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Biomedical subjects

H Xiao

Publications and source records attributed to H Xiao.

At least 145 records · Page 8Linked to original sources
PubMed1997

[The 40 Hertz auditory event-related potential in chick: optimized recording conditions and threshold value].

In order to seek optimized recording parameters for 40 Hz AERP in chick, the present study was carried out with a statistical model of orthogonal test. The following measuring parameters to be selected includ the rise/decay time of tone pip (1, 2 and 3 cycle), platform time (1, 2 and 3 cycle), high-pass filters (5, 20 and 30 Hz), low-pass filter (70, 100 and 250 Hz). The results showed that 1. the filter setting is a high significant factor, the most optimum basswidth is 20-70 Hz; 2. the ideal time of rise/decay and platform of tone pip are 2-1-2 cycle. The adult animals showed the greatest sensitivity nearby 1.5-2 kHz frequency. In sixday-old chicks, the threshold at every frequency has reached the same values as adult, indicating that their auditory function is essentially mature.

Animals↗
PubMed1996

Free radical generation as induced by ochratoxin A and its analogs in bacteria (Bacillus brevis).

Lipid peroxidation is considered as one of the manifestations of cellular damage in the toxicity of ochratoxin A (OA). OA; its three natural analogs, OB, OC, and Oalpha; and four synthetic analogs, d-OA, the ethylamide of OA (OE-OA), O-methylated OA (OM-OA), and the lactone-opened OA (OP-OA) were used to study free radical generation in bacteria with Bacillus brevis as a model system. The uptake of the different ochratoxins by B. brevis varied substantially depending on the molecular structures. Electron paramagnetic resonance spectroscopy using alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone as a spin trapping agent showed an enhanced free radical generation due to the addition of OA and most of the analogs. The EPR signals could be further enhanced by the addition of Ca2+, a calcium ionophore and an ATPase uncoupler, whereas they were eliminated by incubating the growing cells with vitamin E. The spin adduct hyperfine splitting constants indicate the presence of alpha-hydroxyethyl radicals resulting from generated hydroxyl radicals, which are trapped by alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone. The results further suggest that OA induces free radical production in this model system by enhancing the permeability of the cellular membrane to Ca2+.

Bacillus↗
PubMed1996

Characterization of the interaction between the acidic activation domain of VP16 and the RNA polymerase II initiation factor TFIIB.

Contact between a transcriptional activator and one or more components of the RNA polymerase II transcription initiation machinery is generally believed important for activators to function. Several different molecular targets have been suggested for direct contact by herpes simplex virus virion protein VP16, including the general initiation factor TFIIB. In this report we have used several strategies to critically assess this interaction between VP16 and TFIIB. Affinity columns of VP16 bound TFIIB activity from HeLa cell extracts and the binding was reduced by mutations in the activation domain of VP16. In assays of direct binding, VP16 bound recombinant human TFIIB but not Drosophila or yeast TFIIB. Unlike binding from an extract, however, we found that the interaction between VP16 and recombinant human TFIIB was not affected by mutations in VP16 that reduce transactivation. Point mutations within human TFIIB that reduce transactivation by VP16 have been shown to reduce VP16 binding, but we show here that these same mutations critically affect both the important TBP-TFIIB interaction and the ability of TFIIB to support activator-independent basal transcription in vitro. Taken together our results suggest more evidence is needed to support the notion that TFIIB is a functionally important target for the activator VP16.

Animals↗
PubMed1996

Proteolytic activity of human immunodeficiency virus Vpr- and Vpx-protease fusion proteins.

In addition to Gag, Pol, and Env, primate lentiviruses encode other virion-associated proteins, including Vpr, Vpx, and Vif. Vpr- and Vpx-staphylococcal nuclease and chloramphenicol acetyltransferase fusion proteins incorporate into human immunodeficiency virus (HIV) virions and retain enzyme activity when expressed in trans with HIV proviruses (Wu et al., J. Virol. 69, 3389, 1995). To explore whether the viral protease (PR) could be expressed as a proteolytically active fusion protein, the HIV PR coding region was fused in-frame with the HIV-2 vpx and HIV-1 vpr genes. Using a vaccinia virus-T7 expression system, the Vpx-PR fusion protein was expressed and formed homodimers. Coexpression with Pr55Gag demonstrated that Vpx-PR possessed Gag-specific proteolytic activity and inhibited the production of Gag virus-like particles. Trans-expression of a PR-Vpr fusion protein with HIV-1 provirus caused a profound reduction in viral protein expression and virion production. Importantly, the PR-Vpr fusion protein caused a similar level of inhibition and intracellular cleavage of Pr55Gag precursor protein when coexpressed with protease defective HIV-1 provirus. The inhibitory effect of PR-Vpr expression on virion production was markedly greater than that of PR alone. These results indicate that Vpr arguments the intracellular proteolytic activity of PR when expressed as a fusion protein and thus may be relevant for the expression of PR in intracellular immunization strategies against HIV infection. Moreover, the ability to express and package enzymatically active PR-Vpr fusion protein, independent of Gag/Pol, may provide a novel means to study enzyme function.

