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Zhen Xu

Publications and source records attributed to Zhen Xu.

At least 37 records · Page 2Linked to original sources
PubMed2004

Axin stimulates p53 functions by activation of HIPK2 kinase through multimeric complex formation.

Axin and p53 are tumor suppressors, controlling cell growth, apoptosis, and development. We show that Axin interacts with homeodomain-interacting protein kinase-2 (HIPK2), which is linked to UV-induced p53-dependent apoptosis by interacting with, and phosphorylating Ser 46 of, p53. In addition to association with p53 via HIPK2, Axin contains a separate domain that directly interacts with p53 at their physiological concentrations. Axin stimulates p53-dependent reporter transcription in 293 cells, but not in 293T, H1299, or SaOS-2 cells that are defective in p53 signaling. Axin, but not AxindeltaHIPK2, activates HIPK2-mediated p53 phosphorylation at Ser 46, facilitating p53-dependent transcriptional activity and apoptosis. Specific knockdown of Axin by siRNA reduced UV-induced Ser-46 phosphorylation and apoptosis. Kinase-dead HIPK2 reduced Axin-induced p53-dependent transcriptional activity, indicating that Axin stimulates p53 function through HIPK2 kinase activity. Interestingly, HIPK2deltaAxin that lacks its Axin-binding region acts as a dominant-positive form in p53 activation, suggesting that the Axin-binding region of HIPK2 is a putative autoinhibitory domain. These results show that Axin acts as a tumor suppressor by facilitating p53 function through integration of multiple factors.

Apoptosis↗
PubMed2004

Structures of human cytosolic NADP-dependent isocitrate dehydrogenase reveal a novel self-regulatory mechanism of activity.

Isocitrate dehydrogenases (IDHs) catalyze the oxidative decarboxylation of isocitrate to alpha-ketoglutarate, and regulation of the enzymatic activity of IDHs is crucial for their biological functions. Bacterial IDHs are reversibly regulated by phosphorylation of a strictly conserved serine residue at the active site. Eukaryotic NADP-dependent IDHs (NADP-IDHs) have been shown to have diverse important biological functions; however, their regulatory mechanism remains unclear. Structural studies of human cytosolic NADP-IDH (HcIDH) in complex with NADP and in complex with NADP, isocitrate, and Ca2+ reveal three biologically relevant conformational states of the enzyme that differ substantially in the structure of the active site and in the overall structure. A structural segment at the active site that forms a conserved alpha-helix in all known NADP-IDH structures assumes a loop conformation in the open, inactive form of HcIDH; a partially unraveled alpha-helix in the semi-open, intermediate form; and an alpha-helix in the closed, active form. The side chain of Asp279 of this segment occupies the isocitrate-binding site and forms hydrogen bonds with Ser94 (the equivalent of the phosphorylation site in bacterial IDHs) in the inactive form and chelates the metal ion in the active form. The structural data led us to propose a novel self-regulatory mechanism for HcIDH that mimics the phosphorylation mechanism used by the bacterial homologs, consistent with biochemical and biological data. This mechanism might be applicable to other eukaryotic NADP-IDHs. The results also provide insights into the recognition and specificity of substrate and cofactor by eukaryotic NADP-IDHs.

Amino Acid Sequence↗
PubMed2004

Extravasation of blood-borne immunoglobulin G through blood-brain barrier during adrenaline-induced transient hypertension in the rat.

The effect of transient hypertension on blood-brain barrier (BBB) permeability, particularly on extravasation of immunoglobulin G (IgG), has not been fully understood. In the present experiment, we investigated the time course of endogenous albumin and IgG extravasation through BBB and the localization of extravasated IgG in brain parenchyma during adrenaline(AD)-induced transient hypertension in the rat by using Evans blue fluorescence, immunohistochemistry, and Western blot. The results showed that a bolus injection of AD (10 microg/kg) induced a transient elevation of arterial pressure lasting about 1 min. The endogenous albumin and IgG entered the brain parenchyma via BBB only when hypertension occurred. Electron microscopically, the IgG-like immunoreactivities were predominantly seen in the cytoplasm of endothelia of capillaries, pericytes, extracellular space of parenchyma, and the cytoplasm of glial cells. The results suggest that circulating IgG or antibodies might contact the structures of brain parenchyma through passage of BBB when its permeability is temporally changed by transient hypertension. This phenomenon implies a possible mechanism of pathogenesis for immune-mediated diseases in the brain.

