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C Chen

Publications and source records attributed to C Chen.

At least 667 records · Page 37Linked to original sources
PubMed1997

Lipopolysaccharide rapidly activates K+ channels at the intracellular membrane face of rat cerebral artery smooth muscle cells.

Lipopolysaccharide (LPS) may accumulate inside mammalian cells through endocytotic uptake or during the replication in invasive bacterial strains. However, the effects of intracellular LPS on cell function remain unknown. This study therefore examined the action of intracellularly applied E. coli LPS on large-conductance, Ca2+-dependent K+ channels (BK channels) in the membrane of rat cerebrovascular smooth muscle cells (CVSMCs). LPS (10-100 microg/ml) rapidly increased the open probability of BK channels when applied to the cytoplasmic face of CVSMC membrane patches. This response was reversible, dose-dependent and reflected an enhanced rate of channel opening in the presence of LPS. These results show for the first time that LPS can alter the gating behavior of ionic channels when applied to the cytoplasmic face of a eukaryotic cell membrane.

Animals↗
PubMed1997

Virtually identical enhancers containing a segment of homology to murine 3'IgH-E(hs1,2) lie downstream of human Ig C alpha 1 and C alpha 2 genes.

We have isolated sequences downstream of human Ig C alpha 1 and C alpha 2 genes and have identified two enhancers in these regions. One enhancer is located approximately 9 kb downstream of C alpha 1, and the second enhancer is located approximately 11 kb downstream of C alpha 2. These approximately 1.6-kb enhancers are virtually identical to each other except for varying numbers of a approximately 53-bp motif. The C alpha 2-associated enhancer contains four copies of this motif in tandem, whereas the C alpha 1-associated enhancer has only a single copy. Within the human enhancers is a 177-bp segment that is homologous to a 191-bp segment of one of four enhancers from the 3' regulatory region of murine (and rat) DNA, namely 3'IgH-E(hs1,2). Like the murine and rat enhancers, both human enhancers are flanked by inverted repeats; furthermore, the human enhancers generally appear to be inverted with respect to each other. The evolutionarily conserved region of homology has substantial core enhancer activity. Contained within this region are the single octamer and one copy of the approximately 53-bp motif, both of which contribute to the activity of the full-length enhancer. A comparison of the DNA sequences and the results of transient transfection assays imply that the human C alpha-associated enhancers may be regulated (in part) differently than the murine enhancer 3'IgH-E(hs1,2).

Animals↗
PubMed1997

Effects of phospholipase A2 on lumbar nerve root structure and function.

STUDY DESIGN: To investigate the effects of phospholipase A2 on the neurophysiology and histology of rat lumbar spinal nerves and the corresponding behavioral changes. OBJECTIVES: To study possible mechanisms of sciatica. SUMMARY OF BACKGROUND DATA: The pathophysiology of sciatica is uncertain, although mechanical, chemical, and ischemic factors have been proposed. METHODS: Phospholipase A2 was injected into the rat L4-L5 epidural space, and the rats were observed for 3 or 21 days. Behavioral studies were conducted daily during the survival period. On the 3rd or 21st day, extracellular nerve recordings were made from dorsal roots, to determine discharge properties and mechanical sensitivity. The nerve roots were then sectioned for a light-microscopic examination. RESULTS: Motor weakness of hind limbs and altered sensation were observed. In the 3-day phospholipase A2 groups, squeezing the dorsal roots at the L4-L5 disc level (force = 0.8 g) evoked sustained ectopic discharge that lasted approximately 8 minutes. Squeezing the roots distal to the L4-L5 area did not result in sustained discharges. In sham, control, and 21-day phospholipase A2 groups, squeezing the dorsal roots elicited only a transient firing that lasted approximately 0.1 second. Loss of myelin was seen in the nerve root cross sections in the 3-day group, and remyelination was observed in the 21-day group. No abnormality was found in the control groups. CONCLUSIONS: Based on these studies, it is hypothesized that phospholipase A2 causes demyelination that results in hypersensitive regions where ectopic discharge may be elicited by mechanical stimulation. These ectopic discharges may be a source of sciatica. We believe that, as long as these irritating factors are present, the hypersensitive nerve root nerve will continue to fire, and sciatic pain will persist.

