Biomedical subjects

X Xia

Publications and source records attributed to X Xia.

At least 19 recordsLinked to original sources

PubMed1999

Inhibition of adipose differentiation by phosphatidylinositol 3-kinase inhibitors.

Phosphatidylinositol (PI) 3-kinase plays an important role in various cellular signaling mechanisms in several cell systems. The role of PI 3-kinase in adipose differentiation was investigated. For this purpose, we examined the effect of specific inhibitors of PI 3-kinase on the differentiation of two adipogenic cell lines, 1246 and 3T3-L1. The results show that two structurally different inhibitors of PI 3-kinase, i.e., LY294002 and wortmannin, blocked adipose differentiation in a time and dose-dependent fashion. The results from time- course studies indicated that PI 3-kinase activity is most important in the early phase (day 4 to day 6) of the differentiation program. The effect of PI 3-kinase inhibitor on the expression of the peroxisome proliferator-activated receptor (PPAR) gamma, a master regulator in adipogenesis induced during the differentiation process, was also examined. LY294002 significantly inhibited the induction of PPARgamma mRNA expression. During the initiation phase of adipogenesis (day 4 to day 6), the expression of PPARgamma was induced and LY294002 blocked the increase of expression of PPARgamma mRNA. The inhibition of expression of PPARgamma may provide a molecular mechanism for the action of PI 3-kinase inhibitors on adipose differentiation.

3T3 Cells↗

PubMed1999

Protein structure prediction in a 210-type lattice model: parameter optimization in the genetic algorithm using orthogonal array.

We have applied the orthogonal array method to optimize the parameters in the genetic algorithm of the protein folding problem. Our study employed a 210-type lattice model to describe proteins, where the orientation of a residue relative to its neighboring residue is described by two angles. The statistical analysis and graphic representation show that the two angles characterize protein conformations effectively. Our energy function includes a repulsive energy, an energy for the secondary structure preference, and a pairwise contact potential. We used orthogonal array to optimize the parameters of the population, mating factor, mutation factor, and selection factor in the genetic algorithm. By designing an orthogonal set of trials with representative combinations of these parameters, we efficiently determined the optimal set of parameters through a hierarchical search. The optimal parameters were obtained from the protein crambin and applied to the structure prediction of cytochrome B562. The results indicate that the genetic algorithm with the optimal parameters reduces the computing time to reach a converged energy compared to nonoptimal parameters. It also has less chance to be trapped in a local energy minimum, and predicts a protein structure which is closer to the experimental one. Our method may also be applicable to many other optimization problems in computational biology.

Algorithms↗

PubMed1998

A gas chromatographic method for the sugar analysis of 3,6-anhydrogalactose-containing algal galactans.

This paper describes a new gas chromatographic method for the compositional analysis of algal galactans containing 3,6-anhydrogalactose, which is readily destroyed in usual acid hydrolysis and methanolysis. Mercaptolysis of galactans was carried out under an anhydrous condition using the newly developed solvent system, an ethanethiolic HCl solution which had been prepared by blowing dry HCl gas into ethanethiol. By heating galactans in 0.5 N HCl/ethanethiol at 60 degrees C for 12 h, component sugars including 3,6-anhydrogalactose were released quantitatively as their diethyl mercaptals. The monosaccharide diethyl mercaptals were trimethylsilylated and analyzed by gas-liquid chromatography. Each component monosaccharide was detected as a single peak since neither anomeric nor structural isomers can be produced by mercaptolysis. Furthermore, the solvent system was improved by the addition of methanol in a ratio (2/1, v/v) of ethanethiol to methanol. Heating of galactans at 60 degrees C in 0.5 N HCl/[ethanethiol:methanol (2/1, v/v)] released more rapidly and quantitatively monosaccharide diethyl mercaptals without any formation of monosaccharide methyl glycosides. The present method was applicable to not only algal galactans but also algal powders.

Carbohydrate Sequence↗

PubMed1998

Pea polyubiquitin genes: (I) structure and genomic organization.

