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W Li

Publications and source records attributed to W Li.

At least 847 records · Page 47Linked to original sources
PubMed1997

Transcriptional repression at a distance through exclusion of activator binding in vivo.

The yeast repressor Rme1p acts from distant binding sites to block transcription of the chromosomal IME1 gene. Rme1p can also repress the heterologous CYC1 promoter when Rme1p binding sites are placed 250-300 bp upstream of CYC1 transcriptional activator binding sites (UAS1 and UAS2). Here, in vivo footprinting studies indicate that Rme1p acts over this distance by preventing the binding of the CYC1 transcriptional activators to UAS1 and UAS2. Inhibition of activator binding by Rme1p has the same genetic requirements as repression: both depend upon sequences flanking the Rme1p binding sites and upon Rgr1p and Sin4p, two subunits of the RNA polymerase II-associated Mediator complex that are required for normal nucleosome density. Thus Rme1p may alter chromatin to prevent binding of transcriptional activators to distant DNA sequences.

CCAAT-Binding Factor↗
PubMed1997

dl-alpha-tocopherol, a potent inhibitor of phorbol ester induced shape change of erythro- and megakaryoblastic leukemia cells.

Synthetic vitamin E, dl-alpha-tocopherol, added to a human erythroleukemia HEL and a megakaryoblastic leukemia, Meg-01, cell culture produced potent dose-dependent inhibition of phorbol ester-induced adhesion and of the morphologic changes accompanying it. The inhibition was reversible by withdrawal of supplemental vitamin E from the medium. dl-alpha-Tocopherol also inhibited protein kinase C activity both at baseline and after phorbol ester stimulation. Arachidonic acid stimulated protein kinase C activity of erythroleukemia cells and promoted their adhesion, an effect that was also inhibited by dl-alpha-tocopherol. Introduction of a protein kinase C-neutralizing antibody or a protein kinase C-inhibitor substrate into permeabilized HEL cells inhibited phorbol ester-induced adhesion and shape change. dl-alpha-Tocopherol also affected the cellular distribution of protein kinase C, shifting the major portion of the enzyme to the cytosol fraction and reducing phorbol ester-induced membrane association of the enzyme. Thus, protein kinase C appears to mediate shape change and adhesion, both of which are strongly inhibited by dl-alpha-tocopherol.

Arachidonic Acid↗
PubMed1997

Affected-sib-pair analyses of bipolar disorder using data on chromosome 18.

Our aim was to analyze the GAW10 bipolar data on chromosome 18, using three well-known affected-sib-pair methods. Analyses were carried out on both individual and combined data sets. In these analyses we defined the affected phenotype to include only individuals with diagnosis of bipolar I. We observed suggestive evidence for linkage to a few markers on the peri-centromeric region of chromosome 18. In the COLUMBIA data set, D18S45 showed statistically significant results (p-value < or = 0.001). Also for the combined analyses, D18S53 gave a consistently significant linkage signal.

Alleles↗
PubMed1997

Noninvasive comprehensive characterization of renal artery stenosis by combination of STAR angiography and EPISTAR perfusion imaging.

In a small fraction of patients with hypertension, the cause is stenosis of the renal artery. To date, there is no established noninvasive screening technique available to identify this population, for whom treatment with a surgical procedure or percutaneous transluminal angioplasty is often possible. In this study, the sensitivity and specificity of STAR angiography and EPISTAR perfusion imaging in characterizing renal artery stenosis were evaluated in an animal model. Qualitatively, STAR provided projection angiograms that were comparably sensitive to x-ray angiograms but obtained noninvasively. The sensitivity for detecting the stenosis was 100%. The specificity varied according to the definition of the threshold for significance, which varied 78-94%, depending on whether > 70% or > 50% diameter reduction was considered. Improvements in specificity will depend upon use of shorter echo times and higher spatial resolution. Our preliminary data indicate that EPISTAR provides sensitivity and specificity of 100% for characterizing stenosis with diameter reductions of > 70%.

Animals↗
PubMed1997

Human recombinant [C22A] FK506-binding protein amide hydrogen exchange rates from mass spectrometry match and extend those from NMR.

