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Y Xu

Publications and source records attributed to Y Xu.

At least 235 records · Page 13Linked to original sources
PubMed2001

Proteasome-independent disruption of PML oncogenic domains (PODs), but not covalent modification by SUMO-1, is required for human cytomegalovirus immediate-early protein IE1 to inhibit PML-mediated transcriptional repression.

Human cytomegalovirus (HCMV) major immediate-early protein IE1 is an abundant 72-kDa nuclear phosphoprotein that is thought to play an important role in efficient triggering of the lytic cycle, especially at low multiplicity of infection. The best-known properties of IE1 at present are its transient targeting to punctate promyelocytic leukemia protein (PML)-associated nuclear bodies (PML oncogenic domains [PODs] or nuclear domain 10 [ND10]), with associated displacement of the cellular PML tumor suppressor protein into a diffuse nucleoplasmic form and its association with metaphase chromosomes. Recent studies have shown that the targeting of PML (and associated proteins such as hDaxx) to PODs is dependent on modification of PML by ubiquitin-like protein SUMO-1. In this study, we provide direct evidence that IE1 is also covalently modified by SUMO-1 in both infected and cotransfected cells, as well as in in vitro assays, with up to 30% of the protein representing the covalently conjugated 90-kDa form in stable U373/IE1 cell lines. Lysine 450 was mapped as the major SUMO-1 conjugation site, but a point mutation of this lysine residue in IE1 did not interfere with its targeting to and disruption of the PODs. Surprisingly, unlike PML or IE2, IE1 did not interact with either Ubc9 or SUMO-1 in yeast two-hybrid assays, suggesting that some additional unknown intranuclear cofactors must play a role in IE1 sumoylation. Interestingly, stable expression of either exogenous PML or exogenous Flag-SUMO-1 in U373 cell lines greatly enhanced both the levels and rate of in vivo IE1 sumoylation during HCMV infection. Unlike the disruption of PODs by the herpes simplex virus type 1 IE110(ICP0) protein, the disruption of PODs by HCMV IE1 proved not to involve proteasome-dependent degradation of PML. We also demonstrate here that the 560-amino-acid PML1 isoform functions as a transcriptional repressor when fused to the GAL4 DNA-binding domain and that wild-type IE1 inhibits the repressor function of PML1 in transient cotransfection assays. Furthermore, both IE1(1-346) and IE1(L174P) mutants, which are defective in displacing PML from PODs, failed to inhibit the repression activity of PML1, whereas the sumoylation-negative IE1(K450R) mutant derepressed as efficiently as wild-type IE1. Taken together, our results suggest that proteasome-independent disruption of PODs, but not IE1 sumoylation, is required for efficient IE1 inhibition of PML-mediated transcriptional repression.

Animals↗
PubMed2001

Evaluation of interactions of human cytomegalovirus immediate-early IE2 regulatory protein with small ubiquitin-like modifiers and their conjugation enzyme Ubc9.

The human cytomegalovirus (HCMV) major immediate-early protein IE2 is a nuclear phosphoprotein that is believed to be a key regulator in both lytic and latent infections. Using yeast two-hybrid screening, small ubiquitin-like modifiers (SUMO-1, SUMO-2, and SUMO-3) and a SUMO-conjugating enzyme (Ubc9) were isolated as IE2-interacting proteins. In vitro binding assays with glutathione S-transferase (GST) fusion proteins provided evidence for direct protein-protein interaction. Mapping data showed that the C-terminal end of SUMO-1 is critical for interaction with IE2 in both yeast and in vitro binding assays. IE2 was efficiently modified by SUMO-1 or SUMO-2 in cotransfected cells and in cells infected with a recombinant adenovirus expressing HCMV IE2, although the level of modification was much lower in HCMV-infected cells. Two lysine residues at positions 175 and 180 were mapped as major alternative SUMO-1 conjugation sites in both cotransfected cells and an in vitro sumoylation assay and could be conjugated by SUMO-1 simultaneously. Although mutations of these lysine residues did not interfere with the POD (or ND10) targeting of IE2, overexpression of SUMO-1 enhanced IE2-mediated transactivation in a promoter-dependent manner in reporter assays. Interestingly, many other cellular proteins identified as IE2 interaction partners in yeast two-hybrid assays also interact with SUMO-1, suggesting that either directly bound or covalently conjugated SUMO moieties may act as a bridge for interactions between IE2 and other SUMO-1-modified or SUMO-1-interacting proteins. When we investigated the intracellular localization of SUMO-1 in HCMV-infected cells, the pattern changed from nuclear punctate to predominantly nuclear diffuse in an IE1-dependent manner at very early times after infection, but with some SUMO-1 protein now associated with IE2 punctate domains. However, at late times after infection, SUMO-1 was predominantly detected within viral DNA replication compartments containing IE2. Taken together, these results show that HCMV infection causes the redistribution of SUMO-1 and that IE2 both physically binds to and is covalently modified by SUMO moieties, suggesting possible modulation of both the function of SUMO-1 and protein-protein interactions of IE2 during HCMV infection.

