effect of cooling on cutaneous microvascular adrenoceptors in vivo in the rabbit ear.

Previous studies have suggested that moderate cooling increases the responsiveness of vascular alpha2-adrenoceptors. However, limited information is available documenting the influence of temperature changes on adrenoceptor responses in the microvasculature of thermoregulatory organs (e.g., the human digit and the rabbit ear) subjected to a wide range of temperatures. In the present study, the effect of local cooling (24 degrees C) on cutaneous microvascular adrenoceptors in the ear was observed in vivo in male New Zealand White rabbits (total: 66 ears). The rabbit ear was studied in a temperature-controlled tissue bath; the ear preparation was pretreated with terazosin (an alpha1-adrenoceptor antagonist) (10(-5) M) or a combination of terazosin (10(-5) M) and propranolol (a beta-adrenoceptor antagonist) (10(-6) M). The microvascular diameter responses of the ear to norepinephrine (10(-11)-10(-4) M) then were determined at 24 or 34 degrees C, respectively, to determine the influences of low temperature on adrenoceptor responses to norepinephrine stimulation. The results demonstrated that low concentrations of norepinephrine induced vasodilation in arterioles and arteriovenous anastomoses. This vasodilation was followed by vasoconstriction with an increased concentration of norepinephrine in animals with alpha1-adrenergic blockade at 34 degrees C. Moderate tissue cooling increased the microvascular maximal response of the rabbit ear to norepinephrine and abolished the vasodilatation induced by a low concentration of norepinephrine. There was no significant difference in the microvascular response to norepinephrine between the two temperature conditions after simultaneous blockade of alpha1-adrenoceptors and beta-adrenoceptors. Data from the present study indicate that moderate cooling does not enhance the responsiveness of alpha2-adrenoceptors to norepinephrine. In contrast, cooling reduced the beta-adrenergic activity of arterioles and arteriovenous anastomoses after norepinephrine stimulation.

Adrenergic alpha-Agonists↗

PubMed1998

Alterations in glycosyltransferases during myeloid and monocytoid differentiation of HL-60 cells.

HL-60, a human promyelocytic leukemia cell line, can be differentiated to myeloid lineage by all- trans retinoic acid (ATRA), dimethylsulfoxide (DMSO) and n -butyric acid (n -BA), or to monocytoid(monocytic/macrophagic) lineage by phorbol-12-myristate-13-acetate (PMA) and ganglioside GM(3). The activity alterations of N -acetylglucosaminyltransferase III and V (GnT-III, GnT-V) as well as alpha-1,6-fucosyl-tranferase (alpha1,6 Fuc T) were studied during the differentiation of HL-60 cells by the above-mentioned five inducers using the fluorescence (PA)-labeled glycan-HPLC method for GnT assays and biotin-labeled glycan-LCA affinity chromatography combined with the HRP-avidin colorimetric method for alpha1,6 Fuc T assay. It was observed that after 3 days, all three enzymes decreased in HL-60 cells induced by 1 micromol/l ATRA and 0.6 mmol/l n-BA, while GnT-III and alpha1,6 Fuc T increased, but GnT-V still decreased after induction by 1% DMSO. GnT-V and alpha1,6 Fuc T declined, while GnT-III was elevated after induction by 0.1 micromol/l PMA for 3 days. In contrast, GnT-III increased after the treatment with 50 micromol/l GM(3)for 3 or 6 days, but GnT-V was not appreciably changed and alpha1,6 FucT was elevated after 6 days of GM(3)treatment. It may be concluded that the decrease of GnT-V is the common change in myeloid differentiation and the increase of GnT-III is the general alteration in monocytoid differentiation. The changes in the activities of glycosyltransferases were consistent with the structural changes in surface N -glycans previously found in our laboratory, i.e. that the antennary number of N -glycans decreased during myeloid differentiation by ATRA, and the amount of bisecting GlcNAc in N -glycans increased during monocytoid differentiation by PMA.

