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Biomedical subjects

L Zhou

Publications and source records attributed to L Zhou.

At least 307 records · Page 17Linked to original sources
PubMed1998

Chromosome 2 sequence of the human malaria parasite Plasmodium falciparum.

Chromosome 2 of Plasmodium falciparum was sequenced; this sequence contains 947,103 base pairs and encodes 210 predicted genes. In comparison with the Saccharomyces cerevisiae genome, chromosome 2 has a lower gene density, introns are more frequent, and proteins are markedly enriched in nonglobular domains. A family of surface proteins, rifins, that may play a role in antigenic variation was identified. The complete sequencing of chromosome 2 has shown that sequencing of the A+T-rich P. falciparum genome is technically feasible.

Amino Acid Sequence↗
PubMed1998

Cyclic GMP and cGMP-binding phosphodiesterase are required for interleukin-1-induced nitric oxide synthesis in human articular chondrocytes.

This study addressed the role of guanylyl cyclase (GC) and phosphodiesterase (PDE) in interleukin (IL)-1 activation of human articular chondrocytes. The GC inhibitors LY83583 and methylene blue dose-dependently inhibited IL-1-induced nitric oxide (NO) production, inducible NO synthase (iNOS) protein, and mRNA expression. These effects of GC inhibition were consistent with the rapid induction of cGMP by IL-1, which reached maximal levels after 5 min. The effects of GC inhibitors were selective as they did not reduce IL-1-induced cyclooxygenase II protein and mRNA. An inhibitor specific for soluble GC did not affect IL-1-induced NO production, and activators of soluble GC did not induce NO. However, the expression of iNOS mRNA was induced by atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP), activators of particulate GC, indicating that particulate rather than soluble guanylyl cyclases were involved in iNOS induction. The expression of iNOS mRNA and the production of NO were induced by a slowly hydrolyzable analog of cGMP, 8-bromo-cGMP, but not by nonhydrolyzable analog, dibutyryl cGMP, suggesting that PDE rather than cGMP-dependent protein kinase mediates the cGMP effects. Chondrocytes contained extensive cGMP PDE activity. This had PDE5 biochemical features and an inhibitor profile consistent with PDE5. Furthermore, the nonisoformspecific PDE inhibitor IBMX and PDE5-specific inhibitors suppressed IL-1-induced NO release and iNOS mRNA expression. PDE5 mRNA was constitutively expressed in chondrocytes. In addition to increasing PDE5 activities, IL-1 treatment reduced the sensitivity of PDE5 to several pharmacological inhibitors by up to 50-fold. In summary, inhibitors of either GC or PDE5 prevented IL-1 induction of iNOS; IL-1 increased the rates of both cGMP generation and hydrolysis; and exogenous PDE hydrolyzable cGMP analog induced iNOS and NO. These results suggest that increased cGMP metabolic flux is sufficient to induce iNOS, and GC and PDE5 activities are required for IL-1 induction of iNOS expression via increases in coupled cGMP synthesis and hydrolysis.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Demyelination in the central nervous system mediated by an anti-oligodendrocyte antibody.

The factors responsible for the major demyelinating disease of the central nervous system (CNS), multiple sclerosis, are poorly defined. Although T-cell-mediated immune responses play a pivotal role in establishing the inflammatory response, humoral factors also may be critical in disease progress. We have isolated a mouse monoclonal antibody (mAb 2B10) that recognizes a cell-surface molecule expressed exclusively by rat oligodendrocytes, the cells responsible for the formation and maintenance of CNS myelin. In cultures of neonatal rat spinal cord, mAb 2B10 specifically mediated oligodendrocyte cell death in the absence of complement. In the current study, mAb 2B10-producing hybridoma cells were implanted into adult rat brain ventricles, and the effect of mAb 2B10 on CNS cytoarchitecture was examined. In the optic nerves of mAb 2B10-treated animals, there was significant focal myelin degeneration near the optic chiasm. Axons in the myelin degenerate regions were largely healthy. There was no significant infiltration of hematopoietic-derived cells into the affected regions, but microglia were activated focally and phagocytosed the collapsed myelin. This study demonstrates that an antibody directed against myelin-forming cells induces CNS demyelination and supports the hypothesis that autoantibodies may play a role in CNS demyelinating diseases.

Animals↗
PubMed1998

Site-specific mutations of conserved residues in the phosphate-binding loop of the Arabidopsis UMP/CMP kinase alter ATP and UMP binding.

