Biomedical subjects

L Xu

Publications and source records attributed to L Xu.

At least 127 records · Page 7Linked to original sources

PubMed2001

A globally convergent Lagrange and barrier function iterative algorithm for the traveling salesman problem.

In this paper a globally convergent Lagrange and barrier function iterative algorithm is proposed for approximating a solution of the traveling salesman problem. The algorithm employs an entropy-type barrier function to deal with nonnegativity constraints and Lagrange multipliers to handle linear equality constraints, and attempts to produce a solution of high quality by generating a minimum point of a barrier problem for a sequence of descending values of the barrier parameter. For any given value of the barrier parameter, the algorithm searches for a minimum point of the barrier problem in a feasible descent direction, which has a desired property that the nonnegativity constraints are always satisfied automatically if the step length is a number between zero and one. At each iteration the feasible descent direction is found by updating Lagrange multipliers with a globally convergent iterative procedure. For any given value of the barrier parameter, the algorithm converges to a stationary point of the barrier problem without any condition on the objective function. Theoretical and numerical results show that the algorithm seems more effective and efficient than the softassign algorithm.

Algorithms↗

PubMed2001

Expression of frizzled genes in mouse costochondral chondrocytes.

Protein products of frizzled genes are cell membrane receptors for Wnt proteins that play multiple roles during development. We examined the expression of nine frizzled genes in mouse chondrocytes, and detected transcripts of six of the nine genes. We also cloned the entire cDNA of mouse frizzled-1 and compared its cDNA sequence and the cysteine-rich and transmembrane domains of its translated product to sequences of frizzled-1 from C. elegans, Drosophila, chicken and human. We used the T31 Mouse/Hamster radiation hybrid panel to map the mouse frizzled-1 to mouse chromosome 5 (5 cM from the centromere), and frizzled-9 to mouse chromosome 5 (74 cM from the centromere).

Amino Acid Sequence↗

PubMed2001

Notch1 regulates maturation of CD4+ and CD8+ thymocytes by modulating TCR signal strength.

Notch signaling regulates cell fate decisions in multiple lineages. We demonstrate in this report that retroviral expression of activated Notch1 in mouse thymocytes abrogates differentiation of immature CD4+CD8+ thymocytes into both CD4 and CD8 mature single-positive T cells. The ability of Notch1 to inhibit T cell development was observed in vitro and in vivo with both normal and TCR transgenic thymocytes. Notch1-mediated developmental arrest was dose dependent and was associated with impaired thymocyte responses to TCR stimulation. Notch1 also inhibited TCR-mediated signaling in Jurkat T cells. These data indicate that constitutively active Notch1 abrogates CD4+ and CD8+ maturation by interfering with TCR signal strength and provide an explanation for the physiological regulation of Notch expression during thymocyte development.

Animals↗

PubMed2001

The TGF beta receptor activation process: an inhibitor- to substrate-binding switch.

The type I TGF beta receptor (T beta R-I) is activated by phosphorylation of the GS region, a conserved juxtamembrane segment located just N-terminal to the kinase domain. We have studied the molecular mechanism of receptor activation using a homogeneously tetraphosphorylated form of T beta R-I, prepared using protein semisynthesis. Phosphorylation of the GS region dramatically enhances the specificity of T beta R-I for the critical C-terminal serines of Smad2. In addition, tetraphosphorylated T beta R-I is bound specifically by Smad2 in a phosphorylation-dependent manner and is no longer recognized by the inhibitory protein FKBP12. Thus, phosphorylation activates T beta R-I by switching the GS region from a binding site for an inhibitor into a binding surface for substrate. Our observations suggest that phosphoserine/phosphothreonine-dependent localization is a key feature of the T beta R-I/Smad activation process.

Activin Receptors, Type I↗

PubMed2001

Polymorphisms of the CYP1A1 and GSTM1 genes in relation to individual susceptibility to lung carcinoma in Chinese population.

