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Biomedical subjects

C Song

Publications and source records attributed to C Song.

At least 19 recordsLinked to original sources
PubMed2001

Role of the CDC25 homology domain of phospholipase Cepsilon in amplification of Rap1-dependent signaling.

Phospholipase Cepsilon (PLCepsilon) is a novel class of phosphoinositide-specific PLC characterized by possession of CDC25 homology and Ras/Rap1-associating domains. We and others have shown that human PLCepsilon is translocated from the cytoplasm to the plasma membrane and activated by direct association with Ras at its Ras/Rap1-associating domain. In addition, translocation to the perinuclear region was induced upon association with Rap1.GTP. However, the function of the CDC25 homology domain remains to be clarified. Here we show that the CDC25 homology domain of PLCepsilon functions as a guanine nucleotide exchange factor for Rap1 but not for any other Ras family GTPases examined including Rap2 and Ha-Ras. Consistent with this, coexpression of full-length PLCepsilon or its N-terminal fragment carrying the CDC25 homology domain causes an increase of the intracellular level of Rap1.GTP. Concurrently, stimulation of the downstream kinases B-Raf and extracellular signal-regulated kinase is observed, whereas the intracellular level of Ras.GTP and Raf-1 kinase activity are unaffected. In wild-type Rap1-overexpressing cells, epidermal growth factor induces translocation of PLCepsilon to the perinuclear compartments such as the Golgi apparatus, which is sustained for at least 20 min. In contrast, PLCepsilon lacking the CDC25 domain translocates to the perinuclear compartments only transiently. Further, the formation of Rap1.GTP upon epidermal growth factor stimulation exhibits a prolonged time course in cells expressing full-length PLCepsilon compared with those expressing PLCepsilon lacking the CDC25 homology domain. These results suggest a pivotal role of the CDC25 homology domain in amplifying Rap1-dependent signal transduction, including the activation of PLCepsilon itself, at specific subcellular locations such as the Golgi apparatus.

Animals↗
PubMed2001

Methylenetetrahydrofolate reductase polymorphisms increase risk of esophageal squamous cell carcinoma in a Chinese population.

Methylenetetrahydrofolate reductase (MTHFR) plays a central role in folate metabolism that affects DNA methylation and synthesis. Because germ-line mutations at nucleotides 677 (C-->T) and 1298 (A-->C) in the MTHFR gene cause diminished enzyme activity, and aberrant DNA methylation is oncogenic, we examined the relationship between these two MTHFR polymorphisms and susceptibility to esophageal squamous cell carcinoma (ESCC) in 240 ESCC cases and 360 age- and sex-matched controls in northern CHINA: We found that the allele frequency of MTHFR 677T was significantly higher among cases than among controls (63% versus 41%, P < 0.001). Subjects with the 677TT genotype had a more than 6-fold increased risk of developing ESCC [adjusted odds ratio (OR), 6.18; 95% confidence interval (CI), 3.32-11.51] compared with those who had the 677CC genotype. Furthermore, the elevated ESCC risk associated with the 677 polymorphism was in an allele-dose relationship (trend test, P = 0.0001) with ORs of 1.00, 3.14 (95% CI, 1.94-5.08), and 6.18 (95% CI, 3.32-11.51) for the CC, CT, and TT genotype, respectively, after adjustment for age, sex, smoking status, and the MTHFR 1298 polymorphism. The allele frequency for the MTHFR 1298C was 14% among cases and 17% among controls. The 1298CC genotype was extremely rare in both controls (1.4%) and cases (2.9%) and was also associated with an elevated risk of ESCC (adjusted OR, 4.43; 95% CI, 1.23-16.02) compared with the 1298AA genotype, whereas the 1298AC genotype had no effect on the risk of ESCC. Thus, our findings support the hypothesis that genetic polymorphisms in the MTHFR gene may contribute to susceptibility to carcinogenesis of the esophagus in the at-risk Chinese population.

Alleles↗
PubMed2001

Chronic morphine treatment inhibits oxytocin release from the supraoptic nucleus slices of rats.

Effect of chronic morphine treatment on oxytocin (OT) release from the long term-cultured organotypic slice of the supraoptic nucleus (SON) was investigated using radioimmunoassay. The co-localization of oxytocin and mu-opioid receptor in neurons within the SON was observed with the double-labeled methods of in situ hybridization combined with immunohistochemistry. After exposure to morphine for 6days, the OT levels in culture media were significantly decreased. Naloxone caused much greater release of OT in chronic morphine treatment group than in controls. Naloxone has no effect after acute morphine treatment. 90% of OT-ir (immunoreactive) neurons expressed mu-opioid receptor mRNA in the SON and 45% of the neurons that expressed mu-opioid receptor mRNAs were OT-ir neurons. These results indicated that the neurons within SON could develop dependence on morphine in vitro, and these effects might be exerted via mu-opioid receptor in oxytocin neurons of the SON.