Four polyubiquitin genes, PUB1, PUB2, PUB3 and PUB4, were isolated from a pea (Pisum sativum L. cv Alaska) genomic library and completely sequenced. They represent all of the four polyubiquitin genes of the ubiquitin gene family in pea. The coding regions of the genes contain five or six coding units arranged as tandem repeats. The different coding repeats of the four genes share homologies between 75 and 97%, encoding the same protein of 76 amino acids identical to those from other higher plants. The open reading frames of PUB1, PUB2 and PUB4 terminate in the additional amino acid, phenylalanine (F), and PUB3 terminates in isoleucine (I). The polyubiquitin genes all contain intron sequences ranging from 584 to 1114 bp immediately 5' to the ATG initiation codon of the first coding sequence. Of the four genes, three are associated with long AT-rich (85.4-89.4% A+T) sequences ranging from about 331 to 478 bp at their 5' or 3' ends. The PUB4 gene was found to be linked to a moderate to highly repetitive DNA at its 5' flanking sequence. The greater sequence homology between different genes than among individual repeating units of a gene suggests that the polyubiquitin genes may have arisen by gene duplication of a single gene sequence.

Amino Acid Sequence↗

PubMed1998

Identification of cell surface binding sites for PC-cell-derived growth factor, PCDGF, (epithelin/granulin precursor) on epithelial cells and fibroblasts.

PC cell derived growth factor (PCDGF) is an 88-kDa glycoprotein purified from the culture medium of the highly tumorigenic mouse teratoma-derived cell line PC. PCDGF was shown to stimulate the proliferation of 3T3 fibroblasts and PC cells. Amino acid sequencing of PCDGF indicated its identity to the precursor for the 6-kDa polypeptides epithelins and granulins. In this paper, we investigated the binding of PCDGF to the mink lung epithelial cell line CCL64. Scatchard analysis indicates that 125I-PCDGF binding to CCL64 cells is curvilinear, corresponding to the existence of two classes of binding sites: high affinity binding sites (560 +/- 170 sites/cell) with a Kd1 of 43 +/- 15 pM and low affinity binding sites (16,350 +/- 5900 sites/cell) with a Kd2 of 3.9 +/- 1.9 nM. 125I-PCDGF was chemically crosslinked to cell surface receptors on CCL64 cells with disuccinimidyl suberate. A major crosslinked band of about 190 kDa with radiolabeled PCDGF was detected after SDS-PAGE, suggesting the presence of PCDGF binding sites with molecular weight of about 120 kDa. 125I. PCDGF crosslinking studies indicate the presence of PCDGF binding sites with a molecular weight similar to those of binding sites on CCL64 cells on the surface of two other PCDGF-responsive cell lines, 3T3 fibroblasts and PC cells. These data suggest that the receptors for PCDGF are widely distributed on cells of distinct embryonic origin.

Affinity Labels↗

PubMed1998

What amino acid properties affect protein evolution?

We studied 10 protein-coding mitochondrial genes from 19 mammalian species to evaluate the effects of 10 amino acid properties on the evolution of the genetic code, the amino acid composition of proteins, and the pattern of nonsynonymous substitutions. The 10 amino acid properties studied are the chemical composition of the side chain, two polarity measures, hydropathy, isoelectric point, volume, aromaticity, aliphaticity, hydrogenation, and hydroxythiolation. The genetic code appears to have evolved toward minimizing polarity and hydropathy but not the other seven properties. This can be explained by our finding that the presumably primitive amino acids differed much only in polarity and hydropathy, but little in the other properties. Only the chemical composition (C) and isoelectric point (IE) appear to have affected the amino acid composition of the proteins studied, that is, these proteins tend to have more amino acids with typical C and IE values, so that nonsynonymous mutations tend to result in small differences in C and IE. All properties, except for hydroxythiolation, affect the rate of nonsynonymous substitution, with the observed amino acid changes having only small differences in these properties, relative to the spectrum of all possible nonsynonymous mutations.

Amino Acid Substitution↗

PubMed1998

Regulation of mouse colony-stimulating factor-1 gene promoter activity by AP1 and cellular nucleic acid-binding protein.

