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Biomedical subjects

K Zhang

Publications and source records attributed to K Zhang.

At least 289 records · Page 16Linked to original sources
PubMed1996

Active transport of glutathione S-conjugate in human colon adenocarcinoma cells.

The formation of the glutathione S-conjugate of monochlorobimane (GSH-bimane) in human colon adenocarcinoma cells was identified by HPLC-fluorimetry and its transport from the cells was found to be temperature-sensitive, saturable and ATP-dependent. The apparent K(m) and Vmax values were 2.4 +/- 0.5 nmol GSH-bimane/10(6) cells and 0.5 +/- 0.1 nmol GSH-bimane/min per 10(6) cells, respectively. This active transport of GSH-bimane was inhibited by low micromolar concentrations of classical uncouplers of oxidative phosphorylation, namely carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), carbonylcyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP). The efflux of GSH-bimane was competitively inhibited by chlorambucil (CMB) and 1-chloro-2,4-dinitrobenzene (CDNB), two other substrates of GST. This study demonstrates the presence and kinetic measurements of the glutathione S-conjugate export (GS-X) pump in human colon cancer cells, an export pump whose function has been implicated in the phenomenon of multidrug resistance.

2,4-Dinitrophenol↗
PubMed1996

Far-infrared emission spectra of selected gas-phase PAHs: spectroscopic fingerprints.

The emission spectra of the gaseous polycyclic aromatic hydrocarbons (PAHs) naphthalene, chrysene, and pyrene were recorded in the far-infrared (far-IR) region. The vibrational bands that lie in the far IR are unique for each PAH molecule and allow discrimination among the three PAH molecules. The far-IR PAH spectra, therefore, may prove useful in the assignment of unidentified spectral features from astronomical objects.

Astronomical Phenomena↗
PubMed1996

Multiple types of chimeric germ-line Ig heavy chain transcripts in human B cells: evidence for trans-splicing of human Ig RNA.

Germ-line transcripts from Ig heavy chain loci precede the occurrence of isotype switching and are thought to play an important though still controversial role in Ig class switching. In this study, we employed a reverse transcriptase-PCR approach to detect human chimeric Ig germ-line mRNA transcripts. Multiple types of chimeric Ig germ-line transcripts (Imu-Cepsilon, Iepsilon-Cmu, Imu-Cgamma4, Igamma-Cmu, Igamma-Cepsilon, Iepsilon-Cgamma, and Igamma4-Calpha1 transcripts) were readily detected in human B cells stimulated with IL-4 alone. Sequence analysis revealed that all of these chimeric Ig germ-line transcripts represented the I exons from one Ig locus spliced to the CH exons from another locus by using consensus sequences for splicing donor and acceptor sites, indicating that they were generated through splicing machinery. In the case of stimulation of human resting B cells with IL-4 alone, the chimeric Ig germ-line transcripts are likely derived from a trans-splicing mechanism, as the extensive searching did not find evidence that Ig class-switch recombination had occurred, which alternatively could give rise to chimeric Ig mRNA by mechanisms other than trans-splicing. Similarly, an EBV-transformed gamma2 rearranged B cell line, GM1500, which produces IgG2 and contains both gamma2 productive and epsilon germ-line transcripts, also expressed chimeric germ-line RNA (Iepsilon-Cgamma2) and epsilon-productive transcripts (VDJ-Cepsilon). This line had no further sequential Sgamma2-Sepsilon rearrangements, providing evidence that the productive VDJ-Cepsilon mRNA was derived from a transcriptionally active unrearranged epsilon gene locus by trans-splicing. Taken together, these results provide possible evidence that trans-splicing of germ-line Ig RNA transcripts occurs in human B cells.

Antibody Diversity↗
PubMed1996

Vasoactive intestinal peptide induces S(alpha)/S(mu) switch circular DNA in human B cells.

