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Biomedical subjects

Z Wu

Publications and source records attributed to Z Wu.

At least 271 records · Page 15Linked to original sources
PubMed1999

Farnesyl protein transferase: identification of K164 alpha and Y300 beta as catalytic residues by mutagenesis and kinetic studies.

Farnesyl protein transferase (FPT) is an alpha/beta heterodimeric zinc enzyme that catalyzes posttranslational farnesylation of many key cellular regulatory proteins, including oncogenic Ras. On the basis of the recently reported crystal structure of FPT complexed with a CVIM peptide and alpha-hydroxyfarnesylphosphonic acid, site-directed mutagenesis of the FPT active site was performed so key residues that are responsible for substrate binding and catalysis could be identified. Eight single mutants, including K164N alpha, Y166F alpha, Y166A alpha, Y200F alpha, H201A alpha, H248A beta, Y300F beta, and Y361F beta, and a double mutant, H248A beta/Y300F beta, were prepared. Steady-state kinetic analysis along with structural evidence indicated that residues Y200 alpha, H201 alpha, H248 beta, and Y361 beta are mainly involved in substrate binding. In addition, biochemical results confirm structural observations which show that residue Y166 alpha plays a key role in stabilizing the active site conformation of several FPT residues through cation-pi interactions. Two mutants, K164N alpha and Y300F beta, have moderately decreased catalytic constants (kcat). Pre-steady-state kinetic analysis of these mutants from rapid quench experiments showed that the chemical step rate constant was reduced by 41- and 30-fold, respectively. The product-releasing rate for each dropped approximately 10-fold. In pH-dependent kinetic studies, Y300F beta was observed to have both acidic and basic pKa values shifted 1 log unit from those of the wild-type enzyme, consistent with a possible role for Y300 beta as an acid-base catalyst. K164N alpha had a pKa shift from 6.0 to 5.3, which suggests it may function as a general acid. On the basis of these results along with structural evidence, a possible FPT reaction mechanism is proposed with both Y300 beta and K164 alpha playing key catalytic roles in enhancing the reactivity of the farnesyl diphosphate leaving group.

Alkyl and Aryl Transferases↗
PubMed1999

PPARgamma ligand-dependent induction of STAT1, STAT5A, and STAT5B during adipogenesis.

We have recently demonstrated that STAT1, STAT5A, and STAT5B are induced during adipogenesis of cultured preadipocytes in a differentiation-dependent manner. Members of the C/EBP and PPAR families of transcription factors have also been shown to be induced during adipocyte differentiation and to play a significant role in the regulation of fat-specific genes. In this investigation, we have examined the ability of C/EBPs and PPARs to contribute to STAT protein expression during conversion of non-precursor fibroblasts to functionally mature adipocytes. For this study, NIH-3T3 fibroblasts engineered to ectopically co-express C/EBPbeta and C/EBPdelta under the control of a tetracycline-responsive, inducible expression system were utilized to assess STAT expression during controlled adipogenesis. Data presented here demonstrate that STAT1, STAT5A, and STAT5B, but not STAT3 and STAT6, were induced in a tetracycline-responsive manner during the differentiation of these engineered fibroblasts. The STAT protein accumulation resulting from C/EBP expression was tightly coupled to the morphological conversion of fibroblasts to adipocytes and represents an expression profile identical to that reported for mature adipocytes in vivo. Data are also presented demonstrating that STAT protein accumulation and adipocyte conversion occurred only during controlled conditions leading to the expression of PPARgamma and that the expression of these three STATs was tightly regulated in a PPARgamma ligand dose-response fashion. These data illustrate that the cascade of transcriptional events leading to adipogenesis regulate the STAT family of transcription factors and that the differentiation-dependent upregulation of STAT protein expression is regulated downstream of PPARgamma in a ligand-dependent manner.

3T3 Cells↗
PubMed1999

Regulation of stretch-activated intracellular calcium transients by actin filaments.

