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Y Yang

Publications and source records attributed to Y Yang.

At least 1,261 records · Page 70Linked to original sources
PubMed1993

Three-dimensional quantitative structure-activity relationships of 5-HT receptor binding data for tetrahydropyridinylindole derivatives: a comparison of the Hansch and CoMFA methods.

A series of new derivatives of 3-(1,2,5,6-tetrahydropyridin-4-yl)indole (4-THPI) has been synthesized, and their dissociation constants at the 5-HT1A and 5-HT2 serotonin (5-HT) receptor subtypes have been determined. The new data were combined with similar binding data on a related set of THPI analogs reported previously (Taylor et al. Mol. Pharmacol. 1988, 34, 42-53) and used to develop 3-dimensional quantitative structure-activity relationships (3-D QSARs) for these compounds at the 5-HT1A and 5-HT2 receptor sites, by the method of comparative molecular field analysis (CoMFA). Since the previous study included several conventional QSARs obtained by Hansch analysis, and the new compounds in some cases fall within the congeneric series used in those analyses, we were able to make a direct comparison of the predictive capabilities of CoMFA and Hansch analysis using identical training and test data sets. The overall quality of actual predictions of activity by both methods appears to be about the same, as assessed by the root mean square (rms) residuals between actual and predicted pKi values. On the one hand, the compounds most poorly predicted by the Hansch analysis were 34, 35, and 37, while compounds 30-33 were relative poorly predicted by CoMFA. However, a clear advantage of CoMFA is the ability to include diversely substituted or noncongeneric analogs that must be omitted from conventional QSAR analysis. Using the entire data set of 45 THPI analogs reported here, pKi predictions for six additional compounds having 5-heteroarylindole substituents gave rms residuals of 0.46 and 0.36 for the 5-HT1A and 5-HT2 models, respectively; this is close to the experimental error of the binding data. The significance of the CoMFA field graphs in terms of molecular features required for activity and selectivity at these 5-HT receptor subtypes is discussed.

Animals↗
PubMed1993

Insulin activates myelin basic protein (p42 MAP) kinase by a protein kinase C-independent pathway in rat adipocytes. Dissociation from glucose transport.

Myelin basic protein kinase (MBPK) activity of rat adipocytes was measured directly or in gels after purification of p42 microtubule-associated protein kinase (MAPK). Insulin and phorbol esters provoked 2- to 3-fold increases in MBPK/MAPK activity within 5-10 min. Whereas phorbol ester effects were blocked by protein kinase C (PKC) depletion or inhibition, insulin effects were fully intact, indicating that insulin activates MBPK/MAPK independently of PKC. In contrast, PKC depletion or inhibition markedly inhibited insulin effects on [3H]2-deoxyglucose uptake, suggesting that this effect requires PKC, rather than a factor within the ras/MAPK cascade.

Adipocytes↗
PubMed1993

The human MDM-2 oncogene is overexpressed in leukemias.

The human homologue of the mouse double minute 2 (MDM-2) gene codes for a cellular protein that forms a complex with the mutant and wild-type p53 protein and modulates its trans-activation activity. Overexpression of the MDM-2 gene in cells increases their tumorigenic potential and overcomes the growth-suppressive activity of p53. Previous reports have shown that the MDM-2 gene is amplified in approximately one third of human sarcomas. To examine the role of MDM-2 in leukemia, we analyzed MDM-2 gene amplification and mRNA expression in various types of leukemias. We did not detect gene amplification in any of the 48 cases of leukemia that we examined. In contrast, we observed significant MDM-2 mRNA overexpression in 34 of 64 cases (53%). The level of mRNA overexpression in some cases of leukemias was comparable to that observed in some cases of sarcomas, which demonstrate more than 50-fold MDM-2 gene amplification. Furthermore, we divided these cases into different prognostic groups according to their karyotypic abnormalities. MDM-2 overexpression seemed to be associated with unfavorable chromosomal abnormalities. These findings suggest that the expression of the MDM-2 gene is altered in a significant fraction of human leukemias and MDM-2 may play a significant role in leukemogenesis. In addition, these results suggest that mechanisms other than gene amplification may play a significant role in deregulating the MDM-2 expression.

