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Biomedical subjects

Yi Pan

Publications and source records attributed to Yi Pan.

At least 55 records · Page 3Linked to original sources
PubMed2005

[Comparison between PET-CT and MRI in diagnosing nodal metastasis of nasopharyngeal carcinoma].

BACKGROUND & OBJECTIVE: Nodal metastasis pattern of nasopharyngeal carcinoma (NPC) influences treatment planning. This study was to compare the diagnostic value of integrated positron emission tomography-computed tomography (PET-CT) with that of magnetic resonance imaging (MRI) in detecting nodal metastasis of NPC, and explore the regulation of nodal metastasis of NPC. METHODS: Clinical data of 105 NPC patients, treated in Cancer Center of Sun Yat-sen University from Jun. 2003 to May 2004, were analyzed. All patients underwent PET-CT and MRI. Findings of PET-CT and MRI were evaluated with the results of follow-up. Distribution of metastatic nodes in different nodal groups was assessed. RESULTS: Among the 105 patients, nodal metastasis patterns shown on PET-CT and MRI were diverse in 35 patients. Thirty cervical nodes were positive on PET-CT, but negative on MRI; 25 of them were later confirmed positive by follow-up. Thirty-seven cervical nodes were negative on PET-CT, but positive on MRI; 21 of them were confirmed negative by follow-up. Based on the results of follow-up, 77 patients (73.3%) had nodal involvement. Level II nodes were the most frequently involved (87.0%). Along the jugular chain, the frequencies of nodal metastases in level III, level IV, supraclavicular fossa, and level VII were 42.9%, 14.3%, 7.8%, and 1.3%, respectively. The frequency of nodal metastases in retropharyngeal nodes was 70.1%. Cervical nodes involvement without retropharyngeal nodes involvement was seen in 23 patients (29.9%). CONCLUSIONS: The diagnostic accuracy of PET-CT in detecting nodal metastases of NPC is better than that of MRI. The nodal metastases of NPC reveal a decreasing frequency along the jugular chain. Both retropharyngeal and level II nodes are the first-echelon nodes of NPC.

Adolescent↗
PubMed2005

[Carcinoma showing thymus-like differentiation of the thyroid: a study of 2 cases].

OBJECTIVE: To describe the pathologic features and differential diagnosis of carcinoma showing thymus-like differentiation (CASTLE) of thyroid. METHODS: The clinical findings, morphologic features and immunohistochemistry (EnVision) of 2 cases of CASTLE were studied. RESULTS: Macroscopically, the tumor appeared as a hard grayish-white and slightly lobulated mass. Histologic examination revealed well-circumscribed islands of tumor cells associated with desmoplastic stroma. The tumor cells were polygonal to spindle in shape and contained lightly eosinophilic cytoplasm, oval nuclei and small distinct nucleoli. The nuclear atypia was mild to moderate and the mitotic count measured 1 to 2 per 10 high-power fields. Immunohistochemical study showed that the tumor cells expressed CD5 and CD117. CONCLUSIONS: CASTLE is a rare type of thyroid carcinoma with distinctive morphologic findings. It needs to be distinguished from undifferentiated thyroid carcinoma, squamous cell thyroid carcinoma, metastatic lymphoepithelioma-like carcinoma and follicular dendritic cell sarcoma. Immunohistochemical staining for CD5 and CD117 is helpful in confirming the diagnosis.

Adult↗
PubMed2004

Pharmacology of GABAC receptors: responses to agonists and antagonists distinguish A- and B-subtypes of homomeric rho receptors expressed in Xenopus oocytes.