Amino Acid Sequence↗
PubMed1996

A doubly cross-linked human hemoglobin. Effects of cross-links between different subunits.

Human deoxyhemoglobin cross-linked with trimesyl tris(3,5-dibromosalicylate) produces the previously reported cross-linked hemoglobin in which the epsilon amino groups of the two beta chain 82 lysyl residues are joined by a trimesyl bridge. Further specific modification of this protein directed to the alpha subunits with bis(3,5-dibromosalicyl)fumarate gives a doubly cross-linked material in which the epsilon-amino groups of the two alpha chain 99 lysyl residues are now joined by a fumaryl bridge. The singly cross-linked beta chain species binds oxygen cooperatively with a high oxygen affinity (P50 = 4.8 torr at pH 7.4). The addition of the second cross-linking reduces the oxygen affinity to 15.9 torr, which compares with 13.0 torr for the singly cross-linked alpha chain species. The doubly cross-linked hemoglobin retains significant cooperativity with a Hill coefficient of 2.3 compared with 3.0 for unmodified hemoglobin. Because some of the groups responsible for the Bohr effect are acylated, this doubly cross-linked hemoglobin exhibits 25% of the normal Bohr effect and less than 20% of the normal chloride effect. The use of two distinct cross-links within the same tetramer provides a material for physical and structural analysis as well as for further modifications for specific applications. The results indicate that the cross-link introducing the lowest oxygen affinity in the two singly cross-linked species appears to control the overall affinity in this doubly cross-linked species.

Hemoglobins↗
PubMed1996

Toxicity of ochratoxin A, its opened lactone form and several of its analogs: structure-activity relationships.

Ochratoxin A (OA); its three natural analogs, ochratoxin C (OC), B (OB), and alpha (Oalpha); and its six synthetic analogs, the epimere of OA (d-OA), the ethylamide of OA (OE-OA), decarboxylated OA (DC-OA), O-methylated OA (OM-OA), lactone-opened OA (OP-OA), and the methyl ester of Oalpha (M-Oalpha) were assayed for their toxicities in prokaryotic (Bacillus brevis) and eukaryotic (HeLa cell) systems and in animals (mouse and rat). The LC50S (mM) for HeLa cells, were 0.005 (OA), 0.009 (OC), 0.163 (d-OA), 10.1 (OE-OA), 7.6 (DC-OA), 0.83 (OM-OA), 0.054 (OB), and 0.56 Oalpha). The minimum inhibitory doses (nmol/disc) for the growth of B. brevis (pH 6.5) were 8.7 (OA), 2.0 (OC), 5.5 (d-OA), 1.1 (OE-OA), 54 (OB), 390 (Oalpha), and 90 (M-Oalpha) while no inhibition of the bacterial growth was observed for OM-OA, DC-OA, and OP-OA at doses as high as 350 nmol/disc. The results indicate that the toxicities of OA were associated with its isocoumarin moiety but that neither the dissociation of the phenolic hydroxyl group nor the iron-chelating properties of OA were directly related to its toxicities. The lactone carbonyl group of OA, however, appears to be involved in OA toxicity as OP-OA is found in the bile of rats injected with OA and has similar toxicity to that of OA when administered intravenously to the rat. Overall, the structure-activity studies suggest that the toxicity of OA is attributable to its isocoumarin moiety and that the lactone carbonyl group may be involved in its toxicity.

Animals↗
PubMed1996

Alternate functions of the single-minded and rhomboid genes in development of the Drosophila ventral neuroectoderm.

