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M Xing

Publications and source records attributed to M Xing.

At least 19 recordsLinked to original sources
PubMed2005

Quantitative assessment of promoter methylation profiles in thyroid neoplasms.

CONTEXT: Cancer-specific molecular markers are needed to supplement the cytopathological assessment of thyroid tumors, because a majority of patients with cytologically indeterminate nodules currently undergo thyroidectomy without a definitive diagnosis. OBJECTIVE: The aim of this study was the quantitative assessment of promoter hypermethylation and its relation to the BRAF mutation in thyroid tumors. DESIGN: Quantitative hypermethylation of Rassf1A, TSHR, RAR-beta2, DAPK, S100, p16, CDH1, CALCA, TIMP3, TGF-beta, and GSTpi was tested on a cohort of 82 benign and malignant thyroid tumors and five thyroid cancer cell lines. SETTING: The study was conducted at a tertiary research hospital. PATIENTS: Patients underwent surgical resection for a thyroid tumor from 2000 to 2003 at our institution. INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASURE: Final surgical pathology diagnosis was the main outcome measure. RESULTS: Thyroid tumors showed hypermethylation for the following markers: Rassf1A, TSHR, RAR-beta2, DAPK, CDH1, TIMP3, and TGF-beta. A trend toward multiple hypermethylation was evident in cancer tissues, with hypermethylation of two or more markers detectable in 25% of hyperplasias, 38% of adenomas, 48% of thyroid cancers, and 100% of cell lines. A rank correlation analysis of marker hypermethylation suggests that a subset of these markers is epigenetically modified in concert, which may reflect an organ-specific regulation process. Furthermore, a positive correlation was found between the BRAF mutation and RAR-beta2, and a negative correlation was found between the BRAF mutation and Rassf1A. CONCLUSIONS: Methylation-induced gene silencing appears to affect multiple genes in thyroid tissue and increases with cancer progression. Additional markers with better discriminatory power between benign and malignant samples are needed for the diagnostic assessment of cytologically indeterminate thyroid nodules.

Cell Line, Tumor↗
PubMed2005

BRAF mutation in thyroid cancer.

Genetic alteration is the driving force for thyroid tumorigenesis and progression, based upon which novel approaches to the management of thyroid cancer can be developed. A recent important genetic finding in thyroid cancer is the oncogenic T1799A transversion mutation of BRAF (the gene for the B-type Raf kinase, BRAF). Since the initial report of this mutation in thyroid cancer 2 years ago, rapid advancements have been made. BRAF mutation is the most common genetic alteration in thyroid cancer, occurring in about 45% of sporadic papillary thyroid cancers (PTCs), particularly in the relatively aggressive subtypes, such as the tall-cell PTC. This mutation is mutually exclusive with other common genetic alterations, supporting its independent oncogenic role, as demonstrated by transgenic mouse studies that showed BRAF mutation-initiated development of PTC and its transition to anaplastic thyroid cancer. BRAF mutation is mutually exclusive with RET/PTC rearrangement, and also displays a reciprocal age association with this common genetic alteration in thyroid cancer. The T1799A BRAF mutation occurs exclusively in PTC and PTC-derived anaplastic thyroid cancer and is a specific diagnostic marker for this cancer when identified in cytological and histological specimens. This mutation is associated with a poorer clinicopathological outcome and is a novel independent molecular prognostic marker in the risk evaluation of thyroid cancer. Moreover, preclinical and clinical evaluations of the therapeutic value of novel specific mitogen-activated protein kinase pathway inhibitors in thyroid cancer are anticipated. This newly discovered BRAF mutation may prove to have an important impact on thyroid cancer in the clinic.

Age Factors↗
PubMed2004

BRAF T1796A transversion mutation in various thyroid neoplasms.

