Biomedical subjects

D Chung

Publications and source records attributed to D Chung.

At least 37 records · Page 2Linked to original sources

PubMed1998

Two acute pediatric abdominal catastrophes from strangulated left paraduodenal hernias.

We present two cases of catastrophic intestinal obstruction from to strangulation of a left paraduodenal hernia (PDH). PDH is the most common internal hernia. Early diagnosis and treatment are essential because of the high morbidity and mortality associated with strangulation. Early involvement of the surgical team without an overly extensive evaluation in the emergency department is important if this diagnostic suspicion exists. PDH should also be considered when there is a history of chronic, intermittent abdominal pain of unclear cause. To our knowledge, these cases are the first described cases of sudden demise within a few hours of onset of symptoms of a left PDH.

Abdomen, Acute↗

PubMed1997

An alpha-helical minimal binding domain within the H3 domain of syntaxin is required for SNAP-25 binding.

The interaction between the proteins syntaxin 1A and SNAP-25 is a key step in synaptic vesicle docking and fusion. To define the SNAP-25 binding domain on syntaxin, we have prepared peptides that span the syntaxin H3 domain (residues 191-266), the region previously shown to be important for binding to SNAP-25, and then determined the affinities of these peptides for binding to SNAP-25. A minimal binding domain was identified within a region of 32 amino acids (residues 189-220). Its affinity for SNAP-25 is substantially enhanced by C-terminal extension (residues 221-266). Circular dichroism revealed the presence of substantial alpha-helicity in the H3 domain and in the 32-mer minimal binding domain, but not in H3 peptides that do not bind to SNAP-25. At temperatures that denature the alpha-helix of the minimal binding domain peptide, SNAP-25 binding is lost. Selected mutations in evolutionarily conserved residues of the amphiphilic alpha-helix within the minimal binding domain (e.g., residues 205 and 209) greatly reduce the affinity for SNAP-25 but have no major effect on secondary structure, suggesting that these residues may interact directly with SNAP-25. The H3 domain peptide and the minimal binding domain peptide inhibit norepinephrine release from PC12 cells. These results suggest that specific amino acid residues in the H3 domain, positioned by the underlying alpha-helical structure, are important for its binding to SNAP-25 and support the notion that this interaction is important for presynaptic vesicular exocytosis.

Amino Acid Sequence↗

PubMed1997

Selective inhibition of oncogenic ras-p21 in vivo by agents that block its interaction with jun-N-kinase (JNK) and jun proteins. Implications for the design of selective chemotherapeutic agents.

We have obtained evidence that oncogenic and activated normal ras-p21 proteins utilize overlapping but distinct signal transduction pathways. Recently, we found that ras-p21 binds to both jun and its kinase, jun kinase (JNK). We now present evidence that suggests that oncogenic but not normal activated p21 depends strongly on early activation of JNK/jun. This early activation most likely involves direct interaction between oncogenic p21 and JNK/jun because p21 peptides that blocked the binding of p21 to JNK and jun strongly inhibited oncogenic p21-induced oocyte maturation while they did not inhibit insulin-activated normal cellular p21-induced maturation. Very similar results were also obtained for a newly characterized specific inhibitor of JNK which blocked oncogenic but not normal activated p21-induced oocyte maturation. We also found that both jun and JNK strongly enhanced oncogenic p21-induced oocyte maturation while they inhibited insulin-activated normal p21-induced oocyte maturation. These results suggest that the peptides and JNK inhibitor may be useful agents in selectively blocking the effects of oncogenic but not normal p21 in cells.

Animals↗

PubMed1997

Inhibition of oncogenic and activated wild-type ras-p21 protein-induced oocyte maturation by peptides from the ras-binding domain of the raf-p74 protein, identified from molecular dynamics calculations.