Albumins↗
PubMed2004

Controlled ultrasound tissue erosion.

The ability of ultrasound to produce highly controlled tissue erosion was investigated. This study is motivated by the need to develop a noninvasive procedure to perforate the neonatal atrial septum as the first step in treatment of hypoplastic left heart syndrome. A total of 232 holes were generated in 40 pieces of excised porcine atrial wall by a 788 kHz single-element transducer. The effects of various parameters [e.g., pulse repetition frequency (PRF), pulse duration (PD), and gas content of liquid] on the erosion rate and energy efficiency were explored. An Isppa of 9000 W/cm2, PDs of 3, 6, 12, and 24 cycles; PRFs between 1.34 kHz and 66.7 kHz; and gas saturation of 40-55% and 79-85% were used. The results show that very short pulses delivered at certain PRFs could maximize the erosion rate and energy efficiency. We show that well-defined perforations can be precisely located in the atrial wall through the controlled ultrasound tissue erosion (CUTE) process. A preliminary in vivo experiment was conducted on a canine subject, and the atrial septum was perforated using CUTE.

Animals↗
PubMed2004

[Environmental carcinogens and p53 gene mutation].

P53 gene is the most prominent tumor suppressor gene in human cancer among those genes that have been found till now. It not only acts as a tumor suppressor gene, but also participates in many cellular functions: cell cycle control, DNA damage and repair, gene transcription and cell apoptosis. The studies on the etiology of cancer show that 60-90% of human cancer are caused by the carcinogens in ambient environment. In the carcinogenic process, environmental carcinogens or pre-carcinogens can cause the changes in p53 gene and protein, the mutation spectra of p53 gene varies with the different carcinogens and cancer type. In these years, many studies on p53 suppressor gene were reported. This article reviews some of the major carcinogens in ambient environment which can affect the p53 gene and protein, and the carcinogenic effects of them.

Aflatoxin B1↗
PubMed2003

Transforming growth factor-beta1 stimulated protein kinase B serine-473 and focal adhesion kinase tyrosine phosphorylation dependent on cell adhesion in human hepatocellular carcinoma SMMC-7721 cells.

Transforming growth factor-beta1 (TGF-beta1) is a potent growth inhibitor and apoptosis inducer for most normal cells. However, tumor cells are commonly nevertheless sensitive to the tumor-suppressing effects of TGF-beta1. In this paper, we focus on the effects of TGF-beta1 on two important anti-apoptotic protein kinases, protein kinase B (PKB), and focal adhesion kinase (FAK), in SMMC-7721 cells. We found that PKB-Ser-473 phosphorylation was apparently up-regulated by TGF-beta1. In the meantime, PKB-Thr-308 phosphorylation was slightly up-regulated by TGF-beta1. TGF-beta1 could also enhance FAK-Tyr phosphorylation. We observed that integrin-linked kinase (ILK) was also up-regulated by TGF-beta1 in good accordance with PKB-Ser-473 phosphorylation. We first found that TGF-beta1 could stimulate PKB-Ser-473 phosphorylation possibly via up-regulating ILK expression. Furthermore, we also failed to detect PKB-Ser-473 and FAK-Tyr phosphorylation with various concentrations of TGF-beta1 treatment when cells were kept in suspension. The above results indicate that PKB-Ser-473 and FAK-Tyr phosphorylation stimulated by TGF-beta1 are both dependent on cell adhesion.

Carcinoma, Hepatocellular↗
PubMed2003

[p120(ctn) tyrosine phosphorylation are involved in the biologic behavior changes of hepatocellular carcinoma cells].