A high prevalence of activating mutation of the B type Raf kinase (BRAF) gene was recently reported in papillary thyroid cancer (PTC). However, the frequency of this mutation in several other types of thyroid neoplasms was not thoroughly investigated. In the present study, in addition to PTC, we evaluated various thyroid tumor types for the most common BRAF T1796A mutation by direct genomic DNA sequencing. We found a high and similar frequency (45%) of the BRAF T1796A mutation in two geographically distinct PTC patient populations: one composed of sporadic cases from North America, and the other from Kiev, Ukraine, that included individuals who were exposed to the Chernobyl nuclear accident. In contrast, we found BRAF mutation in only 20% of anaplastic thyroid cancers and no mutation in medullary thyroid cancers and benign thyroid hyperplasia. We also confirmed previous reports that the BRAF T1796A mutation did not occur in benign thyroid adenomas and follicular thyroid cancers. Specific analysis of the Ukraine patients with confirmed history of radiation exposure failed to show a higher incidence of BRAF mutation. Our results suggest that frequent occurrence of BRAF mutation is inherently associated with PTC, irrespective of geographic origin, and is apparently not a radiation-susceptible mutation. The lack or low prevalence of BRAF mutation in other thyroid neoplasms is consistent with the notion that other previously defined genetic alterations on the same signaling pathway are sufficient to cause tumorigenesis in most thyroid neoplasms.

Adult↗
PubMed2001

Species- and agonist-dependent differences in the deactivation-kinetics of P2X7 receptors.

In this study we have expressed recombinant P2X7 receptors in HEK293 cells and examined the reasons for the species- and agonist-dependent differences in the time taken for the closure of the P2X7 receptor ion-channels after agonist removal. Channel closure times, measured in electrophysiological studies or by measuring cellular permeability to ethidium cations, were slower at rat than at human or mouse P2X7 channels following washout of the P2X7 agonist 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP). In contrast, there were no species differences in channel closure times when ATP was the agonist. BzATP was more potent than ATP at the three species homologues and exhibited highest potency for rat P2X7 receptors suggesting that channel closure time was related to agonist potency. Furthermore, BzATP potency for the P2X7 receptor could be modified by changing extracellular ionic concentrations or by mutating the receptor and modifications which increased agonist potency also increased the time taken for channel closure. The dependence of channel closure time on agonist potency suggests it reflects agonist dissociation from the P2X7 receptor rather being an intrinsic property of the ion-channel. Consistent with this, our previous studies have shown that agonist potency increases after repeated agonist applications and in this study channel closure time at rat P2X7 receptors increased after repeated agonist applications. Overall these results suggest that the species differences in channel closure times reflect differences in agonist dissociation rates which arise as a consequence of the marked species differences in agonist potency.

Adenosine Triphosphate↗
PubMed2001

Serum constituents can affect 2'-& 3'-O-(4-benzoylbenzoyl)-ATP potency at P2X(7) receptors.

1. 2'-& 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) is the prototypic agonist for P2X(7) receptors. In this study we demonstrate that bovine serum albumin (BSA) can affect the potency of BzATP at P2X receptors. 2. BzATP potency (pEC(50)) to stimulate ethidium accumulation in cells expressing recombinant P2X7 receptors varied between 6.5 and 4, depending upon the species orthologue studied and ionic conditions employed. BSA (0.1 - 1 mg ml(-1)) and foetal bovine serum (FBS, 1 - 10% v v(-1)) inhibited responses to BzATP but only when the BzATP pEC(50) exceeded 5. 3. BSA did not block ATP-stimulated ethidium accumulation, suggesting its effects were independent of P2X(7) receptor blockade. 4. BSA did not cause breakdown of nucleotides, although FBS (10% v v(-1)) exhibited appreciable nucleotidase activity and caused significant breakdown of ATP. 5. In the presence of BSA, lipids such as 11-((5-dimethylaminonaphthalene-1-sulphonyl)amino)undecanoic acid (DAUDA) and arachidonic acid (AA) markedly increased BzATP potency. Lipids had no affect on ATP potency in the presence of BSA and had little effect on responses to BzATP in the absence of BSA. 6. These results suggested that the reduction in BzATP potency by BSA was due to BzATP binding to BSA and that lipids prevented this binding. Consistent with this hypothesis, BzATP inhibited binding of the fluorescent lipid, DAUDA, to BSA. 7. In conclusion, BSA and lipids can markedly affect BzATP potency at P2X(7) receptors but this is probably a consequence of BzATP binding to BSA. This finding has important implications when using BzATP in vivo or in the presence of albumin.

