Biomedical subjects

X Yang

Publications and source records attributed to X Yang.

At least 325 records · Page 18Linked to original sources

PubMed2000

BAG-1 promotes apoptosis induced by N-(4-hydroxyphenyl)retinamide in human cervical carcinoma cells.

N-(4-hydroxyphenyl)retinamide (4-HPR) is a synthetic apoptosis-inducing retinoid with cancer chemopreventive properties and lower toxicity than all-trans retinoic acid. BAG-1 is an antiapoptotic gene that is overexpressed in cervical and other cancers. In this study, we examined whether BAG-1 can inhibit 4-HPR-induced apoptosis in the C33A cervical carcinoma cell line. Surprisingly, although it inhibited apoptosis induced by five different apoptotic stimuli, overexpression of BAG-1 enhanced apoptosis induced by 4-HPR, producing a 2.5-fold lower IC(50) of 4-HPR. The effects of BAG-1 on 4-HPR-induced apoptosis were mediated by enhancing the caspase-3 activation pathway. Deletion mutation experiments showed that the central ubiquitin homology domain of BAG-1 protein was necessary for its promotion of 4-HPR-induced apoptosis, whereas its C-terminal Hsp70/Hsc70-interacting domain was required for its inhibition of staurosporine-induced apoptosis. These in vitro results suggest that the effectiveness of 4-HPR against the development of malignancy may be due to the overexpression of BAG-1 in cancer cells.

Antineoplastic Agents↗

PubMed2000

Synthesis and secretion of selenoprotein P by cultured rat astrocytes.

Selenoprotein P is an extracellular protein that has been postulated to have an oxidant defense function. It has survival-promoting properties for cultured neurons and its mRNA is present in the brain. This study sought to determine the primary structure of rat brain selenoprotein P and to assess its production by cultured brain cells. The cDNA of selenoprotein P was isolated from a rat brain cDNA library and was found to encode the same peptide sequence as rat liver cDNA. Thus the primary structure of brain selenoprotein P is the same as selenoprotein P from liver. Astrocytes and a cerebellar granule cell preparation (CGC) were obtained from rat brains and established in culture. The CGC was estimated to contain up to 5% glial cells. Both preparations were shown to contain selenoprotein P mRNA. During incubation with (75)Se-labeled selenite, both cell preparations secreted a (75)Se-labeled protein into the medium that corresponded in size to selenoprotein P. Also, the (75)Se-labeled protein could be precipitated from both media with an antiserum to selenoprotein P. This shows that astrocytes and the CGC secrete selenoprotein P. Selenoprotein P is made in the brain and may have an oxidant defense function there.

Animals↗

PubMed2000

Discovery of molecular and catalytic diversity among human diphosphoinositol-polyphosphate phosphohydrolases. An expanding Nudt family.

The turnover of the "high energy" diphosphoinositol polyphosphates by Ca(2+)- and cyclic nucleotide-modulated enzymes is considered a regulatory, molecular switching activity. Target processes may include intracellular trafficking. Following our earlier identification of a prototype human diphosphoinositol-polyphosphate phosphohydrolase (hDIPP1), we now describe new 21-kDa human isoforms, hDIPP2alpha and hDIPP2beta, distinguished from each other solely by hDIPP2beta possessing one additional amino acid (Gln(86)). Candidate DIPP2alpha and DIPP2beta homologues in rat and mouse were also identified. The rank order for catalytic activity is hDIPP1 > hDIPP2alpha > hDIPP2beta. Differential expression of hDIPP isoforms may provide flexibility in response times of the molecular switches. The 76% identity between hDIPP1 and the hDIPP2s includes conservation of an emerging signature sequence, namely, a Nudt (MutT) motif with a GX(2)GX(6)G carboxy extension. Northern and Western analyses indicate expression of hDIPP2s is broad but atypically controlled; these proteins are translated from multiple mRNAs that differ in the length of the 3'-untranslated region because of utilization of an array of alternative (canonical and noncanonical) polyadenylation signals. Thus, cells can recruit sophisticated molecular processes to regulate diphosphoinositol polyphosphate turnover.

Acid Anhydride Hydrolases↗

PubMed2000

Event-related brain potentials elicited by a number discrimination task.

To study the number cognition process, we recorded event-related potentials (ERPs) in 14 subjects when they were indicating whether a number pair was the same or not. The two numbers given in sequence were either the same (condition 1) or different (condition 2). After 270 ms following the onset of the second stimulus in condition 2, a negative component N270 was recorded on the scalp with the most negative amplitude at the central and occipital areas. Hemispheric asymmetry was not observed in the potential. This negative component is considered to reflect the mismatching process for numbers in the brain.