OBJECTIVE: In hepatocellular carcinoma cells, the tyrosine phosphorylation of p120(ctn) was stimulated by epidermal growth factor (EGF) to investigate the relationship between the tyrosine phosphorylation of p120(ctn) and the translocation of p120(ctn), also the relationship between the tyrosine phosphorylation of p120(ctn) and the biological behaviour of hepatocellular carcinoma cells. The role of p120(ctn) in the cell adhesion and signaling of hepatocellular carcinoma is to be investigated. METHODS: In BEL-7404 human hepatocellular carcinoma cells, the tyrosine phosphotyrosine of p120(ctn) stimulated by EGF were detected by immunoprecipitation (IP) and Immunoblotting (IB). The cellular distribution and translocation of p120(ctn) and beta-catenin were detected and examined by indirect intracellular immunofluorescence. Cell morphology and cell adhesion potential were also detected using correspondent methods. Antisense nucleotide of p120(ctn) was transfected into BEL-7404 cells. RESULTS: The tyrosine phosphorylation of p120(ctn) was enhanced after EGF treatment than control, especially at 20min after EGF treatment; When BEL-7404 cells were transfected with antiseuse nucleotide of p120(ctn) before EGF treatment, the tyrosine phosphorylation of p120(ctn) stimulated by EGF was obviously lowered. We also observed that the tyrosine phosphorylation of p120(ctn) stimulated by EGF was accompanied by the nuclear translocation of p120(ctn); the similar translocation was also observed in beta-catenin after EGF stimulation. At the meantime, cell adhesion potential was reduced after EGF treatment and cell morphology became thin, elongated and irregular, speudopods increased. CONCLUSIONS: In BEL-7404 cells,the tyrosine phosphorylation of p120(ctn) could be stimulated by EGF, which was accompanied by the nuclear accumulation of p120(ctn). The tyrosine phosphorylation of p120(ctn) stimulated by EGF was also in correlation with the changes of cell adhesion and cell morphology. The results indicated that the tyrosine phosphorylation of p120(ctn) cell correlated with the translocation of p120(ctn) and the biological behavior of cells.

Active Transport, Cell Nucleus↗
PubMed2003

Ephrin-B1 reverse signaling activates JNK through a novel mechanism that is independent of tyrosine phosphorylation.

Eph receptors and their cognate ligand ephrins play important roles in various biological processes such as cell migration, axon guidance, and synaptic plasticity. One characteristic feature of the Eph-ephrin signal transduction is that, upon interaction with the receptor, the transmembrane B-class ephrins become tyrosine-phosphorylated and transduce intracellular signals that lead to reorganization of the cytoskeleton. Although in vitro and genetic studies have demonstrated unequivocally the significance of this reverse signaling, the underlying mechanism remains unclear. We report here that transfection of ephrin-B1 into 293 cells resulted in robust increase in JNK activity, whereas expression of truncated ephrin-B1 lacking the cytoplasmic domain had a negligible effect, indicating that the induction of JNK activity was attributed mainly to the reverse signaling. The ephrin-B1-mediated JNK activation was reduced significantly by dominant-negative TAK1, MKK4, or MKK7. Ephrin-B1 over-expressing 293 cells became rounded in morphology. Surprisingly, ephrin-B1 that lacked all six intracellular tyrosine residues still triggered JNK activation and rounding morphology of the transfected cells. Consistent with these observations, activation of JNK and the resulting morphological changes mediated by ephrin-B1 could be abolished by the JNK inhibitor SP600125 but not the Src inhibitor PP2. Taken together, our findings have identified a novel reverse signaling pathway transduced by ephrin-B1, which is independent of tyrosine phosphorylation but involves the activation of JNK through TAK1 and MKK4/MKK7 and leads to changes in cell morphology.

Animals↗
PubMed2003

PKB phosphorylation and survivin expression are cooperatively regulated by disruption of microfilament cytoskeleton.

