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Y Shen

Publications and source records attributed to Y Shen.

At least 19 recordsLinked to original sources
PubMed1999

The p65 subunit of NF-kappa B is redundant with p50 during B cell proliferative responses, and is required for germline CH transcription and class switching to IgG3.

B cells lacking individual NF-kappa B/Rel family members exhibit defects in activation programs. We generated small resting B cells lacking p65 or p50 alone, or lacking both p50 and p65, then evaluated the ability of these cells to proliferate, secrete Ig, and undergo Ig class switching. B cells lacking p65 proliferated well in response to all stimuli tested. However, these cells demonstrated an isolated defect in switching to IgG3, which was associated with a decrease in gamma 3 germline CH gene expression. Whereas, previously reported, B cells lacking p50 alone had a severe proliferative defect in response to LPS, a moderate defect in response to CD40 ligand (CD40L), and normal proliferation to Ag receptor cross-linking using dextran-conjugated anti-IgD Abs (alpha delta-dex), B cells lacking both p50 and p65 exhibited severely impaired proliferation in response to LPS, alpha delta-dex, and CD40L. This defect could be overcome by simultaneous administration of alpha delta-dex and CD40L. In response to this latter combination of stimuli, B cells lacking both p50 and p65 secreted Ig and underwent isotype switching to IgG1 as efficiently as B cells lacking p50 alone. These data demonstrate a role for the p65 subunit of NF-kappa B in germline CH gene expression as well as functional redundancy between p50 and p65 during proliferative responses.

Animals↗
PubMed1999

Mycobacterium bovis bacille Calmette-Guérin enhances pathogenicity of simian immunodeficiency virus infection and accelerates progression to AIDS in macaques: a role of persistent T cell activation in AIDS pathogenesis.

It has recently been proposed that Mycobacterium tuberculosis may enhance the pathogenicity of HIV infections and accelerate the course of HIV disease. This hypothesis has been tested in the present study using a simian immunodeficiency virus of macaques (SIVmac)/Mycobacterium bovis bacille Calmette-Guérin (BCG)-coinfected macaque model. Naive and chronically SIVmac-infected monkeys were evaluated. Following BCG inoculation, the SIVmac-infected monkeys exhibited the dominant responses of TCR-beta complementarity-determining region 3-restricted T cell subpopulations. This BCG-driven T cell activation correlated with a marked increase in viral loads in SIVmac-infected monkeys. Moreover, the prolonged T cell activation coincided with the enhanced decline of CD4+ PBL counts and the accelerated progression to clinical AIDS in the coinfected monkeys, suggesting that Mycobacterium-driven T cell activation may be the mechanism underlying the enhanced pathogenicity of AIDS virus infection in the coinfected individuals. Within 2 to 7 mo after BCG coinfection, all chronically SIVmac-infected monkeys died from SIV-induced AIDS including tuberculosis-like disease. Surprisingly, the naive monkeys manifested a T cell activation-related toxic shock syndrome and a profound depletion of CD4+ lymphocytes 2 wk after simultaneous SIVmac/BCG inoculation. These naive animals died 2 mo after SIVmac/BCG inoculation, with the evidence of the persistent SIV p27 antigenemia and SIVmac-induced disease. In contrast, the normal monkeys not infected with SIVmac survived BCG infection; the control SIVmac-infected animals showed a natural course of chronic SIV infection. Thus, results from this SIV/BCG coinfection model strongly support the hypothesis that active coinfection with HIV and Mycobacterium can impact remarkably on the AIDS virus-induced disease.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Capillary electrophoresis using diol-bonded fused-silica capillaries.

