Biomedical subjects

T Chen

Publications and source records attributed to T Chen.

At least 145 records · Page 8Linked to original sources

PubMed2000

The three subfamilies of leucine-rich repeat-containing G protein-coupled receptors (LGR): identification of LGR6 and LGR7 and the signaling mechanism for LGR7.

Glycoprotein hormone receptors, including LH receptor, FSH receptor, and TSH receptor, belong to the large G protein-coupled receptor (GPCR) superfamily but are unique in having a large ectodomain important for ligand binding. In addition to two recently isolated mammalian LGRs (leucine-rich repeat-containing, G protein-coupled receptors), LGR4 and LGR5, we further identified two new paralogs, LGR6 and LGR7, for glycoprotein hormone receptors. Phylogenetic analysis showed that there are three LGR subgroups: the known glycoprotein hormone receptors; LGR4 to 6; and a third subgroup represented by LGR7. LGR6 has a subgroup-specific hinge region after leucine-rich repeats whereas LGR7, like snail LGR, contains a low density lipoprotein (LDL) receptor cysteine-rich motif at the N terminus. Similar to LGR4 and LGR5, LGR6 and LGR7 mRNAs are expressed in multiple tissues. Although the putative ligands for LGR6 and LGR7 are unknown, studies on single amino acid mutants of LGR7, with a design based on known LH and TSH receptor gain-of-function mutations, indicated that the action of LGR7 is likely mediated by the protein kinase A but not the phospholipase C pathway. Thus, mutagenesis of conserved residues to allow constitutive receptor activation is a novel approach for the characterization of signaling pathways of selective orphan GPCRs. The present study also defines the existence of three subclasses of leucine-rich repeat-containing, G protein-coupled receptors in the human genome and allows future studies on the physiological importance of this expanding subgroup of GPCR.

Amino Acid Sequence↗

PubMed2000

Three-dimensional in vivo analysis of Dictyostelium mounds reveals directional sorting of prestalk cells and defines a role for the myosin II regulatory light chain in prestalk cell sorting and tip protrusion.

During cell sorting in Dictyostelium, we observed that GFP-tagged prestalk cells (ecmAO-expressing cells) moved independently and directionally to form a cluster. This is consistent with a chemotaxis model for cell sorting (and not differential adhesion) in which a long-range signal attracts many of the prestalk cells to the site of cluster formation. Surprisingly, the ecmAO prestalk cluster that we observed was initially found at a random location within the mound of this Ax3 strain, defining an intermediate sorting stage not widely reported in Dictyostelium. The cluster then moved en masse to the top of the mound to produce the classic, apical pattern of ecmAO prestalk cells. Migration of the cluster was also directional, suggesting the presence of another long-range guidance cue. Once at the mound apex, the cluster continued moving upward leading to protrusion of the mound's tip. To investigate the role of the cluster in tip protrusion, we examined ecmAO prestalk-cell sorting in a myosin II regulatory light chain (RLC) null in which tips fail to form. In RLC-null mounds, ecmAO prestalk cells formed an initial cluster that began to move to the mound apex, but then arrested as a vertical column that extended from the mound's apex to its base. Mixing experiments with wild-type cells demonstrated that the RLC-null ecmAO prestalk-cell defect is cell autonomous. These observations define a specific mechanism for myosin's function in tip formation, namely a mechanical role in the upward movement of the ecmAO prestalk cluster. The wild-type data demonstrate that cell sorting can occur in two steps, suggesting that, in this Ax3 strain, spatially and temporally distinct cues may guide prestalk cells first to an initial cluster and then later to the tip.

Animals↗

PubMed2000

[Latest progress in studies of self-setting calcium phosphate cement].

Self-setting calcium phosphate cement(CPC) is a non-ceramic form of hydrxyapatitic artificial bone material (HAP) which was first exclusively produced in America several years ago. CPC is free from the drawbacksto ceramic HAP, including sintering and difficulties in shaping. CPC has the characteristics of simple-producing and easy applyication. In 1991, the clinical application of CPC to repairing the calvarial bone defects was approved, and the results reportedly so far were good or excellent. This paper presents the latest progress in the studies of CPC, concerning the probing into the setting process, the producing of fast-setting and non-decayed types of CPC, the studies of organic compound CPC, the in vitro results of CPC as a drug delivery system, etc. As the research goes on deeply and broadly, CPC is hopefully becoming a standard material in repairing bone defects at the non- or low-bearing site in the future.