Changes in cell shape can lead to detachment and cell death, and the disruption in the actin cytoskeletal network, as one marker of cell shape changes, can itself induce apoptosis. In this study, the effects of cytochalasin B on the apoptosis-related proteins, protein kinase B and survivin were investigated. Apoptosis induced by disruption of microfilaments with cytochalasin B was found, although it happened at a low level, to simultaneously occur with G2/M arrest in 50% of the cytochalasin B-treated cells. During apoptosis, PKB phosphorylation and survivin expression were decreased by cytochalasin B, and the decline in survivin expression was preceded by PKB dephosphorylation, which implicated that survivin may be a target of PKB protein. The G2/M arrest of cytochalasin B-treated cells may be the direct function of cytochalasin B to microfilaments or the subsequent inhibition of survivin expression, or both. These results suggest that PKB/survivin signaling pathway may be responsible for the apoptosis induced by the disruption of actin cytoskeleton.

Actins↗
PubMed2003

Trichloroacetic acid-induced molten globule state of aminoacylase from pig kidney.

The trichloroacetic acid (TCA)-induced unfolding of aminoacylase was investigated by measurement of aggregation, enzyme activity, intrinsic fluorescence, 8-anilino-1-naphthalene sulfonate (ANS) binding, circular dichroism, and native polyacrylamide gel electrophoresis. The results showed that TCA caused inactivation and unfolding of aminoacylase. Intrinsic fluorescence results demonstrated that the TCA-induced transition of aminoacylase was characterized by two distinct stages during which the fluorescence emission maxima first redshifted to 338 nm and then blueshifted to 332 nm, close to that of native protein. ANS binding measurements revealed that TCA-denatured aminoacylase had a large hydrophobic area for TCA concentration near 2 mM. Comparison of the relative changes in wavelength shift and in the ANS intensity suggested the formation of a stable molten globule state of aminoacylase with a slightly disrupted tertiary structure and more hydrophobic surface than the native protein. Far-UV circular dichroism results provided further support that TCA induced the formation of two partially folded intermediates each with an enhanced native-like secondary structure. The results collectively suggest that a TCA-induced molten globule state is formed and stabilized during unfolding of aminoacylase and that association of the molten globule state may account for precipitation of the protein when denatured by TCA.

Amidohydrolases↗
PubMed2003

TGF-beta1-promoted epithelial-to-mesenchymal transformation and cell adhesion contribute to TGF-beta1-enhanced cell migration in SMMC-7721 cells.

Transforming growth factor-b1 (TGF-beta1), a multi-function polypeptide, is a double-edged sword in cancer. For some tumor cells, TGF-beta1 is a potent growth inhibitor and apoptosis inducer. More commonly, TGF-beta1 loses its growth-inhibitory and apoptosis-inducing effects, but stimulates the metastatic capacity of tumor cells. It is currently little known about TGF-beta1-promoted cell migration in hepatocellular carcinoma (HCC) cells, let alone its mechanism. In this study, we found that TGF-beta1 lost its tumor-suppressive effects, but significantly stimulated cell migration in SMMC-7721 human HCC cells. By FACS and Western blot analysis, we observed that TGF-beta1 enhanced the expression of alpha5beta1 integrin obviously, and subsequently stimulated cell adhesion onto fibronectin (Fn). Furthermore, we observed that TGF-beta1 could also promote SMMC-7721 cells adhesion onto laminin (Ln). Our data also provided evidences that TGF-beta1 induced epithelial-to-mesenchymal transformation (EMT) in SMMC-7721 cells. First, SMMC-7721 cells clearly switched to the spindle shape morphology after TGF-beta1 treatment. Furthermore, TGF-beta1 induced the down-regulation of E-cadherin and the nuclear translocation of beta-catenin. These results indicated that TGF-beta1-promoted cell adhesion and TGF-beta1-induced epithelial-to-mesenchymal transformation might be both responsible for TGF-beta1-enhanced cell migration.

Carcinoma, Hepatocellular↗
PubMed2003

Crystal structure of D-Hydantoinase from Burkholderia pickettii at a resolution of 2.7 Angstroms: insights into the molecular basis of enzyme thermostability.

