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Biomedical subjects

J Chun

Publications and source records attributed to J Chun.

At least 73 records · Page 4Linked to original sources
PubMed2000

Mechanism-based inactivation of cytochromes P450 2B1 and P450 2B6 by 2-phenyl-2-(1-piperidinyl)propane.

2-Phenyl-2-(1-piperidinyl)propane (PPP), an analog of phencyclidine, was tested for its ability to inactivate cytochrome P450s (P450s) 2B1 and 2B6. PPP inactivated the 7-(benzyloxy)resorufin O-dealkylation activity of liver microsomes obtained from phenobarbital-induced rats with a K(I) of 11 microM. The 7-ethoxy-4-(trifluoromethyl)coumarin O-deethylation activity of purified rat liver P450 2B1 and expressed human P450 2B6 was inactivated by PPP in a reconstituted system containing NADPH-cytochrome P450 reductase and lipid. In the presence of NADPH, the loss of activity was time- and concentration-dependent, and followed pseudo first order kinetics. The rate of inactivation for P450 2B1 was 0.3 min(-1), and the concentration of PPP required to achieve half-maximal inactivation was 12 microM. The time for 50% of the P450 2B1 to become inactivated at saturating concentrations of PPP was 2.5 min. P450 2B6 was inactivated with a k(inact) of 0.07 min(-1), a K(I) of 1.2 microM, and a t(1/2) of 9.5 min. The inactivated P450s 2B1 and 2B6 lost about 25 and 15%, respectively, of their ability to form a CO-reduced complex, suggesting that the loss of activity was caused by a PPP modification of the apoprotein rather than the heme. The estimated partition ratio for P450s 2B1 and 2B6 with PPP was 31 and 15, respectively. The inactivation was not reversible and reductase activity was not affected. Coincubation of P450 2B1 and 2B6 with PPP and NADPH in the presence of an alternate substrate protected both enzymes from inactivation. The exogenous nucleophile GSH did not affect the rate of inactivation. PPP-inactivated P450s 2B1 and 2B6 were recognized on Western blots by an antibody generated to phencyclidine that had been conjugated to BSA. Stoichiometries of 1.4:1 and 0.7:1 were determined for the binding of a [3H]PPP metabolite to P450 2B1 and 2B6, respectively.

Animals↗
PubMed1999

Developmental neurobiology: a genetic Cheshire cat?

In the wake of evidence that essential neurogenic processes might involve aspects of DNA rearrangement, recent discoveries about the unusual arrangement of genes encoding neuronal adhesion molecules known as protocadherins are very intriguing. But is this just a coincidence?

Animals↗
PubMed1999

Novel dendritic kinesin sorting identified by different process targeting of two related kinesins: KIF21A and KIF21B.

Neurons use kinesin and dynein microtubule-dependent motor proteins to transport essential cellular components along axonal and dendritic microtubules. In a search for new kinesin-like proteins, we identified two neuronally enriched mouse kinesins that provide insight into a unique intracellular kinesin targeting mechanism in neurons. KIF21A and KIF21B share colinear amino acid similarity to each other, but not to any previously identified kinesins outside of the motor domain. Each protein also contains a domain of seven WD-40 repeats, which may be involved in binding to cargoes. Despite the amino acid sequence similarity between KIF21A and KIF21B, these proteins localize differently to dendrites and axons. KIF21A protein is localized throughout neurons, while KIF21B protein is highly enriched in dendrites. The plus end-directed motor activity of KIF21B and its enrichment in dendrites indicate that models suggesting that minus end-directed motor activity is sufficient for dendrite specific motor localization are inadequate. We suggest that a novel kinesin sorting mechanism is used by neurons to localize KIF21B protein to dendrites since its mRNA is restricted to the cell body.

Animals↗
PubMed1999

Schwann cell survival mediated by the signaling phospholipid lysophosphatidic acid.

Lysophosphatidic acid (LPA) is a bioactive phospholipid with properties of an extracellular growth factor for many cell lines, including those derived from neuroblastomas. However, the relevance of LPA signaling to the normal, developing nervous system is unknown, in part reflecting the previous unavailability of cloned receptor genes. Recent studies of the first such gene, encoding the G protein-coupled receptor LPA1/VZG-1 (lysophospholipid receptor A1/ventricular zone gene-1), revealed a major locus of expression in oligodendrocytes and Schwann cells (SCs) during development, suggesting an influence of LPA on these myelinating cells. Here we report that LPA (>/=10 nM) is a potent survival factor for cultured neonatal SCs, with survival activity equaling the maximal effect of neuregulin, the major peptide SC survival factor. LPA activates a pharmacologically defined signaling pathway in SCs, involving Gi and phosphoinositide 3-kinase. Moreover, LPA's effect depends on Akt, a downstream kinase that can mediate phosphoinositide 3-kinase-dependent survival, as demonstrated by both Western blot and transfection analyses. Overexpression of functional epitope-tagged LPA1/VZG-1 protein decreases SC apoptosis in response to serum withdrawal. These data demonstrate a role for extracellular LPA and its receptor LPA1/VZG-1 in SC survival and, more broadly, implicate G protein-coupled receptor-mediated lysophospholipid signaling as a significant mechanism in neural development.