Cytochrome P450 1A1 (CYP1A1) and glutathione S-transferase M1 (GSTM1) metabolize tobacco-related carcinogens. To investigate the prevalence of CYP1A1 and GSTM1, and their association with increased risk of lung carcinoma in Chinese, allele-specific PCR and multiplex PCR technique were employed to identify the genotypes of CYP1A1 and GSTM1 in a case-control study of 106 lung carcinoma patients with histopathological diagnosis and 106 matched controls free of malignancy in Jiangsu Province, China. Logistic regression analysis was performed to calculate the odds ratio (OR) and 95% confidence intervals (CI). The results showed that individuals with GSTM1 null, and the combined GSTM1 null/CYP1A1 Ile/Val or GSTM1 null/CYP1A1 Val/Val had an elevated risk of lung carcinoma, with the OR, 1.92 (P=0.02; CI, 1.07-3.46), 3.27 (P=0.01; CI, 1.23-8.84) and 9.33 (P=0.04; CI, 1.01-217.42), respectively. Light smokers (<30 pack-years) carrying GSTM1 null genotype were shown to have the increased risk to lung carcinoma (OR=3.47; CI, 1.13-7.57). Our study suggested that the null GSTM1 genotype, independently or in combined with at least one Val allele of CYP1A1, might affect the genetic susceptibility for lung carcinoma in Chinese population.

Adult↗

PubMed2001

In vivo measurement of gene expression, angiogenesis and physiological function in tumors using multiphoton laser scanning microscopy.

Intravital microscopy coupled with chronic animal window models has provided stunning insight into tumor pathophysiology, including gene expression, angiogenesis, cell adhesion and migration, vascular, interstitial and lymphatic transport, metabolic microenvironment and drug delivery. However, the findings to date have been limited to the tumor surface (< 150 microm). Here, we show that the multiphoton laser-scanning microscope can provide high three-dimensional resolution of gene expression and function in deeper regions of tumors. These insights could be critical to the development of novel therapeutics that target not only the tumor surface, but also internal regions.

Cell Adhesion↗

PubMed2001

Pancreas microenvironment promotes VEGF expression and tumor growth: novel window models for pancreatic tumor angiogenesis and microcirculation.

Pancreatic cancer has a poor prognosis, and treatment strategies based on preclinical research have not succeeded in significantly extending patient survival. This failure likely stems from the general lack of information on pancreatic tumor physiology, attributable to the difficulties in developing relevant, orthotopic models that accurately reflect pancreatic cancer in the clinic. To overcome this limitation, we developed abdominal wall windows suitable for intravital microscopy that allowed us to monitor angiogenesis and microvascular function noninvasively during tumor growth in vivo. We used two complementary tumor models in mice: orthotopic (human ductal pancreatic adenocarcinoma, PANC-1, grown in the pancreas), and ectopic (PANC-1 grown in the abdominal wall). We found that orthotopic PANC-1 tumors grew faster than the ectopic tumors and exhibited metastatic spread in the late stage similar to advanced pancreatic cancer in the clinic. Orthotopic PANC-1 tumors expressed vascular endothelial growth factor (VEGF)(121) and VEGF(165), contained higher levels of tumor cell-derived VEGF protein, and maintained vascular density and hyperpermeability during exponential tumor growth. Orthotopic PANC-1 tumors showed lower leukocyte-endothelial interactions in the early stage of growth. In addition, both VEGF(121) and VEGF(165) promoted the growth of PANC-1 cells in vitro. Finally, Anti-VEGF neutralizing antibody inhibited angiogenesis and tumor growth of PANC-1 tumors in both sites. We conclude that the orthotopic pancreas microenvironment enhances VEGF expression, which stimulates growth of PANC-1 tumors (compared with ectopic tumors). The mechanism is autocrine and/or paracrine and also is involved in the maintenance of blood vessels. This comparative system of orthotopic and ectopic pancreatic cancer will provide the rigorous understanding of pancreatic tumor pathophysiology needed for development of novel therapeutic strategies.