Adult↗

PubMed2000

The iron oxidation and hydrolysis chemistry of Escherichia coli bacterioferritin.

Bacterioferritins are members of a class of spherical shell-like iron storage proteins that catalyze the oxidation and hydrolysis of iron at specific sites inside the protein shell, resulting in formation of a mineral core of hydrated ferric oxide within the protein cavity. Electrode oximetry/pH stat was used to study iron oxidation and hydrolysis chemistry in E. coli bacterioferritin. Consistent with previous UV-visible absorbance measurements, three distinct kinetic phases were detected, and the stoichiometric equations corresponding to each have been determined. The rapid phase 1 reaction corresponds to pairwise binding of 2 Fe(2+) ions at a dinuclear site, called the ferroxidase site, located within each of the 24 subunits, viz., 2Fe(2+) + P(Z) --> [Fe(2)-P](Z) + 4H(+), where P(Z) is the apoprotein of net charge Z and [Fe(2)-P](Z) represents a diferrous ferroxidase complex. The slower phase 2 reaction corresponds to the oxidation of this complex by molecular oxygen according to the net equation: [Fe(2)-P](Z) + (1)/(2)O(2) --> [Fe(2)O-P](Z) where [Fe(2)O-P](Z) represents an oxidized diferric ferroxidase complex, probably a mu-oxo-bridged species as suggested by UV-visible and EPR spectrometric titration data. The third phase corresponds to mineral core formation according to the net reaction: 4Fe(2+) + O(2) + 6H(2)O --> 4FeO(OH)((core)) + 8H(+). Iron oxidation is inhibited by the presence of Zn(2+) ions. The patterns of phase 2 and phase 3 inhibition are different, though inhibition of both phases is complete at 48 Zn(2+)per 24mer, i.e., 2 Zn(2+) per ferroxidase center.

Amino Acid Substitution↗

PubMed2000

Tris(8-quinolinolato-N,O)cobalt(III) ethanol solvate.

In the crystal of the title complex, [Co(C(9)H(6)NO)(3)].C(2)H(5)OH, the central Co atom has a distorted octahedral coordination comprised of three N atoms and three O atoms from the three 8-quinolinolato ligands. The three Co-O bond distances are in the range 1.887 (2)-1.910 (2) A, while the three Co-N bond distances range from 1.919 (2) to 1.934 (2) A. The solvent ethanol molecule forms an intermolecular O-H.O hydrogen bonding with a quinolinolato ligand.

Journal Article↗

PubMed2000

Determination of Guan-Fu Base A, a new anti-arrhythmic, in human plasma by gas chromatography and electron-capture detection.

A gas chromatographic-electron capture detection (GC-ECD) method has been developed for determining Guan-Fu Base A (GFA), an experimental anti-arrhythmic, in human plasma. The method was based on one-step liquid-liquid extraction with toluene and chemical derivatization with pentafluoropropionic anhydride followed by GC-ECD. The derivatives of GFA and metoprolol (Met, internal standard) were confirmed by gas chromatography-mass spectrometry (GC-MS) to be dipentafluoropropionyl-GFA and dipentafluoropropionyl-Met. The method was linear over the concentration ranges of 0.1-20.0 and 1.0-30.0 microg/ml with the detection limit of 0.05 microg/ml at S/N=5. The intra- and inter-assay precisions were less than 6 and 10%, and accuracy 99.70+/-3.30 and 97.60+/-5.99%, respectively. The absolute recoveries were 81.88, 77.35, 80.79 and 83.85% for GFA at concentrations of 0.5, 1.0, 5.0 and 14.0 microg/ml and 88.24% for Met at 3.0 microg/ml, respectively.

Adult↗

PubMed2000

Resistance to apoptosis is correlated with the reduced caspase-3 activation and enhanced expression of antiapoptotic proteins in human cervical multidrug-resistant cells.