Vasoactive intestinal peptide (VIP), a major neurotransmitter of peripheral nerves, has been suggested to function in host defense by regulating local human immune function. Indirect evidence has been marshaled that VIP can function as a switch factor for IgA in human Ig isotype recombination. In this study we directly tested the ability of VIP to function as a factor driving human B cells into IgA producing cells by assessing its ability to induce switch circular DNA representing direct mu to alpha switching. In addition we determined the generation of alpha germ-line transcripts and measured the level of IgA protein produced. Stimulation with VIP and CD40 mAb induced IgA production by human IgD+ B cells while VIP or CD40 alone failed to do so. Stimulation of purified IgD+ B cells with VIP plus CD40 mAb induced generation of switch circular DNA representing in vitro driven isotype switching from mu to alpha. CD40 mAb alone induced alpha germ-line transcripts but not IgA switch circles. Thus VIP, a neurogenic factor, can induce alpha-specific switching in CD40-activated human B cells and may thereby play an important role in directing the humoral immune response at mucosal surfaces.

B-Lymphocytes↗
PubMed1996

Decreased gene expression of neuronal nitric oxide synthase in hypothalamus and brainstem of rats in heart failure.

Nitric oxide may act at autonomic sites in the brain to regulate sympathetic outflow. Our goal was to determine whether gene expression of the neuronal isoform of nitric oxide synthase (nNOS) is altered in discrete autonomic brain regions of rats in the chronic phase of heart failure compared to sham-operated control rats. Experiments were performed in rats 4 to 5 weeks after left coronary artery ligation. Histological data indicated that there was a 39% outer and a 45% inner infarct of the left ventricular myocardium in the heart failure group. The myocardium in sham-operated rats showed no observable damage. Total RNA was purified from microdissected brain tissue blocks containing hypothalamus, dorsal pons, dorsal medulla, rostral ventrolateral medulla, and caudal ventrolateral medulla. Changes in nNOS mRNA were semiquantified in each region using reverse transcription-polymerase chain reactions in which known concentrations of deletion mutant of the gene were coamplified as an internal standard. Compared with controls, significant decreases in nNOS mRNA levels were found in hypothalamus (19%), dorsal pons (43%) and dorsal medulla (34%) of rats with heart failure. There were no statistically significant differences in nNOS mRNA levels in rostral or caudal ventrolateral medulla between the control and heart failure groups. Concomitant with the changes nNOS gene expression in central sites, the plasma concentration of norepinephrine was significantly elevated in rats with heart failure compared to sham-operated control rats. Our results show that heart failure is associated with decreases in nNOS gene expression in at least three regions of the brain and with increased sympathetic outflow to the periphery. The decreased NO production that is likely associated with the decreases in nNOS gene expression may lead to the increased sympathetic drive seen in chronic heart failure.

Animals↗
PubMed1996

Laminin 5 deposition promotes keratinocyte motility.

We examined the role of individual integrins in promoting human keratinocyte migration. In short-term assays on collagen type I- or fibronectin-coated substrates, migration was blocked by antibody to the alpha 2 integrin and the alpha 5 integrin, respectively. Unexpectedly, antibodies to integrin alpha 3 also significantly inhibited cell locomotion on both ligands. Time-course immunofluorescence staining revealed that keratinocyte migration was accompanied by deposition of endogenous laminin 5. Since alpha 3 beta 1 is a known receptor for this ligand, this observation suggested that migrating keratinocytes use freshly deposited laminin 5 in locomotion. Indeed, further investigation showed that anti-laminin 5 blocking antibodies effectively inhibited keratinocyte motility on both collagen and fibronectin substrates. Furthermore, cell migration on laminin 5-coated substrates was blocked by both anti-alpha 3 and anti-laminin 5 antibodies. Laminin 5 did not appear important in the initial attachment of keratinocytes, since adhesion of cells to collagen type I- or fibronectin-coated surfaces was not blocked by antibody to alpha 3 integrin or to laminin 5, but could be inhibited by antibody to alpha 2 or alpha 5, respectively. Using an in vitro wound assay, blocking antibodies to alpha 3 integrin and to laminin 5 also blocked reepithelization of the denuded monolayer. These results show that alpha 3 beta 1 integrin plays an important role in the migration of keratinocytes via their interaction with laminin 5. Furthermore, they suggest that cell migration is dependent not only on exogenous ligands but, importantly, on endogenously secreted laminin 5. Finally, the data are consistent with our earlier finding that laminin 5 is the first extracellular matrix component to be expressed and deposited by migrating keratinocytes during wound healing in vivo.

