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Biomedical subjects

L Feng

Publications and source records attributed to L Feng.

At least 181 records · Page 10Linked to original sources
PubMed1996

Expression of photoreceptor cyclic nucleotide-gated cation channel alpha subunit (CNGCalpha) in the liver and skeletal muscle.

Glucagon and beta-adrenergic agents increase cAMP levels and stimulate Ca2+ influx in liver cells. There is no consensus as to the mechanism by which these hormones stimulate the influx of Ca2+. Using mouse retinal rod CNGCalpha cDNA probes, we cloned rat liver and skeletal muscle, and human hepatic CNGCalpha subunit sequences showing 97-100% identity with the human rod channel. In order to assess channel activity, the effect of cyclic nucleotides on free intracellular Ca2+ levels of isolated hepatocytes was measured. Dibutyryl-cAMP was more effective in increasing free Ca2+ levels than dibutyryl-cGMP. These data indicate that the CNGCalpha subunit is expressed in both the liver and skeletal muscle possibly mediating hormonal effects on ion fluxes.

Amino Acid Sequence↗
PubMed1996

Chemokine expression by intraepithelial gamma delta T cells. Implications for the recruitment of inflammatory cells to damaged epithelia.

T cells expressing gamma delta TCR may have evolved to recognize Ag in a different manner as well as perform a broader set of functions than T cells with alpha beta TCR. In this study, we tested the hypothesis that dendritic epidermal T cells (DETC) bearing the invariant V gamma 3V delta 1 TCR may be able to signal the migration of peripheral alpha beta T cells to the epidermis by secreting specific chemokines. Expression of macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, RANTES, and lymphotactin was inducible in DETC 7-17 cells, whereas mRNA for monocyte chemoattractant protein (MCP)-1 could not be detected. Strikingly, lymphotactin was the most abundant chemokine produced by activated DETC 7-17 cells. Activated primary DETC cultures also produced copious amounts of lymphotactin mRNA. Similarly, freshly isolated and activated intestinal intraepithelial T cells (i-IEL) with gamma delta TCR expressed high levels of lymphotactin mRNA. In contrast, lymphotactin mRNA was present in activated spleen gamma delta T cells at low basal levels. Migration of CD8+ T cells induced by culture supernatants from stimulated DETC 7-17 cells was strongly reduced in the presence of a neutralizing anti-lymphotactin antiserum and to a lesser extent by neutralizing anti-MIP-1 alpha, anti-MIP-1 beta, or anti-RANTES antiserum. The presence of lymphotactin in supernatants from activated DETC 7-17 cultures was directly demonstrated by Western blot analysis. These observations are consistent with a model in which gamma delta IEL play an active multi-faceted role in the maintenance of epithelia homeostasis.

Animals↗
PubMed1996

Antigen compartmentation and T helper cell tolerance induction.

The process of antigen recognition depends in part on the amount of peptide antigen available and the affinity of the T cell receptor for a particular peptide-major histocompatibility complex (MHC) molecule complex. The availability of self antigen is limited by antigen processing, which is compartmentalized such that peptide antigens presented by MHC class I molecules originate in the cytoplasm, whereas peptide antigens presented by MHC class II molecules are acquired from the endocytic pathway. This segregation of the antigen-processing pathways may limit the diversity of antigens that influence the development and selection of, e.g., CD4-positive, MHC class II-specific T cells. Selection in this case might involve only a subset of self-encoded proteins, specifically those that are plasma membrane bound or secreted. To study these aspects of immune development, we engineered pigeon cytochrome for expression in transgenic mice in two forms: one in which it was expressed as a type II plasma membrane protein, and a second in which it was targeted to the mitochondria after cytoplasmic synthesis. Experiments with these mice clearly show that tolerance is induced in the thymus, irrespective of antigen compartmentation. Using radiation bone marrow chimeras, we further show that cytoplasmic/mitochondrial antigen gains access to the MHC class II pathway by direct presentation. As a result of studying the anatomy of the thymus, we show that the amount of antigen and the affinity of the TCR affect the location and time point of thymocytes under-going apoptosis.

Animals↗
PubMed1996

Cloning of rat 92-kDa type IV collagenase and expression of an active recombinant catalytic domain.

A full-length cDNA for rat 92-kDa type IV collagenase was isolated and sequenced. RNase protection assay revealed tissue specific differential expression of the 92-kDa type IV collagenase in the rat during development. Natural and modified forms of the 92-kDa type IV collagenase were expressed. One active protein, 92-CD, contained only the putative catalytic domain. Large quantities of the 92-CD were expressed in Escherichia coli, extracted from inclusion bodies, purified, and refolded to an active form. This recombinant protein was able to cleave denatured and native collagen and was inactivated by known MMP inhibitors.