Animals↗

PubMed2001

Molecular cytogenetic characterization and clinical relevance of additional, complex and/or variant chromosome abnormalities in acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is characterized by typical morphological manifestation, t(15;17) translocation and active response to all-trans retinoic acid (ATRA) in the great majority of patients. However, a subset of APL cases may present atypical phenotypic, cytogenetic or molecular features at different stages of the disease. The biological and clinical significance of these features sometimes remains obscure. In this study, 284 APL patients were cytogenetically analyzed and precise diagnosis was performed according to the molecular cytogenetic results. Twenty-six APL patients were identified as having additional, complex and/or variant chromosomal abnormalities at diagnosis or at relapse, 16 of them being further analyzed using fluorescence in situ hybridization (FISH) or chromosome painting (CP). Interestingly, some of these chromosomal aberrations were found to be associated with atypical morphology and/or drug response, indicating a genotype-phenotype correlation. Analysis of the complex karyotype may also allow a better understanding of the levels of cellular origin of the leukemogenesis. Examination of the remission induction and survival data showed that the presence of the additional/complex chromosome abnormalities was related to the prognosis in both primarily diagnosed and relapsed patients in this series.

Adolescent↗

PubMed2001

Feasibility and clinical significance of real-time quantitative RT-PCR assay of PML-RARalpha fusion transcript in patients with acute promyelocytic leukemia.

INTRODUCTION: To study the relationship between the expression level of the PML-RARalpha fusion transcripts and the clinical status and efficiency of the therapy in acute promyelocytic leukemia (APL) patients, we applied a very sensitive and specific real-time Reverse Transcription Polymerase Chain Reaction (RT-PCR) system to quantify the dose of PML-RARalpha fusion transcripts in a series of APL patients at distinct disease stages. MATERIALS AND METHODS: A total of 31 APL patients (19 males and 12 females; aged from 8 to 74 years) from eight hospitals in Shanghai were analysed. Real-time Quantitative RT-PCR was used to measure the normalized dose (DoseN) of PML-RARalpha fusion transcripts. RESULTS: A wide range of PML-RARalpha DoseN above 1 x 10(3) was noted in 25 newly diagnosed patients. PML-RARalpha DoseN was significantly decreased after remission induction with ATRA, ATRA/chemotherapy or As2O3 and further reduced after consolidation. The fact that all patients with long disease free survival had a constantly low PML-RARalpha DoseN below 2 x 10(2) and a higher level predicted impending relapse suggests that this value could serve as a 'threshold' for molecular remission. PML-RARalpha DoseN was also of prognostic value in a group of relapsed patients, since good response to As2O3 reinduction was accompanied by a remarkable reduction of fusion transcript level, whereas patients with high PML-RARalpha Dose(N) after the second CR tended to relapse again rapidly. CONCLUSION: These results confirm that real-time RT-PCR assay for PML-RARalpha transcripts in APL patients is useful in reflecting leukemic burden, assessing response to treatment and indicating the ultimate clinical outcome or curability of disease.

Adolescent↗

PubMed2001

Expression of interleukin-4 in the epidermis of transgenic mice results in a pruritic inflammatory skin disease: an experimental animal model to study atopic dermatitis.

Atopic dermatitis, a common, chronic, inflammatory skin disease that occurs with increasing prevalence, is characterized by hyperactivated cytokines of helper T cell subset 2 and is frequently associated with staphylococcal infection. An experimental animal model of atopic dermatitis induced by transgenically introduced cytokine is not available. We generated a transgenic mouse line expressing epidermal interleukin-4, a critical cytokine of helper T cell subset 2. Here we show that transgenic mice spontaneously developed a pruritic inflammatory skin disease reproducing all key features of human atopic dermatitis, including xerosis, conjunctivitis, inflammatory skin lesions, Staphylococcus aureus infection, histopathology of chronic dermatitis with T cell, mast cell, macrophage-like mononuclear cell, and eosinophil infiltration, and elevation of total serum IgE and IgG1. The onset and early progression of skin disease coincided with increased total serum IgE and IgG1. The mouse disease occurred at a 43% annual incidence rate and primarily affected the poorly haired skin: ear (100%), neck (65%), eye (53%), face (29%), tail (12%), leg (12%), and torso (6%). As a group the affected transgenic mice manifested with a skin disorder that fulfilled the clinical diagnostic criteria established for atopic dermatitis in human patients. Pending further characterization to authenticate it as a model of atopic dermatitis, this experimental animal model of pruritic inflammatory skin disease may facilitate investigations for the roles of interleukin-4 in cutaneous inflammation and skin infection in human patients.