Hydrogen/deuterium exchange behavior of human recombinant [C22A] FK506 binding protein (C22A FKBP) has been determined by protein fragmentation, combined with electrospray Fourier transform ion cyclotron resonance mass spectrometry (MS). After a specified period of H/D exchange in solution, C22A FKBP was digested by pepsin under slow exchange conditions (pH 2.4, 0 degree C), and then subjected to on-line HPLC/MS for deuterium analysis of each proteolytic peptide. The hydrogen exchange rate of each individual amide hydrogen was then determined independently by heteronuclear two-dimensional NMR on 15N-enriched C22A FKBP. A maximum entropy method (MEM) algorithm makes it possible to derive the distributions of hydrogen exchange rate constants from the MS-determined deuterium exchange-in curves in either the holoprotein or its proteolytic segments. The MEM-derived rate constant distributions of C22A FKBP and different segments of C22A FKBP are compared to the rate constants determined by NMR for individual amide protons. The rate constant distributions determined by both methods are consistent and complementary, thereby validating protein fragmentation/mass spectrometry as a reliable measure of hydrogen exchange in proteins.

Amino Acid Sequence↗
PubMed1997

Extracellular matrix of retinal pigment epithelium regulates choriocapillaris endothelial survival in vitro.

The role of extracellular matrix of retinal pigment epithelial cells (RPE-ECM) in the regulation of the survival of choriocapillaris endothelial cells (CCE) was investigated in vitro. The CCE survival was evaluated by trypan blue staining, neutral red uptake, and the counting of viable cells. Results showed that CCE cells survived on RPE-ECM. Pre-treatment of RPE-ECM individually with neutralizing antibodies to acidic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, or transforming growth factor beta(pan specific to TGFbeta1, TGFbeta1.2, TGFbeta2 and TGFbeta5), did not alter the survival rate of CCE cells on RPE-ECM, as compared to that of the control (CCE survival rates on RPE-ECM pretreated with normal rabbit IgG). However, the treatment of RPE-ECM with neutralizing antibody to basic fibroblast growth factor (bFGF) caused CCE death by 77.1+/-15.7%. The CCE death was defined as apoptosis based on the morphological markers (shrinkage in cell size with blebbing of plasma membranes, condensation and fragmentation of nuclei, and DNA fragmentation in multiples of approximately 200 bp). The addition of phorbol 12-myristate 13-acetate (PMA) (2 nM) to the culture medium was effective for complete prevention of CCE apoptosis; the protecting effect of PMA on CCE apoptosis can be abolished by H7 (25 microM), but not HA1004 (50 microM), suggesting the involvement of PKC in protecting CCE from apoptosis. The inhibition of protein synthesis of CCE cells by cycloheximide (0.1 microM) did not affect the apoptotic process of the cells. In a separate experiment, when CCE cells were cultured in a medium saturated with bFGF (5 ng ml-1) without RPE-ECM, the cells also died by apoptosis. However, this apoptotic process was not affected by PMA. Cycloheximide also failed to affect the apoptotic process. These results suggest that both RPE-ECM insoluble molecules and RPE-ECM-bound bFGF modulate choriocapillaris survival by suppressing CCE apoptosis.

Animals↗
PubMed1997

Reversing effects of DDPH on cardiac hypertrophy and increased collagen content induced by partial narrowing of abdominal aorta.

To investigate the reversing effects of DDPH on cardiac hypertrophy and increased collagen content in left ventricle tissue of rats, cardiac hypertrophy of rats were induced by partial narrowing of abdominal aorta. 4 weeks after operation, the rats were given DDPH for 8 weeks. 12 weeks later, it was found that in model group, LVW/WHW and WHW/BW increased by 39.0% and 36.9% than those in control group; collagen content increased by 1.5 times. I phi/E phi, LS decreased (P < 0.01), MMW/E phi, WZ increased (P < 0.01). The above-mentioned changes in two DDPH groups could be partly or completely reversed. It is concluded that DDPH could reverse cardiac hypertrophy of rats induced by partial narrowing of abdominal aorta and reduce collagen content in left ventricle tissue.

Adrenergic alpha-Antagonists↗
PubMed1997

Sex differences in mutation rate in higher primates estimated from AMG intron sequences.

