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Biomedical subjects

E Chen

Publications and source records attributed to E Chen.

At least 217 records · Page 12Linked to original sources
PubMed1989

Collateralization and GAD immunoreactivity of descending pallidal efferents.

The first phase of this study involves injecting a different fluorescent retrograde axonal tracer into the subthalamic nucleus, the substantia nigra, and the mesopontine tegmentum. Multiple labeled cells are found within the caudal third of the globus pallidus. The entopeduncular nucleus and adjacent basal forebrain structures such as the substantia innominata, lateral hypothalamus, bed nucleus of the stria terminalis, and central nucleus of the amygdala all exhibit some dye containing cell, although multiple labeled cells are rare. The second phase of this study involves injecting a different fluorescent retrograde tracer into either the substantia nigra, or the mesopontine tegmentum, and subsequent processing of the tissue for glutamic acid decarboxylase (GAD) immunocytochemistry. Many dye and antibody double-labeled cells could be found within the entopeduncular nucleus and the caudal third of the globus pallidus. This is in contrast to the surrounding basal forebrain regions with brainstem efferents which were rarely GAD-positive. This study indicates that the collateral pattern and immunocytochemistry of globus pallidus neurons with descending efferents are distinct from other basal forebrain neurons having similar efferents. These results also extend previous findings and suggest that the neuron of the pallidal complex are heterogeneous with respect to their patterns of projections. In particular, the present findings question previous assumptions concerning the homology of pallidal segments between primate and rodent species.

Animals↗
PubMed1989

Modulation of Fc gamma receptors on the human macrophage cell line U-937.

Macrophage receptors for the Fc portion of IgG play an important role in host defense, inflammation, and the pathophysiology of autoimmune disorders. We studied one important function of Fc gamma receptors--the ability to bind IgG ligand. Direct binding experiments analyzed by nonlinear regression were consistent with monomeric and trimeric IgG binding to a single class of receptors. Indirect binding experiments were also consistent with this interpretation and revealed that both IgG ligands completely inhibited the binding of the other. In addition, we used an anti-Fc gamma RII monoclonal antibody known to compete for the Fc gamma RII ligand binding site and known to inhibit IgG trimer binding to other cells. At concentrations of antibody which saturated all Fc gamma RII sites, no inhibition of IgG trimer binding to U-937 was observed. This was evident despite the observation that the numbers of Fc gamma RI and Fc gamma RII, determined by equilibrium binding of monomeric IgG and anti-Fc gamma RII antibody, respectively, were similar on U-937. Monoclonal antibodies were used to compare the expression and modulation of Fc gamma receptor proteins with their ability to bind monomeric and trimeric IgG ligands. Dexamethasone and gamma-interferon regulated U-937 Fc gamma RI protein expression and IgG ligand binding to a similar degree. In contrast, the expression of Fc gamma RII was not altered by dexamethasone. Interferon-gamma primarily stimulated Fc gamma RI, as determined both by reactivity with monoclonal antibody (227 +/- 26%) and by monomeric IgG ligand binding (350 +/- 151%). In addition, dexamethasone inhibited by 33% the gamma-interferon effect on Fc gamma RI protein and by 56% the effect on Fc gamma RI binding of monomeric IgG. Preincubation of U-937 with anti-Fc gamma RII antibody did not alter the effect of dexamethasone or gamma-interferon on IgG trimer binding. These data indicate that on U-937 cells Fc gamma RII does not function in the recognition of small molecular weight immune complexes and that Fc gamma RI is the Fc gamma receptor responsible for the binding of both monomeric and trimeric human IgG. Furthermore, Fc gamma RI is the major Fc gamma receptor on U-937 that is modulated by both gamma-interferon and glucocorticoids.

Antibodies, Monoclonal↗
PubMed1989

Human atrial natriuretic peptide receptor defines a new paradigm for second messenger signal transduction.

We isolated cDNAs encoding a 115 kd human atrial natriuretic peptide (alpha ANP) receptor (ANP-A receptor) that possesses guanylate cyclase activity, by low-stringency hybridization with sea urchin Arbacia punctulata membrane guanylate cyclase probes. The human ANP-A receptor has a 32 residue signal sequence followed by a 441 residue extracellular domain homologous to the 60 kd ANP-C receptor. A 21 residue transmembrane domain precedes a 568 residue cytoplasmic domain with homology to the protein kinase family and to a subunit of the soluble guanylate cyclase. COS-7 cells transfected with an ANP-A receptor expression vector displayed specific [125I]alpha ANP binding, and exhibited alpha ANP stimulated cGMP production. These data demonstrate a new paradigm of cellular signal transduction where extracellular ligand binding allosterically regulates cyclic nucleotide second-messenger production by a receptor cytoplasmic catalytic domain.