Base Sequence↗
PubMed1993

Human IM-9 lymphoblasts as a model of the growth hormone-insulin-like growth factor axis: gene expression, and interactions of ligands with receptors and binding proteins.

Human IM-9 lymphoblasts bind growth hormone (hGH) and insulin-like growth factors (IGFs). We have systematically examined the IM-9 cells as a valuable model of the interaction of hGH and the IGFs at the cellular level. Cells were cultured in medium with 10% serum and for a subset of experiments cultured in serum-free medium. Binding of [125I]hGH and [125I]IGF-I and -II to intact IM-9 cells was measured: unlabeled hGH inhibited binding of [125I]hGH (half max. 20 ng/ml). Binding of [125I]IGF-I was inhibited by IGF-I (half max. 7.5 ng/ml), IGF-II (half max. 60 ng/ml), and insulin and anti IGF-I receptor antibody (alpha IR3). [125I]IGF-II was inhibited by IGF-II (half max. 15 ng/ml), IGF-I (half max. 500 ng/ml), insulin (half max. 250 ng/ml) but not by alpha IR3. Crosslinking experiments with [125I]IGF-II and DSS as the crosslinking agent and analysis of radioligand-receptor complexes by SDS-PAGE under reducing conditions revealed that [125I]IGF-II bound to a 250 kDa and a 135 kDa receptor species. The latter possibly represents an insulin-type receptor whereas the 250 kDa species had the characteristics of the IGF-II/M6P receptor. When IM-9 cell conditioned medium was analyzed in ligand blotting experiments with either [125I]IGF-I or -II a 30 kDa IGFBP species was detected on the autoradiographs. Also, IGF-II immunoreactivity (approx. 1 ng/ml medium) was measured in the cell conditioned medium using an IGF-BP blocked RIA employing [125I]IGF-II. In a subset of experiments IM-9 cells were homogenized in 4 M guanidinium-thiocyanate and RNA extracted in 5.7 M CsCl. Denatured RNA was electrophoresed on 0.8% agarose gels and transferred to a nylon membrane, fixed and the blots hybridized with cDNA probes. Probes were labeled with [32P]dCTP using a random prime labeling procedure: a Pst I 700 bp fragment of the human IGF-I cDNA, a 554 bp Pst I-Sal I fragment of the IGF-II cDNA, a 614 bp Pst I fragment of the IGF-I receptor cDNA and a 663 bp Pst I fragment of the IGF-II/M6P receptor. Autoradiographs of Northern blots showed specific hybridization with the IGF-I probe at 3.7 kb and with the IGF-II probe at 5.3 kb. No signal was detected with the IGF-I receptor cDNA probe. Hybridization with the IGF-II/M6P receptor probe yielded a 9 kb RNA species.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding, Competitive↗
PubMed1993

The common variant of cystic fibrosis transmembrane conductance regulator is recognized by hsp70 and degraded in a pre-Golgi nonlysosomal compartment.

The most common cause of cystic fibrosis is deletion of Phe-508 (delta F508) from the cystic fibrosis transmembrane conductance regulator (CFTR). Previous studies have suggested that delta F508 CFTR is an unstable protein that retains a pattern of glycosylation specific to the endoplasmic reticulum. This report examines the mechanism responsible for the mislocalization of delta F508 CFTR in a human cystic fibrosis epithelial cell line overexpressing recombinant CFTR by virtue of adenovirus-mediated gene transfer. Immunoelectron microscopy confirmed that wild-type CFTR is delivered to the plasma membrane of these cells and that delta F508 CFTR is retained in the endoplasmic reticulum. Pulse-chase studies showed that newly synthesized CFTR complexes with the chaperone hsp70. The wild-type protein dissociates from hsp70 before its transport to the Golgi, and the protein is subsequently degraded in lysosomes. By contrast, the complex formed between delta F508 CFTR and hsp70 is retained in the endoplasmic reticulum and delta F508 CFTR is rapidly degraded in a pre-Golgi nonlysosomal compartment. Thus, hsp70 discriminates between the normal form of CFTR and the form of the protein that most commonly causes cystic fibrosis (delta F508). These findings clarify the mechanism by which mutation causing delta F508 affects the intracellular trafficking of CFTR and suggest another function for hsp70 in ensuring quality control during the biosynthesis of plasma-membrane proteins.