In the preceding paper we found from molecular dynamics calculations that the structure of the ras-binding domain (RBD) of raf changes predominantly in three regions depending upon whether it binds to ras-p21 or to its inhibitor protein, rap-1A. These three regions of the RBD involve residues from the protein-protein interaction interface, e.g., between residues 60 and 72, residues 97-110, and 111-121. Since the rap-1A-RBD complex is inactive, these three regions are implicated in ras-p21-induced activation of raf. We have therefore co-microinjected peptides corresponding to these three regions, 62-76, 97-110, and 111-121, into oocytes with oncogenic p21 and microinjected them into oocytes incubated in in insulin, which activates normal p21. All three peptides, but not a control peptide, strongly inhibit both oncogenic p21- and insulin-induced oocyte maturation. These findings corroborate our conclusions from the theoretical results that these three regions constitute raf effector domains. Since the 97-110 peptide is the strongest inhibitor of oncogenic p21, while the 111-121 peptide is the strongest inhibitor of insulin-induced oocyte maturation, the possibility exists that oncogenic and activated normal p21 proteins interact differently with the RBD of raf.

Amino Acid Sequence↗

PubMed1997

Large bowel obstruction: a postoperative complication after laparoscopic bilateral inguinal hernia repair.

Each year in the United States alone over 500,000 inguinal herniorrhaphies are performed. Numerous techniques and methods have been described, all in an attempt to decrease recurrences, complications, and morbidity. One of the newer methods involves laparoscopic, transabdominal, preperitoneal placement of a mesh sheet. Several articles have described complications following this procedure--some inherent in all hernia repairs and some unique to either the laparoscopic approach or mesh placement. Our case appears to represent the first description of a large bowel obstruction secondary to an intense, inflammatory reaction to the inserted mesh. It suggests that mesh insertion, despite reperitonealizing the mesh, is not without complication.

Hernia, Inguinal↗

PubMed1997

Heterotypic protection following oral immunization with live heterologous rotaviruses in a mouse model.

A Jennerian approach using live animal viruses to immunize humans is the current lead strategy for developing rotavirus vaccines. This strategy has been modified by incorporating human rotavirus VP7 genes into vaccine strains to induce serotype-specific neutralizing antibodies to human strains. However, the role of homotypic versus heterotypic immunity in protection is unclear. To investigate the importance of serotype-specific immunity in a mouse model, mice were immunized with rhesus rotavirus (RRV: G3, P5[3]), RRV-based modified Jennerian vaccine strains DxRRV (G1, P5[3]), DS1xRRV (G2, P5[3]), or ST3xRRV (G4, P5[3]), or bovine rotavirus NCDV (G6, P6[1]) and challenged with murine rotavirus ECw (G3, P[16]). Mice immunized with modified Jennerian vaccines exhibited complete to near-complete protection from challenge. NCDV-immunized mice also showed partial protection. The protection was correlated with fecal IgA levels to VP6, not serum IgG responses. Modified Jennerian vaccines induce both heterotypic and homotypic immunity in mice.

Animals↗

PubMed1996

pRb controls proliferation, differentiation, and death of skeletal muscle cells and other lineages during embryogenesis.

Mice deficient for the RB gene (RB-/-), prior to death at embryonic day 14.5, show increased cell death in all tissues that normally express RB1: the nervous system, liver, lens, and skeletal muscle precursor cells. We have generated transgenic mice (RBlox) that express low levels of pRb, driven by an RB1 minigene. RBlox/RB-/- mutant fetuses die at birth with specific skeletal muscle defects, including increased cell death prior to myoblast fusion, shorter myotubes with fewer myofibrils, reduced muscle fibers, accumulation of elongated nuclei that actively synthesized DNA within the myotubes, and reduction in expression of the late muscle-specific genes MCK and MRF4. Thus, insufficient pRb results in failure of myogenesis in vivo, manifest in two ways. First, the massive apoptosis of myoblasts implicates a role of pRb in cell survival. Second, surviving myotubes failed to develop normally and accumulated large polyploid nuclei, implicating pRb in permanent withdrawal from the cell cycle. These results demonstrate a role for pRb during terminal differentiation of skeletal muscles in vivo and place pRb at a nodal point that controls cell proliferation, differentiation, and death.

