Biomedical subjects

Z Yang

Publications and source records attributed to Z Yang.

At least 361 records · Page 20Linked to original sources

PubMed1999

Estrogen modulation of apolipoprotein(a) expression. Identification of a regulatory element.

Elevated plasma levels of the lipoprotein particle Lp(a) are a major risk factor for cardiovascular disease. Lp(a) plasma levels are determined by the level of expression of its characteristic protein component, apo(a). Apo(a) expression is modulated by several hormones, of which estrogens are the best known. The chromosomal region responsible for estrogen response was identified within an apo(a) enhancer located at approximately 26 kilobases from the apo(a) promoter. Although the estrogen-responsive unit contains a potential estrogen response element, binding of estrogen receptor-alpha to DNA was not necessary. The receptor, activated by bound estradiol, interacts through its transactivation domains with a transcription factor necessary for the function of the enhancer, preventing its binding to DNA.

Apolipoproteins A↗

PubMed1999

Identification of a critical motif responsible for gating of Kir2.3 channel by intracellular protons.

Protons are involved in gating Kir2.3. To identify the molecular motif in the Kir2.3 channel protein that is responsible for this process, experiments were performed using wild-type and mutated Kir2. 3 and Kir2.1. CO2 and low pHi strongly inhibited wild-type Kir2.3 but not Kir2.1 in whole cell voltage clamp and excised inside-out patches. This CO2/pH sensitivity was completely eliminated in a mutant Kir2.3 in which the N terminus was substituted with that in Kir2.1, whereas a similar replacement of its C terminus had no effect. Site-specific mutations of all titratable residues in the N terminus, however, did not change the CO2/pH sensitivity. Using several chimeras generated systematically in the N terminus, a 10-residue motif near the M1 region was identified in which only three amino acids are different between Kir2.3 and Kir2.1. Mutations of these residues, especially Thr53, dramatically reduced the pH sensitivity of Kir2.3. Introducing these residues or even a single threonine to the corresponding positions of Kir2.1 made the mutant channel pH-sensitive. Thus, a critical motif responsible for gating Kir2.3 by protons was identified in the N terminus, which contained about 10 residues centered by Thr53.

Amino Acid Sequence↗

PubMed1999

Modular variations of the human major histocompatibility complex class III genes for serine/threonine kinase RP, complement component C4, steroid 21-hydroxylase CYP21, and tenascin TNX (the RCCX module). A mechanism for gene deletions and disease associations.

The frequent variations of human complement component C4 gene size and gene numbers, plus the extensive polymorphism of the proteins, render C4 an excellent marker for major histocompatibility complex disease associations. As shown by definitive RFLPs, the tandemly arranged genes RP, C4, CYP21, and TNX are duplicated together as a discrete genetic unit termed the RCCX module. Duplications of the RCCX modules occurred by the addition of genomic fragments containing a long (L) or a short (S) C4 gene, a CYP21A or a CYP21B gene, and the gene fragments TNXA and RP2. Four major RCCX structures with bimodular L-L, bimodular L-S, monomodular L, and monomodular S are present in the Caucasian population. These modules are readily detectable by TaqI RFLPs. The RCCX modular variations appear to be a root cause for the acquisition of deleterious mutations from pseudogenes or gene segments in the RCCX to their corresponding functional genes. In a patient with congenital adrenal hyperplasia, we discovered a TNXB-TNXA recombinant with the deletion of RP2-C4B-CYP21B. Elucidation of the DNA sequence for the recombination breakpoint region and sequence analyses yielded definitive proof for an unequal crossover between TNXA from a bimodular chromosome and TNXB from a monomodular chromosome.

Adrenal Hyperplasia, Congenital↗

PubMed1999

Riboflavin-mediated delivery of a macromolecule into cultured human cells.

Cell surface receptors for the vitamins folic acid and biotin have been previously reported to mediate the endocytosis of vitamin-conjugated macromolecules into cultured cells. To evaluate whether a similar uptake pathway for riboflavin-conjugated macromolecules might exist, riboflavin was covalently linked to bovine serum albumin (BSA) via the vitamin's ribityl side chain, and uptake of the protein by cultured human cells was examined. Whereas unconjugated BSA was not internalized by KB, A549, SK-LU-1 or SK-OV cells, riboflavin-conjugated BSA was readily internalized (>106 molecules/cell). Analysis of the uptake pathway revealed that the riboflavin-BSA conjugate likely docks on cells at a carrier/transport protein that is distinct from the uptake pathway for free riboflavin and then enters via normal membrane cycling. Evidence for this contention is: (i) the internalized conjugate accumulates in endosomal compartments, (ii) uptake into cells is halted at temperatures near 0 degreesC where membrane trafficking is abrogated, (iii) cell association is inhibited by unlabeled riboflavin-BSA, but not by free riboflavin, and (iv) cellular uptake of [3H]riboflavin is only partially inhibited by riboflavin-BSA. Regardless of the pathway of internalization, these data demonstrate that riboflavin conjugation can facilitate protein entry into human cells in culture.