Biological Transport↗
PubMed1993

Smith-Fineman-Myers syndrome: report on a large family.

Smith-Fineman-Myers syndrome is considered an X-linked mental retardation (XLMR) syndrome. Three families have been reported to date. However, none presented a typical pattern of X-linked inheritance. Here we reported on 5 males with Smith-Fineman-Myers syndrome with similar phenotypic expression as in those cases reported previously; they were distributed in 4 sibships of one large maternal kindred. This finding adds strong support to the hypothesis of the Smith-Fineman-Myers syndrome being a rare XLMR syndrome.

Child↗
PubMed1993

Alcohol-induced protein folding transitions in platelet factor 4: the O-state.

Platelet factor 4 (PF4) (7800 daltons) is an anti-parallel beta-sheet, alpha/beta class protein whose tertiary structure is stabilized by the presence of two disulfide bonds. Titration of PF4 with 2-propanol or similar low molecular weight, aliphatic alcohols induces reversible protein folding transitions which are observed to be in slow exchange on the 600-MHz 1H NMR time scale. Line fitting of resolved resonances assigned to ring protons of Y60, H35, H23, and alpha H of K50 in native and alcohol-induced states (O-states) allows derivation of folding equilibrium constants and exchange kinetics. Folding exchange rates vary between 5 and 100 s-1 on going from 9.8 to 3.3 M2-propanol. Simple linear extrapolation to 0 M2-propanol yields an O-state to N-state exchange rate of about 500 s-1, i.e., millisecond time scale. At relatively high 2-propanol concentration (>9.5 M), where the O-state is predominant (>90%), NMR spectra suggest a more "unfolded" structure, while CD data indicate the preservation of considerable secondary structure. Increasing 2-propanol from 3.3 to 9.8 M, however, shifts the CD-derived fractional compositions significantly, with overall beta-structure decreasing by about 20% and alpha-helix composition increasing by about 25%. Alcohol-jump experiments, which identify O-state long-lived NHs in the NMR spectrum of native PF4, indicate folding transition reversibility and conservation of about 15 long-lived NHs in native and O-states. Most of these NHs are assigned to residues in anti-parallel beta-sheet structure. Of these 15 NHs, H/D exchange rates, although variably reduced in the O-state, are generally still long-lived compared with random coil H/D exchange. Overall, the PF4 O-state is a stable intermediate with an apparently more highly fluctuating anti-parallel beta-sheet structure and a more stabilized C-terminal alpha-helix.

1-Propanol↗
PubMed1993

Residues added to the carboxyl terminus of the Yersinia pseudotuberculosis invasin protein interfere with recognition by integrin receptors.

Escherichia coli strains encoding the Yersinia pseudotuberculosis invasin protein are efficiently internalized by mammalian cells. Bacterial uptake into cultured cell lines became defective, however, if invasin was altered by fusion of its carboxyl terminus to E. coli alkaline phosphatase or by the addition of two hydrophobic amino acids to its carboxyl-terminal end. Probing with anti-invasin monoclonal antibodies revealed that the amino-terminal end of invasin was properly localized on the bacterial cell surface in strains encoding invasin with 2 additional amino acids, whereas the carboxyl terminus was not accessible to the monoclonal antibody. Therefore, the 2 additional amino acids interfered with the folding or orientation of the carboxyl terminus in the outer membrane. Alkylation experiments in the absence of reduction indicated that this defect was not caused by a gross inability to form a critical disulfide bond. Revertants were selected from a strain encoding this mutant protein by enriching for organisms able to enter cultured mammalian cells. The vast majority of revertants that were isolated following this enrichment contained a stop codon at the usual position found in the wild type inv gene. The most efficient of the remaining revertants resulted in the introduction of a glycine residue at the site of the wild type stop codon, presumably restoring proper conformation of the carboxyl-terminal region.