Animals↗

PubMed1996

Organization, evolutionary conservation, expression and unusual Alu density of the human gene for pigment epithelium-derived factor, a unique neurotrophic serpin.

PEDF is a neurotrophic serpin that promotes a neuronal phenotype and augments neuronal cell survival. The isolation, sequence and structural analysis of the human PEDF gene and its promoter along with its evolutionary conservation and expression in human tissues are now described. The gene spans approximately 16 kb and is divided among 8 exons and 7 introns, the junctions of which conform to the AG/GT consensus rule. PEDF appears to fall into the ovalbumin/PAI-2 subgrouping of serpins and is structurally far different from GDN/PN-1, the only other neurotrophic serpin reported to date. The immediate 5'-flanking region is dominated by a dense cluster of Alu repeats in which are embedded several promoter consensus sequences. A CAAT box is present at -43. The putative promoter region is also far different from that reported for GDN/PN-1. Comparable hybridization signals of 23 kb EcoRI fragments containing the PEDF gene are observed by Southern blot analysis in all primate, mammal and avian species examined; conservation is particularly evident among the primates. Northern blot analysis confirms the presence of the PEDF transcript in a broad range of human fetal and adult tissues including almost all brain areas examined, underscoring differences with GDN/PN-1 which, in the adult brain, is only expressed in glia and a subset of neurons.

Animals↗

PubMed1996

Client follow-up at the Adelaide sexually transmitted disease clinic.

This study investigated the extent to which doctor-client communication is associated with follow-up rates at Clinic 275, an Adelaide sexually transmitted diseases (STD) clinic. At Clinic 275, clients are routinely screened for the major STDs at their first visit. They are then asked to return in one week's time for their results and further treatment if necessary. Over a four-week period in April-May 1994, the clinical consultations between doctors and 100 clients attending for their first visit in an episode of care were observed and recorded. Data from the observation schedules were matched with data collected from interviews, either when clients returned for their follow-up visit (n = 78) or from a telephone interview when they failed to return (n = 20). In addition, 18 clients who failed to return for follow-up (but were not part of the original observation sample) were interviewed. Sociodemographic factors did not affect follow-up rates. Of those who did not return for follow-up, social and environmental reasons were cited by about two-thirds. Reasons given by the remaining clients indicate that failure to return for follow-up was related to discrepancies in doctor-client communication in that they were confused about the need to return to obtain test results. In addition, approximately half could not name the infections for which they had been tested. Changes in clinic practice may prove a more useful method of increasing follow-up rates than seeking to identify the characteristics of noncompliant individuals.

Appointments and Schedules↗

PubMed1995

SNX-325, a novel calcium antagonist from the spider Segestria florentina.

A novel selective calcium channel antagonist peptide, SNX-325, has been isolated from the venom of the spider Segestria florentina. The peptide was isolated using as bioassays the displacement of radioiodinated omega-conopeptide SNX-230 (MVIIC) from rat brain synaptosomal membranes, as well as the inhibition of the barium current through cloned expressed calcium channels in oocytes. The primary sequence of SNX-325 is GSCIESGKSCTHSRSMKNGLCCPKSRCNCRQIQHRHDYLGKRKYSCRCS, which is a novel amino acid sequence. Solid-phase synthesis resulted in a peptide that is chromatographically identical with the native peptide and which has the same configuration of cysteine residues as the spider venom peptide omega-Aga-IVa [Mintz, I. M., et al., (1992) Nature 355, 827-829]. At micromolar concentrations, SNX-325 is an inhibitor of most calcium, but not sodium or potassium, currents. At nanomolar concentrations, SNX-325 is a selective blocker of the cloned expressed class B (N-type), but not class C (cardiac L), A, or E, calcium channels. SNX-325 is approximately equipotent with the N-channel selective omega-conopeptides (GVIA and MVIIA as well as closely related synthetic derivatives) in blocking the potassium induced release of tritiated norepinephrine from hippocampal slices (IC50s, 0.1-0.5 nM) and in blocking the barium current through cloned expressed N-channels in oocytes (IC50s 3-30 nM). By contrast, SNX-325 is 4-5 orders of magnitude less potent than is SNX-111 (synthetic MVIIA) at displacing radioiodinated SNX-111 from rat brain synaptosomal membranes. SNX-325 will be a useful comparative tool in further defining the function and pharmacology of the N- and possibly other types of high-voltage activated calcium channels.