Macrophage colony-stimulating factor (M-CSF; CSF-1) is a member of a complex network of cytokines that regulate monocytic cell development and activity. It is produced in nearly all organs by cell types commonly found in connective tissue, including fibroblasts and monocytes. Whether different cell types share common or have divergent mechanisms for regulating CSF-1 gene expression is not known. To address this question, the identity of cis-acting elements and cognate trans-acting factors was characterized in a region of the CSF-1 promoter known to be more active in monocytes than in fibroblasts. The results of DNase I protection assays performed with fibroblast- or monocyte-derived nuclear extracts revealed a difference in the pattern of DNA-binding proteins. One protected region, common to both fibroblasts and monocytes, spans a putative phorbol ester-responsive element (TRE), and binding to the TRE by AP1 was verified with antibodies directed against c-fos and c-jun family members. Mutational analysis revealed that the TRE is required for CSF-1 gene expression in proliferating fibroblasts and monocytes. Binding of a second putative trans-acting factor, preferentially expressed in fibroblasts, to the region immediately upstream of the TRE was also detected. Screening a mouse expression library with oligonucleotides spanning the putative cis-acting element identified cellular nucleic acid-binding protein (CNBP) as the cognate binding activity, and antiserum to CNBP disrupted the electromobility shift assay complex. Mutational analysis revealed that loss of CNBP binding leads to a decrease in CSF-1 promoter activity in fibroblasts but has no effect on CSF-1 promoter activity in monocytes. Our results demonstrate that control of CSF-1 gene expression in monocytes and fibroblasts is mediated by common and cell type-specific trans-acting factors.

Animals↗

PubMed1998

How optimized is the translational machinery in Escherichia coli, Salmonella typhimurium and Saccharomyces cerevisiae?

The optimization of the translational machinery in cells requires the mutual adaptation of codon usage and tRNA concentration, and the adaptation of tRNA concentration to amino acid usage. Two predictions were derived based on a simple deterministic model of translation which assumes that elongation of the peptide chain is rate-limiting. The highest translational efficiency is achieved when the codon recognized by the most abundant tRNA reaches the maximum frequency. For each codon family, the tRNA concentration is optimally adapted to codon usage when the concentration of different tRNA species matches the square-root of the frequency of their corresponding synonymous codons. When tRNA concentration and codon usage are well adapted to each other, the optimal content of all tRNA species carrying the same amino acid should match the square-root of the frequency of the amino acid. These predictions are examined against empirical data from Escherichia coli, Salmonella typhimurium, and Saccharomyces cerevisiae.

Codon↗

PubMed1998

The rate heterogeneity of nonsynonymous substitutions in mammalian mitochondrial genes.

Substitution rates at the three codon positions (r1, r2, and r3) of mammalian mitochondrial genes are in the order of r3 > r1 > r2, and the rate heterogeneity at the three positions, as measured by the shape parameter of the gamma distribution (alpha 1, alpha 2, and alpha 3), is in the order of alpha 3 > alpha 1 > alpha 2. The causes for the rate heterogeneity at the three codon positions remain unclear and, in particular, there has been no satisfactory explanation for the observation of alpha 1 > alpha 2. I attempted to dissect the causes of rate heterogeneity by studying the pattern of nonsynonymous substitutions with respect to codon positions in 10 mitochondrial genes from 19 mammalian species. Nonsynonymous substitutions involve more different amino acid replacements at the second than at the first codon position, which results in r1 > r2. The difference between r1 and r2 increases with the intensity of purifying selection, and so does the rate heterogeneity in nonsynonymous substitutions among sites at the same codon position. All mitochondrial genes appear to have functionally important and unimportant codons, with the latter having all three codon positions prone to nonsynonymous substitutions. Within the functionally important codons, the second codon position is much more conservative than the codon position. This explains why alpha 1 > alpha 2. The result suggests that overweighting of the second codon position in phylogenetic analysis may be a misguided practice.

Animals↗

PubMed1997

Identification of quantitative trait loci controlling levels of radiation-induced thymocyte apoptosis in mice.

Thymocyte apoptosis levels are higher in C57BL/6J mice than in C3Hf/Kam mice. Low-dose irradiation increases the numbers of thymocytes undergoing apoptosis, but the strain difference persists. We mapped three loci controlling radiation-induced thymocyte apoptosis levels in F2 intercross progeny of these strains. The strongest association of a genomic region with an apoptosis level occurred in a region of chromosome 11 known to harbor a locus (or loci) important in the pathogenesis of several rodent models of autoimmune disease. Additional loci influencing radiation-induced thymocyte apoptosis were identified on chromosomes 9 and 16. The genetic polymorphisms underlying these loci may have an evolutionary role in fine-tuning the apoptotic response in T cells and may be important in the etiology of lymphoproliferative disorders and autoimmunity.

Animals↗

PubMed1997

Glutathione S-transferase expression in hepatitis B virus-associated human hepatocellular carcinogenesis.