ATP-Binding Cassette Transporters↗
PubMed1993

Ligand binding induces an asymmetrical transmembrane signal through a receptor dimer.

Two ligand (aspartate)-binding pockets are formed at the interface between the subunits of the Tar homodimer, a bacterial chemoreceptor. Using mutant heterodimers of a hybrid receptor, Taz1, which consists of the external domain of Tar and the cytoplasmic domain of EnvZ, we disrupted either one or the other of the two ligand-binding pockets. We found that occupation of only one of the ligand-binding pockets was sufficient for induction of a transmembrane signal, and that the subunit responsible for the binding of the amino group of the ligand transduces the signal.

Bacterial Outer Membrane Proteins↗
PubMed1993

9-cis-retinoic acid inhibits activation-driven T-cell apoptosis: implications for retinoid X receptor involvement in thymocyte development.

Retinoic acid is a morphogenetic signaling molecule derived from vitamin A and involved in vertebrate development. Two groups of receptors, retinoic acid receptors and retinoid X receptors (RXRs), have been identified. All-trans-retinoic acid is the high-affinity ligand for retinoic acid receptors, and 9-cis-retinoic acid additionally binds RXRs with high affinity. Here we report that although retinoic acid has little inhibitory effect on activation-induced T-cell proliferation, it specifically prevents activation-induced apoptosis of T-cell hybridomas and antigen-specific deletion of immature CD4+CD8+ thymocytes from alpha beta T-cell receptor transgenic mice. 9-cis-Retinoic acid was approximately 10-fold more potent than all-trans-retinoic acid, suggesting that RXRs participate in this process. Thus, although 9-cis-retinoic acid has little immuno-suppressive activity, it is a potent negative regulator of activation-induced T-cell apoptosis, raising the possibility that RXRs may take part in regulating T-cell development.

Animals↗
PubMed1993

Molecular, biochemical, and functional characteristics of tumor necrosis factor-alpha produced by human placental cytotrophoblastic cells.

Previous studies have shown that the TNF-alpha gene is transcribed and translated in fully differentiated human placental syncytiotrophoblast. In this study, TNF transcripts were identified by in situ hybridization in cytotrophoblastic cells, a progenitor subpopulation that proliferates rapidly in early gestation tissues. To establish molecular and biochemical characteristics of cytotrophoblastic TNF and to evaluate potential utilization, experiments were conducted on two cytotrophoblastic cell lines, Jar and JEG-3. Northern blot hybridization and immunocytochemical tests showed that Jar and JEG-3 cells contained TNF mRNA and specific protein. Enzyme immunoassays demonstrated production of TNF, and immunoprecipitation experiments showed that Jar cell TNF protein was the same molecular mass as macrophage TNF. DNA synthesis in both lines was promoted by rTNF, and experiments employing 17-mer TNF antisense and sense oligonucleotides showed specific inhibition of DNA synthesis by antisense sequences. Both p60 and p80 TNF-R mRNA were present in the choriocarcinoma cell lines, and DNA synthesis was inhibited by antibody to the p60 TNF-R. Although the two lines were similar in many respects, Jar cells produced more TNF and demonstrated a greater reliance on TNF for their growth. Collectively, the results indicate that: 1) the TNF gene is expressed in both normal and malignant cytotrophoblast; 2) certain molecular, immunologic, and biochemical characteristics of trophoblast-derived TNF are similar to macrophage TNF; and 3) the p60 TNF-R facilitates utilization of TNF as an autocrine growth factor by choriocarcinoma cells. Although TNF apparently serves important functions in cytotrophoblast during the course of placental development that might include promotion of proliferation and invasion, constitutive expression of this gene in neoplastic cells could account in part for the remarkable ability of trophoblastic tumors to overcome host defenses.

Base Sequence↗
PubMed1993

Requirement of both kinase and phosphatase activities of an Escherichia coli receptor (Taz1) for ligand-dependent signal transduction.

