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Biomedical subjects

L Sun

Publications and source records attributed to L Sun.

At least 433 records · Page 24Linked to original sources
PubMed1994

Structure, chromosomal localization, and methylation pattern of the human mb-1 gene.

The Ag receptor on B lymphocytes is a multimeric complex that is composed of an Ag-specific component, surface Ig, which is noncovalently associated with at least two other proteins, Ig alpha and Ig beta. These are the glycoprotein products of the B lineage-restricted mb-1 and B29 genes and are crucial for the cell surface expression and function of the Ag receptor on B lymphocytes. To better understand the regulation of mb-1, we have cloned and sequenced a 5.7-kb genomic DNA fragment that contained the human gene. The overall structure of human mb-1 is very similar to that of the murine gene, including the number and approximate size of exons. The promoter region lacks a TATA element, but contains two copies of an early B cell factor-binding motif, which previously has been shown to be important for murine mb-1 expression. Other structural features include two nuclear factor-kappa B binding sites at the 5' end of the gene and a long stretch of AG rich-sequence between exons 3 and 4, downstream of an Alu repeat sequence that contains a potential stem-loop structure. The mb-1 gene was localized to chromosome 19q13.2-13.3 by a combination of two methods, PCR amplification of DNA from a somatic cell hybrid-mapping panel and fluorescence in situ hybridization. An examination of the methylation pattern revealed a striking correlation between demethylation in the 5' region of the gene and expression of mb-1. The demethylated HpaII/MspI sites are adjacent to the nuclear factor-kappa B-binding motifs, which suggests a role for this transcription factor in the regulation of human mb-1 gene expression.

Amino Acid Sequence↗
PubMed1994

The proton transfers in the cytoplasmic domain of bacteriorhodopsin are facilitated by a cluster of interacting residues.

The stepwise internal proton transfer reactions across the membrane, and the release and uptake at the surface, are the elementary steps that together constitute the transport mechanism in a proton pump. Although the proton donor and acceptor residues can be usually identified, the directionality and the energetics of the proton transfer must be determined to a large extent also by interactions of these with neighboring groups. We have examined the roles of residues D96, T46 and R227 in proton transfers during the photocycle of bacteriorhodopsin near its cytoplasmic surface, and in general the relationship between the reprotonation of the Schiff base and the subsequent proton uptake from the cytoplasmic side. The phenotypes of single and double mutants suggest close functional interaction among D96, T46, R227, and probably internal bound water. Measurements of the free energies of activation indicate that mechanistic interpretation of the rates changed by residue replacements is hindered by a general tendency toward lowered activation enthalpies in the mutated proteins. There is less ambiguity in the free energy levels of the photointermediates. It appears from these that the inhibitory and stimulatory influences of T46 and R227, respectively, on D96 as a proton donor compensate one another and ensure the effective reprotonation of the Schiff base. T46 and D96 mediate, in turn, proton uptake at the cytoplasmic surface. Although ultimately this will reprotonate D96, the observation of proton uptake from the bulk in R82Q without reprotonation of the aspartate residue suggests that the direct proton acceptor is not D96. The results thus indicate that the passage of the proton from the surface to the Schiff base is facilitated by multiple residue and water interactions in the cytoplasmic domain.

Amino Acids↗
PubMed1994

Study of the irreversible adsorption of proteins on polybutadiene-coated zirconia.

The cause of irreversible adsorption of proteins on polybutadiene-coated zirconia is investigated by comparing the chromatographic properties of polybutadiene-coated zirconia with that of other reversed-phase packing materials such as bonded phase silica, polybutadiene-coated alumina and polybutadiene-coated silica. We find that the polybutadiene-coated zirconia has a micropore size distribution similar to that of the polybutadiene-coated alumina, from which some proteins can be eluted. Thus, the irreversible adsorption of proteins on polybutadiene-coated zirconia is not caused by entrapment of proteins in the micropores of the packing. The high hydrophobicity of the polybutadiene coating and the strong Lewis acid sites on the zirconia surface cause strong interactions between proteins and the stationary phase, the combination of which lead to irreversible adsorption of proteins on polybutadiene-coated zirconia.

Adsorption↗
PubMed1994

Water and fat MR imaging with chemical shift selective 3D steady state methods.