We have investigated the roles of the single-minded (sim) and rhomboid (rho) genes in generating distinct cell fates in the Drosophila embryonic neuroectoderm. We show that sim functions to repress ventral ectodermal cell fates, as in sim mutants mesectodermal cells adopt the fates of neighboring ventral ectodermal cells and targeted sim expression in P[paired.Gal4]/P[UAS-sim] embryos results in loss of epidermal cells. We also find that rho is not required for early expression of sim or ventral nervous system defective in mesectodermal or ventral ectodermal cells; targeted rho expression in P[paired-Gal4]/P[UAS-rho] embryos results in lateral-to-ventral cell fate shifts in the developing neuroectoderm; and midline-targeted rho expression can rescue the medial denticle fusions in rho mutant cuticles.

Animals↗
PubMed1996

Assessment and treatment of facial deformity resulting from radiation to the orbital area in childhood.

Children who receive radiation for malignant tumors in the orbital area frequently develop widespread craniofacial deformities. These affect the skull, orbit, maxilla, and mandible. When these patients seek treatment at a later age, they require careful assessment using cephalometrics and three-dimensional imaging. It is recommended that the four levels of skeletal deformity be corrected in a single procedure, that is frontotemporal expansion with repositioning of the skull base area, orbital expansion and repositioning together with maxillary and mandibular surgery. Bone grafts should be inlay rather than onlay and soft tissue should be supplied by free-tissue transfer. This counteracts any residual ischemia related to the previous radiation therapy. The second surgical stage is designed to reconstruct the socket and the eyelids to allow more satisfactory rehabilitation with an ocular prosthesis. In patients who have a globe present, the usual enophthalmos can be corrected by repositioning of the eye as part of the first procedure by reducing the anteroposterior dimensions of the socket. In bilateral cases, the deformity is hourglass in nature and requires correction in the frontal and temporal area with lateral displacement of the orbits. A bimaxillary procedure is also indicated. It is emphasized that to formulate a satisfactory operative plan an in-depth three-dimensional analysis of the deformity is mandatory.

Child↗
PubMed1996

Metabolites of ochratoxins in rat urine and in a culture of Aspergillus ochraceus.

We studied the metabolic profile of ochratoxin A (OA) in rats and in a culture of OA-producing Aspergillus ochraceus. Ochratoxin alpha (O alpha), ochratoxin beta (O beta), 4-R-hydroxyochratoxin A (4-R-OH OA), 4-R-hydroxyochratoxin B (4-R-OH OB), and 10-hydroxyochratoxin A (10-OH OA) were isolated from a culture of A. ochraceus and structurally characterized by 1H nuclear magnetic resonance spectroscopy, mass spectrometry and high-pressure liquid chromatography. 4-R-OH OA and O alpha were consistently produced and were the dominant biotransformed metabolites in the fungal culture and in rats treated with OA and ochratoxin C (OC), while the formation of 10-OH OA was conditional in the fungal system. Green fluorescent biomacromolecules were isolated by detergent extraction of the fungal culture followed by cold-acetone precipitation and gel filtration. Acid hydrolysis of the fluorescent macromolecules resulted in the release of several ochratoxins, including O alpha (80%), OA (2%), and OC (5%), and other unidentified fluorescent compounds but not OB and O beta. Cross-reactivity studies of the natural macromolecule conjugates of OA with anti-OA polyclonal antibodies indicated that they were covalently linked to the macromolecules via a group other than the carboxyl group. These studies demonstrated that a fungus can produce some of the same metabolites of OA as the rat and that O alpha, OA, and OC may be covalently linked to fungal macromolecules.

Animals↗
PubMed1996

Inhibition of human and simian immunodeficiency virus protease function by targeting Vpx-protease-mutant fusion protein into viral particles.