Animals↗
PubMed1999

Developmental neurobiology: Alternative ends for a familiar story?

Somatic DNA recombination is essential for production of functional antigen receptor genes of T and B lymphocytes, but it is thought to be unique to the immune system. Recent studies have now shown that recombination-related genes are also necessary for normal neuronal development.

Animals↗
PubMed1999

Lysophosphatidic acid stimulates neurotransmitter-like conductance changes that precede GABA and L-glutamate in early, presumptive cortical neuroblasts.

During neurogenesis in the embryonic cerebral cortex, the classical neurotransmitters GABA and L-glutamate stimulate ionic conductance changes in ventricular zone (VZ) neuroblasts. Lysophosphatidic acid (LPA) is a bioactive phospholipid producing myriad effects on cells including alterations in membrane conductances (for review, see Moolenaar et al., 1995). Developmental expression patterns of its first cloned receptor gene, lpA1/vzg-1 (Hecht et al., 1996; Fukushima et al., 1998) in the VZ suggested that functional LPA receptors were synthesized at these early times, and thus, LPA could be an earlier stimulus to VZ cells than the neurotransmitters GABA and L-glutamate. To address this possibility, primary cultures of electrically coupled, presumptive cortical neuroblast clusters were identified by age, morphology, electrophysiological profile, BrdU incorporation, and nestin immunostaining. Single cells from cortical neuroblast cell lines were also examined. Whole-cell variation of the patch-clamp technique was used to record from nestin-immunoreactive cells after stimulation by local administration of ligands. After initial plating at embryonic day 11 (E11), cells responded only to LPA but not to GABA or L-glutamate. Continued growth in culture for up to 12 hr produced more LPA-responsive cells, but also a growing population of GABA- or L-glutamate-responsive cells. Cultures from E12 embryos showed LPA as well as GABA and L-glutamate responses, with LPA-responsive cells still representing a majority. Overall, >50% of cells responded to LPA with depolarization mediated by either chloride or nonselective cation conductances. These data implicate LPA as the earliest reported extracellular stimulus of ionic conductance changes for cortical neuroblasts and provide evidence for LPA as a novel, physiological component in CNS development.

Animals↗
PubMed1999

Comparative analysis of three murine G-protein coupled receptors activated by sphingosine-1-phosphate.

The cloning and analysis of the first identified lysophosphatidic acid (LPA) receptor gene, lpA1 (also referred to as vzg-1 or edg-2), led us to identify homologous murine genes that might also encode receptors for related lysophospholipid ligands. Three murine genomic clones (designated lpB1, lpB2, and lpB3) were isolated, corresponding to human/rat Edg-1, rat H218/AGR16, and human edg-3, respectively. Based on the amino acid similarities of their predicted proteins (44-52% identical), the three lpB genes could be grouped into a separate G-protein coupled receptor subfamily, distinct from that containing the LPA receptor genes lpA1 and lpA2. Unlike lpA1 and lpA2, which contain multiple coding exons, all lpB members contained a single coding exon. Heterologous expression of individual lpB members in a hepatoma cell line (RH7777), followed by 35S-GTPgammaS incorporation assays demonstrated that each of the three LPB receptors conferred sphingosine-1-phosphate-dependent, but not lysophosphatidic acid-dependent, G-protein activation. Northern blot and in situ hybridization analyses revealed overlapping as well as distinct expression patterns in both embryonic and adult tissues. This comparative characterization of multiple sphingosine-1-phosphate receptor genes and their spatiotemporal expression patterns will aid in understanding the biological roles of this enlarging lysophospholipid receptor family.

Amino Acid Sequence↗
PubMed1999

Expanded polyglutamine domain proteins bind neurofilament and alter the neurofilament network.