Animals↗
PubMed2001

Auto-oxidized cholesterol sulfates are antagonistic ligands of liver X receptors: implications for the development and treatment of atherosclerosis.

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are involved in regulation of cholesterol transport and metabolism. Expression of cholesterol 7alpha-hydroxylase, cholesteryl ester transfer protein and certain ATP-binding cassette transporters that are responsible for cholesterol efflux from cells is regulated by LXR and its ligands. In this report we show that 5alpha, 6alpha-epoxycholesterol-3-sulfate (ECHS) and 7-ketocholesterol-3-sulfate inhibit transactivation of a reporter gene by LXR. Non-sulfated forms of these compounds, as well as many other steroid sulfates, had no antagonistic activity. Using chimeric receptors, the antagonistic activity of ECHS was dependent on its interaction with the ligand-binding domain of LXR. ECHS disrupts recruitment of the co-activator Grip 1 into a complex with agonist-bound LXR and this may be responsible for the observed antagonistic properties of these compounds. In various cultured cells, these LXR antagonists also promote de novo cholesterol synthesis and apoptosis. 7-Ketocholesterol and 5alpha, 6alpha-epoxycholesterol are present in blood and have been found in atherosclerotic plaques. If sulfated forms of these oxidized sterols are also present, they may have an important role in foam cell formation by inhibiting LXR function. Since LXR agonists can counteract the activity of these antagonists, they may have therapeutic potential against atherosclerosis.

Arteriosclerosis↗
PubMed2001

PCR-RFLP genotyping assay for the Bcl I polymorphism of the beta-fibrinogen gene.

Polymorphisms of the beta-fibrinogen gene have been shown to affect plasma fibrinogen levels and risk of coronary artery disease (CAD). We were interested in developing an automated, PCR-based genotyping assay for the purpose of exploring relationships between CAD and CAD-associated aortic stiffness and the Bcl I allele of the beta-fibrinogen gene. We have developed a rapid PCR-RFLP assay for the Bcl I polymorphism of the beta-fibrinogen gene. We carried out direct PCR of genomic DNA to facilitate sequencing of the flanking region of the beta-fibrinogen gene. Using this new sequence information, primers were designed which border the site of the Bcl I polymorphism. One of the primers was labeled with a fluorophore to facilitate detection of the fragments. DNA fragment analysis was carried out using an automated capillary electrophoresis instrument (ABI310). We have developed an improved PCR-RFLP high-sample-throughput assay for the semiautomated detection of the Bcl I polymorphism of the beta-fibrinogen gene. This assay will support screening of large sample sizes required for population studies.

Alleles↗
PubMed2001

Investigation of the influence of keloid-derived keratinocytes on fibroblast growth and proliferation in vitro.

Keloids are disfiguring, proliferative scars that represent a pathological response to cutaneous injury. The overabundant extracellular matrix formation, largely from collagen deposition, is characteristic of these lesions and has led to investigations into the role of the fibroblast in its pathogenesis. Curiously, the role of the epidermis in extracellular matrix collagen deposition of normal skin has been established, but a similar hypothesis in keloids has not been investigated. The aim of this study was to investigate the influence of keloid epithelial keratinocytes on the growth and proliferation of normal fibroblasts in an in vitro serum-free co-culture system. A permeable membrane separated two chambers; the upper chamber contained a fully differentiated stratified epithelium derived from the skin of excised earlobe keloid specimens, whereas the lower chamber contained a monolayer of normal or keloid fibroblasts. Both cell types were nourished by serum-free medium from the lower chamber. Epithelial keratinocytes from five separate earlobe keloid specimens were investigated. Four sets of quadruplicates were performed for each specimen co-cultured with normal fibroblasts or keloid-derived fibroblasts. Controls consisted of (1) normal keratinocytes co-cultured with normal fibroblasts, and (2) fibroblasts grown in serum-free media in the absence of keratinocytes in the upper chamber. Fibroblasts were indirectly quantified by 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay, with results confirmed by DNA content measurement, at days 1 and 5 after the co- culture initiation.Significantly, increased proliferation was seen in fibroblasts co-cultured with keloid keratinocytes, as compared with the normal keratinocyte controls at day 5 (analysis of variance, p < 0.001). These results strongly suggest that the overlying epidermal keratinocytes of the keloid may have an important, previously unappreciated role in keloid pathogenesis using paracrine or epithelial-mesenchymal signaling.