Recent studies have indicated that induction of apoptosis is the primary cytotoxic mechanism of most cancer chemotherapeutic agents, and abnormalities in the control of apoptosis can affect the sensitivity of malignant cells to multiple drugs. Here, we treated cells with cisplatin and other apoptotic stimuli and found that multidrug-resistant (MDR) endocervical HEN-16-2/CDDP cells, compared with drug-sensitive parental cells, were significantly more resistant to apoptosis and exhibited decreased proteolytic activation of caspase-3. The latter was further demonstrated by decreased cleavage of its substrate poly(ADP-ribose) polymerase (PARP). Further, Western blot analysis showed that MDR HEN-16-2/CDDP cells had significantly higher levels of the apoptosis-inhibiting proteins BAG-1 p50 and p33 isoforms and Bcl-X(L). This study provided the first evidence that overexpression of antiapoptotic BAG-1 p50 and p33 and Bcl-X(L) may cause resistance to apoptosis through reduction of caspase-3 activity in human cervical cells having an MDR phenotype.

Acetyltransferases↗

PubMed2000

LMP1 of Epstein-Barr virus suppresses cellular senescence associated with the inhibition of p16INK4a expression.

Epstein-Barr virus is associated with a number of human proliferative and malignant diseases. It is capable of immortalizing human primary B-lymphocytes in vitro. Studies indicate that latent membrane protein LMP1 is one of the viral proteins essential for this process. In this report, LMP1 was shown to prevent primary mouse embryonic fibroblasts from entering into replicative senescence in vitro. It further suppresses the senescence-associated induction of p16INK4a, commonly believed to be a key regulator of replicative senescence. In addition, LMP1 was shown to prevent premature senescence provoked by oncogenic ras in mouse embryonic fibroblasts, and to inhibit the oncogene ras-mediated induction of p16INK4a and p21WAF1. In parallel, LMP1 also prevents ras-induced premature senescence in rat embryonic fibroblasts REF52 and human diploid fibroblasts IMR90. Moreover, LMP1 is capable of suppressing the p16INK4a promoter in REF52 and Saos-2 cells in a promoter reporter assay. Our findings suggest that with the expression of p16INK4a and replicative senescence being suppressed, LMP1 may play a key role in Epstein-Barr virus-associated proliferative diseases, and it may further contribute to cancer development by preventing premature senescence induced by mitogenic oncogenes.

Animals↗

PubMed2000

Haploid loss of the tumor suppressor Smad4/Dpc4 initiates gastric polyposis and cancer in mice.

The tumor suppressor SMAD4, also known as DPC4, deleted in pancreatic cancer, is a central mediator of TGF-beta signaling. It was previously shown that mice homozygous for a null mutation of Smad4 (Smad4-/-) died prior to gastrulation displaying impaired extraembryonic membrane formation and endoderm differentiation. Here we show that Smad4+/- mice began to develop polyposis in the fundus and antrum when they were over 6 - 12 months old, and in the duodenum and cecum in older animals at a lower frequency. With increasing age, polyps in the antrum show sequential changes from hyperplasia, to dysplasia, in-situ carcinoma, and finally invasion. These alterations are initiated by a dramatic expansion of the gastric epithelium where Smad4 is expressed. However, loss of the remaining Smad4 wild-type allele was detected only in later stages of tumor progression, suggesting that haploinsufficiency of Smad4 is sufficient for tumor initiation. Our data also showed that overexpression of TGF-beta1 and Cyclin D1 was associated with increased proliferation of gastric polyps and tumors. These studies demonstrate that Smad4 functions as a tumor suppressor in the gastrointestinal tract and also provide a valuable model for screening factors that promote or prevent gastric tumorigenesis.

Age Factors↗

PubMed2000

Transport of low molecular weight anions through a Nafion lonomer membrane: application to kraft cooking liquors

The permeation of low molecular weight anions from liquors having high ionic strengths through a Nafion 811 membrane in Na+ form has been studied. The penetration of solutes through the membrane was monitored using UV-visible spectrometry. A relation between penetration and ionic size has been established. The influence of the presence of other ions on the permeation has also been investigated. The results show that the membrane has great potential as part of a selective interface in applications where the concentration of small anions is to be monitored in media with high ionic strengths. In light of the new results, we have validated a previously developed system for monitoring the concentrations of hydrogen sulfide ion and dissolved lignin in a laboratory-scale kraft cooking system.

Journal Article↗

PubMed2000

Nuclear factor-kappaB activation is involved in LMP1-mediated transformation and tumorigenesis of rat-1 fibroblasts.

