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Biomedical subjects

X Yuan

Publications and source records attributed to X Yuan.

At least 145 records · Page 8Linked to original sources
PubMed1996

Renal cell carcinoma development in the rat independent of alterations at the VHL gene locus.

Germline alterations of the human von Hippel-Lindau (VHL) tumor suppressor gene predispose to renal cell carcinoma and a constellation of other tumor types found in VHL disease. This gene is also mutated or deleted in a high proportion of sporadic nonpapillary renal cell carcinomas. In the Eker rat model, spontaneous renal cell carcinoma develops with a high frequency. We therefore investigated the role of this tumor suppressor gene in the development of these hereditary rat tumors. By using reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis, the sequence of the rat VHL gene was determined over the portion of the gene homologous to regions where most mutations in the human VHL gene occur. The sequence homology was 90% and the amino-acid identity 99% between the rat and human genes. A developmental and tumor-specific pattern of expression for the VHL gene was found; a ubiquitous 3.2-kb transcript was expressed in all rat tissues examined (neonatal kidney, lung, liver, brain, heart, kidney, spleen, testis, and stomach), and an additional 4.5-kb transcript was expressed in neonatal kidney and cell lines derived from Eker rat renal cell carcinomas (ERC cell lines). To determine whether mutations in the VHL gene were involved in tumor development in the Eker model, RT-PCR, single-strand conformation polymorphism (SSCP) analysis, and direct sequencing were used to search for alterations in this gene in the ERC cell lines. Alterations in the VHL gene were not detected by SSCP, and these data were confirmed by direct sequencing. Transformed rat kidney epithelial cell lines derived from Fisher rats also expressed the VHL gene but like the ERC cell lines did not contain mutations in the VHL gene. These data indicate that in the rat, transformation of kidney epithelial cells and the development of solid, nonpapillary renal cell carcinoma can occur via pathways that are independent of alterations at the VHL gene locus.

Animals↗
PubMed1996

Mouse islet cell lysis mediated by interleukin-1-induced Fas.

This study was conducted to investigate the possible involvement of Fas in beta-cell death in insulitis of Type 1 (insulin-dependent) diabetes mellitus. Although primary cultured Balb/c mouse islet cells did not express Fas mRNA, 4-12 hours of treatment with 10(2)-10(3) U/l of mouse interleukin-1 alpha (IL-1 alpha) induced the expression of Fas mRNA. Surface Fas expression was detected by immunofluorescence flow cytometry using a non-cytolytic anti-Fas monoclonal antibody after 6 or 12 h of incubation with 10(3) U/l of IL-1 alpha. Primary islet cells were resistant to an agonistic anti-Fas monoclonal antibody. However, 12 h pretreatment with IL-1 alpha sensitized islet cells to its cytolytic effect. Significant cell death was observed 24 h after the addition of anti-Fas, and progressively increased until 72 h, when specific 51Cr release was 72 +/- 6%. Agarose gel electrophoresis of DNA extracted from cells exposed to IL-1 alpha and agonistic anti-Fas showed internucleosomal DNA fragmentation, a hallmark of apoptotic cell death. Since the Fas antibody showed no cross-reactive activity of tumour necrosis factor (TNF), the cytotoxic effect was not mediated by TNF receptors. A protein synthesis inhibitor cycloheximide augmented Fas-mediated islet cell death. The Fas-mediated killing of islet cells was not L-arginine-dependent, or blocked by N(G)-monomethyl-L-arginine. beta-TC1 cells also expressed Fas mRNA when exposed to IL-1 alpha or IL-1 alpha plus interferon-gamma. These observations suggest that Fas-mediated apoptosis may be a mechanism of islet cell death in autoimmune insulitis.

Animals↗
PubMed1996

Duplicated proteasome subunit genes in Drosophila melanogaster encoding testes-specific isoforms.