Artificial Organs↗

PubMed2000

[The study on relation of human papillomavirus and P53 expression with bladder transitional cell carcinoma].

OBJECTIVE: To study the relationship between the bladder transitional cell carcinoma and the human papillomavirus (HPV) types 6, 11, 16, 18 and P53. METHODS: We used polymerase chain reaction (PCR) to test HPV type 6, 11, 16 and 18 infection from 75 cases of bladder cancer, and used immunohistochemistry method to detect P53 expression. RESULTS: The positive rates of HPV types 6, 11, 16 and 18 were 6.7%, 5.3%, 33.3% and 6.7%, respectively. The positive rate of low risk HPV type (6/11) was 9.3% (7/75), and that of high risk HPV types (16/18) was 34.7% (26/75). There were 8 cases with two or three HPV types mixed infection, accounting for 10.6%, HPV types 6,11,16,18 in tumor metastasis group were significantly higher than that in non-metastasis group. The positive rates of HPV 16, 18 types in G3 were significantly higher than that in G1 and G2. HPV type 16 was the main type in bladder cancer. Positive rate of P53 expression was 44%. CONCLUSIONS: These results implicated that the occurrence and development of bladder transitional cell carcinoma may be closely related to the high risk HPV type infection and P53 expression.

Adult↗

PubMed2000

[Vitrectomy for pseudophakic retinal detachment].

OBJECTIVE: To study the method of vitrectomy for treatment of pseudophakic retinal detachment. METHODS: 32 pseudophakic retinal detachment eyes were treated with vitrectomy, primary vitrectomy in 11 eyes (34.4%), vitrectomy after conventional buckling failure in 21 eyes (65.6%), combined with silicone oil 10 eyes (31.3%), removal of intraocular lens 12 eyes (37.5%). All eyes had passed the 6 months to 5 years of follow-up examination. RESULTS: Intra-operative new retinal breaks were identified in 7 eyes (21.9%). The retinal total reattachment was in 25 eyes (78.1%); part reattachment was in 4 eyes (12.5%), and their visual acuity was improved than that before the operation. Due to severe proliferative vitreoretinopathy (PVR), failure occurred in 3 eyes. CONCLUSIONS: The main advantage of vitrectomy is the better intra-operative sight to the peripheral retinal breaks, removal of retinal traction and the low rate of PVR after vitrectomy. Vitrectomy for complicated type of pseudophakic retinal detachment can improve the success rate of the retinal detachment surgery and the visual acuity outcome.

Adult↗

PubMed2000

[A study on apoptosis and activity of SAPK/JNK in adrenocortical cells induced by cadmium chloride].

OBJECTIVE: To study apoptosis induced by cadmium chloride and the alteration in activity of stress activated protein kinase (SAPK) in adrenocortical cells. METHODS: Fasciculata-glomerulosa (FG) cells of male guinea pigs were dispersed and primarily cultured in vitro. Features of apoptotic cells were observed using combined labeling with annexin-V and propidium iodide (PI) and flow cytometry, and activity of SAPK was determined with immunoprecipitation and chemiluminescence assay. RESULTS: Apoptosis rate of FG cells increased with dose of cadmium chloride (CdCl(2)) two hours after treatment with 6.25 - 200.00 micromol/L of it. The average percentages of apoptotic cells ranged from 9.90% to 82.35%, with significant difference in the groups treated with 25, 50, 100 and 200 micromol/L of CdCl(2), as compared with the control group (P < 0.01). Regression analysis showed that occurrence of apoptosis correlated with the dose of cadmium chloride in a dose-response pattern. In the meanwhile, there were obviously elevated percentages of apoptotic cells as the increase in duration of incubation, ranging from 5.58% to 73.08% for incubating cells with 50.00 micromol/L of CdCl(2), from 15 minutes to four hours. Duration of incubating cells with cadmium chloride correlated to occurrence of apoptosis in a time-effect manner. There were no remarkable changes in the activity of SAPK in adrenocortical cells two hours after incubation with 25.00 - 100.00 micromol/L of CdCl(2). CONCLUSIONS: Apoptosis can be induced by cadmium chloride in adrenocortical cells and its mechanism should be studied further.

Adrenal Cortex↗

PubMed2000

[p16, p53 and c-erbB-2 gene expression in bladder carcinoma].

