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L Xia

Publications and source records attributed to L Xia.

At least 37 records · Page 2Linked to original sources
PubMed2001

Purification and functional characterization of a histone H3-lysine 4-specific methyltransferase.

Methylation of histone H3 at lysine 9 by SUV39H1 and subsequent recruitment of the heterochromatin protein HP1 has recently been linked to gene silencing. In addition to lysine 9, histone H3 methylation also occurs at lysines 4, 27, and 36. Here, we report the purification, molecular identification, and functional characterization of an H3-lysine 4-specific methyltransferase (H3-K4-HMTase), SET7. We demonstrate that SET7 methylates H3-K4 in vitro and in vivo. In addition, we found that methylation of H3-K4 and H3-K9 inhibit each other. Furthermore, H3-K4 and H3-K9 methylation by SET7 and SUV39H1, respectively, have differential effects on subsequent histone acetylation by p300. Thus, our study provides a molecular explanation to the differential effects of H3-K4 and H3-K9 methylation on transcription.

Acetylation↗
PubMed2001

Plant catechols prevent lipid peroxidation in human plasma and erythrocytes.

The antioxidant activity of several plant catechol derivatives was tested in buffer, plasma, and human erythrocytes. In buffer, chlorogenic acid (CGA), caffeic acid (CA), and dihydrocaffeic acid (DCA) reduced ferric iron equally well in the ferric reducing antioxidant power (FRAP) assay. Low concentrations of the polyphenols enhanced the ability of plasma to reduce ferric iron by about 10%. In plasma, lipid hydroperoxide and F2-isoprostane formation induced by a water-soluble free radical initiator were reduced by CGA at concentrations as low as 20 microM. During incubation at 37 degrees C, human erythrocytes took up DCA, but not CGA, and intracellular DCA enhanced the ability of erythrocytes to reduce extracellular ferricyanide. When intact erythrocytes were exposed to oxidant stress generated by liposomes containing small amounts of lipid hydroperoxides, extracellular CGA at a concentration of 5 microM decreased both lipid peroxidation in the liposomes, and spared alpha-tocopherol in erythrocyte membranes. These results suggest that the catechol structure of these compounds convey the antioxidant effect in plasma and in erythrocytes.

Antioxidants↗
PubMed2001

Pigeons (Columba livia) learn to link numerosities with symbols.

After responding to each element in varying, successive numerosity displays, pigeons (Columba livia) had to choose, out of an array of symbols, the symbol designated to correspond to the preceding number of elements. After extensive training, 5 pigeons responded with significant accuracy to the numerosities 1 to 4, and 2 pigeons to the numerosities 1 to 5. Several tests showed that feedback tones accompanying element pecks, the familiarity of element configurations, and the shape of the elements were not crucial to this performance. One test, however, indicated that the number of pecks issued to the elements was important for numerosities above 2. An additional test confirmed that the birds chose the symbol that corresponded to a particular numerosity rather than the positions that the symbols had held during training.

Animals↗
PubMed2001

Reduction of ubiquinone by lipoamide dehydrogenase. An antioxidant regenerating pathway.

Lipoamide dehydrogenase belongs to a family of pyridine nucleotide disulfide oxidoreductases and is ubiquitous in aerobic organisms. This enzyme also reduces ubiquinone (the only endogenously synthesized lipid-soluble antioxidant) to ubiquinol, the form in which it functions as an antioxidant. The reduction of ubiquinone was linear with time and exhibited turnover numbers of 5 and 1.2 min(-1) in the presence and absence of zinc, respectively. The reaction was stimulated by zinc and cadmium but not by the other divalent ions tested. The zinc/cadmium-dependent stimulation of the reaction increased rapidly and linearly up to a concentration of 0.1 mM and was even further increased at 0.5 mM. At pH 6, the activity was three times higher than at physiological pH. Alteration of the NADPH : NADP(+) ratio revealed that the reaction is inhibited by higher concentrations of the oxidized cofactors. FAD reduced ubiquinone in a dose-dependent manner at a considerably lower rate, suggesting that the reduction of ubiquinone by lipoamide dehydrogenase involves the FAD moiety of the enzyme.

Animals↗
PubMed2001

Effector genes altered in MCF-7 human breast cancer cells after exposure to fractionated ionizing radiation.