Animals↗

PubMed2001

Overexpression of the focal adhesion kinase (p125FAK) in the vascular smooth muscle cells of intimal hyperplasia.

PURPOSE: The migration and proliferation of vascular smooth muscle cells (VSMCs) are important events in the development of intimal hyperplasia (IH). The focal adhesion kinase (FAK) gene encodes a protein tyrosine kinase (p125FAK) involved in signal transduction pathways used in cell adhesion, motility, and proliferation. Because alterations in these cellular processes are thought to occur in VSMCs during IH, we studied FAK expression in healthy arteries and veins in comparison with that in pathologic vessels containing IH. METHODS: To determine p125FAK expression at the cellular level, we developed a monoclonal antibody that specifically detected FAK in formalin-fixed, paraffin-embedded tissue sections (5 microm) and analyzed the levels of FAK expression in human arteries and veins. Specificity of monoclonal antibody 4.47 was demonstrated by means of immunofluorescence microscopy showing FAK-specific staining at focal adhesions of healthy human vascular smooth muscle cells (AoSMCs). By using immunohistochemistry techniques, we analyzed the expression of p125FAK in 25 adult human vascular tissue samples from individual patients, which contained a histologically confirmed healthy artery, vein, or IH. RESULTS: FAK expression in healthy and pathologic human vascular tissue was localized predominantly within VSMC cytoplasm. In healthy human artery and vein, borderline FAK expression was detected in the media of seven of 17 vessels and undetectable in the remainder of specimens. However, in vessels containing IH, FAK was overexpressed in the pathologic VSMC populations at moderate-to-strong levels in eight of eight specimens. The levels of FAK expression were directly correlated with structures containing IH, and the results of FAK staining intensity and the percentage of positive cells in these samples were significantly increased compared with normal vascular tissue levels (P <.05, Student t test). CONCLUSION: These results provide the first evidence that FAK is overexpressed in VSMCs involved in IH and suggest that FAK upregulation may be part of a mechanism for migration and proliferation of VSMCs during this process. Furthermore, the dramatic upregulation of FAK in IH and the relative lack of expression in healthy vessels suggest that FAK may be a rational target for controlling IH.

Cells, Cultured↗

PubMed2001

New norditerpenoid alkaloids from the roots of Aconitum geniculatum.

Four new norditerpenoid alkaloids, geniculatines A (1), B (4), C (7) and D (8), were isolated from the roots of Aconitum geniculatum Fletcher, and their structures were elucidated by spectral methods.

Alkaloids↗

PubMed2001

Caenorhabditis elegans MES-3 is a target of GLD-1 and functions epigenetically in germline development.

The maternal-effect sterile (MES) proteins are maternally supplied regulators of germline development in Caenorhabditis elegans. In the hermaphrodite progeny from mes mutant mothers, the germline dies during larval development. On the basis of the similarities of MES-2 and MES-6 to known transcriptional regulators and on the basis of the effects of mes mutations on transgene expression in the germline, the MES proteins are predicted to be transcriptional repressors. One of the MES proteins, MES-3, is a novel protein with no recognizable motifs. In this article we show that MES-3 is localized in the nuclei of embryos and germ cells, consistent with its predicted role in transcriptional regulation. Its distribution in the germline and in early embryos does not depend on the wild-type functions of the other MES proteins. However, its nuclear localization in midstage embryos and its persistence in the primordial germ cells depend on wild-type MES-2 and MES-6. These results are consistent with biochemical data showing that MES-2, MES-3, and MES-6 associate in a complex in embryos. The distribution of MES-3 in the adult germline is regulated by the translational repressor GLD-1: MES-3 is absent from the region of the germline where GLD-1 is known to be present, MES-3 is overexpressed in the germline of gld-1 mutants, and GLD-1 specifically binds the mes-3 3' untranslated region (3' UTR). Analysis of temperature-shifted mes-3(bn21ts) worms and embryos indicates that MES-3 function is required in the mother's germline and during embryogenesis to ensure subsequent normal germline development. We propose that MES-3 acts epigenetically to induce a germline state that is inherited through both meiosis and mitosis and that is essential for survival of the germline.