A new 3D acquisition regimen that enables the collection of conventional, water-suppressed, and fat-suppressed images with no increase in scan times compared with currently implemented 3D sequences is presented. The method is based on conventional 3D steady state with interleaved selective excitation of the fat resonance resulting in acquisition of a fat-based image during the TR period experienced by the water spins. This new sequence is relatively tolerant to susceptibility artifacts and results in excellent water-based images. Because the idea, which we propose, is independent of the type of steady-state imaging protocol utilized, it can be easily applied with regimens that are specifically tailored to enhance contrast.

Fats↗
PubMed1994

Construction of a 28-mm 1H/13C probe and actively shielded Z-gradient set for operation in a 9.4 T/89 mm magnet.

In this work, we present a new RF and gradient assembly for operation in a 9.4 Tesla/89 mm magnet. This assembly was designed in order to enable 1H-NMR perfusion studies that are based on proton-observed carbon-edited approaches or gradient selected double quantum coherence. The RF portion of this probe assembly is comprised of a modified Alderman-Grant coil and a saddle coil operating at 400 and 100 MHz, respectively. These coils are surrounded by an actively shielded Z gradient, which also allows for the use of gradient-based water suppression without the need for carbon selection. We demonstrate that this probe can be used to implement gradient selected double quantum coherence experiments resulting in a high degree of water suppression.

Carbon Isotopes↗
PubMed1994

Autocrine transforming growth factor-beta 1 and beta 2 expression is increased by cell crowding and quiescence in colon carcinoma cells.

Although a great deal is known about the cellular effects of exogenous transforming growth factor-beta (TGF-beta) treatment and the effects of various exogenous agents (including TGF-beta's themselves) on TGF-beta expression, studies of cellular controls for autocrine TGF-beta expression and function have been rare. Since exogenous TGF-beta treatment blocks progression through the cell cycle, it seemed likely that autocrine TGF-beta activity would be induced by growth states in which there was little or no cell division such as confluency or quiescence. Specific TGF-beta 1 or beta 2 neutralizing antibody treatment of a colon carcinoma cell line designated CBS showed that autocrine TGF-beta activity could be demonstrated in quiescent cells but not in preconfluent cells. Studies of kinetics of TGF-beta 1 and beta 2 mRNA levels during the establishment of quiescence revealed a significant increase of both isoforms in quiescent cells. The quiescent cells also secreted three- to fourfold and four-to fivefold higher levels of total (latent plus active) TGF-beta 1 and beta 2 protein in the conditioned media than the confluent cells and preconfluent cells, respectively. There was no detectable active form of either TGF-beta isoform in the conditioned media of preconfluent cells, whereas a significant amount of active TGF-beta 1 and beta 2 was detected in the conditioned media of quiescent cells. Quantitative RNase protection assays were developed to compare the effects of cell crowding vs quiescence on TGF-beta expression. TGF-beta 1 was primarily induced by quiescence. TGF-beta 2 was induced by both quiescence and cell crowding. Increased TGF-beta 1 mRNA levels appeared to be exclusively due to an increase in stability, while increased TGF-beta 2 mRNA levels were due to increased transcription. This growth state-related induction of TGF-beta's was also observed in two other colon carcinoma cell lines. These studies show that TGF-beta 1 and beta 2 are autocrine-negative factors which can be situationally expressed by cells as a function of their growth state. Autocrine expression of the TGF-beta's in this model system appears not to affect exponentially growing cells, but rather to function by maintaining a quiescent state and/or by blocking progression through the cell cycle.

Carcinoma↗
PubMed1994

Detection of gaps in sinusoids by frog auditory nerve fibers: importance in AM coding.

Physiological studies were carried out in the frog (Rana pipiens pipiens) eighth nerve to determine: (i) whether the modulation rate or the silent gap was the salient feature that set the upper limit of time-locking to pulsed amplitude-modulated (PAM) stimuli, (ii) the gap detection capacity of individual eighth nerve fibers. Time-locked responses of 79 eighth nerve fibers to PAM stimuli (at the fiber's characteristic frequency) showed that the synchronization coefficient was a low-pass function of the modulation rate. In response to PAM stimuli having different pulse durations, a fiber gave rise to non-overlapping modulation transfer functions. The upper cut-off frequency of time locking was higher when tone-pulses in PAM stimuli had shorter duration. The fact that the cut-off frequency was different for the different PAM series suggested that the AM rate was neither the sole, nor the main, determinant for the decay in time-locking at high AM rates. Gap detection capacity was determined for 69 eighth nerve fibers by assessing fiber's spiking activities to paired tone-pulses during an OFF-window and an ON-window. It was found that the minimum detectable gap of eighth nerve fibers ranged from 0.5 to 10 ms with an average of 1.23-2.16 ms depending on the duration of paired tone pulses. For each fiber, the minimum detectable gap was longer when the duration of tone pulses comprising the twin-pulse stimuli was more than four times longer. When the synchronization coefficient was plotted against the silent gap between tones pulses in the PAM stimuli, the gap response functions of a fiber as derived from multiple PAM series were equivalent to gap response functions deriving from twin-pulse series suggesting that it was the silent gap which primarily determined the upper limit of time-locking to PAM stimuli.