Adolescent↗
PubMed2001

Generation of oxidative stress contributes to the development of pulmonary hypertension induced by hypoxia.

Chronic hypoxia causes pulmonary hypertension and right ventricular hypertrophy associated with pulmonary vascular remodeling. Because hypoxia might promote generation of oxidative stress in vivo, we hypothesized that oxidative stress may play a role in the hypoxia-induced cardiopulmonary changes and examined the effect of treatment with the antioxidant N-acetylcysteine (NAC) in rats. NAC reduced hypoxia-induced cardiopulmonary alterations at 3 wk of hypoxia. Lung phosphatidylcholine hydroperoxide (PCOOH) increased at days 1 and 7 of the hypoxic exposure, and NAC attenuated the increase in lung PCOOH. Lung xanthine oxidase (XO) activity was elevated from day 1 through day 21, especially during the initial 3 days of the hypoxic exposure. The XO inhibitor allopurinol significantly inhibited the hypoxia-induced increase in lung PCOOH and pulmonary hypertension, and allopurinol treatment only for the initial 3 days also reduced the hypoxia-induced right ventricular hypertrophy and pulmonary vascular thickening. These results suggest that oxidative stress produced by activated XO in the induction phase of hypoxic exposure contributes to the development of chronic hypoxic pulmonary hypertension.

Acetylcysteine↗
PubMed2001

Biodistribution and dosimetry of pretargeted monoclonal antibody 2D12.5 and Y-Janus-DOTA in BALB/c mice with KHJJ mouse adenocarcinoma.

UNLABELLED: Biodistribution and dosimetry of 88Y (and equimolar 90Y) Janus-dodecanetetraacetic acid (DOTA) were performed using a three-step pretargeting protocol in BALB/c mice bearing mouse mammary adenocarcinoma (KHJJ) implants. Pretargeting was performed with mouse monoclonal antibody (mAb) 2D12.5 specific for yttrium-DOTA, and the chase was Y-DOTA-human transferrin conjugate. In this article, we report extensive organ dosimetry and the theoretic limits of the radionuclide physical half-life (T(p)) for pretargeting. METHODS: Organ biodistribution data were obtained from bioassays on tissue taken from tumor mice killed at 3, 24, 48, 72, 96, and 120 h after intravenous injection of 88Y-Janus-DOTA. Uptake and retention of 88Y as a function of time were described by nonlinear least squares fits of the tissue data to multiexponential functions. Radiation dose estimates for equivalent molar amounts of 90Y were subsequently derived from these time-integrated functions. RESULTS: The results were as follows: rapid blood clearance of 88Y-Janus-DOTA; rapid uptake and slow clearance of 88Y-Janus-DOTA from the tumor over 5 d; rapid clearance from all organs and body; largest radiation absorbed dose (AD) per injected dose of 63.52 (cGy/MBq) to tumor; high therapeutic ratios (AD tumor/AD tissue), particularly for blood and bone; and optimal radionuclide T(p) range from 30 min to 10 d. CONCLUSION: Although the absolute concentration of 90Y in the tumor is less using the hapten system than is achieved generally with the chelated radionuclide covalently attached to the mAb, the achievable tumor uptake of radioactivity, coupled with low radioactivity in bone, blood, and other organs, suggests that a three-step pretargeting protocol has considerable promise as a method for 90Y radioimmunotherapy.

Adenocarcinoma↗
PubMed2000

Ca2+- and phosphatidylinositol 3-kinase-dependent nitric oxide generation in lung endothelial cells in situ with ischemia.

Endothelial cells generate nitric oxide (NO) in response to agonist stimulation or increased shear stress. In this study, we evaluated the effects of abrupt cessation of shear stress on pulmonary endothelial NO generation and its relationship to changes in intracellular Ca(2+). In situ endothelial generation of NO and changes in intracellular Ca(2+) in isolated, intact rat lungs were evaluated using fluorescence microscopy with diaminofluorescein diacetate, an NO probe, and Fluo-3, a Ca(2+) probe. The onset of increased NO generation in endothelial cells of subpleural microvessels in situ occurred between 30 and 90 s after onset of ischemia and was preceded by an increase in intracellular Ca(2+) due to both influx of extracellular Ca(2+) and release from intracellular stores. Flow cessation-induced NO generation in endothelial cells in situ was Ca(2+)-, calmodulin-, and PI3-kinase-dependent. The similarity of endothelial cell response (increased NO generation) to either increased flow or cessation of flow suggests that cells respond to an imposed alteration from a state of adaptation. This response to flow cessation may constitute a compensatory vasodilatatory mechanism and may play a role in signaling for cell proliferation and vascular remodeling.