OBJECTIVE: To investigate the expression of p16, p53 and c-erbB-2 proteins in bladder carcinoma and to analyze their correlation with tumor grade, clinic stage and metastasis. METHODS: Immunohistochemical method was used to detect the p16, p53 and c-erbB-2 gene expressions in 75 cases of bladder carcinoma. RESULTS: Positive rates of p16, p53 and c-erbB-2 in 75 cases of bladder cancer were 41.3%, 44.0% and 40.0%, respectively. p16 and c-erbB-2 gene expressions were related to the tumor grade and clinic stage (P < 0.05); p53 and c-erbB-2 gene expressions were related to the clinic stage and metastasis (P < 0.01). Oncogenes and/or antioncogenes altered expressions were found in 77.3% cases of bladder carcinoma, and oncogenes and/or antioncogenes with multiple altered expressions were found in 53.3% cases. CONCLUSION: The analysis of multiple oncogene and/or antioncogene is more valuable than that of single oncogene and/or antioncogene. The altered expression of oncogene c-erbB-2 and antioncogenes p16 and p53 might play a promotive role in the tumorigenesis and development of bladder tumors.

Adult↗

PubMed2000

[Identification of Listeria species in 167 kinds of foods].

Through preliminary identification of isolation of Listeria species in six types foods, which consisted of 167 kinds of foods, we found both S-form and R-form colonies were suspected colonies of Listeria species, and some of them were catalase-negative, urease-positive, methyl red(MR) negative and Voges-Proskauer(VP) negative. The results showed that S-form, catalase-positive, urease-negative, MR-positive and VP-positive colony should not be used as the strict criteria for the identification of Listeria.

Animals↗

PubMed2000

[Study on the characteristics and applications of a new hydrophobic interaction chromatographic packing using chitosan as support].

Based on chitosan, by using valeraldehyd as ligand, a new hydrophobic interaction chromatographic (HIC) packing material was prepared by an improved method. The effects of salt concentration, temperature, pH on the adsorption of bovine serum albumin(BSA) were investigated. The results showed that the adsorption behavior of protein by packing material is in agree with the theory of hydrophobic interaction. The alpha-amylase could be separated by HIC with high recovery of enzymatic activity.

Chitin↗

PubMed2000

[Characterization of the Pt/CeO2-ZrO2/Al2O3 catalysts by spectra].

The performance of Pt/Al2O3 catalysts with CeO2-ZrO2 in difference ways was studied by NIR-FT-Raman, BET, H2 chemisorption, XRD. It shows that the dispersion of Pt on Al2O3 is improved with the increasing of dispersion of CeO2-ZrO2 on the surface of Al2O3, owing to the strong interacting between CeO2-ZrO2 and Pt. And adding with salts is priority.

Aluminum Oxide↗

PubMed1999

Hprt mutant frequency and molecular analysis of Hprt mutations in rats treated with mutagenic carcinogens.

Much of the progress in the field of cancer research has come from the increased understanding of the molecular events associated with the initiation and accumulation of mutational events associated with carcinogenesis. Genetic toxicologists have developed a number of in vitro and in vivo non-mammalian and mammalian systems to predict those genetic events required to induce the cancer process. Several model rodent systems have been proposed that have the ability to detect and quantify in vivo somatic mutation in endogenous genes and transgenes and relate the nature of the mutation to the specific type of chemical damage. One such system, the rat lymphocyte hypoxanthine guanine phosphoribosyl transferase (Hprt) assay is described in this review. Data are presented that describe mutant induction and mutational spectra in N-ethyl-N-nitrosourea (ENU), 7,12-dimethylbenzo[a]anthracene (DMBA) and thiotepa (TEPA) treated rats.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1999

Sequence specificity of Hprt lymphocyte mutation in rats fed the hepatocarcinogen 2-acetylaminofluorene.

Rats fed the hepatocarcinogen 2-acetylaminofluorene (2-AAF) have a low, but significantly increased, frequency of lymphocyte Hprt mutants. In this study, mutants from 2-AAF-fed and control F344 rats were examined for mutations in the Hprt gene in order to determine if the 2-AAF treatment resulted in an agent-specific mutation profile. The most common mutation from 2-AAF-treated rats was G:C-->T:A transversion (32% of all mutations) followed by 1-basepair (bp) deletion (19%); there were very few (5%) G:C-->A:T transitions. Among mutations from control rats, G:C-->A:T transition was the most common (43%), and there were very few G:C-->T:A transversions (5%) and no 1-bp deletions. The profile of mutations from 2-AAF-fed rats was significantly different from control rats (P = 0.003) and was consistent with the types of mutations produced by 2-AAF in vitro. The results of this study indicate that even weak mutational responses in the lymphocyte Hprt assay are capable of producing mutation profiles that reflect the DNA damage inducing them.