Cell Adhesion↗
PubMed1996

Mapping the adhesive domains of the myelin Po protein.

The Po protein holds PNS myelin compact at the intraperiod line by homophilic interactions of its single immunoglobulin (Ig)-like domain. Using transfected Chinese hamster ovary (CHO) cells expressing Po we can monitor this adhesion in vitro and have shown that the cells expressing Po when incubated as a single-cell suspension form large aggregates, whereas control-transfected cells do not. To precisely map the domains of Po responsible for Po:Po-mediated membrane adhesion, the ability of a number of antibodies raised to peptides corresponding to segments of the Ig-domain of Po, and the ability of the Po-peptides themselves, to inhibit aggregation was assessed. Both antibodies to Po-peptide, SDNGT, corresponding to amino acids Po 91-95, and the peptide itself, were able to block adhesion completely. Furthermore, within this Po sequence, amino acids Asp 92 and Gly 94 are conserved in a large number of V-like Ig-domains. To determine if these two amino acids are important for Po-mediated adhesion, the nucleotides coding for Asp 92 and Gly 94 were mutated to encode glutamate and alanine, respectively. Although the mutated Po reached the surface in transfected CHO cells and was glycosylated, the cells did not aggregate. These results suggest that the sequence SDNGT in the extracellular domain of Po is important for adhesion. In addition, antibodies to a second sequence, Po 74-82, and the peptide itself, also partially inhibited Po: Po-mediated adhesion indicating that there is more than one adhesive domain on Po-protein.

Adhesiveness↗
PubMed1996

Penetrative Convection and Zonal Flow on Jupiter

Measurements by the Galileo probe support the possibility that the zonal winds in Jupiter's atmosphere originate from convection that takes place in the deep hydrogen-helium interior. However, according to models based on recent opacity data and the probe's temperature measurements, there may be radiative and nonconvective layers in the outer part of the jovian interior, raising the question of how deep convection could extend to the surface. A theoretical model is presented to demonstrate that, because of predominant rotational effects and spherical geometry, thermal convection in the deep jovian interior can penetrate into any outer nonconvective layer. These penetrative convection rolls interact nonlinearly and efficiently in the model to generate and sustain a mean zonal wind with a larger amplitude than that of the nonaxisymmetric penetrative convective motions, a characteristic of the wind field observed at the cloud level on Jupiter.

Journal Article↗
PubMed1996

Distinct sub-populations of carcinoma-associated MUC1 mucins as detected by the monoclonal antibody 9H8 and antibodies against the sialyl-Lewis a and sialyl-Lewis x epitopes in the circulation of breast-cancer patients.

The cancer-associated epitope defined by the monoclonal antibody (MAb) 9H8 was shown to be closely related to the T antigen (Thomsen-Friedenreich antigen) by its sensitivity to 0-glycanase treatment of a mucin glycopeptide known to express this epitope. The reactivity with this glycopeptide increased upon neuraminiclase treatment, and among several MAbs tested for ability to block binding of the 9H8 antibody, the one specific for the T antigen was the most efficient. Out of 41 serum samples from breast-cancer patients, 11 showed elevated levels of the 9H8 epitope, and several sera also showed elevated levels of the cancer-associated carbohydrate epitopes sialyl-Lewis a and sialyl-Lewis x. By the use of antibodies specific for the MUC1 apoprotein (Ma552 and HMFG-2) it could be shown that these epitopes were attached to the MUC1 apoprotein in at least 4 of the cases. By combining antibodies specific to 9H8, sialyl-Lewis a and sialyl-Lewis x in catcher and tracer positions in several types of immunofluorometric assays, it was shown that the 9H8 epitope was rarely co-expressed with sialyl-Lewis a or sialyl-Lewis x epitopes an the same molecule, though all were expressed on MUC1 mucins. In fact, they can be considered as mutually exclusive epitopes, suggesting that these sera contained different populations of MUC1 mucins distinguishable by different sets of oligosaccharides. The existence of mutually exclusive carbohydrate epitopes on different MUC1 mucins in one and the same patient should be taken into account when designing immunoassays exploiting MUC1-reactive antibodies.