Amino Acid Sequence↗
PubMed1996

Characterization of the structure and function of a novel MAP kinase kinase (MKK6).

Mitogen-activated protein (MAP) kinases require dual phosphorylation on threonine and tyrosine residues in order to gain enzymatic activity. This activation is carried out by a family of enzymes known as MAP kinase kinases (MKKs or MEKs). It appears that there are at least four subgroups in this family; MEK1/MEK2 subgroup that activates ERK1/ERK2, MEK5 that activates ERK5/BMK1, MKK3 that activates p38, and MKK4 that activates p38 and Jun kinase. Here we describe the characteristics of a new MKK termed MKK6. The clones we isolated encode two splice isoforms of human MKK6 comprised of 278 and 334 amino acids, respectively, and one murine MKK6 with 237 amino acids. Sequence information derived from cDNA cloning indicated that MKK6 is most closely related to MKK3. The functional data revealed from co-transfection assays suggests that MKK6, like MKK3, selectively phosphorylates p38. Unlike the previously described MKKs (or MEKs), MKK6 exists in a variety of alternatively spliced isoforms with distinct patterns of tissue expression. This suggests novel mechanisms regulating activation and/or function of various forms of MKK6.

Amino Acid Sequence↗
PubMed1996

Stimulation of NF-kappa B activation and gene expression by platelet-activating factor.

PAF stimulation of NF-kappa B activation and transcription of immediate-early genes have been investigated in peripheral blood mononuclear cells and in transfected Chinese hamster ovary cells expressing the cloned PAF receptor. These studies identified a G protein-coupled pathway for PAF induction of gene expression and transcription factor activation, which differs from the mechanisms employed by other immediate-early gene inducers. Potential significance of PAF induced NF-kappa B activation is discussed.

Animals↗
PubMed1996

Polymorphisms in the human apolipoprotein-J/clusterin gene: ethnic variation and distribution in Alzheimer's disease.

Apolipoprotein-J/clusterin (APOJ/CLI) shares many biological properties with apolipoprotein-E (APOE) including, but not limited to, avid binding with beta-amyloid peptide. Thus, APOJ/CLI warrants scrutiny as a candidate Alzheimer's disease (AD) susceptibility gene. We identified seven nucleotide sequence polymorphisms in APOJ/ CLI, two of which, in exon 7, after the predicted amino acid sequence. The JVIIB variant is an asparagine-to-histidine substitution, which deletes a glycosylation signal at amino acid 317; the JVIIC variant is an aspartate-to-asparagine substitution, which forms a new glycosylation signal at position 328. Both of these coding variants, as well as two neutral polymorphisms in exon 2, were more frequent in African-Americans than Hispanics and were rare in Caucasians. However, no individual coding or noncoding variant was consistently associated with AD. At the population level, APOJ/CLI polymorphisms are frequent among persons of African descent, but probably do not alter susceptibility to AD.

Black or African American↗
PubMed1996

The role of intracellular Ca2+ in the regulation of gluconeogenesis.

A hypothesis for the hormonal regulation of gluconeogenesis, in which increases in cytosolic free-Ca2+ levels ([Ca2+]i) play a major role, is presented. This hypothesis is based on the observation that gluconeogenic hormones evoke a common pattern of Ca2+ redistribution, resulting in increases in [Ca2+]i. Current concepts of hormonally evoked Ca2+ fluxes are presented and discussed. It is suggested that the increase in [Ca2+]i is functionally linked to stimulation of gluconeogenesis. The stimulation of gluconeogenesis is accomplished in two ways: (1) by increasing the activities of the Krebs cycle and the electron-transfer chain, thereby supplying adenosine triphosphates (ATP) and reducing equivalents to the process; and (2) by stimulating the activities of key gluconeogenic enzymes, such as pyruvate carboxylase. The hypothesis presents a conceptual framework that ties together two interrelated manifestations of hormone action: signal transduction and metabolism.

Adrenergic alpha-Agonists↗
PubMed1996

Chromosome 11p15.5 regional imprinting: comparative analysis of KIP2 and H19 in human tissues and Wilms' tumors.