Hepatitis B virus (HBV) and aflatoxin B1 represent the main risk factors for the development of hepatocellular carcinoma (HCC) in areas endemic for liver cancer. The glutathione S-transferases (GSTs) are a family of Phase II detoxification enzymes that catalyze the conjugation of a wide variety of endogenous and exogenous toxins, including aflatoxin B1, with glutathione. This study characterizes the GST isoenzyme composition (alpha, mu, and pi) of both HBV-infected normal hepatic tissues and HCCs. Analysis of matched pairs of hepatic tissue (normal and tumor) from 32 HCC patients indicated that total GST activity was significantly higher in normal tissues than in tumor tissues, although the percentage of samples expressing GST alpha and pi was equivalent. GST mu was detected by Western blot in the normal tissue from 87.5% of the subjects possessing the GST M1 gene but only 28.6% of the corresponding tumor tissues. The GST activity of normal tissue from GST M1 null patients was significantly decreased as compared to that of subjects possessing the GST M1 gene (264.6 and 422.2 nmol/min/mg, respectively; P = 0.005). GST pi appeared to be overexpressed in the normal tissue of GST M1 null patients, a potential compensatory effect. Patients positive for HBV DNA had significantly lower GST activity than those who were HBV negative (302.1 versus 450.0 nmol/min/mg, respectively; P = 0.02). These results suggest that cellular protection within the human liver is compromised by HBV infection and further decreased during hepatocellular tumorigenesis.

Adult↗

PubMed1997

Mutation in the mitochondrial 12S rRNA gene in two families from Mongolia with matrilineal aminoglycoside ototoxicity.

Irreversible hearing loss is a catastrophic complication of treatment with aminoglycoside antibiotics such as streptomycin, gentamycin, and kanamycin. Many kindreds showing a matrilineal pattern of inheritance of this trait have been described in China where the widespread use of aminoglycoside antibiotics accounts for approximately 25% of profound deafness in some districts. Because of the characteristic inheritance pattern, mitochondrial DNA (mtDNA) mutations were postulated to be the cause of the deafness in these pedigrees. In 1993 it was shown that an A to G substitution at base pair 1555 of the mitochondrial 12S ribosomal RNA gene was the only mutation common to all the families with aminoglycoside ototoxicity. We ascertained three Mongolian pedigrees from the School for the Deaf and Blind in Ulaanbaatar, all of which contained multiple affected subjects with streptomycin induced deafness in a pattern consistent with matrilineal transmission. Amplified mtDNA, obtained from transformed lymphoblastoid cell lines using previously described primers, showed the A to G point mutation in the 12S rRNA gene in two of the three families by restriction analysis as well as direct sequencing. No other example of this substitution was found among 400 control samples from Mongolians with normal hearing. We have thus confirmed the clinical relevance of the 1555 A to G mitochondrial mutation in the 12S rRNA gene by identifying it in affected subjects with familial aminoglycoside ototoxicity in another ethnic group. In countries where aminoglycosides are widely used, genetic counselling and screening of high risk families before the use of these drugs could have a dramatic effect on the incidence of deafness.

Anti-Bacterial Agents↗

PubMed1997

A novel case of unilateral blepharophimosis syndrome and mental retardation associated with de novo trisomy for chromosome 3q.

We have evaluated a 3 2/12 year old girl who presented with unilateral blepharophimosis, ptosis of the eyelid, and mental retardation. Additional dysmorphic features include microcephaly, high, narrow forehead, short stubby fingers, and adduction of the right first toe. Cytogenetic analysis showed an unbalanced karyotype consisting of 46,XX,add(7)(q+) that was de novo in origin. Fluorescence in situ hybridisation (FISH) using microdissected library probe pools from chromosomes 1,2,3,7, and 3q26-qter showed that the additional material on 7q was derived from the distal end of the long arm of chromosome 3. Our results indicate that the patient had an unbalanced translocation, 46,XX,der(7)t(3;7)(q26-qter;q+) which resulted in trisomy for distal 3q. All currently reported cases of BPES (blepharophimosis-ptosis-epicanthus inversus syndrome) with associated cytogenetic abnormalities show interstitial deletions or balanced translocations involving 3q22-q23 or 3p25.3. Our patient shares similar features to BPES, except for the unilateral ptosis and absence of epicanthus inversus. It is possible that our patient has a contiguous gene defect including at least one locus for a type of blepharophimosis, further suggesting that multiple loci exist for eyelid development.

Adult↗

PubMed1997

[One-year-result of excimer laser for photorefractive keratectomy in very high myopia].