In this paper, 3-glycidoxypropyltrimethoxysilane was used to produce diol-bonded capillaries at room temperature for capillary electrophoresis (CE). A variety of standard reference compounds and authentic biological samples including ribonucleotides, peptides and proteins were used to test the columns. It was found that greatly suppressed electroosmotic flow was measured over a pH range of 3-10. Lower than 1.6% relative standard deviation (> 10 runs) in migration time was observed for the analysis of test proteins. For real samples of ribonucleotides in tumor cell extracts, approximately 1 million theoretical plates and excellent peak shapes were obtained. The high column efficiency and symmetrical peaks allowed the separation of samples with only 0.6% maximum difference in migration times. The diol-bonded fused-silica capillary columns were stable when used in a pH range of 2-8 under typical CE conditions. The column preparation method involved a simple dynamic coating procedure at room temperature, greatly simplifying the more typical static coating methods that require vacuum pumps and ovens.

Amino Acid Sequence↗
PubMed1999

Zinc modulation of AMPA receptors may be relevant to splice variants in carp retina.

With the use of the whole-cell patch clamp technique, we examined effects of zinc on AMPA receptors of isolated carp retinal horizontal cells, predominantly consisting of flop splice variants. We found that zinc ranging from 30 microM to 1 mM failed to modulate glutamate-induced currents of these cells, which is clearly distinct from the results previously obtained in superior colliculus neurons and Xenopus ooctyes. Furthermore, glutamate responses remained unchanged when zinc was co-applied with PEPA, a flop variant-preferential AMPA receptor potentiator. With the co-application of cyclothiazide, a flip variant-preferential AMPA receptor potentiator, however, a dual effect could be observed: zinc potentiated glutamate responses at low concentrations, but inhibited them at higher concentrations. These results suggest that the action of zinc on AMPA receptors may be splice variant-relevant.

Animals↗
PubMed1999

Prior exposure to neurotrophins blocks inhibition of axonal regeneration by MAG and myelin via a cAMP-dependent mechanism.

MAG is a potent inhibitor of axonal regeneration. Here, inhibition by MAG, and myelin in general, is blocked if neurons are exposed to neurotrophins before encountering the inhibitor; priming cerebellar neurons with BDNF or GDNF, but not NGF, or priming DRG neurons with any of these neurotrophins blocks inhibition by MAG/myelin. Dibutyryl cAMP also overcomes inhibition by MAG/myelin, and cAMP is elevated by neurotrophins. A PKA inhibitor present during priming abrogates the block of inhibition. Finally, if neurons are exposed to MAG/myelin and neurotrophins simultaneously, but with the Gi protein inhibitor, inhibition is blocked. We suggest that priming neurons with particular neurotrophins elevates cAMP and activates PKA, which blocks subsequent inhibition of regeneration and that priming is required because MAG/myelin activates a Gi protein, which blocks increases in cAMP. This is important for encouraging axons to regrow in vivo.

Animals↗
PubMed1999

Parathyroid hormone stimulates cancellous bone formation at skeletal sites regardless of marrow composition in ovariectomized rats.

The purpose of the current report is to compare the skeletal effects of PTH treatment at red (hematopoietic) and yellow (fatty) marrow sites in ovariectomized (ovx) rats. In the first study, mature, slowly growing ovx rats that were 4 months of age and 4 weeks postovariectomy were treated with human parathyroid hormone [hPTH(1-34)] (80 microg/kg, 5 days/week) for 6 weeks. In the second study, aged ovx rats that were 15 months of age and 1 year postovariectomy were treated with PTH according to the same regimen for 10 weeks. The proximal tibial metaphysis (PTM) and first lumbar vertebra (LV), bone sites with red marrow, as well as the distal tibial metaphysis (DTM) and fifth caudal vertebra (CV), bone sites with yellow marrow, were processed undecalcified for quantitative bone histomorphometry. At the end of the first study in mature ovx rats, estrogen depletion induced a 73% loss of cancellous bone in the PTM and a 15% loss in the LV. In contrast, not even a trend for cancellous bone loss was observed in the DTM and CV of vehicle-treated ovx rats. PTH treatment of ovx rats increased cancellous bone volume by 191% in the PTM, 56% in the DTM, 47% in the LV, and 22% in the CV, compared with vehicle treatment of ovx rats. In addition, the hormone markedly increased cancellous bone formation by 177% in the PTM, 679% in the DTM, 309% in the LV, and 833% in the CV. Aged ovx rats (second study) exhibited moderate cancellous osteopenia in the LV but not the CV. PTH treatment increased cancellous bone volume by 67% and 37% and bone formation rate by 635% and 359% in the LV and CV, respectively, compared with vehicle treatment of ovx rats. Although the magnitude of the anabolic response to PTH may vary somewhat within the skeleton, the results indicate that PTH augments cancellous bone mass and markedly stimulates bone formation at skeletal sites, regardless of marrow composition.