Taz1 is a hybrid receptor in the Escherichia coli cytoplasmic membrane, consisting of the N-terminal ligand binding domain of Tar (a chemoreceptor for aspartate) and the C-terminal signaling domain of EnvZ (an osmosensor). The binding of aspartate to an extra cytoplasmic domain induces the transmembrane signal to the cytoplasmic signaling domain. The signaling domain functioning as a protein kinase evokes a response by transferring a phosphate from an intracellular histidine to OmpR. This domain also encodes an OmpR-specific phosphatase whose action is crucial in completing the OmpR phosphorylation cycle. Phosphorylated OmpR acts as a transcriptional activator for the ompC gene. A number of mutations were introduced into the signaling domain in conserved sequences of the prokaryotic histidine kinase family. All Taz1 mutants lost the ability to both autophosphorylate the histidine residue and transfer the phosphate to OmpR. These mutated receptors were unable to activate ompC-lacZ expression. However, ompC-lacZ was able to be activated by complementation of Taz1 mutants. In some combinations, two different defective Taz1 mutants could restore both OmpR kinase and phosphatase activities when co-expressed. In other combinations only kinase activity was restored. Aspartate-inducible ompC-lacZ expression was restored only in the former cases, while in the latter cases ompC-lacZ expression became constitutive. These results indicate that the kinase activity is essential to activate ompC expression while the phosphatase activity is required to regulate ompC gene expression in a ligand-dependent manner.

Aspartic Acid↗
PubMed1993

An approach for treating the hepatobiliary disease of cystic fibrosis by somatic gene transfer.

Cystic fibrosis (CF) is an inherited disease of epithelial cell ion transport that is associated with pathology in multiple organ systems, including lung, pancreas, and liver. As treatment of the pulmonary manifestations of CF has improved, management of CF liver disease has become increasingly important in adult patients. This report describes an approach for treating CF liver disease by somatic gene transfer. In situ hybridization and immunocytochemistry analysis of rat liver sections indicated that the endogenous CFTR (cystic fibrosis transmembrane conductance regulator) gene is primarily expressed in the intrahepatic biliary epithelial cells. To specifically target recombinant genes to the biliary epithelium in vivo, recombinant adenoviruses expressing lacZ or human CFTR were infused retrograde into the biliary tract through the common bile duct. Conditions were established for achieving recombinant gene expression in virtually all cells of the intrahepatic bile ducts in vivo. Expression persisted in the smaller bile ducts for the duration of the experiment, which was 21 days. These studies suggest that it may be feasible to prevent CF liver disease by genetically reconstituting CFTR expression in the biliary tract, using an approach that is clinically feasible.

Adenoviridae↗
PubMed1993

Effect of low molecular weight aliphatic alcohols and related compounds on platelet factor 4 subunit association.

Titration of platelet factor 4 (PF4) with increasing concentrations of various low molecular weight aliphatic alcohols disrupts dimer and tetramer quaternary structure while preserving tertiary structural integrity. Normally observed slow subunit exchange (1H NMR time scale) is shifted into the fast chemical exchange regime. The order of effectiveness is butanol > 2-propanol > propanol > ethanol > methanol. Fluorination of ethanol (trifluoroethanol) and 2-propanol (hexafluoro-2-propanol) increases effectiveness by approximately 2 orders of magnitude. Oxidation to 2-propanone or trifluoro-2-propanone produces a less effective compound, suggesting a mechanistic role for the hydroxyl group. Increasing the number of hydroxyls to three, as in glycerol, however, is relatively ineffective in disrupting aggregate states or modifying subunit exchange rates. While 19F NMR studies indicate that these alcohols specifically interact with PF4, binding alone can not explain their mechanism of action. Dimethyl sulfoxide, structurally similar to 2-propanol, disrupts PF4 aggregation by direct binding, but does not shift subunit exchange kinetics into the NMR fast-exchange regime. Although not fully understood, the effectiveness of these compounds appears to be related to the colligative properties of the solution.

Alcohols↗
PubMed1993

Structural requirements for the binding of modified proteins to the scavenger receptor of macrophages.

