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Biomedical subjects

S Chung

Publications and source records attributed to S Chung.

At least 19 recordsLinked to original sources
PubMed1992

Monoclonal antiprothrombinase (3D4.3) prevents mortality from murine hepatitis virus (MHV-3) infection.

The induction of monocyte/macrophage procoagulant activity (PCA) has been implicated in the pathogenesis of murine hepatitis virus strain 3 (MHV-3) infection and disease. Previously, we have shown that induction of PCA by MHV-3 correlated with resistance/susceptibility to infection in different mouse strains. In this study, all BALB/cJ mice that were infected with 10(3) plaque-forming units of MHV-3 developed severe liver disease and died within 96-120 h. Examination of the livers of these animals showed marked hepatic necrosis, deposition of fibrin, and cellular expression of PCA by direct immunofluorescence staining in areas of necrosis as well as in hepatic sinusoids. Splenic mononuclear cells recovered from these mice expressed high concentrations of PCA with time after infection. Infusion into mice of a high-titered monoclonal antibody that neutralized PCA (3D4.3) attenuated the development of hepatic necrosis and enhanced survival in a dose-dependent manner. All of the animals receiving 100 micrograms, and 44% and 22% of the animals that received 50 and 25 micrograms per day, respectively, survived for 10 d and made a full recovery. Administration of the antibody resulted in a dose-dependent reduction in fibrin deposition, PCA expression as detected by direct immunofluorescence staining and by a functional assay. In animals treated with high concentrations of antibody, titers of antibody to PCA fell from 87 +/- 15 micrograms/ml to 100 +/- 7 ng/ml during the active phase of the disease, consistent with sequestration due to binding of the immunoglobulin to cells expressing PCA. Surviving animals, when rechallenged with MHV-3, had a 40% mortality, consistent with the known rates of metabolism of immunoglobulin. This further suggested that protection was by a passive mechanism. The results reported here demonstrate that a neutralizing antibody to PCA protects animals from fulminant hepatitis and death associated with MHV-3 infection, and supports the notion that PCA is a potent inflammatory mediator that plays a pivotal role in the pathogenesis of liver injury resulting from MHV-3 infection.

Animals↗
PubMed1992

Dual-energy x-ray absorptiometry of the forearm: reproducibility and correlation with single-photon absorptiometry.

Although single-photon absorptiometry (SPA) has been the predominant tool used to assess bone mineral density (BMD) in the forearm, the development of dual-energy x-ray absorptiometry (DEXA) provides the benefits of greater source stability, reduced scanning time, and improved image resolution compared to SPA. In the present study we used the DEXA bone densitometer (Hologic, Inc., Waltham, MA) to (1) measure BMD in the one-third radius and ultradistal radius; (2) examine the reproducibility of these BMD measurements; and (3) compare the BMD at the one-third radius with SPA (SP2, Lunar Corp., Madison, WI). In 65 normal women (ages 22-74 years) we examined changes in the forearm DEXA BMD with age, revealing significant quadratic regression equations. The reproducibility of DEXA BMD (mean +/- SEM) in 7 normal subjects aged 22-50 years is 0.85 +/- 0.16% for the predominantly cortical one-third radius site and 0.97 +/- 0.15% for the more trabecular ultradistal site. The regression relationship between DEXA and SPA of the one-third radius in 26 subjects (ages 22-68 years) is DEXA BMD = 0.105 + 0.826 (SPA BMD); R = 0.97, R2 = 0.94, p less than 0.0001. Bone densitometry of the forearm using DEXA may be performed relatively rapidly, providing reproducibility and image resolution that are generally superior to those observed with SPA.

Absorptiometry, Photon↗
PubMed1992

Reduction mammoplasty with the short submammary scar (S-S-S) technique.

Since its introduction, reduction mammoplasty has undergone a process of evolution and improvement that affects its three surgical goals: (1) safe transposition of the nipple-areola complex, (2) sufficient reduction of volume, and (3) aesthetically acceptable results. Unfortunately, most reduction mammoplasty techniques still result in a long transverse scar on the chest wall which often presents a problem, particularly a hypertrophic condition. In 1957 Arie proposed a vertical scar technique for mastopexy; recently Lassus, Marchac, Peixoto, d'Angieri Basile, and others reported their original methods that try to reduce the length of the transverse scar. We modified these previously proposed techniques and present our experiences with a reduction mammoplasty called the short submammary scar (S-S-S) technique.

Adult↗
PubMed1992

A peptide derived from the Shaker B K+ channel produces short and long blocks of reconstituted Ca(2+)-dependent K+ channels.