Stretch activation of cation-permeable channels may be an important proximal sensory mechanism in mechanotransduction. As actin filaments may mediate cellular responses to changes of the mechanical properties of the substrate and regulate stretch-induced calcium transients, we examined the role of actin filaments and substrate flexibility in modulating the amplitude of stretch-activated intracellular calcium transients. Human gingival fibroblasts were subjected to mechanical stretch through integrins by magnetic force acting on collagen-coated ferric oxide beads. Intracellular calcium concentration was measured in fura-2-loaded cells by ratio fluorimetry. Cytochalasin D-treatment greatly increased (3-fold) the amplitude of stretch-activated calcium transients in well-spread cells grown on glass coverslips while phalloidin, colchicine or taxol exerted no signficant effects, indicating that actin filaments but not microtubules modulate stretch-activated calcium transients. In freshly plated cells with rounded shapes and poorly developed cortical actin filaments, stretch-induced calcium transients were of 3-fold higher amplitude than well-spread cells plated for 6-24 hrs and with well developed actin filaments. Cells plated on soft collagen-polyacrylamide gels showed round morphology but exhibited <50% of the response to stretch of well-spread cells on inflexible gels. Notably, cells on soft gels showed very heavy phalloidin staining for cortical actin filaments compared with cells on more inflexible surfaces which showed only light staining for cortical actin. While cell shape may have some effect on responsiveness to mechanical stretch, the rigidity of the cell membrane mediated by the extensive cortical actin network appears to be a central determinant in the regulation of stretch-induced calcium signals.

Actin Cytoskeleton↗
PubMed1999

Differential toxicities of TCDD in vivo among normal, c-src knockout, geldanamycin- and quercetin-treated mice.

Although we have previously reported the result of our preliminary study on the reduced toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vivo in male c-src deficient, -/+ B6, 129-src(tmlSor) mice as compared to those in wild-type mice, there are still two major shortcomings of the above study: (a) the low number of individuals tested, (b) in some of the comparison tests, C57BL/6J mice (i.e. inbred B6 mice) were used as wild-type control mice. Since then we increased our laboratory breeding program and thereby the availability of B6, 129-/+, -/- and true littermate wild-type +/+ individual mice. The results of critical in vivo toxicity comparison tests, involving 6-13 mice per test group, showed that there are considerable variations expressed in toxicity within each group of c-src deficient mice. Nevertheless, when a large enough number of individuals were tested two toxic effects were found to be less expressed in src-deficient mice. They were: (a) excess fatty deposits and (b) the mottled appearance of the liver which were commonly observed in TCDD-treated wild type mice, but not in c-src deficient mice. The former trend was also confirmed by both liver lipid analysis and histological examinations of the affected livers. As for the biochemical parameters, the hepatic nuclear protein binding to C/EBP (CCAAT/enhancer binding protein) response element appears to be uniformly reduced by the action of TCDD in + / + mice, but not in -/+ or -/- mice.

Adipose Tissue↗
PubMed1999

Mechanisms controlling mitochondrial biogenesis and respiration through the thermogenic coactivator PGC-1.

Mitochondrial number and function are altered in response to external stimuli in eukaryotes. While several transcription/replication factors directly regulate mitochondrial genes, the coordination of these factors into a program responsive to the environment is not understood. We show here that PGC-1, a cold-inducible coactivator of nuclear receptors, stimulates mitochondrial biogenesis and respiration in muscle cells through an induction of uncoupling protein 2 (UCP-2) and through regulation of the nuclear respiratory factors (NRFs). PGC-1 stimulates a powerful induction of NRF-1 and NRF-2 gene expression; in addition, PGC-1 binds to and coactivates the transcriptional function of NRF-1 on the promoter for mitochondrial transcription factor A (mtTFA), a direct regulator of mitochondrial DNA replication/transcription. These data elucidate a pathway that directly links external physiological stimuli to the regulation of mitochondrial biogenesis and function.

3T3 Cells↗
PubMed1999

Tricyclic farnesyl protein transferase inhibitors: crystallographic and calorimetric studies of structure-activity relationships.