Using the previously cloned proteasome alpha-type subunit gene Pros28.1, we screened a Drosophila melanogaster genomic library using reduced stringency conditions to identify closely related genes. Two new genes, Pros28.1A (map position 92F) and Pros28.1B (map position 60D7), showing high sequence similarity to Pros28.1, were identified and characterized. Pros28.1A encodes a protein with 74% amino acid identity to PROS28.1, while the Pros28.1B gene product is 58% identical. The Pros28.1B gene has two introns, located in exactly analogous positions as the two introns in Pros28.1, while the Pros28.1A gene lacks introns. Northern blot analysis reveals that the two new genes are expressed only in males, during the pupal and adult stages. Tissue-specific patterns of expression were examined using transgenic flies carrying lacz-fusion reporter genes. This analysis revealed that both genes are expressed in germline cells during spermatogenesis, although their expression patterns differed. Pros28.1A expression is first detected at the primary spermatocyte stage and persists into the spermatid elongation phase of spermiogenesis, while Pros28.1B expression is prominent only during spermatid elongation. These genes represent the most striking example of cell-type-specific proteasome gene expression reported to date in any system and support the notion that there is structural and functional heterogeneity among proteasomes in metazoans.

Amino Acid Sequence↗
PubMed1995

Test-tube simulated lipofuscinogenesis. Effect of oxidative stress on autophagocytotic degradation.

Cysteine-stimulated oxidation of a rat liver lysosomal-mitochondrial fraction (LMF) was studied. The process would simulate oxidative stress-related events during the degradation of autophagocytosed material within secondary lysosomes, which may contribute to the formation of lipofuscin or age pigment. Millimolar concentration of cysteine was needed to stimulate LMF lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS). The amount of endogenous LMF iron was 545 micrograms/l and was enough to initiate peroxidation, probably through the reduction of ferric to ferrous iron by cysteine with induction of Fenton chemistry. Peroxidation could be completely inhibited by the addition of the iron chelator desferal or the antioxidant BHT. A substantial amount of the formed TBARS was associated with trichloroacetic acid (TCA) precipitable proteins. Elevated protein carbonyls was observed 1-2 h after the increase of TBARS. The tryptophan-tyrosine related protein autofluorescence (280/335 nm) decreased sharply during the first few hours of incubation. In contrast, a lipofuscin-type autofluorescence (345/430 nm) appeared only after a few days, suggesting that the latter fluorophore is not an immediate product of protein oxidation. The sequential formation of TBARS, protein carbonyls and lipofuscin-type autofluorescence as well as their dependence on iron and reducing agent add further support to the concept that lipofuscin forms in secondary lysosomes as a result of iron-catalyzed oxidative reactions involving autophagocytosed materials.

Animals↗
PubMed1995

The molecular basis of ornithine transcarbamylase deficiency: modelling the human enzyme and the effects of mutations.

Human ornithine transcarbamylase is a trimer with 46% amino acid sequence homology to the catalytic subunit of E coli aspartate transcarbamylase. Secondary structure predictions, distributions of hydrophilic and hydrophobic regions, and the pattern of conserved residues suggest that the three dimensional structures of the two proteins are likely to be similar. A three dimensional model of ornithine transcarbamylase was generated from the crystal structure of the catalytic subunit of E coli aspartate transcarbamylase in the holoenzyme, by aligning the sequences, building in gaps, and minimising the energy. The binding sites for carbamyl phosphate in both enzymes are similar and the ornithine binding site in ornithine transcarbamylase appears to be in the same location as the L-aspartate binding site in aspartate transcarbamylase, with negatively charged side chains replaced by positively charged residues. Mutations in the ornithine transcarbamylase gene found in patients with hyperammonaemia of the "neonatal type" are clustered in important structural or functional domains, either in the interior of the protein, at the active site, or at the interchain interface, while mutations found in patients with milder "late onset" disease are located primarily on the surface of the protein. The predicted effects of all known missense mutations and in frame deletions in the ornithine transcarbamylase gene on the structure and function of the mature enzyme are described.

Amino Acid Sequence↗
PubMed1995

Measurement of the forefoot with roentgen stereophotogrammetry in hallux valgus surgery.