D-Hydantoinase (D-HYD) is an industrial enzyme that is widely used in the production of D-amino acids which are precursors for semisynthesis of antibiotics, peptides, and pesticides. This report describes the crystal structure of D-hydantoinase from Burkholderia pickettii (HYD(Bp)) at a 2.7-A resolution. The structure of HYD(Bp) consists of a core (alpha/beta)(8) triose phosphate isomerase barrel fold and a beta-sheet domain, and the catalytic active site consists of two metal ions and six highly conserved amino acid residues. Although HYD(Bp) shares only moderate sequence similarity with D-HYDs from Thermus sp. (HYD(Tsp)) and Bacillus stearothermophilus (HYD(Bst)), whose structures have recently been solved, the overall structure and the structure of the catalytic active site are strikingly similar. Nevertheless, the amino acids that compose the substrate-binding site are less conserved and have different properties, which might dictate the substrate specificity. Structural comparison has revealed insights into the molecular basis of the differential thermostability of D-HYDs. The more thermostable HYD(Tsp) contains more aromatic residues in the interior of the structure than HYD(Bp) and HYD(Bst). Changes of large aromatic residues in HYD(Tsp) to smaller residues in HYD(Bp) or HYD(Bst) decrease the hydrophobicity and create cavities inside the structure. HYD(Tsp) has more salt bridges and hydrogen-bonding interactions and less oxidation susceptible Met and Cys residues on the protein surface than HYD(Bp) and HYD(Bst). Besides, HYD(Tsp) also contains more rigid Pro residues. These factors are likely to make major contributions to the varying thermostability of these enzymes. This information could be exploited in helping to engineer more thermostable mesophilic enzymes.

Amidohydrolases↗
PubMed2003

Treatment of medium and late stage esophageal carcinoma with combined endoscopic metal stenting and radiotherapy.

OBJECTIVE: To evaluate clinical feasibility and efficacy of endoscopic metal stenting combined with radiotherapy for treatment of medium and late stages of esophageal carcinoma. METHODS: Thirty-four patients of late stage esophageal carcinoma were treated with endoscopic stent implantation in combination with radiotherapy. Evaluations of CES stainless steel metal stent on the effect of radiation, clinical symptom alleviation and complication and survival rates in both groups were made. RESULTS: (1) CES stainless steel metal stent had no effect on radiation dosage distribution. (2) Dysphagia was markedly alleviated in both groups and different complication rates were observed between the two groups. (3) Six, nine and twelve month survival rates of inpatients treated with combined therapies were significantly higher than in simple stent implantation patients. CONCLUSION: Endoscopic metal stenting in combination with radiotherapy was a feasible and practical management in treating medium and late stages esophageal carcinoma and was superior to simple metal stent implantation.

Aged↗
PubMed2003

[Main indoor air pollutants and their health impacts].

The quality of indoor air is a very important factor that may directly affect human health. There are many sources as well as a variety of indoor air pollutants. Therefore, the health impact is complicated, affecting different organs and systems of human being such as respiratory and immune system. The main indoor air pollutants are the combustion products from smoking, cooking and heating, the chemical pollutants from renovation materials and the biological contaminants. The kinds, sources and health impacts of these pollutants that affect the indoor air quality are reviewed in this paper.

Air Pollutants↗
PubMed2002

Extracellular signal-regulated kinases1/2 in neurons of the dorsal motor nucleus of the vagus nerve and nucleus of the solitary tract are activated by noxious visceral stimulus in mice.

Phosphorylated extracellular signal-regulated kinases1/2 (pERK1/2) -like immunoreactivity (LI) was enhanced in the neurons of the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus nerve (DMV) 8 min after an intraperitoneal injection of acetic acid in the mouse; the enhancement in pERK1/2-LI was suppressed after vagotomy. With immunofluorescent double labeling technique, the co-localization of acetic acid-induced pERK1/2 and tyrosine hydroxylase-LIs was observed in some of the NTS and DMV neurons. These results suggest that ERK1/2 signal-transducting pathway is involved in neuronal activities in NTS and DMV which are induced by vagus-conveyed nociceptive visceral information, and that some of these pERK1/2- immunoreactive neurons in NTS and DMV are catecholaminergic.

Acetic Acid↗
PubMed2002

SUMO-1 modification of the C-terminal KVEKVD of Axin is required for JNK activation but has no effect on Wnt signaling.