To study sex differences in mutation rate in primates, we sequenced the third introns of the AMGX and AMGY genes from humans, orangutans, and squirrel monkeys and estimated that the male-to-female ratio of mutation rate is alpha = 5.14 with the 95% confidence interval (2.42, 16.6). Combining this data set and the data sets from ZFX/ZFY and SMCX/SMCY introns, we obtained an estimate of alpha = 5.06 with the 95% confidence interval reduced to (3.24, 8.79). The alpha value is significantly higher in higher primates than in rodents.

Animals↗
PubMed1997

Mutation pattern variation among regions of the primate genome.

We sequenced three argininosuccinate-synthetase-processed pseudogenes (PsiAS-A1, PsiAS-A3, PsiAS-3) and their noncoding flanking sequences in human, orangutan, baboon, and colobus. Our data showed that these pseudogenes were incorporated into the genome of the Old World monkeys after the divergence of the Old World and New World monkey lineages. These pseudogene flanking regions show variable mutation rates and patterns. The variation in the G/C to A/T mutation rate (u) can account for the unequal GC contents at equilibrium: 34.9, 36.9, and 41.7% in the pseudogene PsiAS-A1, PsiAS-A3, and PsiAS-3 flanking regions, respectively. The A/T to G/C mutation rate (v) seems stable and the u/v ratios equal 1.9, 1.7, and 1.4 in the flanking regions of PsiAS-A1, PsiAS-A3, and PsiAS-3, respectively. These "regional" variations of the mutation rate affect the evolution of the pseudogenes, too. The ratio u/v being greater than 1.0 in each case, the overall mutation rate in the GC-rich pseudogenes is, as expected, higher than in their GC-poor flanking regions. Moreover, a "sequence effect" has been found. In the three cases examined u and v are higher (at least 20%) in the pseudogene than in its flanking region-i.e., the pseudogene appears as mutation "hot" spots embedded in "cold" regions. This observation could be partly linked to the fact that the pseudogene flanking regions are long-standing unconstrained DNA sequences, whereas the pseudogenes were relieved of selection on their coding functions only around 30-40 million years ago. We suspect that relatively more mutable sites maintained unchanged during the evolution of the argininosuccinate gene are able to change in the pseudogenes, such sites being eliminated or rare in the flanking regions which have been void of strong selective constraints over a much longer period. Our results shed light on (1) the multiplicity of factors that tune the spontaneous mutation rate and (2) the impact of the genomic position of a sequence on its evolution.

Animals↗
PubMed1997

Germ line transposition of the copia retrotransposon in Drosophila melanogaster is restricted to males by tissue-specific control of copia RNA levels.

Germ line transposition rates of the retrotransposon copia were directly measured in males and females of an inbred Drosophila melanogaster line, 2b3, which is highly polymorphic for copia insertion sites. The elevated germ line transposition rate of copia in this line (3-8 x 10(-3) per generation per element) is confined to males, with transposition in females being undetectable under the conditions of the experiment but at most 50-fold lower than the rate for males. To determine the molecular basis of this effect, copia RNA levels were measured in whole bodies and germ lines of male and female flies of both the unstable 2b3 line and a stable line, Oregon RC-iso, which shows normal rates of copia transposition. Both male and female 2b3 flies contain much more copia RNA than flies of the stable line. However, 2b3 male germinal tissues contain much higher levels of copia RNA than the equivalent female tissues. The highest copia expression is detected in maturing primary spermatocytes. Our data show that high rates of germ line copia transposition are restricted to males by tissue-specific control of RNA levels and suggest that transposition of copia only occurs in fly tissues containing more than a relatively high threshold level of copia RNA.

Animals↗
PubMed1997

The toxicity to macrophages of oxidized low-density lipoprotein is mediated through lysosomal damage.

