Biomedical subjects

Y J Chen

Publications and source records attributed to Y J Chen.

At least 37 records · Page 2Linked to original sources

PubMed2001

Cdc42, dynein, and dynactin regulate MTOC reorientation independent of Rho-regulated microtubule stabilization.

In migrating adherent cells such as fibroblasts and endothelial cells, the microtubule-organizing center (MTOC) reorients toward the leading edge [1-3]. MTOC reorientation repositions the Golgi toward the front of the cell [1] and contributes to directional migration [4]. The mechanism of MTOC reorientation and its relation to the formation of stabilized microtubules (MTs) in the leading edge, which occurs concomitantly with MTOC reorientation [3], is unknown. We show that serum and the serum lipid, lysophosphatidic acid (LPA), increased Cdc42 GTP levels and triggered MTOC reorientation in serum-starved wounded monolayers of 3T3 fibroblasts. Cdc42, but not Rho or Rac, was both sufficient and necessary for LPA-stimulated MTOC reorientation. MTOC reorientation was independent of Cdc42-induced changes in actin and was not blocked by cytochalasin D. Inhibition of dynein or dynactin blocked LPA- and Cdc42-stimulated MTOC reorientation. LPA also stimulates a Rho/mDia pathway that selectively stabilizes MTs in the leading edge [5, 6]; however, activators and inhibitors of MTOC reorientation and MT stabilization showed that each response was regulated independently. These results establish an LPA/Cdc42 signaling pathway that regulates MTOC reorientation in a dynein-dependent manner. MTOC reorientation and MT stabilization both act to polarize the MT array in migrating cells, yet these processes act independently and are regulated by separate Rho family GTPase-signaling pathways.

3T3 Cells↗

PubMed2001

Interstitial low-dose-rate brachytherapy as a salvage treatment for recurrent head-and-neck cancers: long-term results.

PURPOSE: Recurrent cancers of the head and neck within previously irradiated volume pose a serious therapeutic challenge. This study evaluates the response and long-term tumor control of recurrent head-and-neck cancers treated with interstitial low-dose-rate brachytherapy. METHODS AND MATERIALS: Between 1979 and 1997, 220 patients with prior radiation therapy with or without surgery for primary tumors of the head and neck were treated for recurrent disease or new primary tumors located within previously irradiated volumes. A majority of these patients had inoperable diseases with no distant metastasis. There were 136 male and 84 female patients, and median age was 56 years. All patients had previously received radiation therapy as the primary treatment or adjuvant treatment following surgery, with a median dose of 57.17 cGy (range, 39-74 cGy). The salvage brachytherapy consisted of a low-dose-rate, afterloading Iridium(192) implant, which delivered a median minimum tumor dose of 53 Gy to a mean tumor volume of 68.75 cm(2). Sixty percent of the patients also received interstitial hyperthermia, and 40% received concurrent chemotherapy as a radiosensitizing and potentiating agent. RESULTS: At a minimum 6-month follow-up, local tumor control was achieved in 77% (217/282) of the implanted tumor sites. The 2, 5, and 10-year disease-free actuarial survival rates for the entire group were 60%, 33%, and 22%, respectively. The overall survival rate for the entire group at 5 years was 21.7%. Moderate to severe late complications occurred in 27% of the patients. CONCLUSION: It has been estimated that approximately 20-30% of head-and-neck cancer patients undergoing definitive radiation therapy have recurrence within the initial treatment volume. Furthermore, similar percentages of patients who survive after successful irradiation develop new primary tumors of the head and neck or experience metastatic neck disease. A majority of such patients cannot be treated with a repeat course of external beam irradiation because of limited normal tissue tolerance, leading to unacceptable morbidity. However, in a select group of these patients, salvage interstitial brachytherapy may play an important role in providing patients with durable palliation and tumor control, as well as a chance for cure.

Adolescent↗

PubMed2001

The primase active site is on the outside of the hexameric bacteriophage T7 gene 4 helicase-primase ring.