Axin is a multifunctional protein, regulating Wnt signaling and the c-Jun N-terminal/stress-activated protein kinase (JNK/SAPK) pathway as well as tumorigenesis. In the present study, we found that Axin interacts with three SUMO-1 (small ubiquitin-related modifier) conjugating enzymes 3 (E3), PIAS1, PIASxbeta, and PIASy. The extreme C-terminal six amino acid residues of Axin are critical for the Axin/E3 interaction as deletion of the six residues (AxinDeltaC6) completely abolished the ability of Axin to interact with E3 enzymes. AxinDeltaC6 also failed to activate JNK, although it was intact in both its interaction with MEKK1 and homodimerization. Consistent with the presence of a doublet of the KV(E/D) sumoylation consensus motif at the C-terminal end (KVEKVD), we found that Axin is heavily sumoylated. Deletion of the C-terminal six amino acids drastically reduced sumoylation, indicating that the C-terminal six amino acids stretch is the main sumoylation site for Axin. Sumoylation-defective mutants failed to activate JNK but effectively destabilized beta-catenin and attenuated LEF1 transcriptional activity. In addition, we show that dominant negative Axin mutants blocked PIAS-mediated JNK activation, in accordance with the requirement of sumoylation for Axin-mediated JNK activation. Taken together, we demonstrate that sumoylation plays a role for Axin to function in the JNK pathway.

Amino Acid Sequence↗
PubMed2002

Evidences for vagus nerve in maintenance of immune balance and transmission of immune information from gut to brain in STM-infected rats.

AIM: To determine whether Salmonella Typhimurium (STM)in gastrointestinal tract can induce the functional activation of brain, whether the vagus nerve involves in signaling immune information from gastrointestinal tract to brain and how it influences the immune function under natural infection condition. METHODS: Animal model of gastrointestinal tract infection in the rat was established by an intubation of Salmonella Typhimurium (STM) into stomach to mimic the condition of natural bacteria infection. Subdiagphragmatic vagotomy was performed in some of the animals 28 days before infection. The changes of Fos expression visualized with immunohistochemistry technique in hypothalamic paraventricular nucleus (PVN) and superaoptic nucleus (SON) were counted. Meanwhile, the percentage and the Mean Intensities of Fluorescent (MIFs) of CD4+ and CD8+ T cells in peripheral blood were measured by using flow cytometry (FCM), and the pathological changes in ileum and mesenteric lymph node were observed in HE stained sections. RESULTS: In bacteria-stimulated groups, inflammatory pathological changes were seen in ileum and mesenteric lymph node. The percentages of CD4+ T cells in peripheral blood were decreased from 42%+/-4.5% to 34%+/-4.9% (P<0.05) and MIFs of CD8+ T cells were also decreased from 2.9+/-0.39 to 2.1+/-0.36 (P<0.05) with STM stimulation. All of them proved that our STM-infection model was reliable. Fos immunoreactive (Fos-ir) cells in PVN and SON increased significantly with STM stimulation, from 189+/-41 to 467+/-62 (P<0.05) and from 64+/-21 to 282+/-47 (P<0.05) individually, which suggested that STM in gastrointestinal tract induced the functional activation of brain. Subdiagphragmatic vagotomy attenuated Fos expression in PVN and SON induced by STM, from 467+/-62 to 226+/-45 (P<0.05) and from 282+/-47 to 71+/-19 (P<0.05) individually, and restored the decreased percentages of CD4+ T cells induced by STM from 34%+/-4.9% to original level 44%+/-6.0% (P<0.05). In addition, subdiagphragmatic vagotomy itself also decreased the percentages of CD8+ T cells (from 28%+/-3.0% to 21%+/-5.9%, P<0.05) and MIFs of CD4+ (from 6.6+/-0.6 to 4.9+/-1.0, P<0.05) and CD8+ T cells (from 2.9+/-0.39 to 1.4+/-0.34, P<0.05). Both of them manifested the important role of vagus nerve in transmitting immune information from gut to brain and maintaining the immune balance of the organism. CONCLUSION: Vagus nerve does involve in transmitting abdominal immune information into the brain in STM infection condition and play an important role in maintenance of the immune balance of the organism.

Animals↗