All eukaryotic UMP/CMP kinases contain a glycine-rich sequence GGPG(S/A)GK at the N-terminus. This sequence is homologous to the conserved sequence GXXGXGK found in other ATP-binding proteins. To study the role of this conserved sequence in Arabidopsis UMP/CMP kinase, five conserved residues were mutated by site-directed mutagenesis to generate seven mutant enzymes: G21A, G22A, G24A, G26A, K27R, K27M, and K27E. The G21A and G26A mutants were degraded during the purification phase and were thus unable to be purified. Kinetic studies on the other mutants, when compared to studies on the wild-type enzyme, revealed that this sequence is important for ATP binding and enzyme catalysis. All mutants had a decreased kcat/KATPm value. The G22A and G24A mutants had about half of the kcat value of wildtype and 3.9-fold and 3.3-fold increases in KATPm values, respectively. The kcat/KATPm values in the K27M and K27E mutants were changed significantly and decreased by 1000-fold and 2600-fold, respectively. The removal of the terminal positive charge of Lys27 in the K27M and K27E mutants resulted in 20% of the kcat value of wildtype. However, both mutants had a remarkable increase in KATPm value by 241-fold and 552-fold, respectively. Therefore, the positive charge of Lys27 plays an important role on both ATP binding and enzyme catalysis. Interestingly, the results also showed that the mutations that affected ATP binding also had an effect on UMP binding.

Adenosine Triphosphate↗
PubMed1998

Temperature-sensitive neuromuscular transmission in Kv1.1 null mice: role of potassium channels under the myelin sheath in young nerves.

In mammalian myelinated nerves, the internodal axon that is normally concealed by the myelin sheath expresses a rich repertoire of K channel subtypes thought to be important in modulating action potential propagation. The function of myelin-covered K channels at transition zones, however, has remained unexplored. Here we show that deleting the voltage-sensitive potassium channel Kv1.1 from mice confers a marked temperature-sensitivity to neuromuscular transmission in postnatal day 14 (P14)-P21 mice. Using immunofluorescence and electrophysiology, we examined contributions of four regions of the peripheral nervous system to the mutant phenotype: the nerve trunk, the myelinated segment preceding the terminal, the presynaptic terminal membrane itself, and the muscle. We conclude that the temperature-sensitive neuromuscular transmission is accounted for solely by a deficiency in Kv1.1 normally concealed in the myelinated segments just preceding the terminal. This paper demonstrates that under certain situations of physiological stress, the functional role of myelin-covered K channels is dramatically enhanced as the transition zone at the neuromuscular junction is approached.

Age Factors↗
PubMed1998

Glucose and ethylene signal transduction crosstalk revealed by an Arabidopsis glucose-insensitive mutant.

Glucose is an essential signaling molecule that controls plant development and gene expression through largely unknown mechanisms. To initiate the dissection of the glucose signal transduction pathway in plants by using a genetic approach, we have identified an Arabidopsis mutant, gin1 (glucose-insensitive), in which glucose repression of cotyledon greening and expansion, shoot development, floral transition, and gene expression is impaired. Genetic analysis indicates that GIN1 acts downstream of the sensor hexokinase in the glucose signaling pathway. Surprisingly, gin1 insensitivity to glucose repression of cotyledon and shoot development is phenocopied by ethylene precursor treatment of wild-type plants or by constitutive ethylene biosynthesis and constitutive ethylene signaling mutants. In contrast, the ethylene insensitive mutant etr1-1 exhibits glucose hypersensitivity. Epistasis analysis places GIN1 downstream of the ethylene receptor, ETR1, and defines a new branch of ethylene signaling pathway that is uncoupled from the triple response induced by ethylene. The isolation and characterization of gin1 reveal an unexpected convergence between the glucose and the ethylene signal transduction pathways. GIN1 may function to balance the control of plant development in response to metabolic and hormonal stimuli that act antagonistically.

Arabidopsis↗
PubMed1998

On the origin of membrane vesicles in gram-negative bacteria.

It is proposed that the genesis of extracellular membrane vesicles in Gram-negative bacteria is a result of cell wall turnover. Peptidoglycan turnover would cause a turgor on the outer membrane, causing the outer membrane to bulge and finally bleb. Mechanical motion would then shear the blebs into the culture medium.

Bacterial Outer Membrane Proteins↗
PubMed1998

Involvement of Sp1 elements in the promoter activity of the alpha1-proteinase inhibitor gene.