Eight hallux valgus patients were marked with tantalum markers in conjunction with hallux valgus surgery (seven proximal osteotomies and one chevron osteotomy). Changes on weightbearing before surgery as well as corrective changes after surgery were analyzed with roentgen stereophotogrammetry (RSA) and with standard x-rays. RSA is accurate to 0.6 degrees in rotational changes and 0.3 mm in translation. Weightbearing changes were inconsistent, and minimal with both standard x-rays and RSA. It was possible to analyze the correction at the osteotomy site with RSA. In half the cases, the correction measured by RSA corresponded with that measured with standard x-rays, within measurement error; in the other cases, RSA showed that the correction was of a different size or direction than that measured on standard x-rays. Corrective changes in hallux valgus surgery are complex, including angular and translational changes at several levels and in several joints in order to produce a clinical resultant. Rotational changes can be evaluated with RSA. Although RSA in an optimal situation is very accurate, it is still limited to a laboratory setting.

Female↗
PubMed1995

The stability of three different cementless tibial components. A randomized radiostereometric study in 45 knee arthroplasty patients.

We conducted a prospective, randomized study of 45 patients to evaluate 3 different uncemented tibial component designs in total knee arthroplasty. The stability of the components was assessed by radiostereometry (RSA), both as migration during 2 years and as inducible displacement at 2 years. The PCA resurfacing, the Tricon stem and the Tricon-M prosthesis groups showed a similar level of migration at 2 years, about 1.4 mm. In response to externally applied rotatory forces, the Tricon groups rotated more than the PCA group, interpreted as a consequence of the more conforming articular surface in the Tricon design. The series was divided into one group of continuously migrating prostheses with a poor prognosis (unstable, one third) and another group of prostheses in which migration stopped after 1 year (stable, two thirds). With this classification, no differences between the prostheses design groups were revealed. However, the unstable group showed a larger inducible displacement by provocation, an association hitherto not established.

Aged↗
PubMed1995

[Pulmonary function detection in newborn infants].

We studied 120 full-term newborn infants and 20 pre-term infants by means of recording tidal breathing flow volume loops, passive flow volume technique and open circuit N2 washout technique. In the preterm infants, ventilatory function, FRC and Crs were lower than those in full-term infants, and Rrs were higher than those of full-term infants. TV, MV and PTEF were positively corelated with age (day), weight and height FRC, Crs and Trs were positively corelated with weight and height. TBFV loop in normal newborn infants did not show round or ellipse curve. The curve of expiration rose quickly, the position of expiration peak closed to the front, and decending line of expiration was relatively tilting. RR, Ti/Ttot, VPF, TPF, PF25, PTEF/TV, ME/MI, FRCkg, Crskg, sCrs, Rrs and sRrs were valuble indices in neonatal pulmonary function test. The results of our study are important in the establishment of normal values of pulmonary function indices for newborn infants in China.

Female↗
PubMed1995

[Primary tumour of the trachea with a report of 24 cases].

Twenty-four cases of primary tumour of trachea are reported in this article. In the 23 operated cases, 19 received curative excision (82.6%) and 4 cases palliative excision with tracheostomy. In these 24 cases, 21 cases were malignant and 3 cases benign. Tumour located at upper trachea in 8 cases, at median trachea in 6 cases and at lower trachea in 10 cases. The 19 operated patients all recovered. The survival rates in 1, 3, 5 and 10 years were 82.3% (14/17), 75% (9/12), 75% (6/8) and 50% (2/4), respectively. The authors suggested that early diagnosis should be paid more attention because misdiagnosis rate was high. The operation condition and procedures are discussed.

Adolescent↗
PubMed1995

Preoperative segmental localization of focal hepatic lesion on MRI.

In order to evaluate the accuracy of preoperative segmental localization of hepatic mass lesions, 68 cases were prospectively studied and evaluated by the correlation of magnetic resonance imaging (MRI) and surgical findings. Right, middle and left hepatic veins were seen in 100%, 97% and 94% of the subjects respectively on MRI. The right and left portal veins were seen in 100% and 95.6% respectively. The accuracy in determining the segmental location of hepatic lesions was 89.7%. The accuracy could be increased to 91.3% if the lesion was located at single segment whereas it was only 86.4% when the lesion extended across several segments. It is possible to say that MRI is an important modality in the preoperative segmental localization of masses.

Adolescent↗
PubMed1994

The rates of commitment to renaturation of rhodanese and glutamine synthetase in the presence of the groE chaperonins.