Oxidized low-density lipoprotein (ox-LDL) has been shown to degrade poorly within the secondary lysosomes of macrophages but its possible effect on lysosomal integrity has received less attention. The effect of ultraviolet-C oxidized LDL (UVox-LDL) on cellular viability, and lysosomal membrane stability, was examined on cultured murine J-774 cells and human monocyte-derived macrophages (HMDMs). The acridine orange (AO) relocalization test was applied to study the lysosomal integrity of living cells. UVox-LDL dramatically reduced J-774 cell proliferation at a concentration of 25 microg/ml. Incubation with 5 microM copper alone, normally used to induce LDL oxidation, was also toxic. In contrast to the effects of ox-LDL, in concentrations up to 75 microg/ml, native LDL (nLDL) rather stimulated J-774 cell replication. Incubation with UVox-LDL (25-75 microg/ml) also altered cellular AO uptake, depending on time and dose: its lysosomal accumulation decreased and its cytosolic accumulation increased. This shift indicates damaged lysosomal membranes with decreased intralysosomal, and increased cytosolic, H+ concentration. Many J-774 cells exposed to UVox-LDL initially transformed into foam cells and then assumed an apoptotic-type morphology with TUNEL-positive nuclei. We conclude that ox-LDL is cytotoxic to macrophages due to oxidative damage of lysosomal membranes, with ensuing destabilization and leakage to the cytosol of lysosomal contents, such as hydrolytic enzymes, causing degeneration of apoptotic type.

Animals↗
PubMed1997

Human discrimination of the implicit orientation of simple symmetrical patterns.

Thresholds for detecting the angle of rotation of vertical symmetrical patterns containing few or no explicit vertical or horizontal contours were found to be almost as low as those for an actual vertical line extending approximately the same range. This hyperacuity performance, which we refer to as implicit orientation discrimination, shares most of its properties with the orientation discrimination of explicit lines, suggesting a category of orientation processing whose neural mechanisms are related to those involved in the processing of straight contours and those underlying the detection of axes of symmetry. Strong binding effects between the components of the figures were demonstrated and their temporal interactions were also investigated. Our results have implications for possible neural interactions early in the cortical visual stream.

Humans↗
PubMed1997

Saccadic suppression of displacement: separate influences of saccade size and of target retinal eccentricity.

The threshold for detection of displacements of visual objects is higher during voluntary saccades than it is during steady gaze ("saccadic suppression of displacement"; SSD). Relative contributions to SSD of extraretinal and retinal factors were investigated by measuring displacement thresholds in four experiments in which three observers judged whether a test flash, presented after a saccade or a period of fixation, was located to the left or right of a reference point viewed earlier. The experiments, involving saccades ranging from 4 to 12 deg in length, separated the effects of saccade size from the effects of retinal eccentricity of the reference point, and also separated the effects of retinal eccentricity of the test flash from both. The influences of the three are nearly linearly independent. Approximately 20% of the total influence on SSD derives from retinal influences of test flash and reference point; 80% is due to extraretinal influence associated with saccade size. A signal/noise model that accounted well for our previous on SSD (Li & Matin, 1990a,b) was extended to account for the present results. The model also provides a unified treatment of SSD and of the saccadic suppression of visibility (SSV).

Fixation, Ocular↗
PubMed1997

Regulation of the signal transduction program by drugs.

The purpose of this paper was to clarify critical aspects of the behavior of signal transduction activity in normal and cancer cells. 1. Signal transduction activity in the conversion of phosphatidylinositol through PI and PIP kinases and PLC to IP3 is regulated at multiple sites. In liver, hepatomas and human carcinomas PIP kinase is the rate limiting enzyme and PLC activity is present in great excess. 2. The steady-state signal transduction activity as measured by the three enzyme activities and IP3 concentration was markedly up-regulated in rat hepatomas of different growth rates. The steady-state specific activities of the three signal transduction enzymes were elevated in ovarian carcinomas as compared to normal ovary. Increased enzyme activities were also observed in human breast carcinoma cells as compared to normal human breast parenchymal cells. In breast, ovarian and rat hepatoma cells as they go through lag, log and plateau phases, IP3 concentration in the early lag phase increased 4.5- to 20-fold and PI and PIP kinase activities peaked in mid-log phase. These events returned to baseline levels in the plateau phase. PLC activity did not change. 3. The bone marrow PI and PIP kinase activities in 3-day starvation were decreased to 13% and IP3 concentration was reduced to 24%; at 1-day refeeding they returned to normal. PLC activity changed little. These alterations are in line with the rapid t1/2 degradation rates (12 min) of PI and PIP kinases observed in studies with cycloheximide. By contrast, PLC has a long half-life. 4. The molecular action of tiazofurin entails inhibition of IMP DH activity, decrease in GTP and IP3 concentrations, reduction of ras and myc oncogene expression, and signal transduction enzyme activities. These events are followed by induced differentiation and apoptosis. There are also decreases in enzyme activities which have rapid turnover, including TdR kinase, dTMP synthase, and GPRT. In vitro studies indicated that these events are abrogated by addition of guanine which restores GTP concentrations. Therefore, most or all these events were brought about by the reduced GTP concentration in the tiazofurin target cells. 5. Quercetin and genistein are able to inhibit PI and PIP kinase activities and reduce IP3 concentration in vivo and in tissue culture systems. These flavonoids are also inhibitors of cell proliferation and clonogenic ability in rat hepatoma 3924A and in human OVCAR-5 and MDA-MB-435 cells. Quercetin down-regulated the expression of c-myc and Ki-ras oncogenes and led to induced differentiation and apoptosis in K562 cells. Genistein reduced IP3 concentration in vivo and in the tissue culture system. Genistein is antiproliferative and has cytototoxicity in human carcinoma cells. All three drugs, tiazofurin, quercetin and genistein, act, in part at least, through depression of cellular IP3 concentration although the mechanisms may not be identical. 6. Quercetin and genistein, which attack different targets and different phases of the cell cycle, proved to be synergistic in OVCAR-5 cells. The impact of tiazofurin, genistein and quercetin is of interest because the drugs crucially inhibit the display of the neoplastic program of cells and lead to induced differentiation and apoptosis.