Amino Acid Sequence↗

PubMed1995

Structure-activity analysis of a Conus peptide blocker of N-type neuronal calcium channels.

The synthetic peptide SNX-111 corresponding to the sequence of the omega-conopeptide MVIIA from the venom of the marine snail Conus magus is a highly potent and selective antagonist of N-type calcium channels. We have synthesized and characterized a large number of analogs of SNX-111 in order to elucidate the structural features of the peptide involved in blocking N-type calcium channels. Comparison of the binding of SNX-111 and its analogs to rat brain synaptosomal membranes rich in N-type channels revealed that, among the four lysines and two arginines in the molecule, lysine in position 2 and arginines at position 10 and 21 are important for the interaction of SNX-111 with N-type channels. The importance of the middle segment from residues 9 through 14 for this binding interaction was revealed by substitution of the individual residues as well as by the construction of hybrid peptides in which the residues 9-12 in SNX-111 and another conopeptide, SNX-183, corresponding to a peptide SVIB from Conus striatus, were interchanged. Introduction of the sequence SRLM from SNX-111 in place of RKTS in position 9-12 in SNX-183 resulted in a 38-fold increase in affinity.

Amino Acid Sequence↗

PubMed1995

5-Oxo-6,8,11,14-eicosatetraenoic acid is a potent stimulator of human eosinophil migration.

Human neutrophils and monocytes contain a highly specific dehydrogenase which converts 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE). We have previously shown that 5-oxo-ETE is a potent stimulus of neutrophil calcium levels and migration and have now investigated its effects on human eosinophils. 5-Oxo-ETE is a potent stimulus of eosinophil migration, with significant effects being detected at concentrations as low as 1 nM and a maximal response at 1 microM. The responses elicited by 5-oxo-ETE were about two to three times greater than those to platelet-activating factor (PAF) and 5-oxo-15-hydroxy-6,8,11,13-eicosatetraenoic acid (5-oxo-15-hydroxy-ETE) at all concentrations tested between 10 nM and 1 microM. Leukotrienes B4 and D4 also significantly stimulated eosinophil migration, but the maximal responses to these agonists were only about 4% of the maximal response to 5-oxo-ETE. A low concentration of 5-oxo-ETE (1 nM) potentiated eosinophil migration in response to PAF. Eosinophils were capable of converting 5-HETE to 5-oxo-ETE, and this reaction was enhanced by phorbol myristate acetate. Stimulation of eosinophils with A23187 in the presence of low concentrations of arachidonic acid and phorbol 12-myristate 13-acetate led to the formation of 5-oxo-ETE and 5-oxo-15-hydroxy-ETE, but the amounts were considerably less than those of other eicosanoids such as leukotriene C4, cysteine-containing lipoxins, and 5,15-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid. In summary, of all the lipid mediators tested, 5-oxo-ETE was the most effective in stimulating migration of human eosinophils. Although eosinophils are capable of synthesizing 5-oxo-eicosanoids, the amounts detected were relatively small, and other leukocytes such as neutrophils, monocytes, or macrophages may be more important sites for the synthesis of this compound.