Antineoplastic Agents↗

PubMed1998

Characterization of bradykinin-related peptides generated in the plasma of six sarcopterygian species (African lungfish, amphiuma, coachwhip, bullsnake, gila monster, and Gray's monitor).

Incubation of heat-denatured plasma from six species occupying different evolutionary positions within the Sarcopterygian lineage [the dipnoan, Protopterus annectens (African lungfish); the urodele, Amphiuma tridactylum (three-toed amphiuma); the colubrid snakes, Pituophis melanoleucus sayi (bullsnake) and Masticophis flagellum (coachwhip); and the lizards Heloderma suspectum (Gila monster) and Varanus Grayi (Gray's monitor)] with trypsin generated bradykinin-related peptides that were detected by radioimmunoassay using an antiserum raised against mammalian bradykinin (BK). The peptides were purified by HPLC and their primary structures were established as lungfish [Tyr1,Gly2,Ala7,Pro8]BK, amphiuma [Phe1,Ile2, Leu5]BK, bullsnake and coachwhip [Val1,Thr6]BK, Gila monster [Leu2, Thr6]BK, and Gray's monitor [Thr6]BK. Monitor BK is identical to the peptide generated in turtle and alligator plasma and coachwhip/bullsnake BK shows one amino acid substitution (Ala1 --> Val) compared with the peptide generated in the plasma of the python. The data provide further evidence for the widespread occurrence of a kallikrein-kininogen system in nonmammalian vertebrates but indicate that the primary structure of BK has been poorly conserved during evolution.

Amino Acid Sequence↗

PubMed1998

Alpha adrenoceptors in the rabbit ear thermoregulatory microcirculation.

The rabbit ear microcirculation was analyzed in a chronic unanesthetized model to evaluate alpha adrenergic microvascular control in a thermoregulatory end organ. This model allowed direct measurement of microcirculatory responses without the effects of anesthetics or inflammatory responses induced by acute surgical intervention. The ipsilateral facial artery was catheterized for drug injections into the experimental ear. Microvascular diameter changes following stimulation or blockade of adrenoceptor (AR) subtypes were observed directly through a chronic microvascular chamber implanted in the rabbit ear. Vascular alpha1- and alpha2-ARs appear to be distributed differently across the arterioles and AVAs of the rabbit ear. Both alpha1- and alpha2-ARs appear to contribute to vasoconstriction of AVAs in the conscious rabbit ear. In contrast, alpha1-AR's (vs alpha2-ARs) appear to predominate in adrenergically mediated sympathetic vasoconstriction of arterioles.

Adrenergic alpha-Agonists↗

PubMed1998

Btk function in B cell development and response.

Mutations in Bruton's tyrosine kinase (Btk) result in the B cell immunodeficiencies XLA in humans and Xid in mice. Both the maintenance of peripheral B cell numbers and their response to B cell antigen receptor (BCR) crosslinking depend on Btk. Btk integrates signals from multiple cell surface receptors, including BCR and G-protein coupled receptors. These Btk dependent signals control B cell proliferation and survival by mediating Ca2+ flux, activating JNK and p38 and inducing cell cycle regulatory genes.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed1998

Mechanisms of neuroendocrine cell excitability.

Oxytocin (OT) and vasopressin (VP), two neuronally synthesized nonapeptides, are made in the hypothalamic paraventricular and supraoptic nuclei of mammals and released into their blood, eventually to have profound hormonal actions on peripheral tissues. In the rat both OT and VP neurons fire slowly and irregularly under conditions of low demand for peptide release, but natural or artificial depolarizing stimuli result in differential patterns of activity: either regular continuous firing, strongly associated with OT cells, or phasic bursting, characteristic of VP neurons. Recently published findings offer an explanation for the dominant presence of certain Ca(2+)-dependent membrane potentials that typically lead to phasic firing in VP neurons. Mechanisms of excitability involved in the differential activities of the two cell types, as well as of the same cell type under different physiological conditions, include such factors as Ca2+ binding proteins, voltage- and ligand-gated ion channels, release of Ca2+ from internal stores and gap junctional conductances. The evidence for these factors is reviewed here.

Animals↗