3' Untranslated Regions↗

PubMed2001

Depletion of a novel SET-domain protein enhances the sterility of mes-3 and mes-4 mutants of Caenorhabditis elegans.

Four maternal-effect sterile genes, mes-2, mes-3, mes-4, and mes-6, are essential for germline development in Caenorhabditis elegans. Homozygous mes progeny from heterozygous mothers are themselves fertile but produce sterile progeny with underproliferated and degenerated germlines. All four mes genes encode chromatin-associated proteins, two of which resemble known regulators of gene expression. To identify additional components in the MES pathway, we used RNA-mediated interference (RNAi) to test candidate genes for enhancement of the Mes mutant phenotype. Enhancement in this assay was induction of sterility a generation earlier, in the otherwise fertile homozygous progeny of heterozygous mothers, which previous results had suggested represent a sensitized genetic background. We tested seven genes predicted to encode regulators of chromatin organization for RNAi-induced enhancement of mes-3 sterility and identified one enhancer, called set-2 after the SET domain encoded by the gene. Depletion of SET-2 also enhances the sterile phenotype of mes-4 but not of mes-2 or mes-6. set-2 encodes two alternatively spliced transcripts, set-2(l) and set-2(s), both of which are enriched in the germline of adults. In the adult germline, SET-2(L) protein is localized in mitotic and mid-late-stage meiotic nuclei but is undetectable in early pachytene nuclei. SET-2(L) protein is localized in all nuclei of embryos. The localization of SET-2(L) does not depend on any of the four MES proteins, and none of the MES proteins depend on SET-2 for their normal localization. Our results suggest that SET-2 participates along with the MES proteins in promoting normal germline development.

Alleles↗

PubMed2001

Overexpression of HSP72 after induction of experimental stroke protects neurons from ischemic damage.

The 72-kD inducible heat shock protein (HSP72) can attenuate cerebral ischemic injury when overexpressed before ischemia onset. Whether HSP72 overexpression is protective when applied after ischemia onset is not known, but would have important clinical implications. Fifty-seven rats underwent middle cerebral artery occlusion for 1 hour. Defective herpes simplex viral (HSV) vectors expressing hsp72 with lacZ as a reporter were delivered 0.5, 2, and 5 hours after ischemia onset into each striatum. Control animals received an identical vector containing only lacZ. Striatal neuron survival at 2 days was improved by 23% and 15% when HSP72 vectors were delayed 0.5 and 2 hours after ischemic onset, respectively ( P < 0.05). However, when delayed by 5 hours, HSP72 overexpression was no longer protective. This is the first demonstration that HSP72 gene transfer even after ischemia onset is neuroprotective. Because expression from these HSV vectors begins 4 to 6 hours after injection, this suggests that the temporal therapeutic window for HSP72 is at least 6 hours after ischemia onset. Future strategies aimed at enhancing HSP72 expression after clinical stroke may be worth pursuing. The authors suggest that in the future HSP72 may be an effective treatment for stroke.

Animals↗

PubMed2001

Reciprocal modulation of voltage-gated and background K(+) channels mediated by nucleotides and corticotropin.