Amino Acid Sequence↗
PubMed1989

Molecular characterization of HIV-1 isolated from a serum collected in 1976: nucleotide sequence comparison to recent isolates and generation of hybrid HIV.

Human immunodeficiency virus type 1 (Z321 designate, HIV-1Z321), the oldest known HIV, was isolated from a serum sample collected in Zaire in 1976 and was molecularly cloned. Restriction enzyme analysis of unintegrated viral DNA revealed the presence of conserved restriction enzyme cleavage sites in the long terminal repeat sequences. Nucleotide sequence analysis of the 3' end of the viral DNA revealed a pattern similar to other HIV-1 isolates described. However, some of the common restriction sites present in other isolates were absent in HIV-1Z321. The extent of differences between HIV-1Z321 and recent isolates from North America and Zaire was 17.86-18.36% on the nucleotide sequence level and 26.5-33.2% difference in the predicted amino acid sequence in the envelope gene. Differences were also noted in 3'-orf (nef: according to HIV gene nomenclature; see Ref. 42) gene and U3 region of the long terminal repeat sequences of HIV-1Z321 and other isolates. Nucleotide sequence of a HIV-1 isolate, 12 years apart from the present isolates, will provide an important time calibration point for the evolutionary divergence of HIV isolates. Hybrid HIV was also generated by transfecting HIV-1Z321 and HIV-1HTLV-III viral DNAs into cells.

Amino Acid Sequence↗
PubMed1989

Activity distribution of cytochrome oxidase in the rat retina. A quantitative histochemical study.

Cytochrome oxidase (CYO) is a key enzyme in the respiratory chain. Therefore, CYO has an important role in the cell metabolism. In the present study CYO activity in the rat retina was identified by histochemical staining. The density of the staining, corresponding to the activity of the CYO, was evaluated quantitatively by densitometry. A high CYO activity was found in the retinal pigment epithelium, in the inner segment of the photoreceptors, in the outer plexiform layer and in the inner plexiform layer. In the outer segment of the photoreceptors, in the outer nuclear layer, and in the inner nuclear layer the CYO activity was relatively low. An analysis of variance demonstrated that the precision in an estimation of a mean depends on the number of animals and the number of retinal sections per animal.

Animals↗
PubMed1989

Fc gamma receptor recognition of IgG ligand by human monocytes and macrophages.

We examined the binding characteristics of human monocytes and macrophages with the IgG ligands, human monomeric IgG and a small human IgG aggregate, trimeric IgG. Our purpose was to utilize fresh monocytes, in vitro cultured monocytes, and alveolar macrophages in direct and indirect binding experiments. Freshly isolated monocytes expressed only a single binding site for IgG monomer and IgG trimer. In contrast, in vitro cultured monocytes, gamma-interferon-treated monocytes, and freshly isolated alveolar macrophages expressed a single binding site for IgG monomer and, in addition, a high and low affinity binding site for IgG trimer. The high affinity binding site for IgG trimer (Kd approximately equal to 1 nM) appeared identical to the binding site for IgG monomer. The low affinity binding site for IgG trimer (Kd = 50 to 250 nM) appeared to be due to Fc gamma RII, because antibody to Fc gamma RII inhibited its expression. Since Fc gamma RII, in contrast to Fc gamma RI, does not bind monomeric IgG, the data suggest that this low affinity receptor for trimeric IgG, Fc gamma RII, can bind low molecular weight circulating immune complexes at concentrations 10- to 100-fold lower than Fc gamma RI. Thus, these studies suggest that at 37 degrees C, macrophage Fc gamma RII may play a functional role in the recognition of small molecular weight immune complexes.

Antigens, Differentiation↗
PubMed1988

A single receptor binds both insulin-like growth factor II and mannose-6-phosphate.