GABA(C) receptors, expressed predominantly in vertebrate retina, are thought to be formed mainly by GABA rho subunits. Five GABA rho subunits have been cloned from white perch retina, four of which form functional homooligomeric receptors when expressed in Xenopus oocytes. These rho subtypes, classified as rho1A, rho1B, rho2A and rho2B receptors based on amino acid sequence alignment, exhibit distinct temporal and pharmacological properties. To examine further the pharmacological properties associated with the various rho receptor subtypes, we investigated the effects of a selective GABA(C) receptor antagonist, TPMPA, on the GABA-mediated activity of receptors formed in Xenopus oocytes by the four GABA rho subunits. In addition, we recorded the activation profiles of beta-alanine, taurine, and glycine, three amino acids that modulate neuronal activity in various parts of the CNS and are purported to be rho receptor agonists. TPMPA effectively inhibited GABA-elicited responses on A-type receptors, whereas B-type receptors exhibited a relatively low sensitivity to the drug. A-type and B-type receptors also displayed distinctly different reactions to agonists. Both taurine and glycine-activated the B-type receptors, whereas these agents had no detectable effect on A-type receptors. Similarly, beta-alanine evoked large responses from B-type receptors, but was far less effective on A-type receptors. These results indicate that, in addition to the characteristic response properties identified previously, there is a pattern of pharmacological reactions that further distinguishes the A- and B-subtypes of GABA rho receptor.

Alanine↗
PubMed2004

Efficient asymmetric oxidation of sulfides and kinetic resolution of sulfoxides catalyzed by a vanadium-salan system.

The asymmetric oxidation of sulfides to chiral sulfoxides with hydrogen peroxide in good yield and high enantioselectivity has been catalyzed very effectively by chiral vanadium-salan [N,N'-alkyl bis(salicylamine)] complex. The salan ligand shows results superior in terms of reactivity and enantioselectivity to those of salen [N,N'-alkylene bis(salicylideneimine)] analogue, and provides the sulfoxide with opposite configuration. The high enantioselectivity of this reaction is the direct result of the asymmetric oxidation. The efficient kinetic resolution of racemic sulfoxides catalyzed by the vanadium-salan system is also described.

Catalysis↗
PubMed2004

Picrotoxin accelerates relaxation of GABAC receptors.

Picrotoxin is a plant alkaloid that is often used to block the activity of neuronal GABA and glycine receptors. However, the mechanism by which picrotoxin inhibits these receptors is still in debate. In this study, we investigated the picrotoxin inhibition on perch-rho subunits expressed heterologously in Xenopus laevis oocytes, and on native GABA(C) receptors of perch bipolar cells. Both competitive and noncompetitive mechanisms were observed for picrotoxin inhibition of the GABA(C) receptor. In oocytes expressing the rho1A subunit, terminating simultaneously the coapplication of GABA and picrotoxin induced a large rebound of membrane current. In addition, picrotoxin significantly accelerated the kinetics of GABA responses, particularly in the relaxation (offset) phase of GABA currents. Both current rebound and the large acceleration of GABA relaxation were unique to picrotoxin inhibition and were not observed with the competitive antagonist (1,2,5,6-tetrahydropyridin-4-yl)-methylphosphinic acid or the allosteric modulator zinc. The change in kinetics induced by picrotoxin was also observed on receptors formed by other GABA rho subunits, as well as on the GABA(C) receptors of retinal bipolar cells. Based on these observations, we proposed a model in which picrotoxin binds to the GABA(C) receptor in both channel open and closed states. Overall, this model provides a remarkably good approximation of the experimental findings we observed for picrotoxin inhibition of GABA(C) receptors. These results support an allosteric mechanism of picrotoxin inhibition of ligand-gated chloride channels.

Animals↗
PubMed2004

A copper- and amine-free sonogashira reaction employing aminophosphines as ligands.

An efficient Pd-catalyzed Sonogashira coupling reaction was achieved in the absence of a copper salt or amine with an inorganic base and easily prepared, air-stable aminophosphine ligands in commonly used organic solvents; good to excellent yields were obtained. Under optimized reaction conditions, the Sonogashira coupling reaction occurred selectively when an enyne substrate was employed and no Heck reaction product was detected; acetone-masked acetylene and trimethylsilylacetylene can also be efficiently coupled, providing a method to make terminal alkynes.

Journal Article↗
PubMed2004

p53 cannot be induced by hypoxia alone but responds to the hypoxic microenvironment.