We corrected 53 cases (84 eyes) of very high myopia using photorefractive keratectomy (PRK) with VISX 20/20 excimer laser, and followed up the cases more than one year. The rates of visual acuity more than or equal to 0.5 or 1.0 were 81.0% and 23.9%, 75.0% eyes were within +/- 2.00 diopter of the desired emmetropia. Grade 2 or more severe corneal haze were presented in 13.1% eyes. PRK with VISX 20/20 excimer laser may be an effective method to correct very high myopia from -10.00 to -16.00 diopters.

Adolescent↗

PubMed1997

[Photorefractive keratectomy to correct myopic astigmatism].

The VISX 20/20 excimer laser was used to treat 260 eyes with myopia and myopic astigmatism of 166 patients. All patients were followed up for one year. The diopter of preoperative astigmatism was from -0.25-(- 4.00 D (-1.00 +/- 0.62 D). The diopter was lowered to -0.07 +/- 0.40 D at 6 months postoperatively (P < 0.05) and -0.06 +/- 0.39 D at 12 months postoperatively (P < 0.01). Photorefractive keratectomy (PRK) is effective and safe for myopic astigmatism.

Adolescent↗

PubMed1997

Clinical and biological relevance of flow cytometric determination of P-glycoprotein expression in acute non-lymphocytic leukemia.

OBJECTIVE: To evaluate the characteristics of P-glycoprotein (P-gp) expression of acute non-lymphocytic leukemia (ANLL) at different status and the prognostic and biological features in ANLL at diagnosis. METHODS: Monoclonal antibody UIC2 and indirect immunofluorescence assay by flow cytometry were used to determine P-gp expression of 169 patients with ANLL, including 152 previously untreated, 7 refractory and 10 at remission. RESULTS: P-gp was expressed in 28.9% of the previously untreated ANLL cases and P-gp was lower than that in 71.4% of the refractory cases (P < 0.05). No P-gp expression was found in the patients at remission. For previously untreated AN-LL, P-gp was highly expressed in hybrid acute leukemia (66.7%) and acute monoblastic leukemia (47.4%). P-gp expression was highly associated with surface markers [cluster of differentiation (CD) 34, CD7, CD14, CD42b and CD61] and unfavorable cytogenetic abnormalities. About 23% of P-gp-ANLL obtained complete remission, which was significantly lower than that (76%) in P-gp-cases. CONCLUSIONS: P-gp expression is higher in refractory ANLL cases than that in cases at diagnosis or at remission. P-gp is an index of poor prognosis in adults with ANLL. P-gp+ ANLL cases have unique clinical and biological characteristics.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1997

[Multiple factors analysis of formation of corneal haze after photorefractive keratectomy].

VISX 20/20 excimer laser was used to correct myopia from 1.00 to 16.00 diopters on 529 myopia eyes in 306 patients. All the patients were followed up for 3 to 12 months (8.1 +/- 3.1 months). At the 12th postoperative month, 0.5-3 grade corneal haze occurred in 62.1% of eyes in high myopia eyes, and only 8.8% in low and moderate myopia eyes (P < 0.01). The factors of formation of the corneal haze were the central corneal thickness, methods of removing epithelium and the number of laser pulses. The results suggest that the photorefractive keratectomy is regarded safe in correction of low and moderate myopia, but not in high myopia.

Adolescent↗

PubMed1997

[Mitomycin C concentrations in rabbit ocular tissues after topical administration during glaucoma filtration surgery].

Using high-performance liquid chromatography, we measured Mitomycin C (MMC) concentrations in conjunctiva, sclera and aqueous of 22 rabbit eyes after single topical administration of 0.2 mg.ml-1 MMC during glaucoma filtration surgery. The peaks of MMC concentrations in conjunctiva, sclera, aqueous were 2.01 micrograms.g-1, 2.95 micrograms.g-1 and 0.16 microgram.ml-1 with half life of 0.63, 0.35 and 0.84 hours respectively. Irrigating the ocular surface with 20 ml of normal saline after MMC application reduced the peak drug concentration to 1/8 in conjunctiva, to 1/5 in sclera and to 1/3 in aqueous. The results showed that the MMC concentrations in conjunctiva and sclera were well above the ID50 of rabbit subconjunctival fibroblast (0.1 microgram.ml-1), and the concentration in aqueous was well below the level known to cause endothelium toxicity (approximately 0.2 mg.ml-1) and retinal toxicity (> 1.3 micrograms.ml-1). Therefore, 0.2 mg.ml-1 MMC can inhibit subconjunctival fibroblast effectively and has no side effect on visual function.

Administration, Topical↗