Understanding the molecular mechanisms involved in the response of tumors to fractionated exposures to ionizing radiation is important for improving radiotherapy and/or radiochemotherapy. In the present study, we examined the expression of stress-related genes in an MCF-7 cell population (MCF-IR20) that has been derived through treatment with fractionated irradiation (2 Gy per fraction with a total dose of 40 Gy). MCF-IR20 cells showed a 1.6-fold increase in sensitization with dose at 10% isosurvival in a clonogenic assay, and a reduced growth delay ( approximately 15 h compared to approximately 27 h), compared to the parental MCF-7 cells treated with a single dose of 5 Gy. To determine which effector genes were altered in the MCF-IR20 cells, the expression of stress-related effector genes was measured using a filter with 588 genes (Clontech) that included major elements involved in cell cycle control, DNA repair, and apoptosis. Compared to MCF-7 cells that were not exposed to fractionated radiation, 19 genes were up- regulated (2.2-5.1-fold) and 4 were down-regulated (2.7-3.4- fold) in the MCF-IR20 cells. In agreement with the array results, 6 up-regulated genes tested by RT-PCR showed elevated expression. Also, activities of the stress-related transcription factors NFKB, TP53 and AP1 showed a 1.2-4.5-fold increase after a single dose of 5 Gy in MCF-IR20 cells compared with parental MCF-7 cells. However, when the radioresistant MCF-IR20 cell were cultured for more than 12 passages after fractionated irradiation (MCF-RV), radioresistance was lost, with the radiosensitivity being the same as the parental MCF- 7 cells. Interestingly, expression levels of CCNB1, CD9 and CDKN1A in MCF-RV cells returned to levels expressed by the parental cells, whereas the expression levels of three other genes, MSH2, MSH6 and RPA remained elevated. To determine if any of the changes in gene expression could be responsible for the induced radioresistance, CCNB1 and CDKN1A, both of which were up-regulated in MCF-IR20 cells and down-regulated in MCF-RV cells, were studied further by transfection with antisense oligonucleotides. Antisense of CCNB1 significantly reduced the clonogenic survival of MCF- IR20 cells at doses of 5 and 10 Gy, from 42% to 26% and from 5.7% to 1.0%, respectively. Antisense of CDKN1A, however, had no effect on radiation survival of MCF-IR20 cells. In summary, these results suggest that stress-related effector genes are altered in cells after treatment with fractionated irradiation, and that up-regulation of CCNB1 is responsible, at least in part, for radioresistance after fractionated irradiation.

Adenocarcinoma↗
PubMed2001

[Expression of leukemia inhibitory factor in the decidua of normal early pregnancy, threatened abortion and inevitable abortion].

OBJECTIVE: To investigate the expression of leukemia inhibitory factor (LIF) in the decidua of normal early pregnancy, threatened abortion and inevitable abortion. METHOD: We examined LIF gene expression in the above-mentioned decidua by a quantitative reverse transcription-polymerase chain reaction (RT-PCR) method, and also examined the serum pregesterone, human chorionic gonadotrapin (hCG) by radioimmunoassay in all cases. RESULTS: (1) Serum levels of pregesterone and hCG are: (91.5 +/- 27.2) nmol/L, (69.9 +/- 14.9) kU/L in normal early pregnancy; (88.4 +/- 24.7) nmol/L, (57.6 +/- 11.2) kU/L in threatened abortion respectively. There was no difference in the levels of pregesterone and hCG between the two groups (P > 0.05). While serum pregesterone, hCG levels in inevitable group were (33.1 +/- 19.6) nmol/L, (10.3 +/- 3.2) kU/L respectively. Compared with normal early pregnancy and threatened abortion group, the levels of serum pregesterone and hCG reduced significantly (P < 0.05). (2) The expression of LIF in three groups: There was no statistically significant difference in the levels of LIF expression between the normal early pregnancy group (2.10 +/- 0.32) and threatened abortion (1.92 +/- 0.20) groups, while the levels of LIF expression in inevitable abortion group (0.7 +/- 0.06) was lower than those in normal early pregnancy group and threatened abortion group (P < 0.05, respectively). CONCLUSION: The reduction of LIFmRNA expression in the decidua of early pregnancy may decrease the serum pregesterone and hCG levels and cause inevitable abortion.

Abortion, Spontaneous↗
PubMed2001

[Simultaneous determination of 11 organic acids in fruit juice by ion exclusion chromatography].

A method for the quantitative determination of 11 organic acids (oxalic acid, citric acid, tartaric acid, malic acid, ascorbic acid, lactic acid, succinic acid, formic acid, acetic acid, glutaric acid and fumaric acid) in fruit juice was developed successfully. It was based on an ion exclusion chromatographic separation under the conditions of isocratic elution with 17 mmol/L sulphuric acid solution with the ICE-ION-300 ion exclusion column, and the UV detection at 210 nm. The precision of the method was investigated and the relative standard deviations were from 1.5% to 9.8% (n = 10).

