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Biomedical subjects

J Chung

Publications and source records attributed to J Chung.

At least 181 records · Page 10Linked to original sources
PubMed1991

Distinct mechanisms for the activation of the RSK kinases/MAP2 kinase/pp90rsk and pp70-S6 kinase signaling systems are indicated by inhibition of protein synthesis.

Previous studies demonstrated that addition of protein synthesis inhibitors to quiescent cells resulted in the stimulation of S6 kinase activity. The present characterization of several growth factor- and oncogene-regulated protein-serine/threonine kinases demonstrated that pp70-S6 protein kinase and not pp90rsk, RSK kinase, or MAP2 kinase activities were rapidly stimulated. Dose-response experiments revealed a close correlation between the extent of protein synthesis inhibition and the level of activation of pp70-S6 kinase activity. Analysis of S6 phosphorylation suggests that activation of pp90rsk S6 phosphotransferase activity, whose Xenopus homologues appear to be responsible for S6 phosphorylation during oocyte maturation, may participate in, but is not essential for, the increase in S6 phosphorylation observed in growth-stimulated somatic animal cells. These studies provide additional evidence for the existence of two distinct, independently regulated protein phosphorylation cascades activated in the early G1 phase of the cell cycle.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1989

Effect of surfactant-associated protein-A (SP-A) on the activity of lipid extract surfactant.

The properties of natural bovine surfactant and its lipid extract have been examined with a pulsating bubble surfactometer which assesses the ability of surfactant lipids to adsorb to the air/liquid interface and reduce the surface tension to near 0 dynes/cm during dynamic compression. Studies conducted at 1 mg/ml phospholipid revealed that the surface activity (i.e., the ability to produce low surface tensions) of lipid extracts could be enhanced by incubating the sample at 37 degrees C for 120 min or by addition of CaCl2. In contrast, incubation at 37 degrees C only slightly improved the biophysical activity of natural surfactant and the addition of CaCl2 had a more modest effect than with lipid extracts. With 20 mM CaCl2, the surfactant activity of lipid extract surfactant was similar to that of natural surfactant. Incubation with EDTA reduced the biophysical activity of natural surfactant. Experiments in which increasing amounts of lipid extract were replaced by natural surfactant revealed that small amounts of natural surfactant enhanced the surfactant activity of lipid extract. The biophysical activity of lipid extract surfactant was also increased by the addition of soluble surfactant-associated protein-A (SP-A) (28-36 kDa) purified from natural bovine surfactant. These results indicate that SP-A (28-36 kDa) improves the surfactant activity of lipid extracts by enhancing the rate of adsorption and/or spreading of phospholipid at the air/liquid interface resulting in the formation of a stable lipid monolayer at lower bulk concentrations of either phospholipid or calcium.

Animals↗
PubMed1989

An evaluation of morphine and oxymorphone administered via patient-controlled analgesia (PCA) or PCA plus basal infusion in postcesarean-delivery patients.

The analgesic efficacy and adverse effects of morphine and oxymorphone in 32 patients who received traditional patient-controlled analgesia (PCA) following cesarean delivery were compared with those in 32 other patients receiving the same agents via PCA plus basal opioid infusion (PCA + BI). All patients were operated upon during epidural anesthesia with 2% lidocaine and 1:200,000 epinephrine to achieve a T4 sensory level. Upon first complaint of pain in the recovery room, patients were given a titrated iv loading dose of the assigned opioid until comfortable and were then provided with a programmable PCA device. Group I (PCA) consisted of two subsets in which incremental boluses of morphine (1.8 mg, n = 16) or oxymorphone (0.3 mg, n = 16) could be self-administered via conventional PCA. Patients in group II (PCA + BI) received a basal infusion of morphine (0.6 mg/hour, n = 16) or oxymorphone (0.1 mg/hour, n = 16) in addition to self-administered boluses of 1.8 and 0.3 mg, respectively. Patients were evaluated for 24 h following initiation of analgesic therapy, and 10-cm visual analog scales (VAS) were utilized at selected intervals to assess pain at rest, pain during movement, and satisfaction with therapy. The level of sedation and incidence of nausea/vomiting and pruritus were also recorded. Patients utilizing PCA + BI noted significant reductions in resting pain scores with oxymorphone and decreased pain during movement with both opioids when compared with individuals using PCA alone (P less than 0.05). There were no significant differences between treatment groups in 24-h dose requirements or patient satisfaction with therapy (P = ns).(ABSTRACT TRUNCATED AT 250 WORDS)

Cesarean Section↗
PubMed1988

Expression of the gene for main intrinsic polypeptide (MIP): separate spatial distributions of MIP and beta-crystallin gene transcripts in rat lens development.