Amino Acid Sequence↗
PubMed2001

Reconstitution of enhancer function in paternal pronuclei of one-cell mouse embryos.

How chromatin-mediated transcription regulates the beginning of mammalian development is currently unknown. Factors responsible for promoter repression and enhancer-mediated relief of this repression are not present in the paternal pronuclei of one-cell mouse embryos but are present in the zygotic nuclei of two-cell embryos. Here we show that coinjection of purified histones and a plasmid-encoded reporter gene into the paternal pronuclei of one-cell embryos at a specific histone-DNA concentration could recreate the behavior observed in two-cell embryos: acquisition of promoter repression and subsequent relief of this repression either by functional enhancers or by histone deacetylase inhibitors. Furthermore, the extent of enhancer-mediated stimulation in one-cell embryos depended on the acetylation status of the injected histones, on the treatment of embryos with a histone deacetylase inhibitor, and on the developmentally regulated appearance of enhancer-specific coactivator activity. The coinjected plasmids in one-cell embryos also exhibited chromatin assembly, as determined by a supercoiling assay. Thus, injection of histones into one-cell embryos faithfully reproduced the chromatin-mediated transcription observed in two-cell embryos. These results suggest that the need for enhancers to stimulate promoters through relief of chromatin-mediated repression occurs once the parental genomes are organized into chromatin. Furthermore, we present a model mammalian system in which the role of individual histones, and particular domains within the histones that are targeted in enhancer function, can be examined using purified mutant histones.

Animals↗
PubMed2001

A common mechanism for concurrent changes of diastolic muscle length and systolic function in intact hearts.

Mechanical properties of the myocardium at end diastole have been thought to be dominated by passive material properties rather than by active sarcomere cross-bridge interactions. This study tested the hypothesis that residual cross-bridges significantly contribute to end-diastolic mechanics in vivo and that changes in end-diastolic cross-bridge interaction parallel concurrent changes in systolic cross-bridge interaction. Open-chest anesthetized pigs were treated with intracoronary verapamil (n = 7) or 2,3-butanedione monoxime (BDM; n = 8). Regional left ventricular external work and end-diastolic pressure (EDP) versus end-diastolic segment length (EDL) relations were determined in the treated and untreated regions of each heart. Both agents reduced external work of treated regions to 31-38% of baseline and concurrently shifted EDP versus EDL relations to the right (i.e., greater EDL at a given EDP) by an average of 5% (P < 0.05). During washout of the drugs, EDP versus EDL returned to baseline in parallel with recovery of external work. Sarcomere length, measured by transmission electron microscopy in BDM-treated and untreated regions of the same hearts after diastolic arrest and perfusion fixation, was 8% greater in BDM-treated regions (P < 0.01). We concluded that residual diastolic cross-bridges significantly and reversibly influence end-diastolic mechanics in vivo. Alterations of end-diastolic and systolic cross-bridge interactions occur in parallel.

Animals↗
PubMed2001

Experimental models of acute respiratory distress syndrome: clinical relevance and response to surfactant therapy.

Surfactant therapy for acute respiratory distress syndrome (ARDS) has shown encouraging results in animal studies, but not always in clinical trials. Efficacy of this therapy may be limited to ARDS caused by indirect injury, but mistiming of its application in clinical trials may be responsible for the discouraging results. In addition, the therapy may not last long enough to be effective. In rats with acidified milk aspiration, the effects of aerosolized surfactant therapy followed by inhalation of aerosolized dextran (molecular weight, 40,000) last significantly longer than those of aerosolized surfactant therapy alone. This mode of surfactant therapy could lead to better results since it can be started and repeated at any time.