The mechanism of latent membrane protein LMP1 of EBV in inducing cell transformation and tumorigenesis was investigated in Rat-1 fibroblasts. A plasmid encoding a site-specific mutant of LMP1 defective in binding to tumor necrosis factor receptor-associated death domain protein was constructed. This LMP1(TRADD) gene is 75% defective in nuclear factor (NF)-kappaB activation and 100% defective in activator protein-1 activation. When introduced into Rat-1 cells through retrovirus, the Rat-1-LMP1(TRADD) cells showed a significant reduction of focus formation and decreased tumor growth in nude mice as compared with Rat-1-LMP1 cells, suggesting that NF-kappaB or activator protein-1 activation may be important for LMP1-induced cell transformation. To further delineate the determinants of LMP1-mediated cellular transformation, a retrovirus with a dominant-negative I kappaB alpha was introduced into the transformed Rat-1-LMP1 cells. The presence of I kappaB alpha significantly suppressed both focus formation and tumorigenicity of Rat-1-LMP1 cells. Our results suggest that the activation of NF-kappaB may play an important role in LMP1-mediated cell transformation and tumorigenesis.

Animals↗

PubMed2000

Transcriptional control of the neuronal nicotinic acetylcholine receptor gene cluster by the beta43' enhancer, Sp1, SCIP and ETS transcription factors.

Receptors assembled from the products of a neuronal beta4alpha3alpha5 NAChR gene cluster depend on these genes being coordinately regulated in particular populations of neurons. Little is known, however, about the transcriptional mechanisms that are likely to underlie their co-expression in correct neuronal cell types. We have identified several regulatory elements and transcription factors that influence transcription of the alpha3 and beta4 genes. The promoters of these genes appear to contain a common cis element that binds Sp1 transcription factors. They can be activated by the POU-domain factor SCIP and activation does not require SCIP binding sites. Between these two promoters is a cell type specific enhancer called beta43'. This enhancer has little activity in non-neuronal cells and is preferentially active in particular populations of central neurons. The clustered genes are potential targets of ETS factors as the ETS domain factor, Pet-1 can activate beta43'-dependent transcription. The neuron-selective properties of beta43' and its location suggest that it is a component of the cis regulatory information required to control expression of the beta4 and alpha3 genes in specific populations of neurons.

Animals↗

PubMed2000

[Protection of metallothionein on the peroxidative injury in testis induced by cadmium].

In order to study the protection effect of metallothionein (MT) on peroxidative injury in testis induced by cadmium and to detect the mechanism of reproduction toxicity of cadmium, the SD rats were injected intraperitoneally with different doses of cadmium (0.2, 0.4 and 0.8 mg/kg BW) for 7 days. The content of MT, the activities of antioxidases and the content of malondialdehyde(MDA) in testis were detected. The results showed that the increase of MT content in the low dose group was not obvious. MT content increased significantly in the 0.4 mg/kg BW group, while decreased in the 0.8 mg/kg BW group. There was a significant reduction of the activities of superoxide dismutase(SOD) and glutathione peroxidase (GSH-Px) in the high dose group. The content of MDA did not change obviously in the low and middle dose groups, but increased significantly in the high dose group. It was concluded that MT might play an important role in protecting testis from oxidative damage. The toxicity of cadmium on male reproduction might be related to the unbalance of anti-oxidation system including MT.

Animals↗

PubMed2000

Impact of progesterone receptor on cell-fate decisions during mammary gland development.

Mammary epithelium contains lineage-limited progenitors that give rise to cells that form distinct morphological structures, ducts vs. lobules, depending on the endocrine status of the female. Progesterone signaling through progesterone receptor (PR) is essential for lobulo-alveolar development that accompanies pregnancy, but not for ductal growth accompanying puberty. PR exists in two molecular forms, A and B, and an imbalance in the native ratio of the two isoforms can lead to alterations in PR signaling. Indeed, as we reported previously, in transgenic mice carrying additional A form of PR, mammary development is abnormal, characterized by excessive lateral ductal branching. This suggests that alterations in PR signaling may have important consequences to mammary development, particularly with regard to ductal vs. alveolar growth. To test this further, we created transgenic mice carrying additional B form of PR and report that mammary development in these mice is also abnormal, characterized by inappropriate alveolar growth. More importantly, these mammary glands, on serial transplantation, undergo a premature arrest in ductal growth without any alteration in the potential for lobulo-alveolar growth. Such an arrest in ductal growth does not occur with transgenics carrying additional A form of PR. These studies, therefore, provide strong evidence to indicate that PR signaling may be of paramount importance for appropriate cell-fate decisions during normal mammary development, and also that this requires a regulated expression of the two isoforms.

Animals↗

PubMed2000

Smad6 as a transcriptional corepressor.