Crystallographic and thermodynamic studies of farnesyl protein transferase (FPT) complexed with novel tricyclic inhibitors provide insights into the observed SAR for this unique class of nonpeptidic FPT inhibitors. The crystallographic structures reveal a binding pattern conserved across the mono-, di-, and trihalogen series. In the complexes, the tricycle spans the FPT active site cavity and interacts with both protein atoms and the isoprenoid portion of bound farnesyl diphosphate. An amide carbonyl, common to the tricyclic compounds described here, participates in a water-mediated hydrogen bond to the protein backbone. Ten high-resolution crystal structures of inhibitors complexed with FPT are reported. Included are crystallographic data for FPT complexed with SCH 66336, a compound currently undergoing clinical trials as an anticancer agent (SCH 66336, 4-[2-[4-(3,10-dibromo-8-chloro-6,11-dihydro-5H-benzo[5, 6]cyclohepta[1, 2-b]pyridin-11-yl)-1-piperidinyl]-2-oxoethyl]-1-piperidinecarbo xamide ). Thermodynamic binding parameters show favorable enthalpies of complex formation and small net entropic contributions as observed for 4-[2-[4-(3,10-dibromo-8-chloro-6,11-dihydro-11H-benzo[5, 6]cyclohepta[1, 2-b]pyridin-11-ylidene)-1-piperidinyl]-2-oxoethyl]pyridine N-oxide where DeltaH degrees bind = -12.5 kcal/mol and TDeltaS degrees bind = -1.5 kcal/mol.

Alkyl and Aryl Transferases↗
PubMed1999

The structural characteristics and mechanical behaviors of nonstoichiometric apatite coatings sintered in air atmosphere.

Two types of nonstoichiometric apatite coatings on Ti6Al4V substrates were prepared in our laboratory by electrodeposition and hydrothermal synthesis. One was composed of highly pure needle-like calcium-deficient hydroxyapatite, and the other consisted of needle-like calcium-deficient hydroxyapatite and plate-like brushite. In this paper, the morphology, phase transition, and bonding strength of these coatings sintered at 450( degrees ) approximately 980 degrees C in an air atmosphere were studied. In addition, the residual stresses in pure calcium-deficient hydroxyapatite coatings and coatings sintered at 800 degrees C were measured by a hole-drilling method. The results show that after being sintered at a higher temperature, the coating/Ti6Al4V samples exhibited structural characteristics such as biphasic [hydroxyapatite + beta-Ca3(PO4)2] coatings and dense TiO2 film/Ti6Al4V in which the residual stresses in the coatings slightly increased. In addition, the results indicate that bonding strength was improved.

Air↗
PubMed1999

Both RNA rearrangement and point mutation contribute to repair of defective chimeric viral genomes to form functional hybrid viruses in plants.

The putative movement protein gene (p27) plus 5' and 3' flanking sequences of cucumber leaf spot aureusvirus (CLSV) was inserted into an infectious cucumber necrosis tombusvirus (CNV) cDNA clone containing a deletion in the cell-to-cell movement protein gene. Approximately 5% of plants inoculated with synthetic transcripts of two such defective chimeric CNV/CLSV cDNA clones developed systemic symptoms 7-19 days postinoculation. Reverse transcription-polymerase chain reaction and sequence analysis of virus obtained from systemically infected leaves indicated that both point mutation and RNA rearrangement (deletion) contributed to the formation of movement competent CNV/CLSV hybrid viruses. The hybrid viruses were found to accumulate to high levels in infected plants, to form stable virions, and to be mechanically transmissible. In addition, a hybrid virus that lacked 50 amino acids at the carboxyl-terminal region of CLSV p27 was still capable of facilitating CNV movement. These data provide experimental evidence for the role of CLSV p27 in viral cell-to-cell movement and demonstrate that p27 can enable efficient movement of the CNV genome. Moreover, the data show that RNA rearrangements known to occur during CNV RNA replication can contribute to rapid evolution of the CNV genome.

Amino Acid Sequence↗
PubMed1999

[Effects of unarmed marching in dry-heat desert environment on the heat shock protein 27 in human blood].

To explore the variation of blood heat shock protein 27(HSP27) for unarmed marching in dry-heat environment, plasma HSP27 levels of 57 marchers and 14 controls were detected. The results revealed a significant difference between exposed and control groups (P < 0.01), and no significant difference among different time exposures at the same speed. HSP27 levels increased slightly with the increase of speed. During the second hour of marching, HSP27 levels were slightly lower, and kept steady in the third hour.

Adolescent↗
PubMed1999

1-(N-alkylamino)-11-(N-ethylamino)-4,8-diazaundecanes: simple synthetic polyamine analogues that differentially alter tubulin polymerization.