Amino acid sequences deduced from rat complementary DNA clones encoding the insulin-like growth factor II (IGF-II) receptor closely resemble those of the bovine cation-independent mannose-6-phosphate receptor (Man-6-P receptorCI), suggesting they are identical structures. It is also shown that IGF-II receptors are adsorbed by immobilized pentamannosyl-6-phosphate and are specifically eluted with Man-6-P. Furthermore, Man-6-P specifically increases by about two times the apparent affinity of the purified rat placental receptor for 125I-labeled IGF-II. These results indicate that the type II IGF receptor contains cooperative, high-affinity binding sites for both IGF-II and Man-6-P-containing proteins.

Amino Acid Sequence↗
PubMed1988

Na+ pump in renal tubular cells is regulated by endogenous Na+-K+-ATPase inhibitor from hypothalamus.

Bovine hypothalamus contains a high affinity, specific, reversible inhibitor of mammalian Na+-K+-ATPase. Kinetic analysis using isolated membrane fractions showed binding and dissociation rates of the hypothalamic factor (HF) to be (like ouabain) relatively long (off rate = 60 min). To determine whether the kinetics of inhibition in intact cells might be more consistent with regulation of physiological processes in vivo, binding and dissociation reactions of HF in intact renal epithelial cells (LLC-PK1) were studied using 86Rb+ uptake and [3H]ouabain binding. As with membranes, a 60-min incubation with HF inhibited Na+-K+-ATPase in LLC-PK1 cells. In contrast to membrane studies, no prolonged incubation with LLC-PK1 was needed to observe inhibition of Na+-K+-ATPase. HF caused a 33% inhibition of ouabain-sensitive 86Rb+ influx within 10 min. Incubation of cells with HF followed by washout showed rapid reversal of pump inhibition and a doubling of pump activity. The dose-response curve for HF inhibition of LLC-PK1 86Rb+ uptake showed a sigmoidal shape consistent with an allosteric binding reaction. Thus HF is a potent regulator of Na+-K+-ATPase activity in intact renal cells, with binding and dissociation reactions consistent with relevant physiological processes.

Animals↗
PubMed1987

Primary structure and mRNA localization of protein F1, a growth-related protein kinase C substrate associated with synaptic plasticity.

Protein F1 is a neuron-specific, synaptic-enriched, membrane-bound substrate of protein kinase C (PKC) whose phosphorylation is related to synaptic plasticity in the adult. The sequence of 26 N-terminal amino acids was determined from purified rat protein F1. A 78-mer synthetic oligonucleotide designed from the partial N-terminal sequence enabled identification of protein F1 cDNA clones in a rat brain library. F1 protein is a 226 amino acid protein encoded by a 1.5 kb brain-specific, developmentally-regulated mRNA. Transcripts for protein F1 can be detected at birth, and their level declines after maturation. A full-length cDNA clone was transcribed and translated in vitro. Translation products could be immunoprecipitated with anti-F1 antibodies. In situ hybridization analysis revealed protein F1 transcripts in hippocampal pyramidal cells, but not in granule cells. In cerebellum, granule cells contained protein F1 mRNA, while Purkinje cells did not. Co-localization of protein F1 with protein kinase C-II [PKC-II (beta)], rather than PKC-I (gamma) suggests that PKC-II may phosphorylate protein F1.

Amino Acid Sequence↗
PubMed1987

Sequence analysis, cellular localization, and expression of a neuroretina adhesion and cell survival molecule.

A cDNA for purpurin, a secreted 20,000 dalton neural retina cell adhesion and survival protein, has been sequenced and expressed in mammalian cells. Purpurin mRNA is found in both embryonic and adult retina, but not the brain, heart, or liver. The protein is highly concentrated in the neural retina between the pigmented epithelium and the outer segments of the photoreceptor cells; it is synthesized by photoreceptor cells. The predicted purpurin sequence contains 196 residues, has approximately 50% sequence homology with serum retinol binding protein, and is a member of the alpha-2 mu-globulin superfamily. Purpurin binds retinol and may play a major role in retinol transport across the interphotoreceptor cell matrix.

Amino Acid Sequence↗
PubMed1987

Human proto-oncogene c-kit: a new cell surface receptor tyrosine kinase for an unidentified ligand.