Current models of chaperonin-assisted folding suggest that proteins undergo multiple rounds of binding and release before they are released in a form that is committed to folding to the native state. Using immunoprecipitation techniques, we have determined the rates at which rhodanese and glutamine synthetase (GS) are released from groEL in a form committed to refold to active enzyme. Rhodanese and glutamine synthetase were chosen as substrates because they exhibit different solution requirements for the chaperonin system and they form stable "folding arrested" complexes with groEL. At various times during the groE-dependent renaturations, groEL was rapidly removed from the renaturation mixture by immunoprecipitation and centrifugation (30 s). The conformers that are committed to the native state remained in the supernatant and were assayed after 1 h. At 25 degrees C, the rate profiles indicate the release and commitment to folding of GS to its native state occurs far earlier (t1/2 < 1 min) than for rhodanese (t1/2 = 5 min). In light of previous results, it appears that GS monomers can attain a groE-independent assembly competent conformation after a brief interaction with the chaperonin. In contrast, the renaturation rate for rhodanese with the groE chaperonins mirrored the committed renaturation rates following groEL depletion. This suggests that rhodanese must interact with groEL throughout most of its folding reaction before it acquires a folding competent (groE independent) state. If current models of chaperonin mechanism are correct, rhodanese undergoes more rebinding and release cycles than does GS. Structurally, the degree of cycling and hence the rate of commitment to folding to the active form are probably dictated by the hydrophobic nature, number, and lifetimes of the folding intermediates that interact with the chaperonins.

Chaperonin 60↗
PubMed1994

Enterokinase, the initiator of intestinal digestion, is a mosaic protease composed of a distinctive assortment of domains.

Enterokinase is a protease of the intestinal brush border that specifically cleaves the acidic propeptide from trypsinogen to yield active trypsin. This cleavage initiates a cascade of proteolytic reactions leading to the activation of many pancreatic zymogens. The full-length cDNA sequence for bovine enterokinase and partial cDNA sequence for human enterokinase were determined. The deduced amino acid sequences indicate that active two-chain enterokinase is derived from a single-chain precursor. Membrane association may be mediated by a potential signal-anchor sequence near the amino terminus. The amino terminus of bovine enterokinase also meets the known sequence requirements for protein N-myristoylation. The amino-terminal heavy chain contains domains that are homologous to segments of the low density lipoprotein receptor, complement components C1r and C1s, the macrophage scavenger receptor, and a recently described motif shared by the metalloprotease meprin and the Xenopus A5 neuronal recognition protein. The carboxyl-terminal light chain is homologous to the trypsin-like serine proteases. Thus, enterokinase is a mosaic protein with a complex evolutionary history. The amino acid sequence surrounding the amino terminus of the enterokinase light chain is ITPK-IVGG (human) or VSPK-IVGG (bovine), suggesting that single-chain enterokinase is activated by an unidentified trypsin-like protease that cleaves the indicated Lys-Ile bond. Therefore, enterokinase may not be the "first" enzyme of the intestinal digestive hydrolase cascade. The specificity of enterokinase for the DDDDK-I sequence of trypsinogen may be explained by complementary basic-amino acid residues clustered in potential S2-S5 subsites.

Amino Acid Sequence↗
PubMed1994

Wilms' tumor suppressor gene expression in rat and human mesothelioma.

Induction of mesothelioma in the rat is an important animal model for assessing the carcinogenic potential of fibers and for understanding the molecular basis underlying the development of these tumors. Mesotheliomas and nephroblastoma (Wilms' tumor) have many developmental, biochemical, and histological similarities; however, the expression of the Wilms' tumor suppressor gene, WT-1, has not been well characterized in the rat, and its expression pattern in rat or human mesothelioma has not been described. We report that WT-1 transcripts (3.2 kilobases) could be detected by Northern analysis in adult rat testis, spleen, kidney, lung, heart, and glomerular mesangial cells. Normal adult mesothelial cells also expressed this gene. Rat mesothelioma cell lines expressed WT-1 transcripts of 3.2 kilobases and an additional 2.8-kilobase transcript, previously only reported to be expressed in the testis. Normal and transformed rat mesothelial cells expressed all four of the WT-1 splice variants, except testis, which only expressed WT-1 splice variants containing exon 5. Seven of seven human mesothelioma cell lines examined also expressed WT-1 transcripts, suggesting that expression of this gene may be useful in the diagnosis of these tumors.

Aged↗