Antibodies↗
PubMed1996

X-ray absorption fine structure as a monitor of zinc coordination sites during oogenesis of Xenopus laevis.

The x-ray absorption fine structure (XAFS) zinc K-edge steps for intact stages I,II and V,VI Xenopus laevis oocytes demonstrate that the zinc concentration is about 3 and 1 mM, respectively. However, the chi(k) function for the early stage oocytes differs markedly from that for the late one. Analysis of the XAFS data for stage I,II oocytes indicates that zinc is bound to 2.0 +/- 0.5 sulfur atoms at an average coordination distance of 2.29 +/- 0.02 angstroms and 2.0 +/- 0.5 nitrogen or oxygen (N/O) atoms at 2.02 +/- 0.02 angstroms. In marked contrast, in stage V,VI oocytes, zinc is bound to 4.1 +/- 0.4 N/O atoms at an average distance of 1.98 +/- 0.01 angstroms. Our previous studies demonstrated that 90% of the zinc in stage VI oocytes is sequestered within yolk platelets, associated with a single molecule, lipovitellin, the proteolytically processed product of vitellogenin. XAFS analysis of yolk platelets, lipovitellin, and vitellogenin demonstrates that zinc is bound to 4.0 +/- 0.5 N/O ligands at an average distance of 1.98 +/- 0.01 angstroms in each case, identical to that of stage V,VI oocytes. The higher shell contributions in the Fourier transforms indicate that two of the N/O zinc ligands are His in both stage V,VI and I,II oocytes. The results show that in stage I,II oocytes, there is a high concentration of a zinc protein whose zinc coordination site likely is composed of (His)2(Cys)2, such as, e.g., TFIIIA. As the oocytes develop, the predominant zinc species becomes one that exhibits the (His)2(N/0)2 zinc site found in lipovitellin. Hence, the ligands to the zinc atoms in intact oocytes and the changes that take place as a function of oogenesis and after their fertilization, during embryogenesis, now can be examined and explored.

Amino Acid Sequence↗
PubMed1996

Secreted MUC1 mucins lacking their cytoplasmic part and carrying sialyl-Lewis a and x epitopes from a tumor cell line and sera of colon carcinoma patients can inhibit HL-60 leukocyte adhesion to E-selectin-expressing endothelial cells.

A secreted MUC1 mucin from the spent medium of the colon carcinoma cell line COLO 205 carrying sialyl-Lewis a and x epitopes (H-CanAg) was purified by trichloroacetic acid precipitation and Superose 6 gel filtration. The purified H-CanAg inhibited adhesion of the leukocyte cell line HL-60 to E-selectin transfected COS-1 cells or interleukin-1 beta (IL-1 beta)-activated human umbilical vein endothelial cells. Sera from two patients with advanced colon carcinoma containing high concentrations of sialyl-Lewis a and x activity inhibited HL-60 cell adhesion to E-selectin-expressing COS-1 cells and IL-1 beta-activated endothelial cells. After affinity column absorption of the sialyl-Lewis a activity, the sera also lost most of their sialyl-Lewis x activity and at the same time their adhesion inhibitory effect. A large part of the sialyl-Lewis a/x activity in the two patients was found in fractions containing mucins having a MUC1 apoprotein, as shown by its size, and reactivity with the two anti-MUC1 apoprotein monoclonal antibodies, Ma552 and HMFG-2. The cell-adhesion inhibitory effect of the purified sialyl-Lewis a-carrying MUC1 mucin fraction from the sera of the two patients was stronger than that of smaller sized sialyl-Lewis a-carrying mucin-type glycoproteins also found in the patient sera. The MUC1 mucin fraction secreted by the COLO 205 cells and from the two sera were all shown to lack their C-terminal portion, in contrast to the MUC1 mucin from cells. It is hypothesized that sialyl-Lewis a- and/or x-containing mucins, especially MUC1, secreted by tumors can interact with E-selectin on endothelial cells and thus inhibit leukocyte adhesion.