Acoustic Stimulation↗
PubMed1994

Cycloversion and cyclovergence: the effects of the area and position of the visual display.

Rotation of a display in the frontal plane evokes a conjugate nystagmic rotation of the eyes (cycloversion) about the visual axes, with slow phases in the direction of stimulus motion--a response known as torsional optokinetic nystagmus (TOKN). Antiphase rotation of large dichoptic displays evokes a disconjugate rotation of the eyes about the visual axes, a response known as cyclovergence. Using the scleral-coil technique for monitoring eye movements we recorded TOKN evoked by black-and-white sectored displays rotating about the visual axis at an angular velocity of 30 degrees/s. The display was confined to central areas with diameters ranging from 5 degrees to full field or with the central 5 degrees to 75 degrees occluded. A 5 degrees central display evoked TOKN with 40% of the gain for the full-field display and gain increased as a function of the size of the display. The gain of TOKN decreased with increasing size of a central occluder. These characteristics of TOKN are similar to those of horizontal OKN. Cyclovergence was virtually absent with a 5 degrees display but was immune to occlusion of the central 40 degrees. Cyclovergence therefore differs from cycloversion in showing no preference for centrally placed stimuli. These effects are free from the influence of stationary edges, since these were concentric with the stimulus motion. The effects are also free from the influence of voluntary pursuit, since humans do not normally have voluntary control over torsional eye movements.

Humans↗
PubMed1994

Toxic heavy metals and other trace elements in foodstuffs from 12 different countries. An IAEA coordinated research program.

A research program related to the assessment of toxic heavy metals and essential trace elements in foodstuffs has been carried out in 12 countries under the auspices of the IAEA. The main purpose of this program was to obtain data on the elemental concentrations of potentially toxic elements in foodstuffs in various countries, and to compare them with the maximum permissible levels specified in national legislation and international guidelines. High-priority elements for this study were As, Cd, Cr, Pb, Hg, and Se. Also of interest, but of lower priority, were Sb, Cu, and Zn. Emphasis was placed on the use of nuclear and nuclear-related analytical techniques, complemented by conventional methods, and on quality assurance.

Food Analysis↗
PubMed1994

Regulation of the Escherichia coli nrd operon: role of DNA supercoiling.

An in vitro RNA transcription assay was used to investigate the regulation of the expression of the nrd promoter. Using a linear DNA template, we found that Fis protein, which has a positive effect on expression of the nrd promoter in an nrd-lacZ fusion in vivo, had a moderate negative effect in vitro. However, with a supercoiled DNA template as substrate, we found that Fis had a concentration-dependent positive effect on nrd transcription in vitro. This positive effect was not present on two templates that had 35- or 37-bp insertions between the Fis binding site and the nrd promoter. In the absence of Fis protein, a dramatic decrease in transcription was observed in templates with reduced supercoiling generated by the treatment with wheat germ topoisomerase I. Templates with insertions of 35 bp into an HpaII site at -102 or 37 bp into the MnlI site at -33 bp from the start of transcription failed to exhibit the DNA supercoiling sensitivity of the nrd promoter. Analysis of cells containing either of these two nrd-lacZ fusion constructs that has an insertion at the regulatory region by flow cytometry indicated that these two constructs, unlike the parental construct, were not cell cycle regulated.

Base Sequence↗
PubMed1994

Cell cycle regulation of the Escherichia coli nrd operon: requirement for a cis-acting upstream AT-rich sequence.