Eight inherited neurodegenerative diseases are caused by genes with expanded CAG repeats coding for polyglutamine domains in the disease-producing proteins. The mechanism by which this expanded polyglutamine domain causes neurodegenerative disease is unknown, but nuclear and cytoplasmic polyglutamine protein aggregation is a common feature. In transfected COS7 cells, expanded polyglutamine proteins aggregate and disrupt the vimentin intermediate filament network. Since neurons have an intermediate filament network composed of neurofilament (NF) and NF abnormalities occur in neurodegenerative diseases, we examined whether pathologic-length polyglutamine domain proteins also interact with NF. We expressed varying lengths polyglutamine-green fluorescent protein fusion proteins in a neuroblast cell line, TR1. Pathologic-length polyglutamine-GFP fusion proteins formed large cytoplasmic aggregates surrounded by neurofilament. Immunoisolation of pathologic-length polyglutamine proteins coisolated 68-kDa NF protein demonstrating molecular interaction. These observations suggest that polyglutamine interaction with NF is important in the pathogenesis of the polyglutamine repeat diseases.

Amino Acid Sequence↗
PubMed1999

A growing family of receptor genes for lysophosphatidic acid (LPA) and other lysophospholipids (LPs).

A missing component in the experimental analysis of cell signaling by extracellular lysophospholipids such as lysophosphatidic acid (LPA) or sphingosine-1-phosphate (S1P) has been cloned receptors. Through studies on the developing brain, the first such receptor gene (referred to as vzg-1) was identified, representing a member of the G-protein coupled receptor (GPCR) super family (1). Here we review the neurobiological approach that led to both its cloning and identification as a receptor for LPA, along with related expression data. Summarized sequence and genomic structure analyses indicate that this first, functionally identified receptor is encoded by a member of a growing gene family that divides into at least two subgroups: genes most homologous to the high-affinity LPA receptor encoded by vzg-1, and those more homologous to an orphan receptor gene edg-1 that has recently been identified as a S1P receptor. A provisional nomenclature is proposed, based on published functional ligand actions, amino acid composition and genomic structure whereby the receptors encoded by these genes are referred to as lysophospholipid (LP) receptors, with subgroups distinguished by letter and number subscripts (e.g., LPA1 for Vzg-1, and LPB1 for Edg-1). Presented expression data support the recently published work indicating that members of the LPB1 subgroup are receptors for the structurally-related molecule, S1P. The availability of cloned LP receptors will enhance the analysis of the many documented LP effects, while their prominent expression in the nervous system indicates significant but as yet unknown roles in development, normal function, and neuropathology.

Base Sequence↗
PubMed1999

Ethmoidal dural arteriovenous fistulae: an assessment of surgical and endovascular management.

OBJECTIVE: Endovascular treatment of ethmoidal dural arteriovenous fistulae (DAVFs) has become technically feasible, but its relative risks and benefits have not justified its use. We present a series of patients with ethmoidal DAVFs treated almost exclusively with surgery at an institution where expert endovascular therapy was available. Surgical risks, treatment efficacy, and patient outcomes were determined for comparison with published endovascular data. METHODS: Sixteen patients with ethmoidal DAVFs were treated during a 17-year period from 1982 to 1999. In three patients, feeding arteries from the internal maxillary artery were embolized; no ophthalmic artery embolizations were performed. A low bifrontal surgical approach was used in most patients to expose, coagulate, and divide the fistulous site. RESULTS: Ethmoidal DAVFs were occluded grossly and angiographically in all 16 patients. There was no treatment-associated neurological morbidity, and clinical outcomes were good in all but one patient who was comatose initially. CONCLUSION: Review of our surgical experience with ethmoidal DAVFs as well as published endovascular results for these lesions suggests that endovascular management of ethmoidal DAVFs has a small but clinically significant risk to vision, is rarely effective in curing the fistula, and does not eliminate the need for surgery. In contrast, surgical management has no associated risk to vision, is highly effective at obliterating the fistula, and can contribute to good clinical outcomes in most patients. For these reasons, surgical management of ethmoidal DAVFs remains the treatment of choice.

Aged↗
PubMed1999

Kitasatospora cheerisanensis sp. nov., a new species of the genus Kitasatospora that produces an antifungal agent.

An actinomycete, strain YC75T, which produced bafilomycin-like antifungal compounds, was identified as a member of the genus Kitasatospora on the basis of morphological and chemotaxonomic characteristics. The strain produced the aerial and fragmenting vegetative mycelia consisting of straight chains of 20 or more smooth-surfaced spores. Submerged spores were formed in tryptic soy broth. No soluble pigments were formed. Whole-cell hydrolysates contained glucose and mannose, but not galactose. The 16S rDNA sequence of YC75T was compared with those of the other representative kitasatosporae and streptomycetes. Strain YC75T formed a significant monophyletic clade with Kitasatospora phosalacinea. The levels of DNA relatedness between strain YC75T and representatives of the genus Kitasatospora ranged from 16 to 59% including K. phosalacinea (28 and 40%). It is clear from polyphasic evidence that the isolate should be classified as Kitasatospora cheerisanensis sp. nov., whose type strain is YC75T (= KCTC 2395T). The presence of galactose in whole-cell hydrolysates may not be a stable chemical marker for the genus Kitasatospora.