Smad6 and Smad7, a subgroup of Smad proteins, antagonize the signals elicited by transforming growth factor-beta. These two Smads, induced by transforming growth factor-beta or bone morphogenetic protein (BMP) stimulation, form stable associations with their activated type I receptors, blocking phosphorylation of receptor-regulated Smads in the cytoplasm. Here we show that Smad6 interacts with homeobox (Hox) c-8 as a transcriptional corepressor, inhibiting BMP signaling in the nucleus. The interaction between Smad6 and Hoxc-8 was identified by a yeast two-hybrid approach and further demonstrated by co-immunoprecipitation assays in cells. Gel shift assays show that Smad6, but not Smad7, interacts with both Hoxc-8 and Hoxa-9 as a heterodimer when binding to DNA. More importantly, the Smad6-Hoxc-8 complex inhibits interaction of Smad1 with Hoxc-8- and Smad1-induced transcription activity. These data indicate that Smad6 interacts with Hox transcription factors as part of the negative feedback circuit in the BMP signaling pathway.

Bone Morphogenetic Proteins↗

PubMed2000

Doubly homologated dihalovinyl and acetylene analogues of adenosine: synthesis, interaction with S-adenosyl-L-homocysteine hydrolase, and antiviral and cytostatic effects.

Treatment of the 6-aldehyde derived by Moffatt oxidation of 3-O-benzoyl-1,2-O-isopropylidene-alpha-D-ribo-hexofuranose (2c) with the dibromo- or bromofluoromethylene Wittig reagents generated in situ with tetrabromomethane or tribromofluoromethane, triphenylphosphine, and zinc gave the dihalomethyleneheptofuranose analogues 3b and 3d, respectively. Acetolysis, coupling with adenine, and deprotection gave 9-(7,7-dibromo-5,6, 7-trideoxy-beta-D-ribo-hept-6-enofuranosyl)adenine (5a) or its bromofluoro analogue 5b. Treatment of 5a with excess butyllithium provided the acetylenic derivative 9-(5,6, 7-trideoxy-beta-D-ribo-hept-6-ynofuranosyl)adenine (6). The doubly homologated vinyl halides 5a and 5b and acetylenic 6 adenine nucleosides were designed as putative substrates of the "hydrolytic activity" of S-adenosyl-L-homocysteine (AdoHcy) hydrolase. Incubation of AdoHcy hydrolase with 5a, 5b, and 6 resulted in time- and concentration-dependent inactivation of the enzyme (K(i): 8.5 +/- 0.5, 17 +/- 2, and 8.6 +/- 0.5 microM, respectively), as well as partial reduction of enzyme-bound NAD(+) to E-NADH. However, no products of the "hydrolytic activity" were observed indicating these compounds are type I mechanism-based inhibitors. The compounds displayed minimal antiviral and cytostatic activity, except for 6, against vaccinia virus and vesicular stomatitis virus (IC(50): 15 and 7 microM, respectively). These viruses typically fall within the activity spectrum of AdoHcy hydrolase inhibitors.

Adenosylhomocysteinase↗

PubMed2000

Activation of a cysteine protease in MCF-7 and T47D breast cancer cells during beta-lapachone-mediated apoptosis.

beta-Lapachone (beta-lap) effectively killed MCF-7 and T47D cell lines via apoptosis in a cell-cycle-independent manner. However, the mechanism by which this compound activated downstream proteolytic execution processes were studied. At low concentrations, beta-lap activated the caspase-mediated pathway, similar to the topoisomerase I poison, topotecan; apoptotic reactions caused by both agents at these doses were inhibited by zVAD-fmk. However at higher doses of beta-lap, a novel non-caspase-mediated "atypical" cleavage of PARP (i.e., an approximately 60-kDa cleavage fragment) was observed. Atypical PARP cleavage directly correlated with apoptosis in MCF-7 cells and was inhibited by the global cysteine protease inhibitors iodoacetamide and N-ethylmaleimide. This cleavage was insensitive to inhibitors of caspases, granzyme B, cathepsins B and L, trypsin, and chymotrypsin-like proteases. The protease responsible appears to be calcium-dependent and the concomitant cleavage of PARP and p53 was consistent with a beta-lap-mediated activation of calpain. beta-Lap exposure also stimulated the cleavage of lamin B, a putative caspase 6 substrate. Reexpression of procaspase-3 into caspase-3-null MCF-7 cells did not affect this atypical PARP proteolytic pathway. These findings demonstrate that beta-lap kills cells through the cell-cycle-independent activation of a noncaspase proteolytic pathway.

Antibiotics, Antineoplastic↗