2-Acetylaminofluorene↗

PubMed1999

A novel element upstream of the Vgamma2 gene in the murine T cell receptor gamma locus cooperates with the 3' enhancer to act as a locus control region.

Transgenic expression constructs were employed to identify a cis-acting transcription element in the T cell receptor (TCR)-gamma locus, called HsA, between the Vgamma5 and Vgamma2 genes. In constructs lacking the previously defined enhancer (3'E(Cgamma1)), HsA supports transcription in mature but not immature T cells in a largely position-independent fashion. 3'E(Cgamma1), without HsA, supports transcription in immature and mature T cells but is subject to severe position effects. Together, the two elements support expression in immature and mature T cells in a copy number-dependent, position-independent fashion. Furthermore, HsA was necessary for consistent rearrangement of transgenic recombination substrates. These data suggest that HsA provides chromatin-opening activity and, together with 3'E(Cgamma1), constitutes a T cell-specific locus control region for the TCR-gamma locus.

Animals↗

PubMed1999

Mutagenicity of 1,3-butadiene at the Hprt locus of T-lymphocytes following inhalation exposures of female mice and rats.

The species specific response to 1,3-butadiene (BD), an important industrial chemical, was investigated by determining the influence of exposure duration and exposure concentration on the mutagenicity of BD in mice and rats and by defining the spectra of mutations in the Hprt gene T-cell mutants from control and BD-exposed mice. Female B6C3F1 mice and F344 rats (4-5 weeks old) were exposed by inhalation to 0, 20, 62.5, or 625 ppm of BD for up to 4 weeks (6 h/day, 5 days/week). Groups of control and exposed animals (n=4-12/group) were necropsied at multiple time points after exposure and the T-cell cloning assay was used to measure Hprt mutant frequencies in lymphocytes isolated from spleen. Mutant clones collected from control and BD-exposed mice were propagated and analyzed by RT-PCR to produce Hprt cDNA for sequencing. In animals necropsied 4 weeks after 2 or 4 weeks of BD exposure (0 or 625 ppm), the rate of accumulation of mutations was greater in mice than in rats. Supra-linear dose-response curves were observed in BD-exposed mice, indicating a higher efficiency of mutant induction at lower concentrations of BD. The mutagenic potency estimates (represented by the differences in the areas under the mutant T-cell 'manifestation' curves of treated vs. control animals) in mice were 11 and 61 following 4 weeks of exposures to 62.5 and 625 ppm of BD, respectively, while mutant frequencies (Mfs) in rats were significantly increased only at 625 ppm BD (mutagenic potency of 7). Molecular analysis of Hprt cDNA from expanded T-cell clones from control and BD-exposed mice demonstrated an increased frequency of mutants in exposed animals that likely contain large deletions in the Hprt gene (P=0.016). These data indicate that both exposure duration and exposure concentration are important in determining the magnitude of mutagenic response to BD, and that mutagenic and carcinogenic properties of BD in mice may be related more to the ability of its metabolites to cause chromosomal deletions than to produce point mutations.

Administration, Inhalation↗

PubMed1999

Astilbin selectively induces dysfunction of liver-infiltrating cells--novel protection from liver damage.

The present study aimed to examine the effect of astilbin, a flavanoid, on liver injury. When administered during the effector but not induction phase, astilbin significantly decreased the liver injury induced by delayed-type hypersensitivity to picryl chloride in mice. The pretreatment of nonparenchymal cells but not hepatocytes with astilbin in vitro caused a concentration- and time-dependent inhibition against the damage. Nonparenchymal cells isolated from astilbin-administered mice also showed a significant incompetence of hepatotoxicity, correlated with the inhibition of serum transaminase elevation. However, astilbin did not protect from CCl4-induced liver damage. Furthermore, the flavanoid markedly promoted the apoptosis of nonparenchymal cells from liver-injured mice, whereas did not influence those from naive mice. These results suggest that astilbin provides improvement against liver injury through a selective dysfunction of liver-infiltrating cells rather than by protecting the hepatocyte membrane. Such characteristics will be of significance to pave a new way for treating immunologically related liver diseases and for developing new drugs.