Gene 4 of bacteriophage T7 encodes a protein (gp4) that can translocate along single-stranded DNA, couple the unwinding of duplex DNA with the hydrolysis of dTTP, and catalyze the synthesis of short RNA oligoribonucleotides for use as primers by T7 DNA polymerase. Electron microscopic studies have shown that gp4 forms hexameric rings, and X-ray crystal structures of the gp4 helicase domain and of the highly homologous RNA polymerase domain of Escherichia coli DnaG have been determined. Earlier biochemical studies have shown that when single-stranded DNA is bound to the hexameric ring, the primase domain remains accessible to free DNA. Given these results, a model was suggested in which the primase active site in the gp4 hexamer is located on the outside of the hexameric ring. We have used electron microscopy and single-particle image analysis to examine T7 gp4, and have determined that the primase active site is located on the outside of the hexameric ring, and therefore provide direct structural support for this model.

Amino Acid Sequence↗

PubMed2001

Humic acid induced growth retardation in a sertoli cell line, TM4.

Humic acid (HA) is a fluorescent deep brown organic, polymeric compound composed of phenolic acid. Intraperitoneal injection of HA in rats induced testicular morphological changes including degeneration of the seminiferous tubule, reduction in the number of Sertoli cells and spermatogonia, and a loss of spermatids. It was suggested that Sertoli cells may be involved in the progression of testicular atrophy. In this study, we used a mouse Sertoli cell Line, TM4, to investigate the effect of HA on Sertoli cells and the mechanism of the testicular atrophy induced by HA. We found that the cell growth of TM4 cells were reduced in 1 to 4 days of HA exposure. FACScan analysis of the DNA content of HA-treated TM4 cells revealed that there was no sub-G1 peak, indicating that the TM4 cells did not commit to the programmed cell death. However, a large proportion of TM4 cells were arrested at the G1 phase. The percentage of TM4 cells at the G1 phase increased from 36% to 84% after HA treatment for 4 days. Western blot assay of HA-treated TM4 cells showed that the expression of cyclin D1 protein decreased while the expression of p27kiP1 protein increased. These results suggest that HA-induced testicular atrophy is linked in part to an inhibitory effect on the growth of Sertoli cells. This model may be useful in investigation of environmental agents inducing testicular atrophy.

Animals↗

PubMed2001

Five-color-based high-information-content fingerprinting of bacterial artificial chromosome clones using type IIS restriction endonucleases.

We have developed a high-information-content fingerprinting (HICF) system for bacterial artificial chromosome (BAC) clones using a Type IIS restriction endonuclease, HgaI, paired with a Type II restriction endonuclease, RsaI. In the method described, unknown five-base overhangs generated with HgaI are partially or fully sequenced by modified fluorescent dideoxy terminators. Using an in-lane size standard labeled with a fifth dye, fragments are characterized by both the size and the sequence of its terminal one to five bases. The enhanced information content associated with this approach significantly increases the accuracy and efficiency of detecting shared fragments among BAC clones. We have compared data obtained from this method to predicted HICF patterns of 10 fully sequenced BACs. We have further applied HICF to 555 BAC clones to assemble contigs spanning 16p11.2 to 16p13.1 of human chromosome 16.

Chromosomes, Artificial, Bacterial↗

PubMed2001

Cloning, mapping, and characterization of the human sorbin and SH3 domain containing 1 (SORBS1) gene: a protein associated with c-Abl during insulin signaling in the hepatoma cell line Hep3B.

SH3P12/CAP/ponsin, a gene product with a sorbin homology domain and three consecutive SH3 domains in the carboxy-terminus, has been isolated from murine adipocytes and identified as an important adaptor during insulin signaling. Here we describe the cloning, mapping, and expression of the human homologue, termed SORBS1 (sorbin and SH3 domain containing 1). Multiple transcripts of this gene with different mRNA isoforms were observed among different tissues. Here we report 13 alternatively spliced exons, which were ascertained from the full-length cDNA cloned in adipose, liver, and skeletal muscle tissues. Among the major isoforms, the shortest, 2223-bp, open reading frame (ORF) encodes a protein with a predicted molecular weight of 81.5 kDa, while the longest, 3879-bp, ORF encodes a protein of about 142.2 kDa. This gene was mapped to human chromosome 10q23.3-q24.1, which is a candidate region for insulin resistance found in Pima Indians. In human hepatoma Hep3B cells, SORBS1 was partly dissociated from the insulin receptor complex and bound to c-Abl protein upon insulin stimulation. This interaction with c-Abl was through the third SH3 domain and a possible conformational change of SORBS1 induced by insulin. Our data suggest that c-Abl oncoprotein via SORBS1 might play a role in the insulin signaling pathway.