1-Phosphatidylinositol 4-Kinase↗
PubMed1997

The study of correlation structures of DNA sequences: a critical review.

The study of correlation structure in the primary sequences of DNA is reviewed. The issues reviewed include: symmetries among 16 base-base correlation functions; accurate estimation of correlation measures; the relationship between 1/f and Lorentzian spectra; heterogeneity in DNA sequences; different modeling strategies of the correlation structure of DNA sequences; the difference of correlation structure between coding and non-coding regions (besides the period-3 pattern); and source of broad distribution of domain sizes. Although some of the results remain controversial, a body of work on this topic constitutes a good starting point for future studies.

Base Sequence↗
PubMed1997

Propagation and titration of murine cytomegalovirus in a continuous bone marrow-derived stromal cell line (M2-10B4).

Murine cytomegalovirus (MCMV) can only be propagated effectively in mouse embryo fibroblast (MEF) cells. We demonstrate that MCMV replicates significantly better in M2-10B4 cells, a continuous line of murine bone marrow stromal cells. M2-10B4 cells were also comparable to MEF cells for detection of small amounts of MCMV reactivating from latently infected spleen explants. M2-10B4 cells will be very useful for studies of MCMV pathogenesis.

Animals↗
PubMed1997

Induction of T1 (cytotoxic lymphocyte) and/or T2 (antibody) responses to a mucin-1 tumour antigen.

Effective vaccination-based control of intracellular pathogens or parasites and various tumours is dependent upon induction of cytotoxic lymphocytes and other mechanisms of cellular immunity. Such responses are usually described as being antagonistic to an antibody-based immune response. This paper elaborates on previous studies that have demonstrated that conjugation of a fusion protein (FP, incorporating copies of the variable number of tandem repeat sequence of human mucin-1 (MUC1)) to oxidized mannan results in a significant shift from a type-2 response towards a type-1 response. This response induces complete protection upon challenge of immunized mice with MUC1 expressing tumour cells. This report details experiments in which the balance between type-1 and type-2 anti-MUC1 responses is manipulated by altering the dose of mannan-FP (M-FP) delivered. It is also shown that type-1 and type-2 responses may be induced simultaneously by administration of both forms of the antigen (FP/M-FP). Further, when a type-2 response is induced after FP immunization, a type-1 response can also be established by subsequent immunization with M-FP without adversely affecting the initial response. The converse also applies when M-FP is used for the initial immunizations, followed by FP administration. Delivery of interleukin-1 beta as a cytokine adjuvant with M-FP immunizations also enhanced antibody responses to levels fourfold that induced by M-FP alone without adversely affecting the cytotoxic activity induced by M-FP immunization. Contrary to the type-1/type-2 paradigm, cellular and antibody responses to MUC1 were not antagonistic. These results have important implications for the development of vaccination strategies against pathogens for which both the cellular and humoral compartments of the immune response contribute to protection.

Adjuvants, Immunologic↗