Animals↗
PubMed1997

Expression of transforming growth factor beta (TGFbeta) type III receptor restores autocrine TGFbeta1 activity in human breast cancer MCF-7 cells.

While transforming growth factor beta (TGFbeta) type III receptor (RIII) is known to increase TGFbeta1 binding to its type II receptor (RII), the significance of this phenomenon is not known. We used human breast cancer MCF-7 cells to study the role of RIII in regulating autocrine TGFbeta1 activity because they express very little RIII and no detectable autocrine TGFbeta activity. A tetracycline-repressible RIII expression vector was stably transfected into this cell line. Expression of RIII increased TGFbeta1 binding to TGFbeta type I receptor (RI) as well as RII. Treatment with tetracycline suppressed RIII expression and abolished TGFbeta1 binding to RI and RII. Growth of RIII-transfected cells was reduced by 40% when plated at low density on plastic. This reduction was reversed by tetracycline treatment and was partially reversed by treatment with a TGFbeta1 neutralizing antibody. The activity of a TGFbeta-responsive promoter construct when transiently transfected was more than 3-fold higher in the RIII-transfected cells than in the control cells. Treating the cells with tetracycline or the TGFbeta1 neutralizing antibody also significantly attenuated the increased promoter activity. These results suggest that expression of RIII restored autocrine TGFbeta1 activity in MCF-7 cells. The RIII-transfected cells were also much less clonogenic in soft agarose than the control cells indicating a reversion of progression. Thus, RIII may be essential for an optimal level of the autocrine TGFbeta activity in some cells, especially in the transformed cells with reduced RII expression.

Breast Neoplasms↗
PubMed1997

BAC and PAC contigs covering 3.5 Mb of the Down syndrome congenital heart disease region between D21S55 and MX1 on chromosome 21.

Chromosome 21 is a model for the study of human chromosomal aneuploidy, and the construction of its physical and transcriptional maps is a necessary step in understanding the molecular basis of aneuploidy-dependent phenotypes. To identify the gene(s) responsible for Down syndrome congenital heart disease (DS-CHD), we constructed a physical map of the D21S55 to MX1 region. A bacterial artificial chromosome (BAC) library was screened using several YACs spanning the interval, and a P1-derived artificial chromosome (PAC) library was screened using radiolabeled STS PCR products and whole BACs in gap-filling initiatives. FISH confirmed the location of all BAC and PAC clones to 21q22.2-q22.3. Overlaps were established using clone-to-clone Southerns and 24 new STSs, generated from the direct sequencing of BAC and PAC ends, along with 35 preexisting STSs. Approximately 3.5 Mb of the 4- to 5-Mb D21S55 to MX1 interval is covered in 85 BACs and 24 PACs, representing fourfold coverage within the contigs. These BAC and PAC contigs are valuable reagents for isolating the genes for DS-CHD.

Base Sequence↗
PubMed1997

Characterization of a novel mammalian RGS protein that binds to Galpha proteins and inhibits pheromone signaling in yeast.

Genetic studies of molecules that negatively regulate G-coupled receptor functions have led to the identification of a large gene family with an evolutionarily conserved domain, termed the RGS domain. It is now understood that RGS proteins serve as GTPase-activating proteins for subfamilies of the heterotrimeric G-proteins. We have isolated from mouse pituitary a full-length cDNA clone encoding a novel member of the RGS protein family, termed RGS16, as well as the full-length cDNA of mRGS5 and mRGS2. Tissue distribution analysis shows that the novel RGS16 is predominantly expressed in liver and pituitary, and that RGS5 is preferentially expressed in heart and skeletal muscle. In contrast, RGS2 is widely expressed. Genetic analysis using the pheromone response halo assay and FUS1 gene induction assay show that overexpression of the RGS16 gene dramatically inhibits yeast response to alpha-factor, whereas neither RGS2 nor RGS5 has any discernible effect on pheromone sensitivity, pointing to a possible functional diversity among RGS proteins. In vitro binding assays reveal that RGS5 and RGS16 bind to Galphai and Galphao subunits of heterotrimeric G-proteins, but not to Galphas. Based on mutational analysis of the conserved residues in the RGS domain, we suggest that the G-protein binding and GTPase-activating protein activity may involve distinct functional structures of the RGS proteins, indicating that RGS proteins may exert a dual function in the attenuation of signaling via G-coupled receptors.