Polyamine analogues such as bis(ethyl)norspermine and N1-(cyclopropylmethyl)-N11-ethyl-4,8-diazaundecane (CPENSpm) act as potent modulators of cellular polyamine metabolism in vitro and possess impressive antitumor activity against a number of cell lines. Some of these polyamine analogues appear to produce their cell-type-specific cytotoxic activity through the superinduction of spermidine/spermine N1-acetyltransferase (SSAT). However, there are several analogues (e.g., N1-(cycloheptylmethyl)-N11-ethyl-4, 8-diazaundecane (CHENSpm)) which are effective cytotoxic agents but do not superinduce SSAT. We have previously demonstrated that CPENSpm and CHENSpm both initiate the cell death program, although by different mechanisms, and that CHENSpm (but not CPENSpm) induces a G2/M cell cycle arrest. We now report that one potential mechanism by which some polyamine analogues can retard growth and ultimately produce cytotoxicity is through interference with normal tubulin polymerization. In these studies, we compare the effects of the polyamine analogues CHENSpm, CPENSpm, and (S)-N1-(2-methyl-1-butyl)-N11-ethyl-4,8-diazaundecane (IPENSpm) on in vitro tubulin polymerization. These spermine analogues behave very differently from spermine and from each other in terms of tubulin polymerization rate, equilibrium levels, and time of polymerization initiation. These results demonstrate that structurally similar polyamine analogues with potent antitumor effects can produce significantly different cellular effects. The discovery of polyamine analogues that can alter tubulin polymerization provides a series of promising lead compounds that may have a similar spectrum of activity to more difficult to synthesize compounds typified by paclitaxel.

Antineoplastic Agents↗
PubMed1999

[Missense mutations of exons 14 and 18 of Wilson's disease gene in Chinese patients]

OBJECTIVE: To investigate the characteristics of mutations of exons 14 and 18 of Wilson's disease (WD) gene in Chinese patients. METHODS: The subjects of study included 60 unrelated normal controls and 44 unrelated WD patients. Genomic DNA was prepared from peripheral blood leukocytes by a salt-out method. Mutations of exons 14 and 18 in these subjects were screened by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and further confirmed by sequencing. RESULTS: One patient was homozygous for Arg1041Pro mutation of exon 14 and another patient was heterozygous for Asn1270Ser mutation of exon 18. CONCLUSION: The mutations of exons 14 and 18 of WD gene in Chinese patients were confirmed by sequencing for the first time in China. Arg1041Pro was identified as a novel missense mutation. In addition, an Asn1270Ser, previously described mutation, was detected in this study. But exons 14 and 18 are not the hot point mutations of WD gene in Chinese patients.

Journal Article↗
PubMed1999

Bone marrow and peripheral blood dendritic cells from patients with multiple myeloma are phenotypically and functionally normal despite the detection of Kaposi's sarcoma herpesvirus gene sequences.

Multiple myeloma (MM) cells express idiotypic proteins and other tumor-associated antigens which make them ideal targets for novel immunotherapeutic approaches. However, recent reports show the presence of Kaposi's sarcoma herpesvirus (KSHV) gene sequences in bone marrow dendritic cells (BMDCs) in MM, raising concerns regarding their antigen-presenting cell (APC) function. In the present study, we sought to identify the ideal source of DCs from MM patients for use in vaccination approaches. We compared the relative frequency, phenotype, and function of BMDCs or peripheral blood dendritic cells (PBDCs) from MM patients versus normal donors. DCs were derived by culture of mononuclear cells in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4. The yield as well as the pattern and intensity of Ag (HLA-DR, CD40, CD54, CD80, and CD86) expression were equivalent on DCs from BM or PB of MM patients versus normal donors. Comparison of PBDCs versus BMDCs showed higher surface expression of HLA-DR (P =.01), CD86 (P =. 0003), and CD14 (P =.04) on PBDCs. APC function, assessed using an allogeneic mixed lymphocyte reaction (MLR), demonstrated equivalent T-cell proliferation triggered by MM versus normal DCs. Moreover, no differences in APC function were noted in BMDCs compared with PBDCs. Polymerase chain reaction (PCR) analysis of genomic DNA from both MM patient and normal donor DCs for the 233-bp KSHV gene sequence (KS330233) was negative, but nested PCR to yield a final product of 186 bp internal to KS330233 was positive in 16 of 18 (88.8%) MM BMDCs, 3 of 8 (37.5%) normal BMDCs, 1 of 5 (20%) MM PBDCs, and 2 of 6 (33.3%) normal donor PBDCs. Sequencing of 4 MM patient PCR products showed 96% to 98% homology to the published KSHV gene sequence, with patient specific mutations ruling out PCR artifacts or contamination. In addition, KHSV-specific viral cyclin D (open reading frame [ORF] 72) was amplified in 2 of 5 MM BMDCs, with sequencing of the ORF 72 amplicon revealing 91% and 92% homology to the KSHV viral cyclin D sequence. These sequences again demonstrated patient specific mutations, ruling out contamination. Therefore, our studies show that PB appears to be the preferred source of DCs for use in vaccination strategies due to the ready accessibility and phenotypic profile of PBDCs, as well as the comparable APC function and lower detection rate of KSHV gene sequences compared with BMDCs. Whether active KSHV infection is present and important in the pathophysiology of MM remains unclear; however, our study shows that MMDCs remain functional despite the detection of KSHV gene sequences.