Animals↗
PubMed1999

Bone and hormonal changes induced by skeletal unloading in the mature male rat.

To determine whether the rat hindlimb elevation model can be used to study the effects of spaceflight and loss of gravitational loading on bone in the adult animal, and to examine the effects of age on bone responsiveness to mechanical loading, we studied 6-mo-old rats subjected to hindlimb elevation for up to 5 wk. Loss of weight bearing in the adult induced a mild hypercalcemia, diminished serum 1,25-dihydroxyvitamin D, decreased vertebral bone mass, and blunted the otherwise normal increase in femoral mass associated with bone maturation. Unloading decreased osteoblast numbers and reduced periosteal and cancellous bone formation but had no effect on bone resorption. Mineralizing surface, mineral apposition rate, and bone formation rate decreased during unloading. Our results demonstrate the utility of the adult rat hindlimb elevation model as a means of simulating the loss of gravitational loading on the skeleton, and they show that the effects of nonweight bearing are prolonged and have a greater relative effect on bone formation in the adult than in the young growing animal.

Aging↗
PubMed1998

Immune-activation gene expression in clinically stable renal allograft biopsies: molecular evidence for subclinical rejection.

BACKGROUND: A significant percentage of biopsies from stable, well-functioning renal allografts have histologic findings consistent with acute rejection or borderline rejection. The implication of this finding is not yet fully understood. We analyzed immune-activation gene transcripts in stable protocol biopsies to determine the extent of immunologic activity of graft-infiltrating cells in this setting. Histologic classification of the biopsies was based on the Banff criteria. To emphasize that the tissue samples were procured from grafts with no clinical evidence of impaired function, we interjected the term "subclinical" into the Banff terminology. This produced three histologic categories: normal, borderline subclinical rejection, and acute subclinical rejection. METHODS: We used competitive template polymerase chain reaction techniques to quantify transcript amounts for the constant region of the T-cell receptor beta chain; the cytokines, tumor necrosis factor alpha, interleukin (IL)-1beta, transforming growth factor beta, interferon gamma, IL-2, IL-4, IL-10, and IL-15; and the cytotoxic T lymphocyte effector molecules, granzyme B, perforin, and Fas ligand. RESULTS: We found that histologically normal biopsies were typically devoid of gene transcripts or had very low amounts. Conversely, biopsies with acute subclinical rejection by histologic examination had heightened amounts of transcripts for many of the genes assayed. Borderline subclinical rejection samples showed an intermediate amount of expression. CONCLUSIONS: These results demonstrate that histologic features of rejection are often accompanied by enhanced expression of pro-inflammatory gene transcripts, despite the absence of clinically overt graft dysfunction. As this state of subclinical rejection could prove detrimental to long-term graft function, a role for surveillance biopsies of stable grafts with intent to treat subclinical rejection should be considered.

Biopsy↗
PubMed1998

Transcriptional regulation of the tissue-type plasminogen-activator gene in human endothelial cells: identification of nuclear factors that recognise functional elements in the tissue-type plasminogen-activator gene promoter.