Antigens, Neoplasm↗
PubMed1996

Representation of spatial orientation by the intrinsic dynamics of the head-direction cell ensemble: a theory.

The head-direction (HD) cells found in the limbic system in freely mov ing rats represent the instantaneous head direction of the animal in the horizontal plane regardless of the location of the animal. The internal direction represented by these cells uses both self-motion information for inertially based updating and familiar visual landmarks for calibration. Here, a model of the dynamics of the HD cell ensemble is presented. The stability of a localized static activity profile in the network and a dynamic shift mechanism are explained naturally by synaptic weight distribution components with even and odd symmetry, respectively. Under symmetric weights or symmetric reciprocal connections, a stable activity profile close to the known directional tuning curves will emerge. By adding a slight asymmetry to the weights, the activity profile will shift continuously without disturbances to its shape, and the shift speed can be controlled accurately by the strength of the odd-weight component. The generic formulation of the shift mechanism is determined uniquely within the current theoretical framework. The attractor dynamics of the system ensures modality-independence of the internal representation and facilitates the correction for cumulative error by the putative local-view detectors. The model offers a specific one-dimensional example of a computational mechanism in which a truly world-centered representation can be derived from observer-centered sensory inputs by integrating self-motion information.

Animals↗
PubMed1996

Expression of novel secreted isoforms of human immunoglobulin E proteins.

Four human IgE isoforms produced by alternative splicing of the epsilon primary transcript were expressed as chimeric mouse/human anti 5-dimethylamino-1-naphthalenesulfonyl antibodies in the murine myeloma cell line Sp2/0. The four isoforms include the classic secreted form and three novel isoforms with altered carboxyl termini. All of these isoforms lack the transmembrane region encoded by the M1/M1' exon and are therefore predicted to be secreted proteins. When expressed in Sp2/0 cells, three of the IgE isoforms are assembled into complete molecules of two Ig heavy chains and two Ig light chains, whereas the fourth isoform is predominately assembled into half-molecules of one Ig heavy chain and one Ig light chain. All four isoforms are secreted with similar kinetics. In contrast, when the isoform containing the C epsilon4 domain joined directly to the M2 exon (IgE grandé) is expressed in the J558L cell line, it is degraded intracellularly, suggesting a cell line-dependent regulation of secretion. These data show that these novel isoforms of human IgE, predicted to occur from in vivo and in vitro mRNA analysis, can be produced and secreted by mammalian cells. The different forms of IgE may have physiologically relevant but distinct roles in human IgE-mediated immune inflammation. The availability of purified recombinant human IgE isoforms makes it possible to analyze the functional differences among them.

Alternative Splicing↗
PubMed1996

Transformation of NIH 3T3 cells by HER3 or HER4 receptors requires the presence of HER1 or HER2.

Members of the epidermal growth factor receptor (EGFR) subfamily of receptor protein tyrosine kinases have been implicated in the pathogenesis of various malignancies. The ability of one EGFR subfamily member to influence, or function synergistically with, another is likely to be a general feature of these receptors. To assess the role of receptor heterodimerization, we analyzed the ability of Neu differentiation factor (NDF) to induce cell growth and transformation of NIH 3T3 cells transfected with different combinations of the EGFR subfamily of receptors. NDF induced mitogenesis, but not transformation, of cells expressing either HER3 or HER4 alone. However, NDF-induced cell transformation was observed when either HER1 or HER2 was coexpressed with HER3 or HER4. In analogous receptor phosphorylation experiments, NDF-induced transphosphorylation appears to be correlated with synergistic transformation of NIH 3T3 cells. Interestingly, transphosphorylation between HER1 and HER4 can be stimulated by either EGF or NDF.