Oxidized low density lipoprotein (LDL) and certain chemically modified LDL are recognized by the scavenger receptor of macrophages. All of these modifications involve charge-neutralizing derivatization of lysine amino groups. However, it remains controversial whether recognition of modified LDL by this receptor is due to the modification per se, or to other factors such as a conformational change of apoB. In this study, LDL and other proteins including bovine serum albumin, human high density lipoprotein, and murine IgG were derivatized with oxidation products generated from arachidonic acid by thermal autoxidation. Modified proteins had increased negative charge, and showed a more than 10-fold enhancement of degradation by mouse peritoneal macrophages via the scavenger receptor pathway. Modification was prevented by blocking lysine residues of the proteins by prior reductive methylation. Amino acid analysis revealed dose-dependent modification of lysine residues with no significant effects on any other amino acid. Fab fragments of monoclonal antibodies specific for adducts of oxidation products with lysine prevented the uptake of oxidation product-modified LDL and oxidized LDL by macrophages. Chromatography of oxidation product-modified LDL over Sepharose CL-4B showed that uptake by macrophages did not require LDL aggregation. These results suggest that a relatively simple domain consisting of a cluster of suitably derivatized lysine residues is sufficient for recognition by the scavenger receptor of macrophages.

Apolipoproteins B↗
PubMed1993

Use of bispecific heteroconjugated antibodies (anti-T cell antigen receptor x anti-MHC class II) to study activation of T cells with a full length or truncated antigen receptor zeta-chain.

Ligand-induced activation of T cells involves recognition of monovalent peptide Ag complexed with a cell surface MHC-encoded molecule. In contrast, antibody-induced activation of T cells typically requires external cross-linking of the TCR. To examine the mechanisms that underlie the ability of these different stimuli to signal, we have created bispecific chimeric antibody molecules (BA) that mimic Ag in several important aspects. Anti-TCR-alpha, -beta, or anti-CD3-epsilon Fab fragments were covalently coupled to an anti-MHC class II Fab fragment. These BA elicited IL-2 production or proliferation from Ag-specific T cell hybridoma cells or splenic T cells, respectively, in the presence, but not the absence, of accessory cells expressing the appropriate MHC class II molecule. This response was prevented by soluble blocking antibodies against the TCR or MHC class II. When "presented" by MHC class II-bearing accessory cells, anti-TCR x anti-MHC class II BA, like cell surface Ag, elicited IL-2 production from T cell transfectants expressing full length TCR zeta-chain but not from otherwise identical cells expressing truncated zeta; when immobilized on a plastic surface these BA were potent stimulators that induced equal amounts of IL-2 from the same cells. Purified Ag/MHC complexes immobilized on plastic were able to induce IL-2 production from T cells expressing the full length, but not the truncated, form of zeta. We hypothesize that TCR-mediated T cell activation requires stable aggregation of the TCR. In this model, activation by mobile cell surface Ag/MHC or BA occurs in two steps, occupancy-induced TCR clustering followed by stable aggregation facilitated by the presence of a full length zeta-chain. Immobilized high affinity anti-TCR antibodies, but not low affinity Ag/MHC complexes, directly promote stable receptor aggregates, and thus would not require a full length zeta-chain.

Animals↗
PubMed1993

Preretinal and optic nerve head neovascularization induced by photodynamic venous thrombosis in domestic pigs.

OBJECTIVE: To develop a reliable model of ischemic preretinal and optic nerve head neovascularization in young male domestic pigs. METHODS: Using laser-induced branch retinal venous obstruction assisted by photodynamic thrombosis with rose bengal, 15 of 15 treated eyes developed neovascularization of the optic nerve head and retina. All cases of neovascularization were followed up clinically for up to 12 weeks. RESULTS: Clinical, fluorescein angiographic, and histopathologic features were consistent with neovascular proliferation into the vitreous. CONCLUSIONS: Further evaluation of the long-term natural history, role of the degree of ischemia, and the effect of interventions for various types of ischemic retinopathy (eg, panretinal photocoagulation) is warranted. This model is simple and relatively inexpensive and allows easy clinical assessment.

Animals↗