A 20 amino acid synthetic peptide, corresponding to the amino-terminal region of the Shaker B (ShB) K+ channel and responsible for its fast inactivation, can block large conductance Ca(2+)-dependent K+ channels from rat brain and muscle. The ShB inactivation peptide produces two kinetically distinct blocking events in these channels. At lower concentrations, it produces short blocks, and at higher concentrations long-lived blocks also appear. The L7E mutant peptide produces only infrequent short blocks (no long-lived blocks) at a much higher concentration. Internal tetraethylammonium competes with the peptide for the short block, which is also relieved by K+ influx. These results suggest that the peptide induces the short block by binding within the pore of Ca(2+)-dependent K+ channels. The long block is not affected by increased K+ influx, indicating that the binding site mediating this block may be different from that involved in the short block. The short block of Ca(2+)-dependent K+ channels and the inactivation of Shaker exhibit similar characteristics with respect to blocking affinity and open pore blockade. This suggests a conserved binding region for the peptide in the pore regions of these very different classes of K+ channel.

Animals↗
PubMed1992

Treatment of postcataract fibrinous membranes with tissue plasminogen activator.

PURPOSE: The purpose of this study is to investigate the efficacy and toxicity of tissue plasminogen activator (tPA) in treatment of postcataract fibrinous membranes. METHODS: The authors injected 25 micrograms of tPA into the anterior chamber of 52 pseudophakic eyes with moderate to severe fibrinous membranes that developed after cataract surgery. RESULTS: Intraocular tPA injection resulted in complete fibrinolysis in 47 of 52 eyes (90%) and partial fibrinolysis in 5 of 52 eyes (10%). In cases of complete fibrinolysis, resolution of the fibrinous membrane occurred within 30 minutes in 22 of 47 eyes (47%) and within 1 hour in 25 of 47 eyes (53%). No evidence of toxicity was observed as measured by slit-lamp biomicroscopy, intraocular pressure, and corneal endothelial cell density, size, and morphology. Complications of tPA administration included periorbital pain (4 eyes), anterior chamber hemorrhage (4 eyes), and anterior chamber turbidity (3 eyes). CONCLUSION: The authors believe that intraocular tPA is effective and safe in the treatment of postcataract fibrinous membranes.

Adult↗
PubMed1991

Monoclonal antibody analysis of a unique macrophage procoagulant activity induced by murine hepatitis virus strain 3 infection.

A panel of 24 IgG2ak monoclonal antibodies was produced against murine hepatitis virus strain 3 (MHV-3)-induced procoagulant activity (PCA) from murine macrophages. The antibodies were specific and did not react in an enzyme-linked immunosorbent assay with purified MHV-3; lipopolysaccharide-induced PCA; crude mouse, human, or rabbit tissue factor, or unstimulated murine macrophages. Sixteen of 24 monoclonal antibodies inhibited functional PCA expression in a one-stage clotting assay. More detailed studies on one monoclonal antibody, 3D4.3, demonstrated that it inhibited prothrombin cleavage at concentrations of greater than or equal to 0.1 microgram/ml, and by Western blot this antibody reacted with proteins of a molecular mass of 140, 74, and 70 kDa on nonreduced gels and 74 and 70 kDa on reduced gels distinct from tissue factor known to have a molecular mass of 47 kDa. Induction of PCA was dependent on both host RNA and protein synthesis. Immunofluorescence studies showed specific binding to MHV-3-stimulated PCA-positive macrophage membranes. Both numbers of positive macrophages and intensity of staining correlated with multiplicity of infection. These monoclonal antibodies will be useful in isolation and characterization of the unique viral-induced PCA as well as in determining its biologic role in MHV infection and other diseases in which the prothrombinase has been implicated.

Animals↗
PubMed1991

Cellular and metabolic requirements for induction of macrophage procoagulant activity by murine hepatitis virus strain 3 in vitro.

The cellular basis for the variation in induction of monocyte procoagulant activity (PCA) by murine hepatitis virus strain 3 (MHV-3) was examined using a set of recombinant inbred strains of mice derived from the resistant (A/J) and susceptible C57B1/6J (B) progenitors. Induction of PCA by MHV-3 required live virus and host protein and RNA synthesis. Absolute restriction for induction of PCA was observed at the level of the macrophage. Peritoneal macrophages from resistant parental A/J and RI strains (AXB5) could not be induced to express PCA when stimulated by MHV-3 alone or in the presence of lymphocytes from susceptible and H-2 compatible RI mice (AXB3) although they did respond to endotoxin (LPS). In contrast, macrophages from both susceptible (AXB3) and semisusceptible (AXB1) RI strains of mice expressed a similar increase in PCA after stimulation with MHV-3 in the absence of lymphocytes. The levels of PCA expressed by macrophages in the presence of Thy-1.2+ lymphocytes correlated with susceptibility to disease. Thy-1.2+ lymphocytes from susceptible RI AXB3 mice could induce levels of PCA in macrophages from semisusceptible RI AXB1 mice equivalent to that seen in cultures of macrophages and lymphocytes from susceptible mice. Further subfractionation of Thy-1.2+ cells demonstrated that L3T4+ cells instructed macrophages to produce PCA. Thy-1.2+ cells from MHV-3 immunized resistant AXB5 mice, but not from non-immunized mice, were able to suppress induction of PCA. This suppressor cell activity could be detected 4 days after immunization, reaching maximal activity at day 7 with significant suppression even at 28 days. The PCA was shown to have direct prothrombin cleaving activity (prothrombinase) by ELISA and immunofluorescence staining using the mAb 3D4.3. These results demonstrate that induction of a unique PCA (prothrombinase) is restricted at the level of the macrophage and define a regulatory role for T lymphocytes in its induction.