The gene encoding human tissue-type plasminogen activator (t-PA) is regulated in a cell-type-specific manner. Previous studies in non-endothelial cells have indicated that basal and phorbol ester mediated induction is controlled by a cAMP response element (CRE) referred to as the tPACRE, and an activating protein 2 (AP-2)-like site. The classification of the AP-2-like site was assigned on the basis of its sequence homology, but has been shown in some cell systems to be recognised by promoter-specific transcription factor-1 (Sp-1). Here, we have investigated the transcriptional regulation of the t-PA gene in endothelial cells and addressed the functional roles of the tPACRE and the Sp-1/AP-2-like sites. 5'-RACE experiments indicate that the t-PA gene uses two transcription initiation sites in these cells with the downstream site being preferred. Functional analyses of the t-PA promoter using reporter-gene constructs transfected into C11STH endothelial cells demonstrate that the first 410 bp of the t-PA promoter confers an increase in reporter-gene activity on treatment with 4beta-phorbol 12-myristate 13-acetate (PMA). Mutagenesis of either the tPACRE or the Sp-1/AP-2 site weakens both basal and inducible expression, while disruption of both sites renders the promoter completely unresponsive. Using supershift assays, we identify the predominant tPACRE-binding proteins in nuclear extracts prepared from both C11STH cells and primary umbilical vein endothelial cells (HUVECs) as activating transcription factor 2, CREB (cAMP-responsive-element-binding protein), CREM (cAMP response element modulator) and c-jun. Treatment of cells with PMA results in a selective recruitment of jun-D to the tPACRE, while Sp-1 was identified as the major transcription factor that recognises the AP-2-like site. Based on this data and previous reports, we have reassigned this as a Sp-1-binding site. Finally, the identification of specific endothelial-derived t-PACRE-binding proteins suggests an integral role for these factors in the regulation of t-PA gene expression in human endothelial cells.

Base Sequence↗
PubMed1998

Interaction of sickle erythrocytes with endothelial cells in the presence of endothelial cell conditioned medium induces oxidant stress leading to transendothelial migration of monocytes.

The abnormal adherence of sickle red blood cells (SS RBC) to endothelial cells has been thought to contribute to vascular occlusion, a major cause of morbidity in sickle cell disease (SCD). We determined whether the interaction of SS RBC with cultured endothelial cells induced cellular oxidant stress that would culminate in expression of cell adhesion molecules (CAMs) involved in the adhesion and diapedesis of monocytes and the adherence of SS reticulocytes. We showed that the interaction of SS RBC at 2% concentration in the presence of multimers of von Willebrand factor (vWf), derived from endothelial cell-derived conditioned medium (E-CM) with cultured human umbilical vein endothelial cells (HUVEC), resulted in a fivefold increased formation of thiobarbituric acid-reactive substances (TBARS) and activation of the transcription factor NF-kB, both indicators of cellular oxidant stress. Normal RBC show none of these phenomena. The oxidant stress-induced signaling resulted in an increased surface expression of a subset of CAMs, ICAM-1, E-selectin, and VCAM-1 in HUVEC. The addition of oxygen radical scavenger enzymes (catalase, superoxide dismutase) and antioxidant (probucol) inhibited these events. Additionally, preincubation of HUVEC with a synthetic peptide Arg-Gly-Asp (RGD) that prevents vWf-mediated adhesion of SS RBC reduced the surface expression of VCAM-1 and NF-kB activation. Furthermore, SS RBC-induced oxidant stress resulted in a twofold increase in the transendothelial migration of both monocyte-like HL-60 cells and human peripheral blood monocytes, and approximately a sixfold increase in platelet-endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation, each of which was blocked by protein kinase C inhibitor and antioxidants. These results suggest that the adherence/contact of SS RBC to endothelial cells in large vessel can generate enhanced oxidant stress leading to increased adhesion and diapedesis of monocytes, as well as heightened adherence of SS reticulocytes, indicating that injury/activation of endothelium can contribute to vaso-occlusion in SCD.

Anemia, Sickle Cell↗
PubMed1998

Identification of genes expressed in human CD34(+) hematopoietic stem/progenitor cells by expressed sequence tags and efficient full-length cDNA cloning.