The expression of the nrd operon encoding ribonucleotide reductase in Escherichia coli has been shown to be cell cycle regulated. To identify the cis-acting elements required for the cell cycle regulation of the nrd promoter, different 5' deletions as well as site-directed mutations were translationally fused to a lacZ reporter gene. The expression of beta-galactosidase from these nrd-lacZ fusions in single-copy plasmids was determined with synchronously growing cultures obtained by repeated phosphate starvation as well as with exponentially growing cultures by flow cytometry analysis. Although Fis and DnaA, two regulatory proteins that bind at multiple sites on the E. coli chromosome, have been found to regulate the nrd promoter, the results in this study demonstrated that neither Fis nor DnaA was required for nrd cell cycle regulation. A cis-acting upstream AT-rich sequence was found to be required for the cell cycle regulation. This sequence could be replaced by a different sequence that maintained the AT richness. A flow cytometry analysis that combined specific immunofluorescent staining of beta-galactosidase with a DNA-specific stain was developed and employed to study the nrd promoter activity in cells at specific cell cycle positions. The results of the flow cytometry analysis confirmed the results obtained from studies with synchronized cells.

Base Sequence↗
PubMed1994

Proteolytic activity of human cytomegalovirus UL80 protease cleavage site mutants.

The human cytomegalovirus UL80 open reading frame encodes protease and assembly protein from its N- and C-terminal regions, respectively. We reported previously that a 30-kDa protease is derived by autoproteolytic processing of a polyprotein which is the translation product of the entire UL80 open reading frame (E. Z. Baum, G. A. Bebernitz, J. D. Hulmes, V. P. Muzithras, T. R. Jones, and Y. Gluzman, J. Virol. 67:497-506, 1993). Three autoproteolytic cleavage sites within the UL80 polyprotein were characterized; site 143 is within the protease domain and inactivates the protease. In this article, we report (i) expression analyses of UL80 in infected cells, including the processing kinetics of the UL80 polyprotein; (ii) the existence of an additional cleavage site (site 209) within the protease domain of the UL80 polyprotein; and (iii) the effect of mutagenesis at each of the cleavage sites upon proteolytic activity and steady-state levels of the UL80 processing products. During the course of infection, UL80 polyprotein processing begins at cleavage site 643 and follows at sites 256 and 143. Cleavage at site 643 and/or 256 within the polyprotein is not a prerequisite for efficient protease activity, since all three proteases (85-, 80-, and 30-kDa proteins) were equally active in cleaving the assembly protein precursor to its mature form. Inhibition of cleavage at site 143 resulted in a three- to sixfold increase in the steady-state level of the 30-kDa protease, supporting the hypothesis that cleavage at this site may represent a mechanism by which cytomegalovirus regulates the level of active protease.

Amino Acid Sequence↗
PubMed1994

Sex influence on renal alpha 2-adrenergic receptor density in the spontaneously hypertensive rat.

Male spontaneously hypertensive rats (SHR) have higher blood pressure than females. We compared renal alpha 2-adrenergic receptor density among intact SHR and Wistar-Kyoto (WKY) rats of both sexes, male and female SHR gonadectomized at 4 weeks of age, and gonadectomized SHR supplemented with testosterone. Additional groups of SHR were treated with enalapril (30 mg/kg per day), an angiotensin-converting enzyme inhibitor, from 5 to 14 weeks of age. Renal alpha 2-adrenergic receptor density was higher in males than females in both SHR and WKY rats. Female SHR and WKY rats had identical low renal alpha 2-adrenergic receptor density. Castration of male SHR reduced the male-female differences in blood pressure and renal alpha 2-adrenergic receptor density by 60%. Treatment with testosterone raised blood pressure and renal alpha 2-adrenergic receptor density to the intact male levels in both gonadectomized males and females. Treatment with enalapril decreased blood pressure but not renal alpha 2-adrenergic receptor density in both male and female SHR. We conclude that (1) both renal alpha 2-adrenergic receptor density and blood pressure are influenced by sex in SHR and WKY, (2) renal alpha 2-adrenergic receptor density like blood pressure is regulated by androgens, and (3) increased renal alpha 2-adrenergic receptor density is not a consequence of high blood pressure in male SHR.

Animals↗
PubMed1994

Cosegregation of the renin gene with an increase in mean arterial blood pressure in the F2 rats of SHR-WKY cross.