Amino Acid Sequence↗
PubMed1997

The role of receptor dimerization domain residues in growth hormone signaling.

While there is a considerable amount of evidence that signal transduction by the growth hormone (GH) receptor requires receptor homodimerization, there has been no systematic study of the role of receptor dimerization domain residues in this process. In conjunction with the distances derived from the crystal structure of the hGH-hGH receptor (extracellular domain) complex, we have used a luciferase-based c-fos promoter reporter assay in transiently transfected Chinese hamster ovary (CHO) cells, and stable receptor expressing CHO cell populations to define the dimerization domain residues needed for effective signaling. In addition to alanine substitution, we have used both aspartate and lysine substitutions to allow us to provide evidence for proximity relations through charge complementation. Introduced cysteine substitutions were also used, but unlike the erythropoietin receptor, these were unable to generate constitutively active receptor. We conclude that serine 145, histidine 150, aspartate 152, tyrosine 200, and serine 201, but not leucine 146 or threonine 147 are required for effective signal transduction through the dimerization domain. This information may be valuable in designing small molecule antagonists of GH and other cytokines that block dimerization by binding to the dimerization domain.

Animals↗
PubMed1997

Induction of T cell adhesion to extracellular matrix or endothelial cell ligands by soluble or matrix-bound interleukin-7.

The putative effects of interleukin (IL)-7, operating in the context of extracellular matrix (ECM), on the adhesion of human T cells were examined. Recombinant human, IL-7 was found to bind ECM or fibronectin (FN) with IC50 values of 10-100 nM. Nanogram amounts of both soluble and, especially, FN- or ECM-bound IL-7, which differentially affected the morphologies of FN-adherent T cells, induced the adhesion of resting CD4+ and CD8+ T cells in dose-dependent and beta 1 integrin-dependent manners. Under static and flow conditions, soluble IL-7 also induced the binding of unstimulated T cells to vascular cell adhesion molecule-1, suggesting that this cytokine can also modulate integrin binding to endothelial cell ligands. The effects of affinity modulation by IL-7 of FN-specific beta 1 integrins depend on the presence of soluble FN, which inhibited T cell adhesion to FN induced by FN-bound IL-7 or by an integrin-specific affinity-modulating monoclonal antibody, but not by soluble IL-7 or phorbol 12-myristate 13-acetate. These findings provide an example of a major ECM integrin ligand, FN, which is capable of modulating its adhesive interactions with specific immune cells by associating with and presenting a cytokine in a bio-active state.

Cell Adhesion↗
PubMed1997

Negligible systemic absorption of topical isotretinoin cream: implications for teratogenicity.

The objective of the study was to assess the extent of systemic exposure of retinoic acid metabolites after excessive application of 0.1% isotretinoin cream in patients with photodamaged skin. This was a single-center, open-label, noncomparative, multiple-dose study of isotretinoin cream. Eighteen female patients with photodamaged skin received a 10 g topical application of isotretinoin cream once daily to a surface area of approximately 2,300 cm2 for 42 days. The patients were not allowed to have high vitamin A-containing foods, vitamin A supplements, or concomitant medications during the entire study period. Plasma levels of four retinoic acids (isotretinoin, tretinoin, 4-oxo-isotretinoin, and 4-oxo-tretinoin) were evaluated after 42 days of isotretinoin application and compared with baseline (pretreatment) levels. The mean area under the curve (AUC) in plasma increased by 48% (+/-SE 9.2) and 77% (+/-13) from the 24-hour pretreatment baseline level for isotretinoin and 4-oxo-isotretinoin, respectively, after treatment with excessive amounts of isotretinoin cream, suggesting systemic absorption of isotretinoin cream. This increase in systemic exposure of retinoic acids was less than that reported earlier after the U.S. recommended daily allowance of 5,000 i.u. of vitamin A supplementation (isotretinoin 141 +/- 19% and 4-oxo-isotretinoin 171 +/- 27%). The minimal systemic availability of isotretinoin cream compared with the U.S. recommended daily allowance for vitamin A supplements provides reasonable evidence for lack of its potential teratogenic risk.

Administration, Cutaneous↗
PubMed1997

Boundary layer infusion of nitric oxide reduces early smooth muscle cell proliferation in the endarterectomized canine artery.