Animals↗
PubMed1991

Cell-free transcription of a mouse ribosomal-protein-encoding gene: the effects of promoter mutations.

The mouse ribosomal protein-encoding gene, rpS16, was accurately transcribed in vitro with a high-efficiency nuclear extract prepared from HeLa cells. An analysis of the relative activities of rpS16 templates containing deletions or deleterious mutations of various promoter elements indicated that the in vitro transcription system can recognize all of the promoter elements that were previously identified by in vivo transfection experiments. The importance of a polypyrimidine initiator, which spans the cap site, and an element termed C, which is located in the region conventionally occupied by a TATA-box, was also assessed with an appropriate set of mutant templates. In agreement with earlier in vivo studies, our in vitro results indicated that the initiator is the primary determinant for selecting the transcription start point. Interestingly, however, the in vitro system exhibited a strong bias for features that are not present in the natural rpS16 gene. Mutant templates that contained a purine rather than a pyrimidine at or near the cap site or that had the C element replaced by a canonical TATA-box were six- to tenfold more active than the wild-type (wt) rpS16 gene in vitro system, whereas in vivo, these mutants were expressed equivalently to the wt gene. A double mutant containing both a cap site substitution and the TATA-box replacement was about 18-fold more active than the wt gene in the in vitro transcription system. These results suggest that the in vitro system may preferentially build a functional transcription complex with components that do not normally interact with the wt rpS16 gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Modulation of calcium-activated potassium channels from rat brain by protein kinase A and phosphatase 2A.

By incorporating plasma membrane vesicles into planar lipid bilayers, we previously characterized a family of four types of Ca(2+)-activated K+ channels from rat brain (Reinhart et al., 1989). Two of these are "large-conductance" or "maxi"-K+ channels, which differ in their gating kinetics and toxin sensitivity and are henceforth referred to as "type 1" and "type 2" channels. Here we show that the gating of these two channel types can be modulated by phosphorylation and dephosphorylation. The effects of cAMP-dependent protein kinase catalytic subunit (PK-A) on type 1 maxi-K+ channels are complex in that, while half of these channels are upregulated by the kinase, about one out of seven channels is downregulated. Thus, there may be several distinct channels within the type 1 category. Type 2 maxi-K+ channels are consistently downregulated by PK-A. The effects of PK-A on both channel types are reversed by the catalytic subunit of protein phosphatase 2A (PP-2A), but not by protein phosphatase 1 (PP-1). Furthermore, some of the type 1 maxi-K+ channels can be modulated by PP-2A, even without any prior PK-A treatment, indicating they are in a phosphorylated state when they are incorporated into the bilayer. The results demonstrate that (1) type 1 and type 2 maxi-K+ channels are substrates for PK-A; (2) phosphorylation can shift the open probability of channels in either direction, by a mechanism involving multiple phosphorylation sites; (3) phosphorylation alters the Ca2+/voltage sensitivity of these channels; and (4) dephosphorylation of type 1 and type 2 channels is catalyzed by specific phosphatases.

Animals↗
PubMed1991

A human epidermal differentiation-specific keratin gene is regulated by calcium but not negative modulators of differentiation in transgenic mouse keratinocytes.

Keratins K1 and K10 represent the major differentiation products of the maturing epidermal keratinocytes. Primary epidermal cell cultures from newborn K1 transgenic mice containing a 12-kilobase human K1 genomic fragment were established in order to examine the expression of both human and mouse K1 in the presence of known modulators of epidermal differentiation. Elevated levels of Ca2+ in the culture medium induced both mouse K1 and human K1. Supplementing the medium with retinoic acid or 12-O-tetradecanoylphorbol-13-acetate or introducing a Harvey viral ras oncogene (v-rasHa) into the cells completely suppressed mouse K1 but not human K1. Our results suggest that: (a) the human 12-kilobase insert contains all the necessary cis-acting elements to respond to the Ca2+ signal, and (b) other cis-acting elements, not present within this insert, may function independently to regulate the response of K1 to retinoids, 12-O-tetradecanoylphorbol-13-acetate, and v-rasHa transformation. This transgenic model provides an approach to identify elements required for the regulation of an epidermal differentiation-specific gene.