Using the restriction endonuclease, BgI I, Samani et al. found a restriction fragment length polymorphism (RFLP) for the renin gene in spontaneously hypertensive rats (SHR) and its normotensive control Wistar-Kyoto (WKY) rats. This RFLP was confirmed in our laboratory in SHR and WKY rats using a rat renin cDNA probe. The correlation of blood pressure and the renin RFLP was examined in 106 F2 rats produced from F1 rats, the offspring of a cross between SHR males and WKY females. Systolic blood pressure was measured by the tail cuff method at 12 weeks of age. Mean arterial blood pressure of anesthetized rats was measured by cannulation of the femoral artery prior to sacrifice. The frequency of renin genotype showed a typical 1:2:1 Mendelian ratio in F2 rats of SHR and WKY cross. The mean arterial blood pressure of F2 rats homozygous with the SHR allele was significantly higher than F2 rats that were heterozygous or homozygous for the WKY allele. No significant difference in systolic blood pressure was observed in these F2 rats. Thus, the renin gene RFLP cosegregates with an increase in mean arterial blood pressure in the F2 rats of SHR and WKY cross.

Alleles↗
PubMed1994

[Low frequency rotational responses in bilateral caloric weakness patients].

Comparative analysis of low frequency (0.01-0.64Hz) sinusoidal harmonic acceleration (SHA) responses of 50 patients with bilateral caloric weakness (summed slowphase velocities SSVs < or = 20 degrees/s) revealed that SHA stimuli reflected not only the existence of bilateral caloric weakness but also the impairment degree. The phase values of the patients with SSVs < or = 10 degrees/s were greater than that of the patients with SSVs > 10 degrees/s and the normals, and the gain values of the patients with SSVs < or = 10 degrees/s were smaller than those with SSVs > 10 degrees/s and the normals. The patients with SSVs < or = 10 degrees/s showed more severe impairments than those with SSVs > 10 degrees/s. However, even in the frequencies having higher impairment identifying rate, such as 0.01 and 0.02 Hz, about 30 percent of the patients with SSVs < or = 10 degrees/s revealed rotational responses that were within normal limits. These findings indicated that even marked bilateral caloric reduction is in sufficient to diagnose vestibular loss.

Caloric Tests↗
PubMed1994

Interleukin-5 mRNA levels in blood and bone marrow mononuclear cells from patients with the idiopathic hypereosinophilic syndrome.

High blood eosinophil counts in humans are usually due to parasitic infections, allergic processes or malignant diseases. Interleukin-5 (IL-5) is thought to be the principal eosinopoietic stimulus in most of these patients. As the causes of persistent eosinophilia in patients with the idiopathic hypereosinophilic syndrome (HES) are (by definition) unknown, a semi-quantitative assay for IL-5 mRNA in eosinophils and mononuclear cells was carried out using samples from 11 patients with HES. In three patients, unstimulated peripheral blood mononuclear cells (PBMC) and bone marrow mononuclear cells (BMMC) had markedly raised levels of IL-5 mRNA. In four of five patients studied, phorbol myristate acetate (PMA) stimulation of PBMC induced them to produce more IL-5 mRNA than four healthy subjects. In five patients, bone marrow IL-5 mRNA levels were related to blood eosinophil counts. Blood eosinophils from all six patients tested, and bone marrow granulocytes from four patients had undetectable levels of IL-5 mRNA. It was concluded that HES can be separated into two groups. One has high levels of IL-5 mRNA and/or an enhanced IL-5 mRNA response to stimulation. They may well respond to treatments which inhibit the effects of this cytokine on eosinophil progenitor cells. The second group appears to have a disease which is IL-5 independent.

Adult↗
PubMed1994

Expression of lacto-N-fucopentaose III (CD15)- and sialyl-Lewis X-bearing molecules and their functional properties in eosinophils from patients with the idiopathic hypereosinophilic syndrome.

As the carbohydrate lacto-N-fucopentaose III (CD15 antigen or X-determinant) and its sialylated derivative sialyl-Lewis X are involved in the adhesion of cells rolling along the surface of endothelial cells, experiments were done to study the presence of these molecules on human eosinophils from patients with the idiopathic hypereosinophilic syndrome. Normal-density eosinophils from some patients showed higher levels of expression for lacto-N-fucopentaose III than light-density eosinophils. In contrast, sialyl-Lewis X was highly expressed by light-density eosinophils. Activation of normal-density eosinophils with calcium ionophore A23187 resulted in increased expression of these molecules for a short time. Monoclonal antibodies to these carbohydrates stimulated eosinophils to secrete eosinophil cationic protein, but not eosinophil peroxidase, and acted as costimulatory signals for C3b-induced degranulation of eosinophil cationic protein. It was suggested that CD15 and sialyl-Lewis X might contribute to eosinophil-mediated tissue injury in patients with the idiopathic hypereosinophilic syndrome.

Adult↗