Adenosine Triphosphate↗
PubMed2001

P2Y receptors of MDCK cells: epithelial cell regulation by extracellular nucleotides.

1. Madin-Darby canine kidney (MDCK) cells, a well- differentiated renal epithelial cell line derived from distal tubule/collecting duct, respond to extracellular nucleotides by altering ion flux and the production of arachidonic acid-derived products, in particular prostaglandin E2 (PGE2). Our work has defined the receptors and signalling events involved in such responses. 2. We have found evidence for expression of at least three P2Y receptor subtypes (P2Y1, P2Y2 and P2Y11) in MDCK-D1 cells, a subclone from parental MDCK. 3. These receptors appear to couple to increases in calcium and protein kinase C activity, probably via a Gq/G11-mediated activation of phospholipase C. 4. In addition, P2Y receptor activation can promote a prominent increase in cAMP. This includes both a P2Y2 receptor-mediated cyclo-oxygenase (COX)-dependent component and another COX-independent component mediated by other P2Y receptors. 5. We have documented that changing media in which cells are grown releases ATP and, in turn, activates P2Y receptors. Such release of ATP contributes in a major way to basal cAMP levels in these cells. 6. The data indicate that MDCK cells are a useful model to define the regulation of epithelial cells by extracellular nucleotides. Of particular note, spontaneous or stretch-induced release of ATP and subsequent activation of one or more P2Y receptors contributes to establishing the basal activity of signalling pathways.

Adenosine Triphosphate↗
PubMed2001

Complexities of measuring antagonist potency at P2X(7) receptor orthologs.

The ability of P2 antagonists to affect agonist-stimulated fluorescent dye accumulation in cells expressing human, rat, or mouse P2X(7) receptors was examined. Several compounds, including pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), which was previously thought to be a weak P2X(7) receptor antagonist, possessed high potency (nanomolar IC(50)) at human and rat P2X(7) receptors. However, there were species differences in antagonist potency with PPADS, pyridoxal 5'-phosphate (P5P), and periodate-oxidized ATP (OxATP) exhibiting 20- to 500-fold higher potency for human than for mouse P2X(7) receptors. HMA (5-(N,N-hexamethylene)amiloride) was also selective for human over rat P2X(7) receptors but potentiated responses at mouse P2X(7) receptors. Coomassie Brilliant Blue G (CBB) was a nonselective antagonist with high potency at mouse P2X(7) receptors (IC(50) approximately 100 nM). All compounds were noncompetitive antagonists, and potency could only be quantified by measuring IC(50) values. These values were similar when determined against EC(50) concentrations of ATP or 2'- and 3'-O-4(-benzoylbenzoyl)-ATP and, for most compounds, only slightly (3- to 5-fold) affected by agonist concentration. However, IC(50) values for KN62 (1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine) and suramin, varied up to 25-fold depending upon agonist concentration. Furthermore, IC(50) values for KN62 and OxATP were 10-fold lower at 22 degrees C than at 37 degrees C, whereas IC(50) values for PPADS, P5P, suramin, and OxATP were up to 20-fold lower in NaCl than in sucrose buffer. Potency estimates for CBB and PPADS decreased 5-fold in the presence of bovine serum albumin, possibly due to protein binding. Given the species differences, and the effects of assay conditions on antagonist potency, caution must be exercised when interpreting results obtained with the available antagonists.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed2001

[Actin is located in the nucleus and nuclear matrix of HeLa cells].

HeLa cell nuclei were isolated and the nuclear matrix specimens were prepared. After labelled with an anti-actin antibody and FITC-conjugated secondary antibody, both the nuclei and nuclear matrix specimens were observed to emanate specific yellow-green fluorescence. The fluorescent signals in the nuclear matrix were much stronger than that in the nuclei, and the signals in former were widespread throughout the whole structure while that in the latter were mainly defined to their peripheral regions. A 43 kD band was revealed in nuclei and nuclear matrix specimens by SDS-PAGE, and was then proved to be actin by Western blot, confirming the immuno-fluorescence observations. When stained with TRICT-conjugated phalloidin, both the nuclei and nuclear matrix specimens were found to give off specific, red fluorescent signals which represent the location of F-actin (filamentous actin), and the pattern of TRITC signals distribution in the nuclei and nuclear matrix showed similarity with that of FITC signals. The existence and significance of actin and F-actin in the nuclei and nuclear matrix were discussed.