Arachidonic Acid↗

PubMed1995

Structural effects of the binding of GTP to the wild-type and oncogenic forms of the ras-gene-encoded p21 proteins.

Molecular dynamics calculations have been performed to determine the average structures of ras-gene-encoded p21 proteins bound to GTP, i.e., the normal (wild-type) protein and two oncogenic forms of this protein, the Val 12- and Leu 61-p21 proteins. We find that the average structures for all of these proteins exhibit low coordinate fluctuations (which are highest for the normal protein), indicating convergence to specific structures. From previous dynamics calculations of the average structures of these proteins bound to GDP, major regional differences were found among these proteins [Monaco et al. (1995), J. Protein Chem., in press]. We now find that the average structures of the oncogenic proteins are more similar to one another when the proteins are bound to GTP than when they are bound to GDP [Monaco et al. (1995), J. Protein Chem., in press]. However, they still differ in structure at specific amino acid residues rather than in whole regions, in contradistinction to the results found for the p21-GDP complexes. Two exceptions are the regions 25-32, in an alpha-helical region, and 97-110. The two oncogenic (Val 12- and Leu 61-) proteins have similar structures which differ significantly in the region of residues 97-110. This region has recently been identified as being critical in the interaction of p21 with kinase target proteins. The differences in structure between the oncogenic proteins suggest the existence of more than one oncogenic form of the p21 protein that can activate different signaling pathways.

Binding Sites↗

PubMed1995

Comparison of the computed three-dimensional structures of oncogenic forms (bound to GDP) of the ras-gene-encoded p21 protein with the structure of the normal (non-transforming) wild-type protein.

The ras-oncogene-encoded p21 protein becomes oncogenic if amino acid substitutions occur at critical positions in the polypeptide chain. The most commonly found oncogenic forms contain Val in place of Gly 12 or Leu in place of Gln 61. To determine the effects of these substitutions on the three-dimensional structure of the whole p21 protein, we have performed molecular dynamics calculations on each of these three proteins bound to GDP and magnesium ion to compute the average structures of each of the three forms. Comparisons of the computed average structures shows that both oncogenic forms with Val 12 and Leu 61 differ substantially in structure from that of the wild type (containing Gly 12 and Gln 61) in discrete regions: residues 10-16, 32-47, 55-74, 85-89, 100-110, and 119-134. All of these regions occur in exposed loops, and several of them have already been found to be involved in the cellular functioning of the p21 protein. These regions have also previously been identified as the most flexible domains of the wild-type protein and have been bound to be the same ones that differ in conformation between transforming and nontransforming p21 mutant proteins neither of which binds nucleotide. The two oncogenic forms have similar conformations in their carboxyl-terminal domains, but differ in conformation at residues 32-47 and 55-74. The former region is known to be involved in the interaction with at least three downstream effector target proteins. Thus, differences in structure between the two oncogenic proteins may reflect different relative affinities of each oncogenic protein for each of these effector targets. The latter region, 55-74, is known to be a highly mobile segment of the protein. The results strongly suggest that critical oncogenic amino acid substitutions in the p21 protein cause changes in the structures of vital domains of this protein.

Cell Transformation, Neoplastic↗

PubMed1994

Auer rod-like inclusions in adult common acute lymphoblastic leukemia.

We report a case of adult common acute lymphoblastic leukemia, defined by enzyme histochemistry and immunophenotypic analysis, which had rod-shaped cytoplasmic inclusions that on Wright's-stained peripheral blood smear resembled Auer rods. Electron microscopic analysis of a buffy coat preparation revealed that the inclusions were not characteristic of Auer rods, but rather that they were composed of concentric lamellar structures with no limiting membrane and were closely associated with the nuclear membrane. Therefore, the presence of Auer rod-like inclusions in blasts on a Wright's-stained peripheral blood smear does not preclude a diagnosis of acute lymphoblastic leukemia.

Adult↗

PubMed1993

Small bowel obstruction secondary to incarcerated Richter's hernia from laparoscopic hernia repair.