The imprinted H19 gene is frequently inactivated in Wilms' tumors (WTs) either by chromosome 11p15.5 loss of heterozygosity (LOH) or by hypermethylation of the maternal allele and it is possible that there might be coordinate disruption of imprinting of multiple 11p15.5 genes in these tumors. To test this we have characterized total and allele-specific mRNA expression levels and DNA methylation of the 11p15.5 KIP2 gene in normal human tissues, WTs and embryonal rhabdomyosarcoma (RMS). Both KIP2 alleles are expressed but there is a bias with the maternal allele contributing 70-90% of mRNA. Tumors with LOH show moderate to marked reductions in KIP2 mRNA relative to control tissues and residual mRNA expression is from the imprinted paternal allele. Among WTs without LOH most cases with H19 inactivation also have reduced KIP2 expression and most cases with persistent H19 expression have high levels of KIP2 mRNA. In contrast to the extensive hypermethylation of the imprinted H19 allele, both KIP2 alleles are hypomethylated and WTs with biallelic H19 hypermethylation lack comparable hypermethylation of KIP2 DNA. 5-aza-2'-deoxycytidine (aza-C) increases H19 expression in RD RMS cells but does not activate KIP2 expression. These data indicate coordinately reduced expression of two linked paternally imprinted genes in most WTs and also suggest mechanistic differences in the maintenance of imprinting at these two loci.

Adult↗
PubMed1996

Endotoxin tolerance is induced in Chinese hamster ovary cell lines expressing human CD14.

Changes in patterns of gene induction by myeloid lineage cells following multiple exposures to endotoxin (lipopolysaccharide; LPS) is a feature of LPS tolerance. To further understand the mechanism of this phenomenon we describe studies using stably transfected Chinese hamster ovary cell lines that express human CD14 (CHO-hCD14). Using NF-kappa B activation as a measure of LPS-induced cell activation we show that a single treatment with LPS renders CHO-hCD14 cells tolerant to subsequent challenge with LPS, but not with other stimuli such as tumor necrosis factor. Tolerance may result from the induction of gene(s) that control LPS-induced signaling pathways and here we suggest that such genes may be found in the group of immediate, early response genes characterized by the protein phosphatase 3CH134. The CHO-hCD14 cell lines provide a novel model system to further explore the mechanism of endotoxin tolerance.

Animals↗
PubMed1996

Intra-alveolar macrophage-inflammatory peptide 2 induces rapid neutrophil localization in the lung.

Endotoxin-induced lung injury is characterized by neutrophil infiltration of the lungs. The various mechanisms which mediate movement of neutrophils from vascular space to lung interstitium and alveoli remain unclear. Macrophage-inflammatory protein 2 (MIP-2) is a potent chemoattractant for neutrophils and may play a significant role in recruiting neutrophils in acute lung injury in rats. Experiments were performed in male Sprague Dawley rats to: (1) evaluate the kinetics of neutrophil influx in the lung following intraperitoneal administration of Salmonella enteritidis lipopolysaccharide (LPS); (2) determine the expression of transcripts for chemokines and adhesion molecules in the lung following intraperitoneal LPS; and (3) elucidate the effects of intra-alveolar instillation of recombinant rat MIP-2 on neutrophil influx into the lung. Intraperitoneal LPS resulted in an increase in neutrophil sequestration in the lung capillaries of rats as early as 45 min following administration, and there was a parallel increase in lung myeloperoxidase activity. There were also major increases in mRNA in whole-lung homogenates of LPS-treated rats for chemokines MIP-2 and KC (cytokine-induced neutrophil chemoattractant) and adhesion molecules P- and E-selectin at 1 and 2 h following LPS. When recombinant rat MIP-2 was instilled into the alveolar space of rats through a catheter wedged into a bronchus, there was profound neutrophil localization both in the vascular and alveolar space which significantly differed (P < 0.05) from the contralateral lungs of the same animals, and lungs of control animals instilled with control buffer. These observations reveal that MIP-2 is a potent chemoattractant in rat lungs, and suggest that chemoattractants locally released in alveoli can recruit neutrophils to those alveoli. This suggests that alveolar macrophages may play an important role in neutrophil sequestration in sepsis and other inflammatory lung diseases which produce a neutrophilic alveolitis.

Animals↗
PubMed1996

Relative risk of Alzheimer disease and age-at-onset distributions, based on APOE genotypes among elderly African Americans, Caucasians, and Hispanics in New York City.

Apolipoprotein-E epsilon 4 (APOE-epsilon 4) has been consistently associated with Alzheimer disease (AD) and may be responsible for an earlier age at onset. We have previously reported a diminished association between APOE-epsilon 4 and AD in African Americans. Using a new method, which allows inclusion of censored information, we compared relative risks by APOE genotypes in an expanded collection of cases and controls from three ethnic groups in a New York community. The relative risk for AD associated with APOE-epsilon 4 homozygosity was increased in all ethnic groups (African American relative risk [RR]=3.0; 95% confidence interval [CI]=1.5-5.9; Caucasian RR=7.3, 95% CI=2.5-21.6; and Hispanic RR=2.5, 95% CI=1.1-5.7), compared with those with APOE-epsilon 3/epsilon 3 genotypes. The risk was also increased for APOE-epsilon 4 heterozygous Caucasians (RR=2.9, 95% CI=1.7-5.1) and Hispanics (RR=1.6, 95% CI=1.1-2.3), but not for African Americans (RR=0.6, 95% Ci=0.4-0.9). The age distribution of the proportion of Caucasians and Hispanics without AD was consistently lower for APOE-epsilon 4 homozygous and APOE-epsilon 4 heterozygous individuals than for those with other APOE genotypes. In African Americans this relationship was observed only in APOE-epsilon 4 homozygotes. These results confirm that APOE genotypes influence the RR of AD in Caucasians and Hispanics. Differences in risk among APOE-epsilon 4 heterozygote African Americans suggest that other genetic or environmental factors may modify the effect of APOE-epsilon 4 in some populations.