Hematopoietic stem/progenitor cells (HSPCs) possess the potentials of self-renewal, proliferation, and differentiation toward different lineages of blood cells. These cells not only play a primordial role in hematopoietic development but also have important clinical application. Characterization of the gene expression profile in CD34(+) HSPCs may lead to a better understanding of the regulation of normal and pathological hematopoiesis. In the present work, genes expressed in human umbilical cord blood CD34(+) cells were catalogued by partially sequencing a large amount of cDNA clones [or expressed sequence tags (ESTs)] and analyzing these sequences with the tools of bioinformatics. Among 9,866 ESTs thus obtained, 4,697 (47.6%) showed identity to known genes in the GenBank database, 2, 603 (26.4%) matched to the ESTs previously deposited in a public domain database, 1,415 (14.3%) were previously undescribed ESTs, and the remaining 1,151 (11.7%) were mitochondrial DNA, ribosomal RNA, or repetitive (Alu or L1) sequences. Integration of ESTs of known genes generated a profile including 855 genes that could be divided into different categories according to their functions. Some (8.2%) of the genes in this profile were considered related to early hematopoiesis. The possible function of ESTs corresponding to so far unknown genes were approached by means of homology and functional motif searches. Moreover, attempts were made to generate libraries enriched for full-length cDNAs, to better explore the genes in HSPCs. Nearly 60% of the cDNA clones of mRNA under 2 kb in our libraries had 5' ends upstream of the first ATG codon of the ORF. With this satisfactory result, we have developed an efficient working system that allowed fast sequencing of 32 full-length cDNAs, 16 of them being mapped to the chromosomes with radiation hybrid panels. This work may lay a basis for the further research on the molecular network of hematopoietic regulation.

ATPases Associated with Diverse Cellular Activitie↗
PubMed1998

Induced expression of neuronal membrane attack complex and cell death by Alzheimer's beta-amyloid peptide.

beta-amyloid peptide (A beta) and complement-derived membrane attack complex (MAC) are co-localized in senile plaques of brains from Alzheimer's disease (AD) patients. But the relationship between A beta and complement activation is unclear. We have used human neurotypic cells, differentiated SH-SY5Y, as a model system to examine regulation of neuronal MAC expression and cell death by A beta. We demonstrated that mRNAs (C1q, C2, C3, C4, C5, C6, C7, C8 and C9) and proteins (C1q, C3 and C9) for the major components of the classical complement cascade are present in the SH-SY5Y neurotypic cells, indicating that neuronal cells can synthesize the necessary proteins required for MAC formation. Furthermore, immunocytochemical studies showed the A beta-induced neuronal MAC expression on the SH-SY5Y cells after CD59 was removed by PIPLC or blocked by anti-CD59 antibody. Meanwhile, increased A beta-induced neuronal cell death was observed following treatment with anti-CD59. Taken together, these results suggest that A beta activates neuronal complement cascade to induce MAC, and a deficiency of endogenous complement regulatory proteins, e.g., CD59, may increase the vulnerability of neurons to complement-mediated cytotoxicity.

Alzheimer Disease↗
PubMed1998

Cloning of human PEX cDNA. Expression, subcellular localization, and endopeptidase activity.

Mutations in the PEX gene are responsible for X-linked hypophosphatemic rickets. To gain insight into the role of PEX in normal physiology we have cloned the human full-length cDNA and studied its tissue expression, subcellular localization, and peptidase activity. We show that the cDNA encodes a 749-amino acid protein structurally related to a family of neutral endopeptidases that include neprilysin as prototype. By Northern blot analysis, the size of the full-length PEX transcript is 6.5 kilobases. PEX expression, as determined by semi-quantitative polymerase chain reaction, is high in bone and in tumor tissue associated with the paraneoplastic syndrome of renal phosphate wasting. PEX is glycosylated in the presence of canine microsomal membranes and partitions exclusively in the detergent phase from Triton X-114 extractions of transiently transfected COS cells. Immunofluorescence studies in A293 cells expressing PEX tagged with a c-myc epitope show a predominant cell-surface location for the protein with its COOH-terminal domain in the extracellular compartment, substantiating the assumption that PEX, like other members of the neutral endopeptidase family, is a type II integral membrane glycoprotein. Cell membranes from cultured COS cells transiently expressing PEX efficiently degrade exogenously added parathyroid hormone-derived peptides, demonstrating for the first time that recombinant PEX can function as an endopeptidase. PEX peptidase activity may provide a convenient target for pharmacological intervention in states of altered phosphate homeostasis and in metabolic bone diseases.