Solid tumors frequently contain hypoxic subregions due to insufficient blood supply. In these domains, cells can undergo p53-dependent apoptosis. Therefore, hypoxia has been implicated as a physiological stimulus for p53 accumulation and activation. In such an environment, p53 mutant cells exhibit a selective growth advantage. Hypoxic regulation of p53 has been proposed to be hypoxia inducible factor (HIF) dependent; however, controversy remains over whether and to what extent low oxygen (O(2)) tension by itself enhances p53 protein stability. Here, we examined the p53 response to hypoxia and hypoxia mimetics in several cell lines expressing different HIF-alpha proteins. Most cells exhibited elevated levels of p53 in response to hypoxia mimetics such as deferoxamine mesylate and CoCl(2), regardless of their HIF-alpha protein expression profile. However, over a range of O(2) levels, from 1.5% to less than 0.02%, we failed to observe p53 accumulation or p53 nuclear translocation in any cell lines tested. Only after treatment with a combination of hypoxia and acidosis/nutrient deprivation did some cells exhibit p53 induction. Our results suggest that, although hypoxia induces p53 accumulation in vivo, secondary effects such as acidosis caused by a hypoxic Pasteur effect (instead of low O(2) by itself) are necessary for p53 accumulation. Therefore, the expression of HIF-1alpha and p53 proteins is not coupled during the cellular hypoxia response.

Apoptosis↗
PubMed2004

Genome-wide ORFeome cloning and analysis of Arabidopsis transcription factor genes.

Here, we report our effort in generating an ORFeome collection for the Arabidopsis transcription factor (TF) genes. In total, ORFeome clones representing 1,282 Arabidopsis TF genes have been obtained in the Gateway high throughput cloning pENTR vector, including 411 genes whose annotation lack cDNA support. All the ORFeome inserts have also been mobilized into a yeast expression destination vector, with an estimated 85% rate of expressing the respective proteins. Sequence analysis of these clones revealed that 34 of them did not match with either the reported cDNAs or current predicted open-reading-frame sequences. Among those, novel alternative splicing of TF gene transcripts is responsible for the observed differences in at least five genes. However, those alternative splicing events do not appear to be differentially regulated among distinct Arabidopsis tissues examined. Lastly, expression of those TF genes in 17 distinct Arabidopsis organ types and the cultured cells was profiled using a 70-mer oligo microarray.

Alternative Splicing↗
PubMed2004

Improved protein secondary structure prediction using support vector machine with a new encoding scheme and an advanced tertiary classifier.

Prediction of protein secondary structures is an important problem in bioinformatics and has many applications. The recent trend of secondary structure prediction studies is mostly based on the neural network or the support vector machine (SVM). The SVM method is a comparatively new learning system which has mostly been used in pattern recognition problems. In this study, SVM is used as a machine learning tool for the prediction of secondary structure and several encoding schemes, including orthogonal matrix, hydrophobicity matrix, BLOSUM62 substitution matrix, and combined matrix of these, are applied and optimized to improve the prediction accuracy. Also, the optimal window length for six SVM binary classifiers is established by testing different window sizes and our new encoding scheme is tested based on this optimal window size via sevenfold cross validation tests. The results show 2% increase in the accuracy of the binary classifiers when compared with the instances in which the classical orthogonal matrix is used. Finally, to combine the results of the six SVM binary classifiers, a new tertiary classifier which combines the results of one-versus-one binary classifiers is introduced and the performance is compared with those of existing tertiary classifiers. According to the results, the Q3 prediction accuracy of new tertiary classifier reaches 78.8% and this is better than the best result reported in the literature.

Algorithms↗
PubMed2004

Focal nodular hyperplasia of the liver: pathological analysis of 11 cases.

BACKGROUND: Focal nodular hyperplasia (FNH) is a benign tumor-like lesion of the liver, predominantly affecting women. Its etiology is obscure and its pathogenesis is poorly understood. FNH should be differentiated from other benign and malignant hepatic lesions. The aim of this study was to explore the pathological characteristics of FNH of the liver. METHODS: Eleven patients with FNH were studied retrospectively by using hematoxylin and eosin, immunohistochemical and histochemical staining. RESULTS: In 8 female and 3 male FNH patients aged 19 to 54 years (mean 32), most of lesions showed central scars macroscopically. Microscopically 8 patients were found of classical type, 2 were of telangiectic type, and 1 was of mixed type. CONCLUSION: FNH is an uncommon benign hyperplastic lesion of the liver. It should be differentiated from hepatocellular adenoma, alpha-fetoprotein negative hepatocellular carcinoma, and fibrolamellar carcinoma.