Amino Acid Sequence↗

PubMed2001

Enantiomeric recognition of chiral 3,3-bridged-1,1'-binaphthol dimer toward alpha-phenylethylamine and alpha-amino acid ester.

The 1,1'-binaphthol-based dimers with p-phenylenebis(2-ethynyl) spacer, (+)-6 and (+)-2, were synthesized as chiral host compounds. (1)H NMR, UV-vis, and fluorescent titration were used to evaluate the enantiomeric recognition abilities of the chiral host dimers toward the guest amine 7 and alpha-amino acid ester 8. The chiral BINOL-based dimers were found to have good enantiomeric recognition ability. The computer simulation of the host-guest complex molecules was carried out to describe the conformational changes of both naphthyl ring in the molecule of chiral host dimer after complexation with the guest molecule.

Alkynes↗

PubMed2001

Using dose addition to estimate cumulative risks from exposures to multiple chemicals.

The Food Quality Protection Act (FQPA) of 1996 requires the EPA to consider the cumulative risk from exposure to multiple chemicals that have a common mechanism of toxicity. Three methods, hazard index (HI), point-of-departure index (PODI), and toxicity equivalence factor (TEF), have commonly been considered to estimate the cumulative risk. These methods are based on estimates of ED(10) (point of departure) and reference doses from the dose-response functions of individual chemicals. They do not incorporate the actual dose-response function of the mixture from multiple chemical exposures. Dose addition is considered to be an appropriate approach to cumulative risk assessment because it assumes that the chemicals of interest act in accordance with a common mode of action (a similar action). This paper proposes a formal statistical procedure to estimate the cumulative risk by fitting the dose-response model of the mixture under dose addition. The relative potency between two chemicals is estimated directly from the joint dose response model of the mixture. An example data set of four drugs representing four chemicals is used to illustrate the proposed procedure and compare it to the HI, PODI, and TEF methods.

Dose-Response Relationship, Drug↗

PubMed2001

Image display for collision avoidance of radiation therapy: treatment planning.

Patient treatment in a medical linear accelerator is characterized by many angular and translational movements of the gantry and couch. The direction and orientation of each treatment beam is specified by a set of gantry, turntable, and collimator angles. It is possible that some selected treatment field configurations will result in gantry/couch or gantry/patient collisions that remain undetected during the treatment planning process. In this work, a digital camera has been used to record all the workable gantry/ patient set-up images, and a Windows programming language is used to edit and display these images on a personal computer for the treatment planner to screen the treatment plans. These graphical displays enable the planner to be aware of any potential collision hazards by an actual visualization of each selected gantry/turntable or gantry/patient angle configuration.

Accident Prevention↗

PubMed2001

The 11beta hydroxysteroid dehydrogenase 2 exists as an inactive dimer.

The 11beta-hydroxysteroid dehydrogenase types 1 and 2 enzymes (11beta-HSD1 and 11beta-HSD2), modulate glucocorticoid occupation of the mineralocorticoid and glucocorticoid receptors by interconverting corticosterone and cortisol to the inactive metabolites 11-dehydrocorticosterone and cortisone within the target cells. The NAD(+)-dependent 11-HSD 2 in the kidney inactivates corticosterone and cortisol, allowing aldosterone, which is not metabolized, access to the receptor. Studies of the kinetics of 11-HSD 2 activity in the rat kidney have produced inconsistent results. Western blots done in the absence of the reducing agent beta-mercaptoethanol showed two bands with approximate MW of 40 and 80 kDa. When beta-mercaptoethanol was used, only the 40 kDa was detected, indicating that under non-denaturing conditions a significant proportion of the 11beta-HSD 2 exists as a dimer. NAD(+)-dependent conversion of 3H-corticosterone by 20 microg of microsomal protein increased approximately 10 fold with the addition of 5 mM DTT concentration. NADP(+)-dependent activity with 20 microg of microsomal protein was very low and did not change significantly when using DTT. In the presence of DTT, the predominant 11-HSD activity in the rat kidney is NAD(+)-dependent with a K(m) of 15.1 nM, similar to that of the cloned and expressed enzyme. These data suggest that dimerization and subsequent enzyme inactivation occur when protocols promoting oxidation of this protein are used.