Actins↗
PubMed2001

[Somatic embryogenesis and plant regeneration in vitro from young shoots of Aralia elate (Miq.) Seem].

Explants excised from the young shoots of Aralia elata (Miq.) Seem. were cultured on MS media. Calli were induced from the explants on MS medium supplemented with 0.5 mg/L 2, 4-D, 0.5 mg/L BA and 0.5 mg/L NAA. Then these calli were transferred onto the MS medium containing 2.0 mg/L 2,4-D + 0.5 mg/L BA + 0.5 mg/L NAA and 0.2% activated charcoal. Under these conditions the somatic embryoids were observed and regenerated plants were obtained from somatic embryogenesis. Then, a experimental system with stability and high regenerating efficiency has been set up for the propagation of the young plants, the cell breeding technology and the control of somatic embryogenesis of Aralia elata (Miq.).

Aralia↗
PubMed2000

[Effects of cytochalasin B upon mitosis of Physarum polycephalum].

Cytochalasin B, known as a functional inhibitor of actin, was microinjected into naturally synchronous plasmodia of Physarum polycephalum, and the mitotic behaviours of both CB-treated specimens and the control were examined with light and electron microscopy. Mitosis in the CB-treated specimens began about 20 to 60 minutes later than that of the control. It was delayed 35 minutes in the specimens treated with CB in the S phase of the cell cycle, and the delayed time was 20 minutes and 45 minutes, respectively. In the specimens treated with CB in early and middle G2 phase, the longest delay was 60 minutes found in the specimens treated in late G2 phase, indicating that mitosis was affected in Physarum polycephalum when the function of actin was inhibited by CB treatment. The CB-treated specimens and the control showed similarities in the process of mitosis and dynamic changes of nuclear structures, suggesting that the main effect of CB treatment upon mitosis may be to delay the triggering of the mitosis.

Animals↗
PubMed2000

[ScII-like protein is localized in the nuclei, chromosomes and chromosome scaffolds of Allium cepa].

The nuclei were isolated from the root meristematic cells of Allium cepa and the nuclear matrices were prepared. A 135 kD polypeptide, which is equivalent to Sc II in molecular weight, was revealed in the nuclei by SDS-PAGE and was then demonstrated to be an Sc II-like protein by Western blot with an anti-chicken Sc II antiserum. Neither the 135 kD polypeptide nor the positive labelling of the anti-Sc II antiserum was found in the nuclear matrices. The immuno-fluorescence tests showed that the nuclei labelled with the anti-Sc II antiserum emanated strong, specific fluorescence, while the fluorescence of the nuclear matrices was too weak to be detected. The results of immunoelectron microscopy indicated that a large number of the gold particles were concentrated in the condensed chromatin of the nuclei, but very few gold particles were distributed in cytoplasm and nucleoplasm. These results strongly suggested that an Sc II like protein is a component of the nuclei of A. cepa and is mainly located in the condensed chromatin regions, but the nuclear matrices contain no or very little amount of that protein. By means of immunofluorescence and immunoelectron microscopy, the chromosomes and chromosomal scaffolds of A. cepa labelled with the anti-chicken Sc II antiserum were observed to send off specific fluorescence and have many gold particles representing the presence of the Sc II-like protein distributed among them. The significance of the Sc II-like protein as a novel component in the nuclei, chromosomes and chromosome scaffolds of higher plants is discussed.

Allium↗
PubMed1999

Inhibition of phospholipase A2-mediated arachidonic acid release by cyclic AMP defines a negative feedback loop for P2Y receptor activation in Madin-Darby canine kidney D1 cells.