Adult↗
PubMed2003

Clinical significance of chromosome 8p, 10q, and 16q deletions in prostate cancer.

BACKGROUND: We lack simple and reliable diagnostic tools to predict pathological staging as well as further progression of prostate cancer in individual cases. METHODS: We studied deletions on 8p (8p22 and 8p23-pter), 10q (10q24-qter), and 16q (16q24) by fluorescence in situ hybridization in 53 specimens from patients with prostate cancer, and compared the status of these deletions with various clinical parameters. Forty-five cases were further evaluated regarding disease progression with a median follow-up period of 62 months. RESULTS: The overall frequencies of deletions for 8p, 10q, and 16q were 74, 55, and 55%, respectively. The frequency of 8p and 16q deletions increased significantly in parallel with tumor grade (P < 0.01 and < 0.05, respectively), while that of 10q deletions did not. Patients whose tumors showed 8p22 deletions had a significantly higher frequency in pT3 or metastatic tumors than in pT2 tumors. Patients whose tumors showed both 8p22 and 16q24 deletions had a significantly higher frequency of nodal metastases than non-metastases. A Cox hazard proportional model revealed 8p22 deletion to be the strongest parameter predictive of disease progression (hazard ratio = 6.624; P = 0.0001). CONCLUSION: Estimation of 8p22 and 16q24 deletions may serve as a genetic diagnosis for predicting pathological staging as well as disease progression in prostate cancer.

Aged↗
PubMed2003

Expansion of human SCID-repopulating cells under hypoxic conditions.

It has been proposed that bone marrow (BM) hematopoietic stem and progenitor cells are distributed along an oxygen (O2) gradient, where stem cells reside in the most hypoxic areas and proliferating progenitors are found in O2-rich areas. However, the effects of hypoxia on human hematopoietic stem cells (HSCs) have not been characterized. Our objective was to evaluate the functional and molecular responses of human BM progenitors and stem cells to hypoxic conditions. BM lineage-negative (Lin-) CD34+CD38- cells were cultured in serum-free medium under 1.5% O2 (hypoxia) or 20% O2 (normoxia) for 4 days. Using limiting dilution analysis, we demonstrate that the absolute number of SCID-repopulating cells (SRCs) increased by 5.8-fold in hypoxic cultures compared with normoxia, and by 4.2-fold compared with freshly isolated Lin-CD34+CD38- cells. The observed increase in BM-repopulating activity was associated with a preferential expansion of Lin-CD34+CD38- cells. We also demonstrate that, in response to hypoxia, hypoxia-inducible factor-1alpha protein was stabilized, surface expression of angiogenic receptors was upregulated, and VEGF secretion increased in BM Lin-CD34+ cultures. The use of low O2 levels to enhance the survival and/or self-renewal of human BM HSCs in vitro represents an important advance and could have valuable clinical implications.

ADP-ribosyl Cyclase↗
PubMed2003

[Combined recombinant DNA vaccine results in significant protection against Mycobacterium tuberculosis].

Three proteins secreted from Mycobacterium tuberculosis, Ag85B, ESAT-6 and MPT63 were selected as antigens for making combined DNA vaccine by immunizing mice. The immune response induced by the vaccine and its protective efficacy were studied. It was demonstrated that when mice were immunized with the combined DNA vaccine, the titer of antibody for Ag85B in serum increased to more than 10(5), but the titers of ESAT-6 and MPT63 specific antibodies were undetectable. After the final immunization, the level of gamma specific for Ag85B, ESAT-6 and MPT63 reached (17.0+/-7.0) u/ml, (6.0+/-0.8) u/ml and (11.9+/-8.0) u/ml, respectively. Mice, that were inoculated with the empty eukaryotic expression vector pJW4303 DNA, produced negligible amounts of antigen-specific INF-gamma. The combined DNA vaccine resulted also in significantly reduced amount of bacteria in the lungs of experimental mice. Microphotographs showed clearly that these lungs were better protected against Mycobacterium tuberculosis challenge than control mice. The combined DNA vaccine reported in this work shed new lights on the prophylactic protection against tuberculosis.