11-beta-Hydroxysteroid Dehydrogenase Type 2↗

PubMed2001

Frequent gain of copy number on the long arm of chromosome 3 in human cervical adenocarcinoma.

We analyzed genomic aberrations in 20 cervical adenocarcinomas by comparative genomic hybridization (CGH). Most tissue samples (85%) showed DNA copy number changes; gains were more common than losses. The most consistent region of chromosomal gain was mapped to chromosome arm 3q, found in 70% of the cases, with a minimal common region of 3q28-ter. Other recurrent amplifications of genetic material were detected on 17q (45%), 1p (30%), 1q (25%), and 11q (20%). High-level copy number increases were found in chromosomal regions 3q27-ter and 9pter-13. DNA losses were seldom observed, occurring primarily in underrepresented regions of chromosome arms 4q, 13q, and 18q. The presence of high-risk human papilloma virus genomes in the cervical adenocarcinoma samples was detected in 90% of the cases. However, there was no correlation between human papilloma virus type and the pattern of genomic changes. This study is the first report of CGH analysis in human cervical adenocarcinoma. Among the major genomic alterations, our results demonstrate the importance of DNA copy increases of chromosome arm 3q in the development of cervical adenocarcinoma and identify other amplified chromosomal regions that are also associated with cervical carcinogenesis.

Adenocarcinoma↗

PubMed2001

Effect of caffeic acid phenethyl ester, an antioxidant from propolis, on inducing apoptosis in human leukemic HL-60 cells.

Caffeic acid phenethyl ester (CAPE) is an active component isolated from propolis. The aim of this study was to investigate the mechanism of CAPE-induced apoptosis in human leukemic HL-60 cells. It was found that CAPE entered HL-60 cells very quickly and then inhibited their survival in a concentration- and time-dependent manner. CAPE induced characteristic DNA fragmentation and morphological changes typical of apoptosis in these cells. Estimation of the apoptotic percentage showed a time-dependent increase after CAPE (6 microg/mL) treatment (up to 66.7 +/- 2.0% at 72 h). Treatment with CAPE caused rapid activation of caspase-3 after 4 h, down-regulation of Bcl-2 expression after 6 h, and up-regulation of Bax expression after 16 h. These results suggest that CAPE is a potent apoptosis-inducing agent; its action is accompanied by activation of caspase-3, down-regulation of Bcl-2, and up-regulation of Bax in human leukemic HL-60 cells.

Antioxidants↗

PubMed2001

Three xanthones and a benzophenone from Garcinia mangostana.

Investigation of the constituents of Garcinia mangostana has led to the isolation of four new compounds: three minor xanthones, garcimangosone A (1), garcimangosone B (2), and garcimangosone C (3), and a benzophenone glucoside, garcimangosone D (4). The structures of these four compounds were established by spectral (NMR and MS) and chemical methods.

Benzophenones↗

PubMed2001

Taxane diterpenoids from the stem bark of Taxus mairei.