The human immunodeficiency virus type I (HIV-1) Vpr and HIV-2 Vpx proteins package into virions through interactions with their cognate Gag polyprotein precursor. The targeting properties of Vpr and Vpx have been exploited to incorporate foreign proteins into virions by expression as heterologous fusion molecules (X. Wu, H.-M. Liu, H. Xiao, J. Kim, P. Seshaiah, G. Natsoulis, J. D. Boeke, B. H. Hahn, and J. C. Kappes, J. Virol. 69:3389-3398, 1995). To explore the possibility of utilizing Vpx and Vpr to target dominant negative mutants of the HIV Pol proteins into virions, we fused HIV-2 Vpx with an enzymatically defective protease (PR) mutant. Using a vector system to facilitate transient coexpression with HIV provirus, Vpx-PR-mutant (VpxPR(M)) fusion protein was expressed and packaged efficiently into HIV-2 and simian immunodeficiency virus virions. Immunoblot analysis of purified virions demonstrated that the packaging of VpxPR(M) interfered with the processing of the Gag and Gag/Pol precursor proteins, similar to that of a well-characterized active-site PR inhibitor. The incomplete processing of Gag and Gag/Pol was consistent with a 25-fold reduction in virion infectivity. The coexpression of a packaging defective VpxPR(M) fusion protein with HIV-2 provirus produced virions with fully processed Gag protein, similar to wild-type virions. Importantly, virions trans complemented with a Vpx-chloramphenicol acetyltransferase fusion protein were normal with respect to the processing of Gag protein and the ability to infect and replicate in vitro. These results indicate that VpxPR(M) specifically inhibited the function of the viral protease and provide for the first time proof of principle that the incorporation of foreign proteins into virions via fusion with Vpx can inhibit HIV replication. The use of accessory proteins as vehicles to deliver deleterious proteins to virions, including dominant negative mutants of Pol proteins, may provide new opportunities for application of gene therapy-based antiretroviral strategies. The ability to package PR by expression in trans, independent of the Gag/Pol precursor, also represents a novel approach that may be exploited to study the function of the Pol proteins.

Amino Acid Sequence↗
PubMed1996

Three functional classes of transcriptional activation domain.

We have studied the abilities of different transactivation domains to stimulate the initiation and elongation (postinitiation) steps of RNA polymerase II transcription in vivo. Nuclear run-on and RNase protection analyses revealed three classes of activation domains: Sp1 and CTF stimulated initiation (type I); human immunodeficiency virus type 1 Tat fused to a DNA binding domain stimulated predominantly elongation (type IIA); and VP16, p53, and E2F1 stimulated both initiation and elongation (type IIB). A quadruple point mutation of VP16 converted it from a type IIB to a type I activator. Type I and type IIA activators synergized with one another but not with type IIB activators. This observation implies that synergy can result from the concerted action of factors stimulating two different steps in transcription: initiation and elongation. The functional differences between activators may be explained by the different contacts they make with general transcription factors. In support of this idea, we found a correlation between the abilities of activators, including Tat, to stimulate elongation and their abilities to bind TFIIH.

Base Sequence↗
PubMed1996

[Protective effect of lipid A monoclonal antibody against burn sepsis in rats].

A lipid A monoclonal antibody(mAb) was prepared and it was used to study its protective effect against burn sepsis. Wistar rats were inflicted with 30% TBSA third degress burn, and they were given LPS to mimic early sepsis after burn. The rats were divided randomly into burn with LPS, monoclonal antibody treatment, and control groups. The levels of endotoxin, tumor necrosis factor, light and electron microscopic studies of the morphological changes in the liver were studied. The results showed that the anti-lipid A monoclonal antibody demonstrated capacity to cross-react with several Gram-negative bacteria and their endotoxins. The mAb improved the survival rate of rats and decreased the levels of endotoxin and TNF as well as the liver damage significantly.

Animals↗
PubMed1996

[Video-assisted thoracoscopic surgical technique for interruption of patent ductus arteriosus].

We developed a new operation with clipping of a patent ductus arteriosus (PDA) by video-assisted thoracoscopic surgical technique. Twenty-one patients underwent this procedure, since May, 1994. The average age was 5.8 years (range 2-16 years), and average weight was 16.5 kg (range 8-37 kg). All patients had successful closure of PDA, except one whe had open surgical PDA division and one who had opening of the clip after 72 hours. One had recurrent larygeal nerve injury and two had pneumothora on the left side. There were no other complications and no deaths. The need for a chest tube is in doubt if there is no air leak or bleeding. Closure of PDA by VATS is marked by safe, less postoperative pain and early recovery.

Adolescent↗
PubMed1995

Binding of heat shock factor to and transcriptional activation of heat shock genes in Drosophila.