Aerosols↗
PubMed2001

Induction of urokinase receptor expression in nephrotoxic nephritis.

The urokinase receptor (uPAR) is a multifunctional molecule involved in pericellular, fibrinolytic, and proteolytic activities, as well as in cell adhesion and chemotaxis and may play a role in the pathogenesis of tissue remodeling occurring during glomerulonephritis. We analyzed sequentially the expression of uPAR by immunohistochemistry and in situ hybridization in an accelerated model of nephrotoxic nephritis in rats. A strong induction of uPAR mRNA expression was observed in glomeruli as soon as 1 h after nephrotoxic serum injection. The intensity of glomerular uPAR mRNA and antigen expression increased and peaked at 24 h. At that time, numerous glomerular fibrin deposits, monocyte/marcrophage infiltration, and heavy proteinuria were observed. Fibrin deposition was detected at 6 h, peaked at 24 h, and progressively declined over the next 3 weeks, while uPAR antigen expression remained elevated until the end of the study (3 weeks). By double labeling, we showed that the expression of uPAR was mediated by both intrinsic glomerular cells and infiltrating macrophages. Severe podocytic lesions developed within 3 days after antiserum injection, and glomerulosclerosis rapidly progressed within 2-3 weeks. These results show that glomerular uPAR expression is induced in nephrotoxic nephritis and suggest that uPAR may promote local proteolysis and also tissue remodeling, leading to the late development of glomerulosclerosis.

Animals↗
PubMed2001

Dorsal and ventral medullary catecholamine cell groups contribute differentially to systemic interleukin-1beta-induced hypothalamic pituitary adrenal axis responses.

Medial parvocellular paraventricular corticotropin-releasing hormone (mPVN CRH) cells are critical in generating hypothalamic-pituitary-adrenal (HPA) axis responses to systemic interleukin-1beta (IL-1beta). However, although it is understood that catecholamine inputs are important in initiating mPVN CRH cell responses to IL-1beta, the contributions of distinct brainstem catecholamine cell groups are not known. We examined the role of nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM) catecholamine cells in the activation of mPVN CRH, hypothalamic oxytocin (OT) and central amygdala cells in response to IL-1beta (1 microg/kg, i.a.). Immunolabelling for the expression of c-fos was used as a marker of neuronal activation in combination with appropriate cytoplasmic phenotypic markers. First we confirmed that PVN 6-hydroxydopamine lesions, which selectively depleted catecholaminergic terminals, significantly reduced IL-1beta-induced mPVN CRH cell activation. The contribution of VLM (A1/C1 cells) versus NTS (A2 cells) catecholamine cells to mPVN CRH cell responses was then examined by placing ibotenic acid lesions in either the VLM or NTS. The precise positioning of these lesions was guided by prior retrograde tracing studies in which we mapped the location of IL-1beta-activated VLM and NTS cells that project to the mPVN. Both VLM and NTS lesions reduced the mPVN CRH and OT cell responses to IL-1beta. Unlike VLM lesions, NTS lesions also suppressed the recruitment of central amygdala neurons. These studies provide novel evidence that both the NTS and VLM catecholamine cells have important, but differential, contributions to the generation of IL-1beta-induced HPA axis responses.

Adrenal Glands↗
PubMed2001

Expression of yeast apurinic/apyrimidinic endonuclease (APN1) protects lung epithelial cells from bleomycin toxicity.