Three new 11(15-->1)-abeo-taxanes, taxumairols U-W (1-3), have been isolated from extracts of the stem bark of Formosan Taxus mairei. The structures of 1-3 were identified as 5alpha,7beta,9alpha,13alpha,20-pentaacetoxy-2alpha,10beta,15-trihydroxy-11(15-->1)-abeo-taxene, 5alpha,7beta,9alpha,20-tetraacetoxy-2alpha,10beta,13alpha,15-tetrahydroxy-11(15-->1)-abeo-taxene, and 2alpha,4alpha,7beta,10beta-tetraacetoxy-5beta,20-epoxy-9alpha,13alpha,15-trihydroxy-11(15-->1)-abeo-taxene, respectively, on the basis of 2D NMR techniques including COSY, HSQC, HMBC, and NOESY experiments as well as chemical reactions of compounds 1-3 to give 4 (5alpha,7beta,9alpha,10beta,13alpha,20-hexaacetoxy-2alpha,15-dihydroxy-11(15-->1)-abeo-taxene) and 5 (4alpha,7beta,10beta-triacetoxy-9alpha,13alpha-dibenzoxy-5beta,20-epoxy-2alpha,15-dihydroxy-11(15-->1)-abeo-taxene), which are also novel taxane derivatives. Taxumairols U (1) and V (2) exhibited significant cytotoxicities against human hepatoma tumor cells, while taxumairol W (3) was inactive.

Antineoplastic Agents, Phytogenic↗

PubMed2001

Phylogeography of Kandelia candel in East Asiatic mangroves based on nucleotide variation of chloroplast and mitochondrial DNAs.

Vivipary with precocious seedlings in mangrove plants was thought to be a hindrance to long-range dispersal. To examine the extent of seedling dispersal across oceans, we investigated the phylogeny and genetic structure among East Asiatic populations of Kandelia candel based on organelle DNAs. In total, three, 28 and seven haplotypes of the chloroplast DNA (cpDNA) atpB-rbcL spacer, cpDNA trnL-trnF spacer, and mitochondrial DNA (mtDNA) internal transcribed spacer (ITS) were identified, respectively, from 202 individuals. Three data sets suggested consistent phylogenies recovering two differentiated lineages corresponding to geographical regions, i.e. northern South-China-Sea + East-China-Sea region and southern South-China-Sea region (Sarawak). Phylogenetically, the Sarawak population was closely related to the Ranong population of western Peninsula Malaysia instead of other South-China-Sea populations, indicating its possible origin from the Indian Ocean Rim. No geographical subdivision was detected within the northern geographical region. An analysis of molecular variance (AMOVA) revealed low levels of genetic differentiation between and within mainland and island populations (phiCT = 0.015, phiSC = 0.037), indicating conspicuous long-distance seedling dispersal across oceans. Significant linkage disequilibrium excluded the possibility of recurrent homoplasious mutations as the major force causing phylogenetic discrepancy between mtDNA and the trnL-trnF spacer within the northern region. Instead, relative ages of alleles contributed to non-random chlorotype-mitotype associations and tree inconsistency. Widespread distribution and random associations (chi2 = 0.822, P = 0.189) of eight hypothetical ancestral cytotypes indicated the panmixis of populations of the northern geographical region as a whole. In contrast, rare and recently evolved alleles were restricted to marginal populations, revealing some preferential directional migration.

Alleles↗

PubMed2001

Predicting factors of malignancy in dermatomyositis and polymyositis: a case-control study.