Beverages↗
PubMed2001

[Substituting esophagus with colon in the treatment of hypopharyngeal and esophageal disease].

OBJECTIVE: To study the feasibility and effect of substituting esophagus with colon in the treatment of advanced stage hypopharyngeal carcinoma, cervical esophagus cancer and serious esophageal stenosis on the basis of laryngeal function preservation. METHODS: From 1989 to 1996. 25 patients in our department were retrospectively reviewed among them, nine were hypopharyngeal carcinoma, T3 (No1, N1 4, N2 2), T4 N1 M0 2 (UICC 1997), thirteen were cervical esophagus cancer, T1N0M0 2, T2 (N0 4, N1 7), there were serious esophageal stenosis, length was 3-5 cm. The patients with carcinoma were given postoperation radiotherapy. RESULT: The total survival rates in 3, 5 years are 54.5%, 42.9% respectively. The 3-year survival rates are 44.4% in the cases with advanced stage hypopharyngeal carcinoma, and 61.5% with cervical esophagus cancer, respectively. CONCLUSION: Substituting esophagus with colon is in conformity with physical demand, can reduce complication and improve life quality.

Aged↗
PubMed2001

[Value of surgical margin in directing the treatment of early laryngeal carcinoma after partial laryngectomy].

OBJECTIVE: To investigate the value of surgical margin in directing the treatment of early laryngeal carcinoma after partial laryngectomy. METHODS: We studied 87 cases of T1N0M0 and T2N0M0 laryngeal carcinoma in which the surgical margins were reserved during partial laryngectomy. The recurrence and survival rates between the positive and negative margin groups were compared; the survival between the positive margin groups with postoperative radiotherapy and negative groups; the survival between groups with and without postoperative radiotherapy in negative margins. RESULTS: Recurrent rate of the negative group was lower than that of the positive group (5.8% vs 33.3%, chi 2 = 10.64 P = 0.001). The estimated survival was higher in the negative group than in the positive group(P = 0.011), and also in tumor-free time(P = 0.007). The survival of those with positive surgical margin and received postoperative RT was lower than that with negative margins(P = 0.01). In the negative group, the difference in the survival between those with or without postoperative RT was not significant (P = 0.405). CONCLUSION: The prognosis of the positive margin group of the early laryngeal carcinoma was worse than that of the negative group, but postoperative RT can improve it; it is not necessary for the negative group to be treated by postoperative RT.

Adult↗
PubMed2000

Polyglycylation of tubulin is essential and affects cell motility and division in Tetrahymena thermophila.

We analyzed the role of tubulin polyglycylation in Tetrahymena thermophila using in vivo mutagenesis and immunochemical analysis with modification-specific antibodies. Three and five polyglycylation sites were identified at glutamic acids near the COOH termini of alpha- and beta-tubulin, respectively. Mutants lacking all polyglycylation sites on alpha-tubulin have normal phenotype, whereas similar sites on beta-tubulin are essential. A viable mutant with three mutated sites in beta-tubulin showed reduced tubulin glycylation, slow growth and motility, and defects in cytokinesis. Cells in which all five polyglycylation sites on beta-tubulin were mutated were viable if they were cotransformed with an alpha-tubulin gene whose COOH terminus was replaced by the wild-type COOH terminus of beta-tubulin. In this double mutant, beta-tubulin lacked detectable polyglycylation, while the alpha-beta tubulin chimera was hyperglycylated compared with alpha-tubulin in wild-type cells. Thus, the essential function of polyglycylation of the COOH terminus of beta-tubulin can be transferred to alpha-tubulin, indicating it is the total amount of polyglycylation on both alpha- and beta-tubulin that is essential for survival.

Amino Acid Sequence↗
PubMed2000

Pharmacological characterization of the cloned neuropeptide Y y(6) receptor.