Bleomycin is a well-established anti-tumor drug. Its major untoward effect, pulmonary toxicity, has limited its usage. In this study, we used a DNA repair protein, yeast apurinic/apyrimidinic endonuclease (APN1) to reduce the toxicity of bleomycin on lung cells. A549 cells, an alveolar epithelial cell line, were transduced by MIEG3 retroviral vector encoding both enhanced green fluorescent protein (EGFP) and APN1. Transduced cells were sorted by fluorescent-activated cell sorter (FACS) analysis and were cloned. The APN1 expression of transduced A549 cell population and four selected clones expressing different levels of EGFP was confirmed by Northern, Western, and apurinic/apyrimidinic (AP) endonuclease activity analyses. The expression of APN1 was positively correlated with the expression of EGFP. The protective effect of APN1 against bleomycin was determined by single cell gel electrophoresis/Comet assay and by clonogenic survival assay following bleomycin treatment. The A549 population expressing APN1 showed a significant reduction of DNA damage in the presence of 20, 50, and 100 microg/ml bleomycin; similarly, the APN1-expressing A549 population also demonstrated increased survival in the presence of bleomycin compared with the vector-transduced A549 population. In selected clones, three of four APN1-expressing clones resulted in significantly improved cell survival. The current study suggests that the yeast DNA repair protein, APN1, can reduce bleomycin toxicity to target lung cells.

Bleomycin↗
PubMed2001

Epidemiological studies on hearing impairment with reference to genetic factors in Sichuan, China.

Hearing impairment is the most common disorder of sensorineural function and is an economically and socially important cause of human morbidity. A large-scale epidemiological survey of hearing loss was conducted with 126,876 unselected subjects (63,741 male and 63,135 female) from Sichuan, China. The overall prevalence of hearing loss was 3.28% (4,164 of 126,876), and the prevalence increased with age, reaching 12.8% (1,465 of 11,421) at 60 years of age. In 73.03% of all cases (3,041 of 4,164), the hearing loss was sensorineural, and in 20.39% (849 of 4,164), it was conductive; the remaining cases (6%) were mixed hearing loss. Bilateral loss was found in 74.5% of cases (3,103 of 4,164). In 63.79% of cases (2,656 of 4,164), the degree of hearing loss was less than 55 dB hearing level (HL), and in 5.67% of cases (236 of 4,164), it was greater than 90 dB HL. The prevalence of hearing loss in childhood (<15 years of age) was 0.67% (227 of 34,157), of which 57.7% of cases were conductive and 38.8% were sensorineural. The prevalence of genetic hearing loss was 0.28% (349 of 126,876). Persons who lived in the flatlands appeared to have a higher prevalence than those who lived in the hills. Several ethnic groups, including Tibetans, the Yi, and the Lisu, had a higher prevalence of hearing loss. Presbycusis, otitis media, and genetic factors were the most commonly recognized causes of hearing impairment overall, but otitis media and genetic factors were the main causes of hearing loss in children. Causes for the observed differences in prevalence and etiologic factors between China and industrialized countries will be discussed. In China, infections and genetic factors appear to be of major importance as causes of hearing loss.

Adolescent↗
PubMed2001

Longitudinal study of health maintenance organization efficiency.

Longitudinal studies looking at health maintenance organization (HMO) efficiency in the United States have not been performed before this study--previously there have only been small inter-group studies comparing efficiencies. The objectives here were twofold: to analyse HMO efficiency longitudinally, using a data envelopment analysis (DEA) model; and to compare the various types of HMOs and their efficiency using DEA. A cohort of HMOs was followed longitudinally and a number of variables measuring efficiency were studied. Data were derived from the HMO database survey (HCIA Inc.) for 1993-1997. Thirty-six HMOs were followed over a five-year period, and baseline input and output variables were collected. These measures are proxies for efficiency using the DEA methodology. Over all, using the DEA model it was demonstrated that HMOs tended to improve efficiency over time. Independent Practice Association HMOs appeared to show the highest level of improved efficiency. HMO type, profit status, federal eligibility and age were predictive variables for efficiency. Results of this study demonstrate that HMOs are improving efficiency longitudinally, and in general, certain specific models are longitudinally more efficient than others. Moreover, attributes of efficient HMOs have been identified. For policy-makers looking at efficiency, this information can be used to determine which HMO models are more appropriate when trying to achieve cost containment and effectiveness.

Benchmarking↗
PubMed2001

Effect of chronic AT(1) receptor antagonism on postischemic functional recovery and AT(1)/AT(2) receptor proteins in isolated working rat hearts.