Adult↗
PubMed1998

Mantle discontinuity structure beneath the southern east pacific rise from P-to-S converted phases

Receiver functions derived from teleseismic body waves recorded by ocean-bottom seismometers on the southern East Pacific Rise reveal shear waves converted from compressional waves at the mantle discontinuities near 410- and 660-kilometer depth. The thickness of the mantle transition zone between the two discontinuities is normal relative to the global average and indicates that upwelling beneath the southern East Pacific Rise is not associated with an excess temperature in the mantle transition zone.

Journal Article↗
PubMed1998

Phase velocities of rayleigh waves in the MELT experiment on the east pacific rise

The phase velocities of Rayleigh waves increase more rapidly with distance from the East Pacific Rise (EPR) axis than is predicted by models of conductive cooling of the lithosphere. Low velocities near the axis are probably caused by partial melt at depths of 20 to 70 kilometers in a zone several hundred kilometers wide. The lowest velocities are offset to the west of the EPR. Wave propagation is anisotropic; the fast direction is approximately perpendicular to the ridge, parallel to the spreading direction. Anisotropy increases from a minimum near the axis to 3 percent or more on the flanks.

Journal Article↗
PubMed1998

Parametric likelihoods for multiple non-fatal competing risks and death.

Clinical trials of fatal diseases often focus on one or more non-fatal events, in addition to survival, both to characterize morbidity and to improve survival estimates. Three statistical complications are that the time to each non-fatal event and subsequent residual survival may be either positively or negatively associated, the times to death with or without an antecedent event often have very different distributions, and death may censor some of the non-fatal event times. Consequently, the overall survival time distribution is a mixture of the distributions corresponding to the possible antecedent non-fatal events. These conditions violate the usual assumptions underlying many statistical methods for analysing multivariate time-to-event data. In this paper, we consider a general parametric model for multiple non-fatal competing risks and death. The model accounts for positive or negative association between the time of each non-fatal event and subsequent survival while accommodating covariates and the usual administrative censoring. Each event time distribution is specified marginally by a three-parameter generalized odds rate model, and the time of each non-fatal event and subsequent residual survival are combined under a bivariate generalized von Morgenstern distribution. The approach is illustrated by application to two data sets from clinical trials in colon cancer and acute leukaemia.

Carcinoma↗
PubMed1998

In vivo effects of a bacterial superantigen on macaque TCR repertoires.

A macaque model was employed to explore staphylococcal enterotoxin B (SEB) superantigen-driven T lymphocyte responses. The SEB-reactive Vbeta+ cell subpopulations demonstrated a striking tri-phase response in rhesus monkeys following an SEB challenge in vivo. The hyperacute down-regulation, seen as early as 2 h through 2 days after SEB injection, was characterized by a disappearance of the reactive Vbeta-restricted PBL subpopulations from the circulation and decreased expression of these cell subpopulations in lymphoid tissues. Following this, a dominant expansion of reactive Vbeta-expressing CD4+ cell subpopulations occurred in lymph nodes and spleens, whereas in the peripheral blood a preferential expansion of reactive Vbeta-expressing CD8+ cell subpopulations was seen. An exhaustion of this response was then seen, with a prolonged decrease in the number of the reactive Vbeta+ CD4+ lymphocyte subpopulations. Interestingly, monoclonal or oligoclonal dominance was seen in the reactive Vbeta+ cell subpopulations in the period of the transition from the polyclonal cellular expansion to the exhaustion of the response, suggesting that some Vbeta+ cell clones may be more resistant than others to superantigen-mediated depletion. These results indicate that in vivo SEB superantigen-mediated effect on lymphocyte subpopulations in macaques is complex, suggesting that profound dynamics in the TCR repertoires may in part account for the susceptibility of higher primates to SEB-induced diseases.

Animals↗