Animals↗
PubMed2000

Regulation of a novel human phospholipase C, PLCepsilon, through membrane targeting by Ras.

Phosphoinositide-specific phospholipase C (PI-PLC) plays a pivotal role in regulation of intracellular signal transduction from various receptor molecules. More than 10 members of human PI-PLC isoforms have been identified and classified into three classes beta, gamma, and delta, which are regulated by distinct mechanisms. Here we report identification of a novel class of human PI-PLC, named PLCepsilon, which is characterized by the presence of a Ras-associating domain at its C terminus and a CDC25-like domain at its N terminus. The Ras-associating domain of PLCepsilon specifically binds to the GTP-bound forms of Ha-Ras and Rap1A. The dissociation constant for Ha-Ras is estimated to be approximately 40 nm, comparable with those of other Ras effectors. Co-expression of an activated Ha-Ras mutant with PLCepsilon induces its translocation from the cytosol to the plasma membrane. Upon stimulation with epidermal growth factor, similar translocation of ectopically expressed PLCepsilon is observed, which is inhibited by co-expression of dominant-negative Ha-Ras. Furthermore, using a liposome-based reconstitution assay, it is shown that the phosphatidylinositol 4,5-bisphosphate-hydrolyzing activity of PLCepsilon is stimulated in vitro by Ha-Ras in a GTP-dependent manner. These results indicate that Ras directly regulates phosphoinositide breakdown through membrane targeting of PLCepsilon.

Amino Acid Sequence↗
PubMed2000

Yb14ZnSb11: charge balance in zintl compounds as a route to intermediate Yb valence

The results of thermodynamic, transport, and x-ray diffraction measurements of single crystals of the new compound Yb14ZnSb11 are presented. These data indicate an intermediate Yb valence scenario, with a spin fluctuation temperature of approximately 85 K. The compound is weakly metallic and is isostructural with the charge-balanced Zintl compound Yb14AlSb11. The intermediate Yb valence can be qualitatively accounted for by considering the charge counting arguments of the nonmetallic parent, and charge balance in Zintl-related materials appears to be a viable route to designing other compounds with intermediate valence constituents.

Journal Article↗
PubMed2000

Morphing the shell model into an effective theory

We describe a strategy for attacking the canonical nuclear structure problem-bound-state properties of a system of point nucleons interacting via a two-body potential-which involves an expansion in the number of particles scattering at high momenta, but is otherwise exact. The required self-consistent solutions of the Bloch-Horowitz equation for effective interactions and operators are obtained by an efficient Green's function method based on the Lanczos algorithm. We carry out this program for the simplest nuclei, d and 3He, in order to explore the consequences of reformulating the shell model as a controlled effective theory.

Journal Article↗
PubMed2000

Role of Raf-1 conserved region 2 in regulation of Ras-dependent Raf-1 activation.

Full activation of Raf-1 requires the interaction of its CRD with Ras. The serine/threonine-rich region, CR2, of Raf-1 was implicated in Raf-1 regulation, but the underlying mechanism was unclear. Here we show that CRD loses its Ras-binding activity when expressed in connection with CR2, suggesting that CR2 masks CRD. This masking effect is abolished by substitution of Asp or Ala for Ser-259, a growth factor- and TPA-induced phosphorylation site in CR2. Treatment of COS-7 cells expressing Ha-Ras(Val-12) and Raf-1 with TPA enhances the Ha-Ras(Val-12)-dependent Raf-1 kinase activity. In contrast, the Ha-Ras(Val-12)-dependent activities of the Raf-1(S259D) and Raf-1(S259A) mutants are comparable to that of wild-type Raf-1 stimulated by both Ha-Ras(Val-12) and TPA and cannot be further stimulated by TPA treatment. These results suggest that the in vivo phosphorylation of Ser-259 may comprise a crucial step for Ras-dependent Raf-1 activation by unmasking CRD and promoting its association with Ras.

Animals↗
PubMed2000

Immunosuppressive effects of clozapine and haloperidol: enhanced production of the interleukin-1 receptor antagonist.