To determine whether chronic angiotensin II (Ang II) type I receptor (AT(1)R) antagonism improves recovery of left ventricular (LV) function after ischemia-reperfusion (IR) and increases AT(1)R and Ang II type 2 receptor (AT(2)R) protein expression in isolated working rat hearts, rats were randomized to pretreatment with either losartan (30 mg/kg/day) or UP269-6 (3 mg/kg/day), or no drug (control), for 1 week or 3 weeks before IR (50 min perfusion, 25 min ischemia, 40 min reperfusion). In vitro LV work and power and ex vivo AT(1)R and AT(2)R proteins (immunoblots) were measured. Compared to baseline perfusion, LV work and power showed variable recovery in control, losartan, and UP269-6 groups. Compared to control, losartan preserved recovery of LV work and power while UP269-6 showed less recovery after IR at both 1 week and 3 weeks. Both antagonists increased AT(2)R but not AT(1)R protein. The duration of pretreatment did not affect the expression of AT(1)R or AT(2)R proteins. The results indicate that chronic AT(1)R blockade over 1 or 3 weeks increases AT(2)R (not AT(1)R) protein expression and may preserve but not improve postischemic functional recovery compared to controls in isolated working rat hearts.

Analysis of Variance↗
PubMed2001

Systemic lupus erythematosus and B-cell hematologic neoplasm.

The association of systemic lupus erythematosus (SLE) and B-cell malignancy is widely reported in the literature. Here we report nine cases of concurrent of SLE or discoid lupus erythematosus (DLE) and lymphoma or plasma cell disorder. A MEDLINE search was done using the keywords, 'SLE' and 'lymphoma' and the characteristics of all identified cases were summarized and analyzed, along with data from our own cases. Numerous variants of B-cell malignancies were encountered in these patients. B-cell malignancy occurs after the diagnosis and treatment of SLE in most reported cases, although it may precede SLE, or occur synchronously with it. The age at onset of the B-cell neoplasm in SLE patients is similar to that in the general population. Mortality in patients with both diseases is associated with progressive B-cell neoplasm, sepsis secondary to either disease, or both. B-cell malignancy and SLE seem to run independent clinical courses rather than being affected by each other. The use of immunosuppressive drugs is common in patients with SLE diagnosed prior to B-cell lymphoma, arguing that the effect of immunosuppression on the pathogenesis of lymphoma can not be excluded. Three areas worthy of study regarding the probable mechanisms for the occurrence of SLE and B-cell malignancies are discussed. A tumor suppressor gene PTEN may link the two disorders via a defective apoptosis pathway to eliminate hyperactive B and T cells in SLE. The accumulation of clonally expanded hyperactive B-cells that recognize self-antigens in the lymph nodes of SLE may predispose these B-cells to DNA breaks, facilitating tumorigenesis. Lastly, EBV infection, found to have a high prevalence in SLE patients, may serve as a common etiological factor in both disorders.

Adult↗
PubMed2001

Clinicopathologic analysis of CD10+ and CD10- diffuse large B-cell lymphoma. Identification of a high-risk subset with coexpression of CD10 and bcl-2.

We analyzed 53 cases of diffuse large B-cell lymphoma (DLBCL) to determine whether expression of CD10 is a relevant biologic parameter. Tumor morphologic features were assessed semiquantitatively. Bcl-2 protein expression was studied by immunohistochemical analysis. The presence or absence of CD10 by flow cytometry was correlated with clinical and pathologic characteristics. CD10+ (23 cases) and CD10- (30 cases) DLBCLs were indistinguishable based on age, sex, extranodal presentation, B symptoms, clinical stage, morphologic features, or bcl-2 expression. However, cases with a CD10+ phenotype showed a significantly lower rate of complete remission. Cases expressing bcl-2 showed trends toward a lower rate of complete remission and poorer overall survival. Examination of CD10 and bcl-2 interaction revealed that the prognostic effects for both of these antigens were due to a subset of CD10+ bcl-2-positive cases. Compared with cases expressing one or neither of these markers, patients with dual-positive tumors had a poorer complete response rate to initial therapy and strikingly worse overall survival. While CD10+ and CD10- DLBCLs are similar with regard to a variety of clinical and pathologic features, CD10 and bcl-2 coexpressing tumors are an extremely high-risk subset based on response to therapy and overall survival.

Adolescent↗
PubMed2001

The effect of fulvic acid on the dose effect of selenite on the growth of wheat.