BACKGROUND: An association between dermatomyositis (DM)/polymyositis (PM) and malignancies has been widely reported in the literature. The validity of extensive evaluation for malignancies in those patients has also been questioned for decades. Only limited papers regarding the signs of malignancy and the prognostic factors in DM/PM have been reported. OBJECTIVES: To define the potential risk factors of concomitant neoplastic diseases in patients diagnosed as having DM/PM. METHODS: From 1 April 1983 to 30 June 1999, 147 patients were diagnosed as having probable or definite DM/PM at the Veterans General Hospital, Taichung, Taiwan. We excluded four patients who had preceding neoplastic diseases diagnosed before DM/PM, then retrospectively reviewed the data of the remaining 143 patients and subgrouped the cases as four main types: primary idiopathic DM, primary idiopathic PM, juvenile DM/PM and amyopathic DM (ADM). We next performed univariate analysis using logistic regression to evaluate the possible predictive factors for malignancies, such as mean age at onset, gender, manifestations at onset, association with other connective tissue diseases, initial skin presentations, complications and laboratory data. Then we chose the significant factors for multivariate analysis by logistic regression, to determine the independent risk factors of malignancies in DM/PM patients. RESULTS: Among the 143 patients, DM was the most common type (64%), followed by ADM (14%), juvenile DM/PM (13%) and PM (10%). The mean age at onset overall was 42.4 years. Other connective tissue diseases were present in 22% of all patients, especially PM (50%) and juvenile DM/PM patients (28%). Internal malignancies were present in 13% of patients, and most were associated with DM. Nasopharyngeal carcinomas (NPCs) were the most common tumours. Patients with primary idiopathic DM, with an older age at onset, higher serum creatine phosphokinase levels and male gender, had more chance of developing concomitant malignancies. Those associated with complications, especially interstitial lung diseases, had a lower risk of associated neoplasia. In multivariate analysis, an older age at onset (odds ratio 9.10) and male gender (odds ratio 4.06) were associated with greater risk of developing malignancies. CONCLUSIONS: The two independent predictive factors for malignancy (P < 0.05) in patients with DM/PM were an older age at onset (> 45 years) and male gender. The primary idiopathic DM group was shown to have higher risk of developing internal malignancies, especially NPC. However, this was not identified as an independent predictive factor for concomitant neoplastic diseases in multivariate analysis. In addition, patients who had the complication of interstitial lung disease had a significantly lower frequency of malignancies (P < 0.001).

Adult↗

PubMed2001

Mechanisms of transition between double paroxysmal supraventricular tachycardias.

INTRODUCTION: Coexistence of double tachycardias in one patient has been infrequently reported. Furthermore, the mechanisms of transition between double paroxysmal supraventricular tachycardias have not been well studied. METHODS AND RESULTS: Thirty-five patients with two paroxysmal supraventricular tachycardias were studied. Group IA consisted of 3 patients with spontaneous transition between AV reciprocating tachycardia (AVRT) and AV nodal reentrant tachycardia (AVNRT). Group IB consisted of 13 patients without spontaneous transition between AVRT and AVNRT. Group IIA consisted of 5 patients with spontaneous transition between AVNRT and atrial tachycardia (AT). Group IIB consisted of 14 patients without spontaneous transition between AVNRT and AT. The absolute values of differences between the two tachycardia cycle lengths were significantly smaller in patients with than in those without transition between the two tachycardias (25+/-8 msec vs 90+/-46 msec, P < 0.05, IA vs IB; 21+/-25 msec vs 99+/-57 msec, P < 0.01, IIA vs IIB). The cutoff point of 25 msec had 80% positive predictive value for transition between the two tachycardias. Transition between two tachycardias occurred due to a spontaneous premature atrial complex (30%), conduction block at one limb of tachycardia (20%), or tachycardia-induced tachycardia (50%). Absence of transition between two tachycardias might be explained by the absence of a spontaneous premature atrial complex, longer cycle length of the first tachycardia, larger difference between two tachycardia cycle lengths, or induction of each tachycardia under different situations. CONCLUSION: Double supraventricular tachycardias with similar tachycardia cycle lengths are vulnerable to transition between different tachycardias.

Adolescent↗

PubMed2001

The inhibitory effects of ginsenosides on protein tyrosine kinase activated by hypoxia/reoxygenation in cultured human umbilical vein endothelial cells.

27 individual ginsenosides and aglycones, together with five extracts from ginseng roots, ginseng leaves, American ginseng roots, American ginseng leaves and non-saponin fraction from roots of Panax ginseng, were tested for their effects on protein tyrosine kinase (PTK) activation induced by an in vitro hypoxia/reoxygenation (H/R) model in cultured human umbilical vein endothelial cells (HUVEC). The results indicated that ginsenoside-Rb1 (3), -Rd (7), -Ra1 (1) and -Ro (27) showed significant inhibitory effects on PTK activation induced by H/R. Dose-response experiments revealed that ginsenoside-Rb1 was the most active compound and it completely blocked PTK activation at a wide range of concentrations. Most protopanaxadiol-type ginsenosides and some protopanaxatriol-type saponins also showed significant effects on PTK activation. However, the crude extracts did not protect against H/R-induced PTK activation.

Cell Hypoxia↗