Adult↗
PubMed1999

The role of CD80, CD86, and CTLA4 in alloimmune responses and the induction of long-term allograft survival.

Blocking the interaction of the CD28 costimulatory receptor with its ligands, CD80 and CD86, inhibits in vivo immune responses, such as allograft rejection, and in some instances induces tolerance. Previously, we found that CTLA4Ig, which blocks the CD28/CTLA-4 (CD152) ligands CD80 and CD86, can be used to induce transplantation tolerance to vascularized allografts. Recent data suggest that an intact CD152-negative signaling pathway is essential for induction of tolerance to nominal Ags. Here, we show that blockade of CD152 using an anti-CD152 mAb at the time of transplantation prevents the induction of long-term allograft survival by agents that target CD80 and CD86. In contrast, CD152 signals are not required for the maintenance of established graft survival. We also report for the first time that blockade of CD86 alone can induce long-term graft survival. This requires that anti-CD86 mAb is given on the day of transplantation and also depends upon an intact CD152 pathway. This result, plus experiments using CD80-deficient mice, suggests a dominant role for CD80 molecules on donor cells as the relevant ligand for CD152. We additionally find that blockade of CD152 at the time of transplantation does not interfere with the effectiveness of anti-CD154 mAbs, suggesting distinct mechanisms for inhibition of graft rejection by blocking the CD28 vs CD154 pathways.

Abatacept↗
PubMed1999

[Content of metals in different diameter airborne particles and effect on micronuclei formation in human lymphocytes].

Using a five stage sampling scheme, airborne particles were collected in a residential area of Taiyuan city. The contents of four metals, including Ni, Pb, Cd and Cr in different diameter airborne particles were determined by atomic absorption spectrophotometry. The mutagenicity of the extracts of airborne particles was investigated by means of Cytokinesis-blocking(CB) method. The results showed that the pollution of airborne particles in the residential area was very serious. The smaller the airborne particles are the more it contains metal elements. The metal content of the particles less than 1.1 microns is the highest among different diameter airborne particles. The extracts of airborne particles induced a significant increase in micronuclei formation to a certain degree, especially the particles less than 1.1 microns increased in micronuclei formation. It is suggested that the extracts of different diameter particles are with strong mutagenicity.

Air Pollutants↗
PubMed1999

Genetic analysis of the role of the drosophila fat facets gene in the ubiquitin pathway.

The Drosophila fat facets gene encodes a deubiquitinating enzyme required during eye development to limit the number of photoreceptors in each facet to eight. Ubiquitin is a small polypeptide that targets proteins for degradation by the proteasome. Deubiquitinating enzymes cleave ubiquitin-protein bonds. In order to investigate the role of FAT FACETS in the ubiquitin pathway, genetic interactions between fat facets and the Drosophila UbcD1 gene were assessed. In addition, three yeast deubiquitinating enzyme genes were tested for their ability to substitute for fat facets in the developing Drosophila eye and for their effects on eye morphology. The results of these experiments support the hypothesis that FAT FACETS activity antagonizes that of the proteolytic machinery. The implications of these results for the specificity of FAF and yeast UBPs are discussed as well.

Animals↗