Bovine adrenal zona fasciculata (AZF) cells express two types of K(+)-selective ion channels including a rapidly inactivating bKv1.4 current (I(A)) and an ATP-dependent noninactivating background current (I(AC)) that sets the resting membrane potential. Whole-cell, patch-clamp recording from cultured AZF cells was used to demonstrate a novel reciprocal modulation of these two K(+) channels by intracellular nucleotides and corticotropin. Specifically, increases in I(AC) activity induced by intracellular ATP, as well as GTP and 5'-adenylyl-imidodiphosphate (AMP-PNP), were accompanied by a corresponding decrease in the amplitude of the voltage-gated I(A) current. The reduction in I(A) current was observed only when patch pipettes contained ATP or other nucleotides at concentrations sufficient to support activation of I(AC). Conversely, the nearly complete inhibition of I(AC) by corticotropin was accompanied by the coincident reappearance of functional I(A) channels. In the absence of I(AC) current, corticotropin failed to alter I(A). The reciprocal modulation of AZF cell K(+) channels by nucleotides and corticotropin was independent of membrane voltage. These results demonstrate a new form of channel modulation in which the activity of two different K(+) channels is reciprocally modulated in tandem through hormonal and metabolic signaling pathways. They further suggest that I(A) and I(AC) K(+) channels may be functionally coupled in a dynamic equilibrium driven by intracellular ATP and G-protein-coupled receptors. This may represent a unique mechanism for transducing biochemical signals to ionic events involved in cortisol secretion.

Adenosine Triphosphate↗

PubMed2001

Role for phospholipase D in receptor-mediated endocytosis.

In response to epidermal growth factor (EGF), the EGF receptor is endocytosed and degraded. A substantial lag period exists between endocytosis and degradation, suggesting that endocytosis is more than a simple negative feedback. Phospholipase D (PLD), which has been implicated in vesicle formation in the Golgi, is activated in response to EGF and other growth factors. We report here that EGF receptor endocytosis is dependent upon PLD and the PLD1 regulators, protein kinase C alpha and RalA. EGF-induced receptor degradation is accelerated by overexpression of either wild-type PLD1 or PLD2 and retarded by overexpression of catalytically inactive mutants of either PLD1 or PLD2. EGF-induced activation of mitogen-activated protein kinase, which is dependent upon receptor endocytosis, is also dependent upon PLD. These data suggest a role for PLD in signaling that facilitates receptor endocytosis.

1-Butanol↗

PubMed2001

Best harmony, unified RPCL and automated model selection for unsupervised and supervised learning on Gaussian mixtures, three-layer nets and ME-RBF-SVM models.

After introducing the fundamentals of BYY system and harmony learning, which has been developed in past several years as a unified statistical framework for parameter learning, regularization and model selection, we systematically discuss this BYY harmony learning on systems with discrete inner-representations. First, we shown that one special case leads to unsupervised learning on Gaussian mixture. We show how harmony learning not only leads us to the EM algorithm for maximum likelihood (ML) learning and the corresponding extended KMEAN algorithms for Mahalanobis clustering with criteria for selecting the number of Gaussians or clusters, but also provides us two new regularization techniques and a unified scheme that includes the previous rival penalized competitive learning (RPCL) as well as its various variants and extensions that performs model selection automatically during parameter learning. Moreover, as a by-product, we also get a new approach for determining a set of 'supporting vectors' for Parzen window density estimation. Second, we shown that other special cases lead to three typical supervised learning models with several new results. On three layer net, we get (i) a new regularized ML learning, (ii) a new criterion for selecting the number of hidden units, and (iii) a family of EM-like algorithms that combines harmony learning with new techniques of regularization. On the original and alternative models of mixture-of-expert (ME) as well as radial basis function (RBF) nets, we get not only a new type of criteria for selecting the number of experts or basis functions but also a new type of the EM-like algorithms that combines regularization techniques and RPCL learning for parameter learning with either least complexity nature on the original ME model or automated model selection on the alternative ME model and RBF nets. Moreover, all the results for the alternative ME model are also applied to other two popular nonparametric statistical approaches, namely kernel regression and supporting vector machine. Particularly, not only we get an easily implemented approach for determining the smoothing parameter in kernel regression, but also we get an alternative approach for deciding the set of supporting vectors in supporting vector machine.

Algorithms↗