To evaluate the direct effect of nitric oxide (NO) on vascular smooth muscle cell (SMC) proliferation in vivo, we used an expanded polytetrafluoroethylene (ePTFE)-based local infusion device to deliver an NO donor, proline/NO (PROLI/NO), to the luminal boundary layer of endarterectomized artery and the distal anastomosis of the graft in a canine model. Once delivered to the blood, PROLI/NO releases NO by a mechanism involving pH-dependent decomposition. Six dogs underwent bilateral femoral artery endarterectomies. ePTFE infusion devices, blindly primed with PROLI/NO to one artery or proline to the contralateral vessel, were anastomosed proximal to the injured segments so that each animal served as its own control. PROLI/NO or proline was continuously delivered for 7 days from an osmotic reservoir, through the wall of the graft infusion device. Euthanasia was carried out at 7 days, and the processed specimens were blindly analyzed for SMC proliferation at both graft anastomoses and endarterectomized segments by a bromodeoxyuridine index assay. All dogs survived with no clinical side effects. In comparing the treated and control vessels, NO released from PROLI/NO significantly reduced SMC proliferation by 43% (13.24 +/- 1.24% versus 23.24 +/- 1.01%, P = 0.004) at the distal anastomoses and by 68% (10.58 +/- 1.63% versus 25.17 +/- 3.39%, P = 0.007) at endarterectomized segments. However, there was no significant difference in blood flow measurements between treated and control arteries (56.25 +/- 6.50 ml/min versus 46.50 +/- 3.20 ml/min, P = 0.094). These data demonstrate that local boundary layer infusion of NO released from PROLI/NO significantly reduces SMC proliferation in injured arteries with no effect on regional blood flow. This study suggests a new strategy to inhibit early SMC proliferation in injured arteries and probably to control intimal hyperplastic lesion formation in the manipulated vessels.

Anastomosis, Surgical↗
PubMed1997

Time-course study of intimal hyperplasia in the endarterectomized canine artery.

In an effort to characterize intimal hyperplastic lesions, we have undertaken a time-course study in a canine endarterectomy model of intimal hyperplasia. Twenty dogs underwent surgical endarterectomies of the carotid arteries. A total of 23 of 27 (85%) injured arteries were patent, which consisted of 6, 8, 5, and 4 arteries found to be patent at 1, 2, 5, and 11 weeks, respectively. Measurable intimal thickening developed at 1 week (0.08 +/- 0.01 mm) and at 2 weeks (0.13 +/- 0.02 mm), maximized at 5 weeks (0.29 +/- 0.03 mm), and subsided at 11 weeks (0.21 +/- 0.01 mm) after injury. Endothelial cells covering intimal hyperplastic tissues were seen only at 11 weeks. The intimal cell proliferation rate reached a maximum of 24% at 1 week, decreased dramatically at 2 weeks, and remained at low levels but higher than baseline levels at 5 and 11 weeks. Extracellular matrix (ECM) content accounted for 29% of total intimal volume at 1 week after endarterectomy and increased to 37, 40, and 47% at 2, 5, and 11 weeks, respectively. These data demonstrate that maximum intimal cell proliferation occurs at 1 week and maximum intimal hyperplasia at 5 weeks after arterial injury. Intimal ECM content increased with time after injury throughout the duration of this study. The uniform and consistent intimal lesion that was established in this large animal model is clinically relevant and can be used to study cellular and molecular mechanisms of restenosis and to evaluate therapeutic interventions.

Animals↗
PubMed1997

Boundary layer infusion of basic fibroblast growth factor accelerates intimal hyperplasia in endarterectomized canine artery.