3T3 Cells↗
PubMed1996

Cytokinin controls the cell cycle at mitosis by stimulating the tyrosine dephosphorylation and activation of p34cdc2-like H1 histone kinase.

In excised pith parenchyma from Nicotiana tabacum L. cv. Wisconsin Havana 38, auxin (naphthalene-1-acetic acid) together with cytokinin (6-benzylaminopurine) induced a greater than 40-fold increase in a p34cdc2-like protein, recoverable in the p13suc1-binding fraction, that had high H1 histone kinase activity, but enzyme induced without cytokinin was inactive. In suspension-cultured N. plumbaginifolia Viv., cytokinin (kinetin) was stringently required only in late G2 phase of the cell division cycle (cdc) and cells lacking kinetin arrested in G2 phase with inactive p34cdc2-like H1 histone kinase. Control of the Cdc2 kinase by inhibitory tyrosine phosphorylation was indicated by high phosphotyrosine in the inactive enzyme of arrested pith and suspension cells. Yeast cdc25 phosphatase, which is specific for removal of phosphate from tyrosine at the active site of p34cdc2 enzyme, was expressed in bacteria and caused extensive in-vitro activation of p13suc1-purified enzyme from pith and suspension cells cultured without cytokinin. Cytokinin stimulated the removal of phosphate, activation of the enzyme and rapid synchronous entry into mitosis. Therefore, plants can control cell division by tyrosine phosphorylation of Cdc2 but differ from somatic animal cells in coupling this mitotic control to hormonal signals.

Amino Acid Sequence↗
PubMed1996

Effect of lactic acid isomers on keratinocyte ceramide synthesis, stratum corneum lipid levels and stratum corneum barrier function.

Alpha-hydroxy acids are effective agents for the treatment of skin xerosis and it is known that, following treatment with lotions containing D,L-lactic acid, the stratum corneum prevents xerosis more effectively. To date, the relative efficacy of the different isomers of lactic acid has not been evaluated and the mode of action of lactic acid in improving stratum corneum resilience is not known. The objective of the present studies was to determine the effects of lactic acid isomers on keratinocyte ceramide biosynthesis, stratum corneum barrier function and the resistance of the stratum corneum to the appearance of skin xerosis. In vitro, lactic acid enhanced the production of ceramides by keratinocytes. L-Lactic acid was more effective than the D isomer (300% increase vs 100% increase). Carbon label from lactic acid was incorporated into all keratinocyte lipid species and a greater incorporation of label into ceramides was achieved with L-lactate than with D-lactate. In vivo, lactic acid increased the levels of stratum corneum ceramides. Whereas, lotions containing L-lactic acid resulted in the greatest increase (48% increase) followed by D,L-lactic acid (25% increase), D-lactic acid had no effect on stratum corneum ceramide levels. The increases in stratum corneum ceramide levels following lactic acid treatment also led to improvements in stratum corneum barrier function, measured by transepidermal water loss following a challenge to the skin with SLS and in the regression phase of a moisturization efficacy study. Significant improvements in barrier function and resistance to the appearance of skin xerosis were observed following L-lactic acid and D,L-lactic acid, but not following D-lactic acid treatment. From these results we believe that lactic acid, particularly the L isomer, stimulates ceramide biosynthesis leading to increased stratum corneum ceramide levels which results in superior lipid barrier and a more effective resistance against xerosis.

Adult↗
PubMed1996

Surgical treatment of ascending aortic dissecting aneurysm--clinical application of modified Cabrol's operation.

This paper reported 3 cases of ascending aortic dissecting aneurysm treated by modified Cabrol's operation. An 8 mm Gore-Tex connected with coronary arteries was employed to prevent high tension, intimal tearing and bleeding of anastomosis. Unremoved aneurysmal wall used as a sac for enclosing conduit graft could minimize the bleeding and oozing so that leaked blood can be drained to right atrium via a bypass.

Adult↗