The transcripts of the alpha1-proteinase inhibitor in the cornea are different from those in hepatocytes and monocytes, suggesting that alpha1-proteinase inhibitor gene transcription may respond to different cell-specific regulatory mechanisms. Although information on alpha1-proteinase inhibitor gene structure has been obtained, little is known regarding the cis- and trans-acting factors that regulate its expression. In this study, we cloned and sequenced a 2. 7-kilobase 5'-flanking region upstream from the corneal transcription initiation site of the gene, demonstrated functional promoter activity, and identified the regulatory elements. Sequencing revealed that the 5'-flanking element was highly G/C-rich in regions proximal to the corneal transcription start site. DNase I footprinting located 10 potential Sp1-binding sites between nucleotides -1519 and +44. The putative promoter was functional in human corneal stromal cells, but not in human skin, scleral, and conjunctival fibroblasts, suggesting that the promoter may be corneal cell-specific. The promoter activity in the corneal cells was repressed when Sp1 was coexpressed. In the cornea-thinning disease keratoconus, down-regulation of the alpha1-proteinase inhibitor gene and increased Sp1 expression have both been demonstrated. The current results suggest that down-regulation of the inhibitor in keratoconus corneas may be related directly to overexpression of the Sp1 gene. This information may help elucidate the molecular pathways leading to the altered alpha1-proteinase inhibitor expression in keratoconus.

Base Sequence↗
PubMed1998

Antibody-mediated oligodendrocyte cell death requires an astrocyte-derived cosignal.

We have described a monoclonal antibody (mAb), 2B10, that identifies a cell-surface protein expressed only on oligodendrocytes, the myelin-forming cells in the vertebrate central nervous system. To examine the effect of mAb 2B10 on oligodendrocyte development and survival, purified antibody was added to dissociated cultures of neonatal rat spinal cord. Addition of mAb 2B10 induced significant cell death, with a reduction of approximately 70% in the number of differentiated oligodendrocytes. The number of astrocytes was unaltered. Addition of mAb 2B10 did not affect the proliferation or differentiation of oligodendrocyte precursors. MAb 2B10-induced death of differentiated oligodendrocytes was independent of complement but did require an environmental signal. In purified oligodendrocyte cultures, binding of the antibody to oligodendrocytes did not induce cell death. Conditioned medium and transwell coculture experiments indicated that the required environmental signals were not soluble. By contrast, when oligodendrocytes were cocultured with astrocytes, addition of mAb 2B10 specifically induced cell death of differentiated oligodendrocytes, suggesting that a locally acting cosignal from astrocytes was required to facilitate the cell death. This cosignal was provided by live astrocytes but not by fixed astrocytes, microglia, or fibroblasts. Such antibody-induced oligodendrocyte cell death may explain in part the loss of myelin-forming cells in demyelination conditions, such as multiple sclerosis.

Animals↗
PubMed1998

Hippocampal neuronal dysfunction in schizophrenia as measured by proton magnetic resonance spectroscopy.

BACKGROUND: Previous neuropathological and neuroimaging studies have documented neuronal loss in the hippocampal region in schizophrenia. N-acetylaspartate (NAA) is a neuronal/axonal marker that may be utilized to assess neuronal loss or dysfunction by proton magnetic resonance spectroscopy (1H MRS). This study measured NAA, choline, and creatine in the hippocampal region of patients with schizophrenia using in vivo proton magnetic resonance spectroscopic imaging (1H MRSI). METHODS: 1H MRSI was performed on the right and left hippocampal regions in 30 chronic schizophrenic patients and 18 control subjects. Concentration estimates of NAA, creatine, and choline were determined. RESULTS: Relative to the control group, the patients with schizophrenia demonstrated significantly lower NAA in both the right and left hippocampal regions. No group differences in choline were noted; however, there was a trend for creatine to be higher on the left than the right hippocampus in the schizophrenic group. There was also no association between NAA and duration of illness or medication dosage. CONCLUSIONS: This preliminary study provides support for neuronal dysfunction and/or decreased neuronal density in the hippocampal region. The absence of choline signal elevation does not support accelerated turnover of membrane phospholipids, which might be expected if there were ongoing neuronal atrophy or neuronal necrosis.

Adult↗
PubMed1998

The pattern of disulfide linkages in the extracellular loop regions of connexin 32 suggests a model for the docking interface of gap junctions.

Connexins, like true cell adhesion molecules, have extracellular domains that provide strong and specific homophilic, and in some cases, heterophilic interactions between cells. Though the structure of the binding domains of adhesion proteins have been determined, the extracellular domains of connexins, consisting of two loops of approximately 34-37 amino acids each, are not easily studied in isolation from the rest of the molecule. As an alternative, we used a novel application of site-directed mutagenesis in which four of the six conserved cysteines in the extracellular loops of connexin 32 were moved individually and in all possible pairwise and some quadruple combinations. This mapping allowed us to deduce that all disulfides form between the two loops of a single connexin, with the first cysteine in one loop connected to the third of the other. Furthermore, the periodicity of movements that produced functional channels indicated that these loops are likely to form antiparallel beta sheets. A possible model that could explain how these domains from apposed connexins interact to form a complete channel is discussed.