Presented herein is a case of a patient who, during a laparoscopic herniorrhaphy, developed profound bradycardia upon introduction of the pneumoperitoneum. Following discharge, the patient presented 24 h later with herniation through the trocar port incision. With laparoscopic surgery being used more frequently, there will be an increase in the incidence of these types of complications; however, with better awareness, they may be avoided.

Hernia, Inguinal↗

PubMed1993

Arterial pressure-flow relationships in hypertensive dogs: effect of carotid sinus baroreflex.

The effect of the carotid sinus baroreflex reflex on arterial pressure-flow relationships was studied in Goldblatt hypertensive and normotensive dogs on cardiopulmonary bypass. Dogs were anesthetized with pentobarbital sodium, vagotomized, and the carotid sinuses were isolated at controlled carotid sinus pressures (CSP). The mean arterial pressure-flow relationships were measured at different levels of CSP. The arterial pressure-flow relationship was found to be linear except at extreme levels of flow. The slopes derived from the linear regression of the pressure-flow relationships [total peripheral resistance (TPR)] were 1.466 +/- 0.111 and 0.786 +/- 0.13 mmHg.ml-1 x min.kg at CSP of 50 and 200 mmHg in the normotensive group and 1.758 +/- 0.183 and 0.937 +/- 0.114 mmHg.ml-1 x min.kg at CSP of 50 and 250 mmHg in the hypertensive group. The increases in slope measured when CSP was decreased from saturation to threshold were 0.68 mmHg.ml-1 x min.kg (187% increase) in the normotensive group and 0.82 mmHg.ml-1 x min.kg (188% increase) in the hypertensive group. Zero-flow arterial pressures at CSP of 50, 125, and 200 mmHg were found to be 23.1 +/- 2.9, 21.7 +/- 2.2, and 17.1 +/- 1.8 mmHg in the normotensive group and 28.4 +/- 2.2, 23.8 +/- 1.5, and 20.0 +/- 1.2 mmHg in the hypertensive group. A nonlinear model fit was found to give a significantly better fit [coefficient of determination (r2) = 0.932 linear, 0.956 nonlinear] of the arterial pressure-flow relationships. We conclude that, in experimental hypertension, carotid baroreflex control of TPR is shifted to a higher operating point without any reduction in overall reflex gain.

Animals↗

PubMed1993

Molecular cloning of the murine JAK1 protein tyrosine kinase and its expression in the mouse central nervous system.

Degenerate oligonucleotide primers were employed in PCRs to clone protein tyrosine kinases that may play potential roles in the development of the mammalian CNS. Using one PCR clone to screen a mouse eye cDNA library, a full-length cDNA of a cytoplasmic tyrosine kinase, the homolog of human JAK1, was obtained. The murine JAK1 kinase belongs to a new family of cytoplasmic kinases that contain two tandem catalytic domains. Northern analyses indicated that murine JAK1 mRNA is expressed in a variety of tissues and cell lines. In the adult mouse eye, in situ hybridization and immunohistochemistry showed that JAK1 mRNA and protein were expressed in the retinal ganglion cell layer and the inner part of the inner nuclear layer, presumably in amacrine cells. JAK1 protein was also detected in horizontal cells and in the two synaptic layers of the adult retina. During retinal development, JAK1 protein was first detected in retinal ganglion cells and in their axons as early as embryonic day 14. Expression of JAK1 protein in amacrine cells and horizontal cells occurred only postnatally. This pattern of expression was also observed in the chick retina, suggesting an evolutionarily conserved function of JAK1 kinase in vertebrate retinal development and/or function. Immunohistochemical staining against JAK1 was detected in two areas of the adult mouse brain, the olfactory bulb and a group of cells in the hypothalamus. Together, these expression studies suggest a role for JAK1 kinase in the differentiation or function of a subset of CNS neurons.

Aging↗