The main intrinsic polypeptide (MIP) is the major protein present in the lens fiber cell membrane and is the product of a gene which, as far as is known, is expressed only in the lens. We have used in situ hybridization and immunofluorescence microscopy to characterize the expression of this gene during the course of development in the rat. At progressive stages of lens morphogenesis, we find that synthesis of the protein is closely tied to the accumulation of MIP mRNA in cells that are committed to terminal differentiation, first in the elongating presumptive primary lens fibers and later in the secondary fibers as they differentiate from the anterior epithelial cells. The transcripts accumulate in the basal cytoplasm of the primary fibers and in the cytoplasm which surrounds the cell nucleus in the secondary fibers. We have compared this pattern of expression with that of a gene for a cytoplasmic protein, beta-crystallin beta-A1/A3. In sharp contrast to the localized concentrations seen for the MIP mRNA, beta-A1/A3 transcripts are relatively uniformly distributed throughout the cytoplasm. Neither MIP nor crystallin gene appears to be transcriptionally active in the undifferentiated epithelial cell, but transcripts from the beta-A1/A3 gene appear earlier in fiber cell differentiation than do those from the gene for MIP.

Animals↗
PubMed1988

Reduced release of TNF and PCA from macrophages of tolerant mice.

An early-phase tolerance to toxic doses of lipopolysaccharide (LPS) can be induced in mice by prior administration of sublethal doses of LPS or lipid A. These tolerant mice exhibit no hypothermia on subsequent administration of LPS and can survive a challenge dose of LPS that would normally be lethal. Peritoneal exudate cells of LPS-tolerant mice synthesized significantly reduced amounts of prostaglandins and of procoagulant activity (PCA) and tumor necrosis factor (TNF) when stimulated with LPS in vitro (compared to macrophages of control animals). Tolerance induction with lipid A was somewhat less effective. A regulatory mechanism of E-series prostaglandins (PGE) might be involved in the induction of hyporesponsiveness in macrophages of tolerant mice, as the LPS-stimulated TNF release could be inhibited in a dose dependent manner by preincubation with PGE1. Since PCA and TNF are mediators that are proposed to play a very important role in the pathophysiology of septic and endotoxic shock, a reduction in the release of these mediators may be partially responsible for early-phase tolerance to LPS.

Animals↗
PubMed1987

The c-myc gene encodes superimposed RNA polymerase II and III promoters.

The first exon of the c-myc gene has unusual properties that suggest some further role in gene regulation. It encodes a large, evolutionarily conserved leader exon that is transcribed more frequently than the remaining exons of the c-myc gene. In what follows, we provide a possible explanation for these observations. We find that the major promoter of the c-myc gene is bifunctional; that is, it supports transcription by RNA polymerases II and III (pol II and III). Both enzymes initiate in vitro transcription from the major c-myc initiation site (P2), but pol III is completely blocked near the 3' end of the first exon while pol II, though partially blocked, transcribes through this region. These superimposed transcriptional activities suggest a potential regulatory mechanism by which one polymerase system could influence the activity of another.

Animals↗
PubMed1987

Protein sequence analysis studies on the low molecular weight hydrophobic proteins associated with bovine pulmonary surfactant.

Lipid extracts of bovine pulmonary surfactant, which exhibit biophysical and biological activity, contain two hydrophobic proteins which have been designated surfactant protein-B (SP-B) and SP-C. Amino terminal amino acid sequence analysis of whole lipid extracts and partially purified protein fractions gave rise to three sequences, two major and one minor. The first sequence, identified as a member of the SP-B family, extended for 60 amino acids beginning with an amino terminal phe. The second polypeptide, identified as a member of the SP-C family, sequenced for 35 amino acids and had a leu amino terminus. The third minor sequence corresponded to amino acids 2-9 of SP-C (N-leu) and was designated SP-C (N-ile). Sequence analysis of cyanogen bromide peptides derived from methyl isocyanate-blocked lipid extract material produced two peptides which extended the amino acid sequence of SP-B to residue 79, which appears to be a glycine.

Amino Acid Sequence↗
PubMed1987

The production of tumor necrosis factor by mouse bone marrow-derived macrophages in response to bacterial lipopolysaccharide and a chemically synthesized monosaccharide precursor.

Lipid X, a monosaccharide biosynthetic precursor of lipid A, has been chemically synthesized and was shown to induce bone marrow-derived macrophages to release tumor necrosis factor (TNF) in vitro. However, relatively high amounts of lipid X were necessary for induction, and the levels of TNF were much less than those induced by small amounts of lipid A itself or LPS. Lipid X prepared by extraction of Escherichia coli mutants induced higher levels of TNF than the chemically synthesized material, but this is probably partially due to amounts of impurities in the extracted material. Pretreatment of macrophages with IFN-gamma resulted in the release of higher amounts of TNF on subsequent induction with either LPS or lipid X. In contrast, pretreatment of macrophages with LPS induced hyporesponsiveness for TNF production on subsequent rechallenge with LPS. Lipid X, on the other hand, was incapable of making macrophages hyporesponsive for TNF production.