Animals↗

PubMed1999

Structural alterations of transforming growth factor-beta receptor genes in human cervical carcinoma.

The development and progression of invasive uterine cervical carcinomas appear to be associated with the progressive loss of sensitivity to transforming growth factor-beta (TGFbeta)-mediated cell cycle arrest. In order to identify possible molecular mechanisms responsible for TGFbeta resistance, we screened the 7 exons of the type II (TbetaR-II) TGFbeta receptor and the 9 exons of the type I (TbetaR-I) TGFbeta receptor genes for mutations in 16 paraffin-embedded primary invasive cervical carcinoma specimens. In one of these carcinomas, we found a novel G-->T transversion in exon 3 of TbetaR-II that introduces a premature stop codon (E142Stop) and presumably results in the synthesis of a truncated soluble exoreceptor. In one tumor, a silent A-->C transversion mutation that may affect mRNA splicing was present in exon 6 of TbetaR-I. In addition, 7 of 16 cases were heterozygous for a G-->A polymorphism in intron 7 of TbetaR-I. Finally, we identified a 9 base pair in-frame germline deletion in exon 1 of TbetaR-I resulting in loss of 3 of 9 sequential alanine residues at the N-terminus in 6 of 16 cases. Analysis of specimens from case-control studies indicated that carriers of this del(GGC)3 TbetaR-I variant allele may be at a increased risk for the development of cervical carcinoma (p=0.22). Furthermore, the response of cells expressing the variant receptor to TGFbeta was diminished. Our results support the notion that diverse alterations in the TGFbeta signaling pathway may play a role in the development of cervical cancer.

Adult↗

PubMed1999

Development of a carbon dioxide-capture assay in microtiter plate for aspartyl-beta-hydroxylase.

CO2-capture methods have been used for assaying many decarboxylating enzymes including hydroxylation-coupled decarboxylation reactions. The traditional CO2-capture method involves performing the reaction in capped tubes and radiometric measurement of trapped 14CO2 by scintillation counting. In this report, a 14CO2-capture method in a 96-well microtiter plate format has been developed and a phosphor imaging system has been employed for sample measurement. The new assay method has been used successfully to assay aspartyl-beta-hydroxylase activity in microtiter plate format. The results obtained here compare favorably with those obtained from the traditional tube method. The method is sensitive, suitable for high throughput, and generally applicable to many CO2-releasing enzyme assays.

Carbon Dioxide↗

PubMed1999

Pattern of FHIT gene expression in normal and leukaemic cells.

Chromosomal aberrations and inactivation of tumour suppressor genes are frequent in acute leukaemia. To determine whether the FHIT gene is involved in the development of leukaemia, we examined the FHIT transcript in 65 leukaemia cell lines, 5 fresh acute leukaemia patients at diagnosis and in complete remission, normal peripheral blood lymphocytes obtained from 14 healthy volunteers and Epstein-Barr (EB) virus transformed 5 B-cell lines (EB-lines), using nested reverse transcription-polymerase chain reaction and direct sequencing. The transcripts were classified into 4 patterns: pattern I revealed the normal transcripts only, pattern II the altered transcripts in addition to the normal transcripts, pattern III the altered transcripts without the normal transcripts and pattern IV an absence of normal and altered FHIT transcripts. Nineteen cell lines were classified as pattern I, 32 as pattern II, 2 as pattern III and 12 as pattern IV. The frequency of loss of FHIT expression (pattern III or IV) varied in each type of leukaemia cell line; the order ranked from the highest incidence was acute myeloid leukaemia (AML), T-cell acute lymphoblastic leukaemia (T-ALL), B-precursor ALL, B-ALL, and chronic myeloid leukaemia (CML). No genomic rearrangement was found in any samples examined. All of 5 patients showed same pattern II FHIT transcripts at 2 different stages of the disease. All normal peripheral blood lymphocytes and EB-lines were classified as pattern I or II. Our results suggested that patterns III and IV of FHIT transcripts might be associated with the development of a subset of leukaemia, while pattern II which has so far been reported as an aberrant transcript in varieties of malignant tumours might not be associated with leukaemogenesis.

Acid Anhydride Hydrolases↗