The effect of fulvic acid on the dose effect of selenite has been studied by using the hydroponics culture of wheat in the presence of selenite and fulvic acid (FA). The bioavailability of Se was investigated by 5 morphological end points and 12 biological and biochemical end points at different phases of growth of wheat seedling and seed germination. The "platform" of the dose effect observed indicates that the presence of FA can have both the beneficial effects and antagonists on the toxicity of Se to a certain extent.

Benzopyrans↗
PubMed2001

Different pathways mediate cytochrome c release after photodynamic therapy with hypericin.

In this study we show that overexpression of Bcl-2 in PC60R1R2 cells reveals a caspase-dependent mechanism of cytochrome c release following photodynamic therapy (PDT) with hypericin. Bcl-2 overexpression remarkably delayed cytochrome c release, procaspase-3 activation and poly(adenosine diphosphate-ribose)polymerase cleavage during PDT-induced apoptosis while it did not protect against PDT-induced necrosis. PDT-treated cells showed a reduction in the mitochondrial membrane potential which occurred with similar kinetics in PC60R1R2 and PC60R1R2/Bcl-2 cells, and was affected neither by the permeability transition pore inhibitor cyclosporin A nor by the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk). Hypericin-induced mitochondrial depolarization coincided with cytochrome c release in PC60R1R2 cells while it precedes massive cytochrome c efflux in PC60R1R2/Bcl-2 cells. Preincubation of PC60R1R2 cells with zVAD-fmk or cyclosporin A did not prevent the mitochondrial efflux of cytochrome c, and caspase inhibition only partially protected the cells from PDT-induced apoptosis. In contrast, in PC60R1R2/Bcl-2 cells cytochrome c release and apoptosis were suppressed by addition of zVAD-fmk or cyclosporin A. These observations suggest that the progression of the PDT-induced apoptotic process in Bcl-2-overexpressing cells involves a caspase-dependent feed-forward amplification loop for the release of cytochrome c.

Animals↗
PubMed2001

Antisense of ATP synthase subunit e inhibits the growth of human hepatocellular carcinoma cells.

Differentially expressed genes between normal and hepatocellular carcinoma tissues were investigated using differential display. We identified a cDNA fragment that was overexpressed in cancer tissue. Homology analysis showed that the sequence was identical to human ATP synthase subunit e (hAS-e). Moreover, Northern blot analysis demonstrated that hAS-e was overexpressed in 10 of 11 (91%) specimens of hepatocellular carcinoma compared with corresponding normal tissues. We introduced antisense hAS-e into a human hepatocellular carcinoma BEL-7404 cell and found that downregulation of the hAS-e led to cell growth inhibition. It was also found that the antisense transfection could decrease the serum-stimulated activation of mitogen-activated protein kinase (MAP kinase). Together, the results suggest that antisense of hAS-e can inhibit cell proliferation through the MAP kinase pathway. Our data indicate that hAS-e may become a new target in gene therapy.

Base Sequence↗
PubMed2001

Clinicopathological and molecular genetic analysis of 4 typical Chinese HNPCC families.

AIM: To study the clinicopathological and molecular genetic characteristics of typical Chinese hereditary nonpolyposis cotorectal cancer (HNPCC) families. METHODS: Four typical Chinese HNPCC families were analyzed using microdissection, microsatellite instability analysis, immunostaining of hMSH2 and hMLH1 proteins and direct DNA sequencing of hMSH2 and hMLH1 genes. RESULTS: All five tumor tissues of 4 probands from the 4 typical Chinese HNPCC families showed microsatellite instability at more than two loci (MSI-H or RER+ phenotype). Three out of the 4 cases lost hMSH2 protein expression and the other case showed no hMLH1 protein expression. Three pathological germline mutations (2 in hMSH2 and 1 in hMLH1), which had not been reported previously, were identified. The same mutations were also found in other affected members of two HNPCC families,respectively. CONCLUSION: Typical Chinese HNPCC families showed relatively frequent germline mutation of mismatch repair genes. High-level microsatellite instability and loss of expression of mismatch repair genes correlated closely with germline mutation of mismatch repair genes. Microsatellite instability analysis and immunostaining of mismatch repair gene might serve as effective screening methods before direct DNA sequencing. It is necessary to establish clinical criteria and molecular diagnostic strategies more suitable for Chinese HNPCC families.

Adult↗