Animals↗
PubMed1986

Trans-acting elements modulate expression of the human c-myc gene in Burkitt lymphoma cells.

We have used a competition assay to identify the targets of trans-acting elements that modulate the expression of the human c-myc gene (designated MYC in human gene nomenclature). For this purpose, a c-myc hybrid indicator gene was formed by joining the c-myc promoter region, first noncoding exon, and intron to the bacterial gene for chloramphenicol acetyltransferase (CAT). The test assay consisted of cotransfecting the indicator gene with competing fragments of DNA derived from suspected control regions of the c-myc gene. Such experiments test the hypothesis that control regions are often targets for the binding of trans-acting regulatory factors that can be diverted to competing fragments of DNA. A negatively acting element will be diverted from the indicator gene, allowing the gene's enhanced expression, whereas a positively acting element will behave oppositely. Control indicator genes driven by non-myc promoters assess the specificity of the effect. Using this approach, we find three c-myc regions that are capable of enhancing the expression of the indicator gene in competition assays (i.e., putative sites of negative modulation). In addition, we find sequences near the c-myc promoters that suppress expression in competition assays (i.e., putative binding sites of positively acting factors). These results, with appropriate controls, suggest the existence of target sites near the c-myc gene that specifically modulate its expression both positively and negatively. Their locations fit well with regions damaged or lost in many Burkitt lymphoma and murine plasmacytoma translocations.

Acetyltransferases↗
PubMed1985

In vivo activation of murine natural killer cell functions by human recombinant DNA interleukin 2.

Intraperitoneal (i.p.) injections of purified human recombinant DNA (rDNA)-interleukin 2 (IL 2) resulted in in vivo activation of local natural killer (NK) cell activities in wild-type and congenitally athymic mice. NK cells were identified by short-term cytotoxicity assays against YAC tumor targets and by cell-surface phenotyping. The magnitude of the cytolytic responses was dependent on the IL 2 dose (greater than or equal to 0.1 microgram per injection) and the time period of treatment (the maximum response was on days 3 to 4 after daily treatment). In vivo application of antisera against the murine NK marker asialo GM1 (asGM1) and against interferon-alpha/beta and -gamma (IFN) significantly inhibited NK cell activation. Limiting dilution analysis revealed high frequencies (up to 1 in 1.8 X 10(3)) of in vitro IL 2 reactive mononuclear cells among the peritoneal exudate cells (PEC) of normal mice. rDNA-IL 2 activated non-adherent PEC to proliferate. The majority of these cultures also displayed cytotoxicity against YAC targets. No exogenous IFN was required for either response. Endogenous IFN production did not appear to play an important role for induction of cytotoxicity in this system either. Only a minority of cultures produced measurable levels of IFN without showing excessive cytotoxic activity. In vivo IL 2 treatment resulted in a rapid increase of the total numbers and frequencies of the IL 2 reactive PEC. Hence, IL 2 alone was apparently sufficient for in vitro activation of NK-like activities, whereas IFN-induction by IL 2 was required for in vivo elicitation of similar responses in perhaps the same cell populations.

Animals↗
PubMed1984

Scanning electron microscopy of urinary stone as a diagnostic tool.

On the basis of an extensive electron microscopic study of human urinary stones, a step by step method of stone analysis by scanning electron microscopy (SEM) morphology was developed. A preliminary blind study of 100 consecutive stones demonstrated that the method requires minimum amounts of training and is highly accurate. With several hours of training, accuracy of the stone analysis by SEM morphology alone exceeded 95%. The data indicate that, with further refinements, SEM stone analysis can be accomplished expeditiously and exceed other methods known for stone analysis with economy and accuracy.

Crystallization↗
PubMed1982

Properties and metabolic fate of two very low density lipoprotein subfractions from rhesus monkey serum.