Age of Onset↗
PubMed1996

[Methodological study of hemodynamic analysis of lung mass by contrast enhanced dynamic CT].

We investigated a method of analyzing the hemodynamics of the lung mass by contrast enhanced dynamic computed tomography (dynamic CT) to determine the difference in vascular supply between the pulmonary artery and bronchial artery using an experimental model. Our experimental model consisted of two injectors connected to two tubes, representing the pulmonary artery and bronchial artery, which were further connected to a chamber representing the lung mass. Following infusion of contrast medium into each tube with some delay time, dynamic CT scans were performed to obtain time density curves of the two tubes and the chamber. Using the time-density curve of contrast passage, flow rates from the two tubes into the chamber were calculated by the curve fitting method. Calculated values correlated well with the adopted flow rates of fluid from the injectors (r = 0.893) in the experiment. The results indicate our method of individually measuring flow rates of dual-input blood flow, i.e., from the pulmonary artery and bronchial artery, into the lung mass is applicable clinically to determine blood flow by the two arteries supplying the lung mass.

Animals↗
PubMed1996

[Investigation and preventive strategy of post-transfusion hepatitis C virus infection].

Among the hospital infections, the posttransfusion hepatitis C virus infection is gradually important. We investigated 30 cases with this infection, confirmed by positive anti-HCV (ELISA test) and HCV RNA (PCR). All cases had an history of receiving blood (or its preparations) with an amount of 50 to 2800 ml. Twenty-three cases were diagnosed as acute hepatitis, icterus 10 and non-icterus 13. Six were chronic hepatitis and one asymptomatic virus carrier. In order to prevent and reduce the posttransfusion HCV infection, the key points are to screen donors and to follow the safe regulations of transfusion.

Enzyme-Linked Immunosorbent Assay↗
PubMed1996

[Diagnosis of uterine diseases by combined hysteroscopy and ultrasonography].

OBJECTIVE: To investigate the diagnostic value of combined hysteroscopy with ultrasonography. METHODS: 477 patients were diagnosed by hysteroscopy, ultrasonography, or hysteroscopy combined with ultrasound. The results of the 3 groups were compared with the findings after operations. RESULTS: This study indicated to diagnose intrauterine lesions, intramural diseases or pelvic disorders, hysteroscopy with ultrasonography was significantly better than either methods alone. The accuracy rate, false positive rate as well as false negative rate were 98.32%, 1.26% and 0.04% respectively. CONCLUSION: Hysteroscopy is used for diagnosis and treatment of intrauterine lesions, and ultrasonography is difficult to show actual location of lesions within uterine cavity. The present study has shown that hysteroscopy combined with ultrasound could increase the effectiveness and accuracy of uterine diseases' diagnosis.

Adult↗
PubMed1996

[Safety of 5% dextrose as distending medium during transcervical resection of endometrium].

OBJECTIVE: To observe the changes of plasma electrolytes and osmolarity during and after transcervical resection of endometrium using 5% dextrose solution as distending medium. METHODS: We used 5% dextrose solution as distending medium for 500 cases of operative hysteroscopy. Plasma sodium, potassium, chloride, glucose concentrations and plasma osmolarity were measured before, at the end of 1 hour, 4 hours and the day after operation respectively in 22 cases. RESULTS: None of the 500 cases presented with transurethral resection of prostate (TURP) syndrome. No apparent change were found in plasma sodium, chloride concentrations and plasma osmolarity. Plasma potassium concentration decreased gradually but significantly 4 hours after surgery. The elevation of plasma glucose concentration was significant and was positively correlated with the absorption of 5% dextrose. All changes of plasma electrolytes and osmolarity restored in the next morning. It was 1 hour after surgery that the lowest plasma sodium, potassium concentration as well as the highest plasma glucose concentration appeared. Therefore, it is important to observe patient 1 hour after operation. CONCLUSIONS: 5% dextrose solution, used as the distending medium, is safe and inexpensive, and could be widely applied in transcervical resection of endometrium.

Adult↗