Animals↗
PubMed1990

Human alpha B-crystallin gene and preferential promoter function in lens.

alpha B-Crystallin, first identified as a structural component of the vertebrate eye lens, is expressed at high levels in lens and at lower levels in a number of other tissues, most notably cardiac and skeletal muscle, kidney, and brain. We have cloned and sequenced the human alpha B-crystallin gene and show that it is structurally similar to its hamster homolog. We have also identified its transcription initiation site in human lens RNA. Functional analysis of a promoter fragment extending from -537 to +21 (relative to the transcription initiation site) and fused to the bacterial chloramphenicol acetyltransferase gene suggests that this fragment contains regulatory elements that function preferentially, but not exclusively, in lens. In contrast, this fragment is apparently insufficient to promote transcription in glial cells, as this construct functioned poorly in a glioblastoma-astrocytoma cell line (U-373MG) that synthesizes high levels of the endogenous alpha B-crystallin gene product.

Amino Acid Sequence↗
PubMed1989

Cloning and sequence determination of human placental aldose reductase gene.

The human aldose reductase gene has been cloned by screening a human placental cDNA library with antibodies against bovine lens aldose reductase. The nucleotide sequence of the entire coding region has been determined. The deduced amino acid sequence indicates that the human enzyme is 84% identical to the bovine lens aldose reductase and 85% identical to the rat lens aldose reductase. It is also very similar to the human aldehyde reductase, the bovine prostaglandin F synthase, and to the European common frog rho-crystallin. The deduced amino acid sequence also indicates that maturation of aldose reductase involves removal of the N-terminal methionine.

Alcohol Dehydrogenase↗
PubMed1989

A family of calcium-dependent potassium channels from rat brain.

By incorporating rat brain plasma membrane vesicles into planar lipid bilayers, we have found and characterized four types of Ca2(+)-activated K+ channels. The unitary conductances of these channels are 242 +/- 14 pS, 236 +/- 16 pS, 135 +/- 10 pS, and 76 +/- 6 pS in symmetrical 150 mM KCI buffers. These channels share a number of properties. They are all activated by depolarizing voltages, activated by micromolar concentrations of internal Ca2+ with a Hill coefficient for Ca2+ activation of between 2 and 3, noninactivating under our assay conditions, blocked by low millimolar concentrations of TEA from the outside, apamin-insensitive, and very selective for K+ over Na+ and Cl-. Three of the four channels are also blocked by nanomolar concentrations of charybdotoxin. One of the high conductance Ca2(+)-activated K+ channels is novel in that it is not blocked by charybdotoxin and exhibits gating kinetics highlighted by long closed times and long open times. This family of closely related Ca2(+)-activated K+ channels may share structural domains underlying particular functions.

Animals↗
PubMed1989

Reverse-flow postauricular arterial flap for auricular reconstruction.

Two patients with an ear defect, each reconstructed with a reverse-flow postauricular arterial flap are presented; one defect was caused by accidental exposure of bare cartilage at the posterior helix and the other by traumatic loss of earlobe. After the flaps were transposed, a line of auditory signals was dictated by Doppler probing, which suggested the presence of reverse blood flow in the flaps from the anteroauricular vessels. We believe that the reverse-flow postauricular arterial flap is a reliable and convenient optional tool in the reconstruction of auricular defects.

Adult↗
PubMed1989

Importance of introns for expression of mouse ribosomal protein gene rpL32.

The importance of intronic sequences for expression of the mouse ribosomal protein gene rpL32 was evaluated by transfection experiments with a series of mutant constructs in which one or more of the three rpL32 introns was totally or partially deleted. When transiently transfected into monkey kidney (COS) cells or stably transfected into mouse L cells, a mutant that lacked all three introns was completely inactive. Constructs that contained intron 1, either alone or in combination with another intron, were expressed as efficiently as was the normal intact rpL32 gene. Constructs that lacked intron 1 but contained another spliceable intron, even one from a foreign gene, were expressed at about 10 to 20% of the maximum level. These results indicated that intron 1 contains an element that increases the level of expression by 5- to 10-fold. A comparison of internal deletion mutants localized the element to within the first 27 base pairs of intron 1. Nuclear run-on experiments with stably transfected COS cells demonstrated that this element functions at the transcriptional level. The element was inactive when translocated to a position upstream of the transcriptional start site or to a position within intron 3, which indicated that it does not have the properties of a typical enhancer. From these and other results, we conclude that introns have both a general and a specific role in rpL32 expression. The general role, which can be satisfied by any spliceable intron, is to ensure an efficient yield of RNA transcripts. The specific role is uniquely attributable to intron 1, which contains a transcriptional regulatory element near its 5' end.

Animals↗