Neuropeptide Y has potent appetite stimulating effects which are mediated by hypothalamic receptors believed to be of the neuropeptide Y Y(1) and/or neuropeptide Y Y(5) subtype. In mice, the neuropeptide Y y(6) receptor is also expressed in the hypothalamus, suggesting that it too may function as a feeding receptor in this species. Several laboratories have studied the pharmacology of the neuropeptide Y y(6) receptor, but their results are not in agreement. Using neuropeptide Y and a variety of peptide analogs and small molecule antagonists, we have determined that the pharmacology of the cloned mouse neuropeptide Y y(6) receptor is distinct from that of the other known neuropeptide Y receptors. The rank order of binding affinity for the mouse neuropeptide Y y(6) receptor is [(Ile, Glu,Pro,Dpr,Tyr,Arg,Leu,Arg,Tyr-NH(2))(2)human peptide YY=human, rat neuropeptide Y=human, rat neuropeptide Y-(2-36)=human, rat [Leu(31), Pro(34)porcine (Cys(2))-neuropeptide Y-(1-4)-8-aminooctanoyl-(D-Cys(27)porcine [D-Trp(32)rat pancreatic polypeptide=human pancreatic polypeptide. A similar rank order of potency is seen for inhibition of forskolin-stimulated cyclic AMP. The neuropeptide Y Y(5) receptor antagonist trans-naphthalene-1-sulfonic acid ¿4-[4-amino-quinazolin-2-ylamino)-methyl]-cyclohexylmethy l¿-amide hydrochloride (CGP 71683A) and the neuropeptide Y Y(1) receptor antagonist ((R)-N(2)-diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininam ide) (BIBP3226) bind weakly to the neuropeptide Y y(6) receptor (K(i)10, 000 nM, respectively). Although the function of the neuropeptide Y y(6) receptor remains to be elucidated, its pharmacology is not consistent with a role in appetite regulation.

Animals↗
PubMed2000

Somatic mutation of hPMS2 as a possible cause of sporadic human colon cancer with microsatellite instability.

Inactivation of DNA-mismatch repair underlies the genesis of microsatellite unstable (MSI) colon cancers. hPMS2 is one of several genes encoding components of the DNA-mismatch repair complex, and germline hPMS2 mutations have been found in a few kindreds with hereditary nonpolyposis colorectal carcinoma (HNPCC), in whom hereditary MSI colon cancers develop. However, mice bearing null hPMS2 genes do not develop colon cancers and hPMS2 mutations in sporadic human colon cancers have not been described. Here we report that in Vaco481 colon cancer the hPMS2 gene is inactivated by somatic mutations of both hPMS2 alleles. The cell line derived from this tumor is functionally deficient in DNA mismatch repair. This deficiency can be biochemically complemented by addition of a purified hMLH1-hPMS2 (hMutLalpha) complex. The hPMS2 deficient Vaco481 cancer cell line demonstrates microsatellite instability, an elevated HPRT gene mutation rate, and resistance to the cytotoxicity of the alkylator MNNG. We conclude that somatic inactivation of hPMS2 can play a role in development of sporadic MSI colon cancer expressing the full range of cancer phenotypes associated with inactivation of the mismatch repair system.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Murine immune responses to mucosally delivered Salmonella expressing Lassa fever virus nucleoprotein.

Arenaviruses are emerging pathogens known to infect via the mucosa, however no formal attempts to make mucosal vaccines have been undertaken. Here we describe a recombinant aroA attenuated Salmonella typhimurium that expresses the nucleoprotein (NP) gene of Lassa fever virus (LAS). The complete NP gene was cloned downstream of the bacterial groEL promotor and integrated into the aroA locus of S. typhimurium. Lassa NP protein was detected in whole cell extracts from the recombinant Salmonella by immunoblot analysis with serum from Lassa-infected people. Mice were inoculated by intragastric intubation with 5 x 10(9) S. typhimurium and boosted with the same recombinant Salmonella 21 days after the primary inoculation. Both local mucosal IgA and serum immunoglobulins against Lassa NP were observed. Splenic cytotoxic T-lymphocyte responses to LAS NP were detected after the boost and they cross-reacted with target cells infected with the related arenavirus, lymphocytic choriomeningitis virus. Recombinant Salmonella elicits humoral and cell mediated immune responses against Lassa fever virus in mice and should be considered as a potential vaccine strategy in man.

Animals↗
PubMed2000

Strategies for genetic mapping of categorical traits.

The search for efficient and powerful statistical methods and optimal mapping strategies for categorical traits under various experimental designs continues to be one of the main tasks in genetic mapping studies. Methodologies for genetic mapping of categorical traits can generally be classified into two groups, linear and non-linear models. We develop a method based on a threshold model, termed mixture threshold model to handle ordinal (or binary) data from multiple families. Monte Carlo simulations are done to compare its statistical efficiencies and properties of the proposed non-linear model with a linear model for genetic mapping of categorical traits using multiple families. The mixture threshold model has notably higher statistical power than linear models. There may be an optimal sampling strategy (family size vs number of families) in which genetic mapping reaches its maximal power and minimal estimation errors. A single large-sibship family does not necessarily produce the maximal power for detection of quantitative trait loci (QTL) due to genetic sampling of QTL alleles. The QTL allelic model has a marked impact on efficiency of genetic mapping of categorical traits in terms of statistical power and QTL parameter estimation. Compared with a fixed number of QTL alleles (two or four), the model with an infinite number of QTL alleles and normally distributed allelic effects results in loss of statistical power. The results imply that inbred designs (e.g. F2 or four-way crosses) with a few QTL alleles segregating or reducing number of QTL alleles (e.g. by selection) in outbred populations are desirable in genetic mapping of categorical traits using data from multiple families.