Amino Acid Sequence↗
PubMed1998

A splicing variant of a death domain protein that is regulated by a mitogen-activated kinase is a substrate for c-Jun N-terminal kinase in the human central nervous system.

The mitogen-activated kinase activating death domain protein (MADD) that is differentially expressed in neoplastic vs. normal cells (DENN) was identified as a substrate for c-Jun N-terminal kinase 3, the first demonstration of such an activity for this stress-activated kinase that is predominantly expressed in the brain. A splice isoform was identified that is a variant of MADD. A protein identical to MADD has been reported to be expressed differentially in neoplastic vs. normal cells and is termed "DENN." We demonstrated differential effects on DENN/MADD in a stressed vs. basal environment. Using in situ hybridization, we localized both the substrate and the kinase to large pyramidal neurons in the human hippocampus. It was interesting that, in four of four patients with neuropathologically confirmed acute hypoxic changes, we detected a unique translocation of DENN/MADD to the nucleolus. These changes were apparent only in neurons sensitive to hypoxia. Moreover, in those cells, translocation of the substrate was accompanied by nuclear translocation of JNK3. These findings place DENN/MADD and JNK in important hypoxia insult-induced intracellular signaling pathways. Our conclusions are important for future studies for understanding these stress-activated mechanisms.

Alternative Splicing↗
PubMed1998

Frontotemporal dementia: neuropil spheroids and presynaptic terminal degeneration.

We compared the neuropathological changes of 6 patients with clinically diagnosed lobar dementia. In the 4 patients with histopathology consistent with frontotemporal dementia (FTD), moderate neuronal loss contrasted with marked cortical and subcortical gliosis. We found silver-positive, carbohydrate-rich, spheroidal enlargements of presynaptic terminals within the neuropil of specific central nervous system regions. The spheroids were immunopositive for the cytoskeletal proteins tau, the high molecular weight neurofilament subunit (NF-H), and beta-tubulin. No abnormal tau phosphorylation and only rare ubiquitin immunoreactivity were detected in these structures. Carbohydrate modifications, including advanced glycation end products within the spheroid matrix, were confirmed by lectin binding, and by anti-pentosidine immunoreactivity, an indicator of oxidative stress. Ultrastructurally, the spheroids consisted of unmyelinated, membrane-enclosed structures filled with randomly arrayed pairs of filaments, approximately 8 to 10 nm in diameter, that were sparsely labeled with antibodies to unmodified tau (T14) and NF-H. Despite clinical overlap, the central nervous systems of our FTD patients are distinguishable from those of other patients with other lobar dementias, including Pick's disease and corticobasal degeneration, by the absence of abnormally phosphorylated neuronal or glial tau inclusions. The neuropil spheroids are dystrophic changes of certain selectively vulnerable presynaptic terminals, suggesting a retrograde degenerative process in FTD.

Adult↗
PubMed1998

Genomic organization, expression of the human CBFA1 gene, and evidence for an alternative splicing event affecting protein function.

The Cbfa1 gene, which encodes the transcription factor Osf2/Cbfa1 required for osteoblast differentiation in mouse and human, is mutated in cleidocranial dysplasia, a skeletal dysplasia. We describe here the isolation of the full-length human OSF2/CBFA1 cDNAs, the genomic organization of the entire CBFA1 gene, its expression, and the existence of an alternative splicing event. Nucleotide sequence analysis of the human and mouse OSF2/CBFA1 cDNAs showed a 98% homology in the coding sequence and 96% in the 5' untranslated (UTR) sequence. Analysis of CBFA1 genomic clones revealed that the 5' UTR sequence of the human OSF2/CBFA1 cDNA lies 75 kb upstream of the originally described 5' end of the gene. The existence of two OSF2/CBFA1 cDNAs is due to an alternative splicing event around exon 8 that affects the transcriptional activity of the protein. Northern blot analysis demonstrates that the expression of the human OSF2/CBFA1 gene is restricted to osteoblastic cells.

Alternative Splicing↗
PubMed1998

Cloning, characterization, and chromosomal assignment of the human ortholog of murine Zfp-37, a candidate gene for Nager syndrome.