Heat shock factor (HSF) binds to heat shock elements (HSEs) and the binding can be highly cooperative. Here we report an analysis of binding of Drosophila HSF to both native and synthetic heat shock regulatory regions. We find that cooperative binding of HSF requires close proximity, rather than helical alignment, of HSEs. Two or more trimeric HSEs organized as contiguous 5 bp units show much higher levels of cooperativity than multiple but separated HSEs. We discuss these in vitro observations in the context of the in vivo status of heat shock genes under mild and full heat shock conditions. Finally, we show that the DNA binding and trimerization domains alone may be sufficient for the full level of binding cooperativity between HSF trimers. This last result suggests that close proximity of HSEs for cooperative binding of HSF is a result of protein-protein interactions near the point of DNA contact.

Animals↗
PubMed1995

Assembly of a chromosomal replication machine: two DNA polymerases, a clamp loader, and sliding clamps in one holoenzyme particle. IV. ATP-binding site mutants identify the clamp loader.

The gamma complex (gamma delta delta' chi psi) and tau complex (tau delta delta' chi psi) clamp loaders require ATP hydrolysis to load beta sliding clamps onto DNA. The beta sliding clamp tethers the polymerase (Pol) III* replicase to DNA for processive synthesis. Pol III* contains both gamma and tau, but only one each of the delta, delta', chi, and psi subunits. Hence, there is ambiguity with respect to which clamp loader, the gamma or tau complex, exists in the Pol III* replicase structure. In this study, ATP-binding site mutants of gamma and tau have been prepared, and these mutants, when assembled into either the gamma or tau complex, are inactive in clamp loading. These mutants have been used as a tool to determine the identity of the clamp loader in Pol III*. The nine-subunit Pol III* has been assembled using either mutant gamma or tau in place of wild-type gamma or tau. The results show that mutation of gamma inactivates Pol III* activity, but mutation of tau does not, indicating that the gamma complex (and not the tau complex) is the clamp loader of Pol III*. The tau subunit carries the task of dimerizing the core polymerase, and it is this association of tau with core that appears to direct the single copy subunits away from tau and onto gamma.

Adenosine Triphosphate↗
PubMed1995

MHC class I gene organization in > 1.5-Mb YAC contigs from the H2-M region.

Sixteen yeast artificial chromosome (YAC) clones have been mapped to the H2-M region at the distal end of the mouse major histocompatibility complex (MHC) on chromosome 17. Analysis of the YACs with single- and multicopy probes yielded a proximal contig spanning a minimum of 800 kb and a distal contig of 700 kb. A probe for the conserved fourth exon of MHC class I genes detected 19 restriction fragments, including 6 of the 8 previously characterized H2-M class I genes, in the proximal contig. This contig spans the gap from the M to the T region and includes the T1 gene. By contrast, only two class I genes, M2 and M3, were found in the distal contig. These two genes, which are both expressed, may mark the end of the MHC. The order among nine class I genes and seven other markers was determined in the cloned DNA from the centromere as T1, Tu32A, (M1-M7-M8), Tu32B, B30, M6, M4, M5, Mog, Tu42A parallel M2, Leh525, M3, Tu42B, where the orientation with respect to the centromere is unknown for M1-M7-M8.

Animals↗
PubMed1995

Augmentation of metalloproteinase (gelatinase) activity secreted from Rous sarcoma virus-infected cells correlates with transforming activity of src.

To search for the biochemical properties of cells relevant to transformation by p60v-src, we examined the activities and amounts of metalloproteinase (gelatinase) released from chicken embryonic fibroblasts infected with various mutants of Rous sarcoma virus by zymography and immunoblotting. While nontransforming Src proteins, including cellular p60c-src and its nonmyristylated form, had no stimulatory effect, wild-type p60v-src and the transforming mutant of cellular p60c-src stimulated the secretion and proteolytic activation of metalloproteinases. Moreover, the activation of metalloproteinase secretion strongly correlated with the invasiveness of cells assayed by the modified Boyden Chamber method. Chimeric mutants between v-src and c-src, which are transforming but produce less distinct morphological changes in infected cells, also stimulated the secretion of metalloproteinases as well as wild-type p60v-src. Deletion mutants of v-Src in which varying portions of the NH2-terminal half of p60v-src are deleted stimulated secretion to a level similar to that of wild-type regardless of the degree of morphological change they induce. Together with Src protein, other oncogene products including Yes, Fps, ErbB and Crk were also found to stimulate the secretion of metalloproteinases. Thus, these results suggest that transformation of cells with src and other oncogenes is closely associated with the enhanced secretion of metalloproteinases that may play an important role in tumor invasion and metastasis.

Animals↗