Structural features of v-kit, the oncogene of HZ4 feline sarcoma virus, suggested that this gene arose by transduction and truncation of cellular sequences. Complementary DNA cloning of the human proto-oncogene coding for a receptor tyrosine kinase confirmed this possibility: c-kit encodes a transmembrane glycoprotein that is structurally related to the receptor for macrophage growth factor (CSF-1) and the receptor for platelet-derived growth factor. The c-kit gene is widely expressed as a single, 5-kb transcript, and it is localized to human chromosome 4 and to mouse chromosome 5. A c-kit peptide antibody permitted the identification of a 145,000 dalton c-kit gene product that is inserted in the cellular plasma membrane and is capable of self-phosphorylation on tyrosine residues in both human glioblastoma cells and transfected mouse fibroblasts. Our results suggest that p145c-kit functions as a cell surface receptor for an as yet unidentified ligand. Furthermore, carboxy- and amino-terminal truncations that occurred during the viral transduction process are likely to have generated the transformation potential of v-kit.

Amino Acid Sequence↗
PubMed1987

Negative and positive regulation of human leukocyte antigen class I gene transcription in K562 leukemia cells.

The mechanism of transcriptional activation of human leukocyte antigen class I genes by gamma interferon and 5-azacytidine was studied in K562 human leukemia cells. Nuclear run-on transcription assays with various protein and RNA synthesis inhibitors yield evidence for both stimulation of a positive regulatory factor and inhibition of an mRNA that codes for a labile repressor. A novel mechanism is proposed to explain how 5-azacytidine can activate repressed genes without affecting DNA methylation.

Azacitidine↗
PubMed1987

Israeli adolescents and military service: encounters.

Problems of mental health during combat activities are well documented in Israel (Dasberg, 1976). Much less attention has been paid to the problems of the young soldier who enters army life in Israel. This paper delineates some areas of friction and vulnerability between the worlds of the youth and the military. These encounters are systematized into groups, creating the "Binary Model." This model, based on the authors' experience as clinicians in the I.D.F. Central Mental Health Clinic, helps in locating and treating young soldiers in crisis situations.

Adolescent↗
PubMed1986

Cloning and expression of human apolipoprotein D cDNA.

The amino acid sequence of human apolipoprotein D, a component of high density lipoprotein, has been obtained from the cloned cDNA sequence. The 169-amino acid protein has no marked similarity to other apolipoprotein sequences, but has a high degree of homology to plasma retinol-binding protein and other members of the alpha 2u-globulin protein superfamily. Apolipoprotein D mRNA has been detected in human liver, intestine, pancreas, kidney, placenta, adrenal, spleen, and fetal brain tissue. Tissue culture cells transfected with the cloned cDNA secrete material that reacts with anti-apoD antibodies.

Amino Acid Sequence↗
PubMed1986

Two interleukin 1 genes in the mouse: cloning and expression of the cDNA for murine interleukin 1 beta.

A human interleukin 1 beta (IL 1 beta) cDNA probe was utilized to identify a homologous murine cDNA clone. The murine cDNA encodes a 269-residue protein which is 67% homologous to human IL 1 beta. The murine sequence was engineered for expression in mammalian cells and directs the synthesis of biologically active IL 1. This protein, termed murine IL 1 beta, is only 22% homologous with the previously described murine IL 1 sequence. Both IL 1 alpha and IL 1 beta are encoded by single genes, but IL 1 beta mRNA is about fivefold more abundant in a stimulated macrophage cell line.

Amino Acid Sequence↗
PubMed1986

Stimulation of tyrosine-specific protein phosphorylation in the rat liver plasma membrane by oxygen radicals.

Incorporation of 32P from [gamma-32P]ATP into endogenous proteins, added histone and the copolymers Glu 80 Tyr 20 by rat liver plasma membranes was markedly increased by several naphthoquinones, including menadione. This stimulation was most marked with Glu 80 Tyr 20, has an absolute requirement for either dithiothreitol or reduced glutathione, and was inhibited by superoxide dismutase, catalase, and desferrioxamine to varying degrees depending on the quinones used. Their effectiveness in stimulating the apparent tyrosine-specific protein phosphorylation correlated with the rates of DTT-dependent redox cycling measured by oxygen consumption. Increased protein phosphorylation was also seen with particulate fractions isolated from hepatocytes incubated with quinones. A free radical-mediated mechanism is suggested for the quinone stimulation of protein phosphorylation.

Adenosine Triphosphate↗