In an effort to identify putative transcription factors involved in chondrocyte differentiation during human endochondral bone formation, a human fetal cartilage-specific cDNA library was screened with a degenerate oligonucleotide probe corresponding to a conserved stretch of eight amino acids from the zinc finger region of the Drosophila Krüppel gene family of DNA-binding proteins. Using this strategy, we have identified a novel zinc finger gene ZFP-37. ZFP-37 corresponds to a putative transcription factor containing 12 tandemly repeated zinc finger motifs and a Krüppel-associated box (KRAB) domain. The KRAB domain has been reported to function as a transcriptional repressor and is located in the amino terminus, while the zinc finger repeats are positioned at the carboxy-terminal end of ZFP-37. Gene mapping with a somatic cell hybrid panel and fluorescence in situ hybridization (FISH) localized ZFP-37 to human Chr 9q32. The gene is expressed at low level as a 3.2-kb mRNA in several tissues including fetal human cartilage. Sequence comparison revealed that ZFP-37 may represent the human homolog of the mouse gene Zfp-37. The map location and expression pattern suggest ZFP-37 as a candidate gene for a craniofacial-limb malformation, Nager syndrome (acrofacial dysostosis).

Amino Acid Sequence↗
PubMed1998

E-Cadherin in human brain tumours: loss of immunoreactivity in malignant meningiomas.

Cadherins are a family of glycoproteins that are associated with cell adhesion mechanisms. They are divided into subclasses. The E- and P-cadherins are regarded as the epithelial subtype. Their expression has been demonstrated in many different carcinoma types. Using immunomorphological techniques, we studied the expression of E-cadherin in a series of 145 human brain tumours with the monoclonal antibody 5H9. Western blot analysis was used to confirm the immunohistochemical data. The tumour types represented were astrocytoma WHO I (n = 7), astrocytoma WHO II (n = 6), astrocytoma WHO III (n = 14), glioblastoma WHO IV (n = 8), oligodendroglioma WHO II (n = 5), ependymoma WHO II (n = 5), choroid plexus papilloma WHO I (n = 5), pineoblastoma WHO IV (n = 5), medulloblastoma WHO IV (n = 5), neurinoma WHO I (n = 5), meningioma WHO I and WHO III (n = 75) and pituitary adenoma WHO I (n = 5). Only choroid plexus papillomas (5/5) and meningiomas showed E-cadherin expression. In benign meningiomas (n = 45; 100%), positive E-cadherin immunoreactivity was found regardless of the histomorphological subtype. E-Cadherin was also expressed in 21 WHO I meningiomas (100%) invading dura, bone, brain, and muscle. In contrast, E-cadherin was absent from the majority of morphologically malignant meningiomas (6/9, 66.6%). In addition, in recurrent meningiomas (n = 9), E-cadherin expression in the recurrent tumours was identical to that in the primary neoplasm except in cases with malignant progression, where the malignant recurrent tumour was E-cadherin negative. In 2 cases of metastasizing meningiomas, no E-cadherin immunoreactivity was found in the primary tumours or their metastases.

Adult↗
PubMed1998

Cholecystokinin inhibits peripheral opioid analgesia in inflamed tissue.

There is abundant evidence that opioid receptors are present on peripheral terminals of primary afferent neurons. Experimental and clinical studies have shown that activation of these peripheral opioid receptors produces potent analgesia. In addition to peripheral opioid receptors, cholecystokinin receptors are present in sensory neurons. We examined the hypothesis that cholecystokinin receptors may be present on the same primary afferent neuron and that either exogenous or endogenous cholecystokinin may modulate peripheral antinociceptive effects of mu-opioid receptor agonists. Administration of cholecystokinin into inflamed paws, of the rat, but not intravenously attenuated peripheral antinociceptive effects induced by two mu-opioid receptor agonists, [D-Ala2,N-methyl-Phe4,Gly-ol5]-enkephalin and fentanyl. Only the desulphated form of cholecystokinin produced significant and dose-dependent attenuation. Cholecystokinin alone did not alter nociceptive baseline values in inflamed or non-inflamed paws. The anti-opioid effect of cholecystokinin was dose-dependently antagonized by the cholecystokininB receptor-selective antagonist L-365260, but not by the cholecystokininA receptor-selective antagonist L-364718. Local pretreatment with the protein kinase C specific inhibitor calphostin C abolished cholecystokinin's effect. Peripheral antinociceptive effects of [D-Ala2,N-methyl-Phe4,Gly-ol5]-enkephalin and fentanyl were not altered by intraplantar L-365260 alone. These results indicate that activation of peripheral cholecystokininB but not cholecystokininA receptors attenuates the local antinociceptive effects of mu-opioid receptor agonists in inflamed tissue. This anti-opioid effect may be mediated by protein kinase C in sensory nerve terminals. Endogenous cholecystokinin does not seem to influence the efficacy of peripheral opioids under both normal and inflammatory conditions.

Analgesics, Opioid↗