In Madin-Darby canine kidney D1 cells extracellular nucleotides activate P2Y receptors that couple to several signal transduction pathways, including stimulation of multiple phospholipases and adenylyl cyclase. For one class of P2Y receptors, P2Y2 receptors, this stimulation of adenylyl cyclase and increase in cAMP occurs via the conversion of phospholipase A2 (PLA2)-generated arachidonic acid (AA) to prostaglandins (e.g. PGE2). These prostaglandins then stimulate adenylyl cyclase activity, presumably via activation of prostanoid receptors. In the current study we show that agents that increase cellular cAMP levels (including PGE2, forskolin, and the beta-adrenergic agonist isoproterenol) can inhibit P2Y receptor-promoted AA release. The protein kinase A (PKA) inhibitor H89 blocks this effect, suggesting that this feedback inhibition occurs via activation of PKA. Studies with PGE2 indicate that inhibition of AA release is attributable to inhibition of mitogen-activated protein kinase activity and in turn of P2Y receptor stimulated PLA2 activity. Although cAMP/PKA-mediated inhibition occurs for P2Y receptor-promoted AA release, we did not find such inhibition for epinephrine (alpha1-adrenergic) or bradykinin-mediated AA release. Taken together, these results indicate that negative feedback regulation via cAMP/PKA-mediated inhibition of mitogen-activated protein kinase occurs for some, but not all, classes of receptors that promote PLA2 activation and AA release. We speculate that receptor-selective feedback inhibition occurs because PLA2 activation by different receptors in Madin-Darby canine kidney D1 cells involves the utilization of different signaling components that are differentially sensitive to increases in cAMP or, alternatively, because of compartmentation of signaling components.

Animals↗
PubMed1999

Tropomyosin is localized in the nuclear matrix and chromosome scaffold of Physarum polycephalum.

The nuclei and chromosomes were isolated from plasmodia of Physarum polycephalum. The nuclear matrix and chromosome scaffold were obtained after the DNA and most of the proteins were extracted with DNase I and 2 M NaCl. SDS-PAGE analyses revealed that the nuclear matrix and chromosome scaffold contained a 37 kD polypeptide which is equivalent to tropomyosin in molecular weight. Immunofluorescence observations upon slide preparations labeled with anti-tropomyosin antibody showed that the nuclear matrix and chromosome scaffold emanated bright fluorescence, suggesting the presence of the antigen in them. Immunodotting results confirmed the presence of tropomyosin in the nuclear matrix and chromosome scaffold. Immunoelectron microscopic observations further demonstrated that tropomyosin was dispersively distributed in the interphase nuclei and metaphase chromosomes.

Animals↗
PubMed1999

[Immunolocalization of actin in synaptonemal complexes in spermatocytes of Mesocricetus auratus].

Opinions upon whether actin is present in synaptonemal complexes of eukaryotes are still controversial. We detected actin in synaptonemal complexes of spermatocytes of Mesocricetus auratus with indirect immunofluorescence technique and observed bright fluorescence in the SCs, indicating the presence of actin in the structure. We labelled sections of the spermatocytes of M. auratus with immunogold technique, gold particels were observed over the lateral elements and attachment plaques of the SCs, and many of the gold were found in clusters, confirming the results of the immunofluorescence observations. Further examinations revealed the gold particles representing actin in SCs of autosomes and sex chromosomes and also in SCs of zygotene and pachytene. Our results are in favour of the point of view that actin is a component of the SC.

Actins↗
PubMed1999

[Video-assisted thoracic surgery in the management of chest diseases].

OBJECTIVE: To summarize short-term results of video-assisted thoracic surgery for 322 patients with chest diseases in Beijing from October 1992 to October 1998 and discuss the role of thoracoscopy in the diagnosis and therapy of thoracic diseases in China. METHODS: Three hundred and twenty-two patients (273 men and 85 women) underwent video-assisted thoracic surgery for spontaneous pneumothorax (113), lung cancer (83), solitary pulmonary nodules (52), pleural diseases (19), mediastinal tumors (11), myasthenia gravis (5), thoracic trauma (10), esophageal cancer (7), benign esophageal diseases (11), and other indications (11). Data on thoracoscopic procedures, morbidity and mortality, conversion to open procedures were collected for all patients. RESULTS: Three hundred and thirty-nine thoracoscopic procedures were performed in 322 patients. These procedures included blebectomy and pleurodesis (121), wedge resections of pulmonary nodules (57), lobectomy and pneumonectomy (48), pleural biopsies and pleurodesis (52), excision of mediastinal mass (11), thymectomy (5), esophagectomy (6), and other procedures (39). Conversion to thoracotomy was required in 9 patients (0.28%). The overall incidence of postoperative complications was 7.5% (24/322). Two patients died postoperatively. CONCLUSIONS: Video-assisted thoracic surgery is a safe and effective technique in selected patients with chest diseases. The results in this group were similar to those reported previously in North American.