Antifungal Agents↗
PubMed1999

Nocardia salmonicida nom. rev., a fish pathogen.

An almost complete gene sequence of 16S rDNA of 'Nocardia salmonicida' strain JCM 4826T was determined following cloning and sequencing of the amplified gene. The sequence was aligned with those available for nocardiae and phylogenetic trees inferred using four tree-making algorithms. The organism and the type strain of Nocardia asteroides consistently formed a monophyletic clade with a distant sequence similarity of 97%. However, previous DNA relatedness experiments showed that strain JCM 4826T and Nocardia asteroides ATCC 19247T belong to different genomic species. The organism was also distinguished from representatives of all validly described species of Nocardia using a combination of phenotypic features. The polyphasic evidence showed that the strain merits recognition as a new species of the genus Nocardia. The name proposed for the new species is Nocardia salmonicida nom. rev.

Animals↗
PubMed1999

Nocardia uniformis nom. rev.

A soil isolate representing the putatively novel species 'Nocardia uniformis' was found to have morphological, staining and chemotaxonomic properties consistent with its classification in the genus Nocardia. An almost complete sequence of the 16S rDNA of the strain was determined following cloning and sequencing of the amplified gene. The sequence was aligned with those available for nocardiae and phylogenetic trees were inferred using four tree-making algorithms. The organism was consistently associated with the type strain of Nocardia otitidiscaviarum albeit with a relatively low bootstrap value recorded for neighbour-joining analysis. The strain was also readily separated from representatives of all validly described Nocardia species using a set of phenotypic properties. The genotypic and phenotypic data indicate that the strain should be assigned to the genus Nocardia as a new species. The name proposed for the new species is Nocardia uniformis. The type strain is JCM 3224T.

Algorithms↗
PubMed1999

Amycolatopsis thermoflava sp. nov., a novel soil actinomycete from Hainan Island, China.

A soil isolate, which had been assigned to the genus Nocardia, was shown to have properties consistent with its classification in the genus Amycolatopsis. An almost complete nucleotide sequence of the 16S rDNA of the strain was determined following cloning and sequencing of the amplified gene. The sequence was aligned with those available for members of the family Pseudonocardiaceae and related taxa and phylogenetic trees were inferred using three tree-making algorithms. The organism consistently formed a distinct monophyletic clade with the type strain of Amycolatopsis methanolica, but DNA-DNA relatedness data showed that the two strains belonged to distinct genomic species. The organism was also distinguished from the type strains of all validly described species of Amycolatopsis using a battery of phenotypic properties. The genotypic and phenotypic data show that the strain merits recognition as a new species of the genus Amycolatopsis. The name proposed for the new species is Amycolatopsis thermoflava sp. nov. The type strain is IFO 14333T.

Actinomycetales↗
PubMed1999

Population dynamics of chesapeake bay virioplankton: total-community analysis by pulsed-field gel electrophoresis

Recognition of viruses as the most abundant component of aquatic microbial communities has stimulated investigations of the impact of viruses on bacterio- and phytoplankton host communities. From results of field studies to date, it is concluded that in most aquatic environments, a reduction in the number of bacteria on a daily basis is caused by viral infection. However, the modest amount of in situ virus-mediated mortality may be less significant than viral infection serving to maintain clonal diversity in the host communities directly, through gene transmission (i.e., transduction), and indirectly, by elimination of numerically dominant host species. If the latter mechanism for controlling community diversity prevails, then the overall structure of aquatic viral communities would be expected to change as well over short seasonal and spatial scales. To determine whether this occurs, pulsed-field gel electrophoresis (PFGE) was used to monitor the population dynamics of Chesapeake Bay virioplankton for an annual cycle (1 year). Virioplankton in water samples collected at six stations along a transect running the length of the bay were concentrated 100-fold by ultrafiltration. Viruses were further concentrated by ultracentrifugation, and the concentrated samples were embedded in agarose. PFGE analysis of virus DNA in the agarose plugs yielded several distinct bands, ranging from 50 to 300 kb. Principal-component and cluster analyses of the virus PFGE fingerprints indicated that changes in virioplankton community structure were correlated with time, geographical location, and extent of water column stratification. From the results of this study, it is concluded that, based on the dynamic nature of the Chesapeake Bay virioplankton community structure, the clonal diversity of bacterio- and phytoplankton host communities is an important component of the virus community.

Journal Article↗