Acyltransferases↗
PubMed2002

c-FLIP(L) is a dual function regulator for caspase-8 activation and CD95-mediated apoptosis.

Activation of the caspase cascade is a pivotal step in apoptosis and can occur via death adaptor-mediated homo-oligomerization of initiator procaspases. Here we show that c-FLIP(L), a protease-deficient caspase homolog widely regarded as an apoptosis inhibitor, is enriched in the CD95 death-inducing signaling complex (DISC) and potently promotes procaspase-8 activation through hetero-dimerization. c-FLIP(L) exerts its effect through its protease-like domain, which associates efficiently with the procaspase-8 protease domain and induces the enzymatic activity of the zymogen. Ectopic expression of c-FLIP(L) at physiologically relevant levels enhances procaspase-8 processing in the CD95 DISC and promotes apoptosis, while a decrease of c-FLIP(L) expression results in inhibition of apoptosis. c-FLIP(L) acts as an apoptosis inhibitor only at high ectopic expression levels. Thus, c-FLIP(L) defines a novel type of caspase regulator, distinct from the death adaptors, that can either promote or inhibit apoptosis.

Apoptosis↗
PubMed2002

Co-assembly of GABA rho subunits with the GABA(A) receptor gamma(2) subunit cloned from white perch retina.

Although it is well established that GABA(C) receptors are comprised in part of GABA rho subunits, the exact subunit composition of neuronal GABA(C) receptors is yet to be determined. A detailed comparison of GABA(C)-mediated neuronal responses elicited from retinal neurons with those obtained from receptors formed by GABA rho subunits revealed a number of significant differences both in the kinetics and the pharmacology of the responses. Our previous studies indicated that the human GABA(A) receptor gamma(2) subunit could co-assemble with one (rho(1B)) of the white perch GABA rho subunits to form a heterooligomeric receptor with properties that resembled those of the GABA(C) receptors on white perch bipolar cells. In this study, we cloned the white perch gamma(2) subunit, and investigated its co-assembly with four white perch GABA rho subunits. When expressed in Xenopus oocytes, perch gamma(2) and rho(1B) subunits form heterooligomeric receptors with distinct properties: the GABA-elicited responses have fast kinetics and are sensitive to pentobarbital modulation. The enhancement of GABA-elicited responses by pentobarbital on the heterooligomeric receptors could be eliminated by a single mutation in the third transmembrane domain of the gamma(2) subunit, indicating that pentobarbital sensitivity is mediated by the incorporated gamma(2) subunit. On the other hand, co-expression of the perch gamma(2) subunit with the other perch GABA rho subunits produced no detectable changes in the kinetics of GABA-elicited response or the sensitivity to pentobarbital modulation. These results suggest that the gamma(2) subunit can co-assemble only with one (rho(1B)), but not with other white perch GABA rho subunits.

Amino Acid Sequence↗
PubMed2002

Fine mapping of a semi-dwarf gene brachytic 1 in barley.

RFLP markers isolated from barley, wheat and rice were applied to construct a fine structure map of brachytic1, a semi-dwarf gene located on chromosome 1(7H) short arm in barley. The map covered 15.2 cM with the average distance 0.8 cM between markers. A barley cDNA clone, MWG2074B co-segregated with brh1 gene in the test population. Another major band of this clone MWG2074A was 0.8 cM away from brh1 toward centromere. CDO545 and BCD129 were two flanking markers mapped on both sides of brh1, toward distal and pistal, respectively. CDO545 fitted the systenic region of rice genome, chromosome 6 short arm perfectly. However, two major bands of MWG2074 could not be mapped to the target position of rice genome.

Chromosome Mapping↗