Physical, chemical and physiological approaches were used to examine the properties of two very low density lipoproteins, VLDL-I (slow-beta), and VLDL-II (pre-beta), which were isolated by agarose column chromatography from the serum of rhesus monkeys fed either Purina Chow or one of four hyperlipidemic diets containing 0.5-20% cholesterol suspended in either coconut oil, peanut oil, mixed coconut oil and butter fat or lard. In the coconut oil-fed hyperlipidemic animals, the majority of the apolar lipids of VLDL-I was represented by cholesteryl esters. The small percentage of triacylglycerol (15%) had a fatty acid composition which resembled that of the fatty acid in each of the diets. In turn, VLDL-II had a triacylglycerol-rich core and differed from VLDL-I in apolipoprotein distribution (VLDL-I: low molecular weight apolipoprotein B, 36%; apolipoprotein E, 64%; and VLDL-II: high molecular weight apolipoprotein B, 38%; apolipoprotein E, 3%; and apolipoprotein C, 65%). Both VLDLs were hydrolyzed in vitro by milk lipoprotein lipase by first-order kinetics although VLDL-I exhibited a slightly slower reaction rate. When an oral dose of [3H]retinol was given to one of the animals, both VLDLs became labeled but the specific activity of VLDL-I was six times higher than that of VLDL-II and the other lipoproteins. We conclude that VLDL-I represents a cholesteryl ester-rich lipoprotein probably of intestinal origin, whereas VLDL-II may be a particle of hepatic derivation modified by its interaction with the other plasma lipoproteins.

Animals↗
PubMed1982

In vitro mass: activity distribution of lecithin--cholesterol acyltransferase among human plasma lipoproteins.

In order to compare the mass-activity distribution of lecithin-cholesterol acyltransferase (LCAT) among plasma lipoproteins separated by various ultracentrifugal or chromatographic procedures, we have quantified the enzyme by an electroimmunoassay technique using a specific antibody raised in the rabbit. This antibody, when added to whole serum, inhibited all of the enzyme activity present in it. The percent mass distribution of the enzyme among the lipoproteins isolated by rate-zonal ultracentrifugation (d 1.00-1.36 g/ml, SW 40 rotor, 37 000 rpm, 16 h) was as follows: very low density lipoproteins (VLDL), 0; low density lipoproteins (LDL), 6.2; HDL2, 6.5; HDL3, 12 and d greater than 1.21 g/ml fraction, 75. Measurement of LCAT activity of each lipoprotein fraction against mixed single bilayer lecithin-cholesterol vesicles (molar ratio, 4:1) containing apo A-I, indicated that VLDL, LDL and HDL2 were inactive or minimally active under the experimental conditions used, whereas HDL3 and the d greater than 1.21 g/ml fraction contained 17.5 and 79.9% of the total enzyme activity. Prolonged ultracentrifugation of the LCAT-containing lipoproteins resulted in the recovery of activity in the lipoprotein-free infranatant. In studies with lipoproteins linked to Sepharose 4B, LCAT was found to bind LDL, HDL2, and HDL3. It is concluded that LCAT is present in all the major lipoproteins except for VLDL. The activity appears to be dependent, at least in part, on the type of lipoproteins to which the enzyme is associated with.

Centrifugation, Isopycnic↗
PubMed1982

Neutrophils are required for the DNA synthetic response of human lymphocytes to mevalonic acid: evidence suggesting that a nonsterol product of mevalonate is involved.

Human peripheral blood lymphocytes, in the presence of human neutrophils, initiate DNA synthesis and cell cycling when exposed to mevalonic acid. The ability of lymphocytes to respond in this manner is a radiosensitive property of cells, whereas the help provided by neutrophils is maintained despite their exposure to x-irradiation. Other organic acid anions, including precursors of mevalonic acid biosynthesis and a variety of products of mevalonate metabolism, fail to initiate DNA synthesis when added to human lymphocytes. Because only the metabolically active R(--) enantiomer of mevalonic acid initiates lymphocyte DNA synthesis, we presume that physiological pathways of mevalonate metabolism are involved. The response to mevalonic acid of ML-236B (compactin)-inhibited lymphocytes is increased, and the threshold concentration of meyalonate at which lymphocyte DNA synthesis first appears is decreased, when the cells are cultured in lipoprotein-containing (as opposed to lipoprotein-depleted) medium. The response to mevalonic acid of lymphocytes cultured in lipoprotein-depleted medium can be enhanced by addition to the cultures of low density lipoprotein but not by addition of high density lipoprotein. Based upon the flux diversion hypothesis of mevalonate metabolism, these observations suggest that a nonsterol product of mevalonate metabolism may be responsible for the initiation of lymphocyte DNA synthesis by mevalonic acid.

Cell Cycle↗
PubMed1981

Serum lipoproteins modulate oxygenated sterol insertion into human red cell membranes.

The insertion of oxygenated sterol compounds into human red blood cell membranes as well as the consequent transformation of the red cells to an echinocyte shape and the expansion of the membranes are impeded by the presence of serum lipoproteins in the incubation medium. All density classes of human serum lipoproteins bind oxygenated sterol compounds, and lipoproteins can act as acceptors of oxygenated sterols previously inserted into red cells. Since oxygenated sterols have been reported to be atherogenic, the modulating and possibly protective effects of serum lipoproteins on oxygenated sterol-induced derangement of cell membrane structure and function may provide a useful model for further study.

Cholesterol↗