Adolescent↗
PubMed1999

[Localization with BrUTP labeling technique of RNA polymerase II transcription in meristematic cells of Allium cepa].

The technique of pulse-labeling of cells with 5-bromouridine-5'-triphosphate (BrUTP) and immunological detection of the incorporated BrUTP is a newly-developed experimental approach to localize nascent RNA polymerase II transcripts in the nucleus. This technique has been widely used since it was first reported in 1993, but most of the studies were carried out with fluorescence microscopy and animal cells, we are still limited in the knowledge about ultrastructural localization of RP II transcripts in the nucleus of eukaryotes, especially in that of plant cells. Attempts have been made in this paper to localize nascent RP II transcripts in the nucleus of meristematic cells of Allium cepa with the technique of pulse-labeling of BrUTP and immunoelectron microscopy. After labeling with BrUTP and detection with anti-BrdU antibody, a large number of gold particles representing RP II transcripts were observed in the periphery of chromatin domains, the gold particles in the periphery accounted for 92.70% of the total gold particles in the extranucleolar regions, and the gold density of the periphery was 75.42/micron 2, much higher than that of the center of the chromatin domains and the interchromatin domains which were only 5.89/micron 2 and 2.00/micron 2 respectively, indicating that RP II transcripts were being actively synthesized in the periphery of the chromatin domains. When the specimens were treated with alpha-amanitin which can specifically inhibits the activity of RP II, gold particles in the extranucleolar regions of the specimens were decreased dramatically and the gold density of the regions dropped strikingly from 44.60/micron 2 to 2.67/micron 2, confirming that the gold particles in the regions represent RP II transcripts. The distribution of nascent RP II transcripts in the nucleus of the intact plant cells is discussed.

Allium↗
PubMed1999

[Localization of SC35 in the nucleolus and nucleoplasm of the root meristematic cells of Vicia faba].

SC35 is a non-snRNP spliceosome component purified from mammalian cells by Fu and Maniatis in 1990. In vitro splicing assays showed that SC35 plays a key role in splicing site selection and ATP-dependent pre-spliceosome assembly. In the mammalian nucleus, SC35 has been localized to distinct and dynamic nuclear domains: immunofluorescence observations revealed the presence of SC35 in speckles distributed in various regions throughout the nucleoplasm, which, as identified with immunoelectron microscopy, correspond to the interchromatin granules (IGs) and perichromatin fibrils (PFs). However, there has been no report regarding the presence and distribution pattern of SC35 in higher plant nuclei. Engage in such studies will surely contribute to our understanding of RNA processing and the spatial organization or structure basis of this process in higher plant. In this article, we studied the distribution pattern of SC35 in the nucleus of the root meristematic cells of Vicia faba by immunoelectron microscopy. After immunolabeling with anti-SC35 mAb and protein A-colloidal gold, IGs and PFs in the nucleoplasm and dense fibrillar component (DFC) of the nucleolus were heavily labeled with gold particles, while only a few of the gold particles were found in fibrillar centers (FC) and nucleolar vacuoles (NV) of the nucleolus and the central domains of the condensed chromatin. Densities of gold particles in the areas of DFC and the area of IGs plus PFs were 65.89/microns 2 and 36.28/microns 2 respectively, much higher than that of the central domain of condensed chromatin and that of FC plus NV, which were only 5.90/microns 2 and 6.26/microns 2 respectively. This indicates that DFC of the nucleolus and the area of IGs plus PFs of the nucleoplasm are enriched with SC35 or SC35-like protein. The distribution pattern of SC35 or SC35-like protein in the nucleoplasm of Vicia faba is similar to that of the mammalian nuclei. To the authors' knowledge, it is a new finding that SC35 or SC35-like protein exists in the nucleolus.

Cell Nucleolus↗