In schizophrenic patients, multiple immune abnormalities have been reported, including increased production of proinflammatory cytokines. There is some evidence that antipsychotic drugs may have immunosuppressive effects. The aim of this study was to examine the in-vitro effects of different concentrations of antipsychotic agents on cytokine production by human whole blood. We examined the effects of clozapine and haloperidol, 10(-4), 10(-6) and 10(-8)M, on the unstimulated and stimulated (lipopolysaccharide+phytohemagglutinin) production of interleukin-6 (IL-6), IL-10, interferon-gamma (IFNgamma), and the IL-1 receptor antagonist (IL-1RA). Clozapine, 10(-6) and 10(-8)M, and haloperidol, 10(-4), 10(-6), and 10(-8)M, significantly increased the unstimulated and stimulated production of IL-1RA. Clozapine 10(-6)M significantly increased the stimulated production of IFNgamma. Clozapine 10(-4)M significantly suppressed the unstimulated production of IL-6 and IL-1RA and the stimulated production of IL-6, IL-10, IFNgamma and IL-1RA. The results suggest that both clozapine and haloperidol, at concentrations within the therapeutic range, may exert immunosuppressive effects through an enhanced production of IL-1RA.

Adult↗
PubMed2000

A transcriptional defect underlies B lymphocyte dysfunction in a patient diagnosed with non-X-linked hyper-IgM syndrome.

To establish the underlying cause of hyper-IgM syndrome in one female patient, B cell function was examined in response to CD40- and IL-4-mediated pathways. When CD40-induced functional responses were measured in unfractionated B cells, CD80 up-regulation, de novo Cmu-Cgamma recombination, and Igamma transcription were all found to be relatively unaffected. However, CD40- and IL-4-mediated CD23 up-regulation and VDJ-Cgamma transcription were clearly diminished compared to control cells. IL-4-induced CD23 expression was measurably reduced in the CD20- population as well. These results suggested that the patient's defect is positioned downstream of CD40 contact and affects both CD40- and IL-4 signal transduction pathways. Further analysis of B cell function in CD19+ B cells revealed a clear B cell defect with respect to Igamma and mature VDJ-Cgamma transcription and IgG expression. However, under the same conditions Iepsilon transcription was relatively normal. Partial restoration of B cell function occurred if PBMC or CD19+ B cells were cultured in vitro in the presence of CD154 plus IL-4. Because addition of IL-4 to cocultures containing activated T cells failed to induce B cells to undergo differentiation, the ability of the patient's B cells to acquire a responsive phenotype correlated with receiving a sustained signal through CD40. These findings support a model in which the patient expresses an intrinsic defect that is manifested in the failure of specific genes to become transcriptionally active in response to either CD154 or IL-4 and results in a functionally unresponsive B cell phenotype.

B-Lymphocytes↗
PubMed2000

Superoxide possibly produced in endothelial cells mediates the neutrophil-induced lung injury.

BACKGROUND: The mechanism by which stimulated neutrophils (polymorphonuclear leukocytes [PMNs]) damage pulmonary vascular endothelium was investigated. METHODS: The ability of unstimulated and mechanically stimulated PMNs to adhere to pulmonary endothelial cells and, thereby, alter pulmonary vascular permeability was tested. Each series was conducted on 6 rats. To stimulate PMNs, they were agitated gently in a glass vial for 10 seconds. RESULTS: Perfusing lungs with the stimulated PMNs elicited a fivefold increase in permeability compared with lungs perfused with the unstimulated cells. This increase in permeability was blocked completely by preincubation of stimulated PMNs with CD18 monoclonal antibody. This increase in permeability was also blocked completely by superoxide dismutase (SOD) or the xanthine oxidase (XO) inhibitor allopurinol. Pulmonary vascular hemodynamics were unaffected by any treatment protocol. The accumulation of stimulated PMNs within the lungs was not inhibited by SOD but was partially blocked by allopurinol. CONCLUSIONS: These findings suggest that stimulated PMN-induced increases in pulmonary vascular filtration resulted from endothelial cell injury caused by superoxide anion possibly generated by XO, exclusively present in the endothelial cells.

Animals↗
PubMed2000

Selective activation of liver X receptor alpha by 6alpha-hydroxy bile acids and analogs.

We have found that certain natural 6alpha-hydroxylated bile acids are receptor-specific activators of nuclear liver X receptor alpha (LXRalpha) (NR1H3), a nuclear receptor regulating the expression of the cholesterol 7alpha-hydroxylase gene, coding for the rate-limiting enzyme in the major pathway of bile acid synthesis. The LXR homolog, ubiquitous nuclear receptor (UR/LXRbeta) (NR1H2), was also activated by these bile acids, but at higher concentrations than for LXRalpha. Synthetic 6alpha-hydroxylated bile acid analogs were synthesized with LXRalpha-selective agonistic activity, with potential to modulate cholesterol catabolism in hypercholesterolemia.

Bile Acids and Salts↗