We examined the effects of human recombinant basic fibroblast growth factor (bFGF) on the proliferation and migration of cultured dog smooth muscle cells (SMCs) and endothelial cells (ECs) and the effect of continuous local boundary layer infusion of bFGF on intimal hyperplasia in endarterectomized dog artery. In vitro proliferation and migration of dog SMCs or ECs were performed using direct counting and Boyden's chamber, respectively. At a dose of 10 ng/mL, bFGF significantly promoted both SMC and EC proliferation (7- and 4-fold, respectively) and migration (2.3- and 1.9-fold, respectively). Six dogs underwent bilateral carotid endarterectomies. A newly designed local infusion device with an osmotic pump continuously delivered bFGF to one artery or vehicle solution to the contralateral artery for 14 days. The intimal thickness and area in the bFGF-treated vessels were increased by 72 and 81%, respectively, compared with control arteries (P < 0.05). As assessed by the bromodeoxyuridine index, the proliferative activity was increased by 73% in bFGF-treated arteries (P = 0.03). Furthermore, cell proliferation at the distal anastomoses of local infusion device was significantly increased in the bFGF-infused grafts compared with distal anastomoses in the control grafts (13.24 +/- 1.24% versus 5.24 +/- 1.01%, P < 0.01). These data demonstrate that human recombinant bFGF has a potent effect on dog SMC and EC proliferation and migration, and that local infusion of exogenous bFGF significantly enhances the intimal hyperplasia formation and cell proliferation to vascular injury. We conclude that the bFGF pathway may contribute to the development of intimal hyperplastic lesions.

Anastomosis, Surgical↗
PubMed1997

Interstitial fluid flow in tendons or ligaments: a porous medium finite element simulation.

The purpose of this study is to describe interstitial fluid flow in axisymmetric soft connective tissue (ligaments or tendons) when they are loaded in tension. Soft hydrated tissue was modelled as a porous medium (using Darcy's Law), and the finite element method was used to solve the resulting equations governing fluid flow. A commercially available computer program (FiDAP) was used to create an axisymmetric model of a biomechanically tested rat ligament. The unknown variables at element nodes were pressure and velocity of the interstitial fluid (Newtonian and incompressible). The effect of variations in fluid viscosity and permeability of the solid matrix was parametrically explored. A transient loading state mimicking a rat ligament mechanical experiment was used in all simulations. The magnitude and distribution of pressure, stream lines, shear (stress) rate, vorticity and velocity showed regular patterns consistent with extension flow. Parametric changes of permeability and viscosity strongly affected fluid flow behaviour. When the radial permeability was 1000 times less than the axial permeability, shear rate and vorticity increased (approximately 5-fold). These effects (especially shear stress and pressure) suggested a strong interaction with the solid matrix. Computed levels of fluid flow suggested a possible load transduction mechanism for cells in the tissue.

Animals↗
PubMed1997

Effect of selenium supplementation on mice infected with LP-BM5 MuLV, a murine AIDS model.

LP-BM5 Murine leukemia virus (MuLV) infection of C57BL/6 mice develop a disease that has many features in common with human acquired immunodeficiency syndrome (AIDS), in particular abnormal lymphoproliferation and severe immunodeficiency. Thus, this MAIDS model may be useful for evaluation of potent antirival agents in vivo. Deficiency in antioxidant micronutrients such as selenium, zinc, and glutathione have been observed in AIDs and AIDS-related complex (ARC) patients. In the present study, the MAIDS model was used to evaluate immunological and oxidative effect of Se as sodium selenite. Results indicated that Se treatment 0.1 mg/kg/d (p.o.) inhibited splenomegaly and sera IgG elevation effectively. In addition to abnormal immunity, oxidative imbalance possibly existed in MAIDS model, as lipid peroxide increased significantly in spleen and whole blood glutathione peroxidase (GSH-Px) activity decreased markedly. Se supplementation had good protective effect.

Animals↗
PubMed1997

Endoscopic venous valve transplantation with a valve-stent device.

In this report we describe the outcome of a 6-week study of the valve-stent device in a goat model. Six female goats underwent endoscopic subcutaneous harvest of a valve-containing segment of external jugular vein. This segment was sutured inside a 10-mm Wallstent (Schneider Inc., USA), and the device was compressed and loaded into a 12 Fr. introducer sheath and deployed through a venotomy into the contralateral external jugular vein. The animals were anticoagulated for 1 week and euthanized at 6 weeks. Flow studies, manual strip test, and angioscopic evaluation were performed prior to sacrifice. All six valve-stents were patent at harvest by Doppler flow studies, and five of six were competent as demonstrated by the manual strip test. At angioscopic evaluation, the valves were open. Gross and histologic examination revealed intact valve leaflets in five specimens. This technique is a minimally invasive approach to valve harvest and transplantation with a valve-stent device. We have demonstrated that valve-stent can remain patent and competent for up to 6 weeks. This technique may have potential application in venous valvular incompetence.

Animals↗