Alleles↗
PubMed2000

Nitrite uptake and metabolism and oxidant stress in human erythrocytes.

Nitric oxide, when released into the bloodstream, is quickly scavenged by Hb in erythrocytes or oxidized to nitrite. Nitrite can also enter erythrocytes and oxidize Hb. The goals of this work were to determine the mechanism of erythrocyte nitrite uptake and whether this uptake causes oxidant stress in these cells. Erythrocytes took up 0.8 mM nitrite with a half-time of 11 min. Nitrite uptake was sensitive to temperature and to the pH and ionic composition of the medium but was not inhibited by the specific anion-exchange inhibitor DIDS. About 25% of nitrite uptake occurred on the sodium-dependent phosphate transporter and the rest as diffusion of nitrous acid or other species across the plasma membrane. Methemoglobin formation increased in proportion to the intracellular nitrite concentration. Nitrite reacted with erythrocyte ascorbate, but ascorbate loading of cells decreased nitrite-induced methemoglobin formation only at high nitrite concentrations. In conclusion, nitrite rapidly enters erythrocytes and reacts with oxyhemoglobin but does not exert a strong oxidant stress on these cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2000

Solid-state fermentation with Aspergillus niger for cellobiase production.

Aspergillus niger NRRL3 was cultivated in a moist wheat bran and ground corncob solid medium supplemented with inorganic minerals for the production of cellobiase (beta-1,4-glucosidase, EC 3.2.1.21). With this method, A. niger NRRL3 was able to produce a high concentration of cellobiase (215 IU/g of solid substrate) after 96 h of incubation. Temperature and moisture content affected final cellobiase titers. The best conditions for cellobiase production from solid substrate by A. niger NRRL3 were determined to be 70% moisture and 35 degrees C.

Aspergillus↗
PubMed2000

[Antagonistic characterization of 1-(2,6-dimethylphenoxyl)-2-(3,4-dimethylphenyl ethylamino) propane hydrochloride on alpha 1-adrenoceptor].

AIM: To study the antagonistic effect of 1-(2,6-dimethylphenox)-2-(3,4-dimethylphenyl ethylamino) propane hydrochloride (DDPH) on alpha 1-adrenoceptor (AR). METHODS: Radioligand binding assay was used. Specific 125I-BE2254 (2-beta(4-hydroxyphenyl)-ethyl aminomethyl-tetralone) binding was measured by incubating membrane of rat cerebral cortex, spleen and the three cloned alpha 1-AR subtypes (alpha 1A, alpha 1B, alpha 1D) stably expressed in human embryonic kidney 293 cell preparation with a single concentration of 125I-BE2254 in the presence of 14 concentrations of DDPH. Equilibrium binding constant (KI) and Hill coefficients (nH) were determined from Hill plots. The -log value of the KI was expressed as pKI. Contractile responses of isolated rat aorta, renal artery ring and spleen were determined. The pA2 values for DDPH in competitively inhibiting NE-stimulated contraction of tissues were measured with the method of Ainlakshana and Schild. RESULTS: DDPH competitively inhibited binding of 125I-BE2254 to alpha 1-AR in a concentration-dependent manner. The pKI values for DDPH in rat cerebral cortex and spleen were 7.17 +/- 0.06 and 7.41 +/- 0.11, respectively, and the Hill efficiency values were not significantly different from unit. The pKI values for cloned alpha 1A, alpha 1B and alpha 1D-AR were 7.21 +/- 0.12, 6.88 +/- 0.04 and 7.26 +/- 0.06, respectively, and the Hill efficiency values were not significantly different from unit. Contractile studies showed that DDPH competitively antagonized the NE concentration-response curve with a pA2 values of 7.40 +/- 0.23 in aorta, 7.41 +/- 0.04 in renal artery and 7.63 +/- 0.07 in spleen and the slopes of schild plot were not significantly different from unit. The pKI values for DDPH in tissues and the cloned alpha 1A or alpha 1D-AR were shown to fit well in with the pA2 values in antagonizing NE-induced constriction in rat isolated aorta, renal artery and spleen. CONCLUSION: These results suggest that DDPH appear to be a non-subtype selective competitive antagonist for alpha 1-AR.

Adrenergic alpha-Antagonists↗