Binding Sites↗

PubMed1999

New mutations, polymorphisms, and rare variants in the ATM gene detected by a novel SSCP strategy.

The gene for ataxia-telangiectasia, ATM, spans about 150 kb of genomic DNA. ATM mutations are found along the entire gene, with no evidence of a mutational hot spot. Using DNA as the starting material, we screened the ATM gene in 92 A-T patients, using an optimized single-strand conformation polymorphism (SSCP) technique that detected all previously known mutations in the polymerase chain reaction (PCR) segments being analyzed. To expedite screening, we sequentially loaded the SSCP gels with three different sets of PCR products that were pretested to avoid overlapping patterns. Many of the DNA changes we detected were intragenic polymorphisms. Of an expected 177 unknown mutations, we detected approximately 70%, mostly protein truncating mutations (that would have been detectable by protein truncation testing if RNA starting material had been available). Mutations have now been defined for every exon of the ATM gene. Herein, we present 35 new mutations and 34 new intragenic polymorphisms or rare variants within the ATM gene. This is the most comprehensive compilation of ATM polymorphisms assembled to date. Defining polymorphic sites as well as mutations in the ATM gene will be of great importance in designing automated methods for detecting mutations.

Ataxia Telangiectasia↗

PubMed1999

Measurement of retinal thickness in normal subjects with retinal thickness analyzer.

The retinal thickness at posterior pole of normal subjects was measured by using retinal thickness analyzer (RTA) to determine the values of retinal thickness and to establish map of retinal thickness in normal subjects. The retina of 6 mm x 6 mm in size (approximately 20 degrees, centered on the macula) at the posterior pole was scanned by using RTA to obtain images of 116 normal eyes of 77 cases of various age group. The images were processed by a computer to obtain the retinal thickness values and the thickness map of this location. The data were analyzed with SAS software package. The mean retinal thickness was 171.77 +/- 26.13 microns with no significant difference among the various age groups (P > 0.05). The thickness maps of the retina of 6 mm x 6 mm size at the posterior pole around the macula rendered a "U"-shaped pattern, extending from the disc to the superior and inferior of the fovea. The retina was found to be thin at temporal side of the fovea, with the thinnest area being at the macula central fovea. The U-shaped pattern of the retinal thickness maps was well in agreement with the topography of the ganglion cells and the retinal nerve fibers in human retina. The measurement of the retinal thickness by RTA reflected the changes in the layers of ganglion cells and the retinal nerve fiber. Each scanning session of RTA examination can yield multiple optical cross-section images of the retina and obtain retinal thickness maps of posterior pole of living eyes.

Humans↗

PubMed1999

Histological measurement of human retinal thickness.

The fresh eye balls from the accidental death adults were placed on low temperature slicer to cut into slices. The fresh sections was subjected to the direct measurement of retinal thickness by using CMIAS multi-function real color pathologic imaging analysis system. The results showed that in the total of 6 eye balls measured, the mean retinal thickness was 310.92 +/- 34.14 microns. It was concluded that it was simple and had high confidence for the fresh eye ball low temperature frozen sections to directly measure the retinal thickness, which provided a histological method for the measurement of retinal thickness and the reference of retinal thickness of Chinese adults.

Anthropometry↗

PubMed1999

Studies on hepatocyte apoptosis, proliferation and oncogene c-fos expression in carbon tetrachloride-induced cirrhotic rat liver.

To investigate the significance of hepatocyte apoptosis, proliferation and oncogene c-fos expression in carbon tetrachloride (CCl4)-induced cirrhotic rat liver. Rat cirrhosis was induced by subcutaneous injection of 50% (v:v 1:1) CCl4. Hepatocyte apoptosis, proliferation and oncogene c-fos expression were examined with TUNEL, PCNA and c-fos immunohistochemical methods in control group and treatment group 72 h, 5, 7, 11 and 15 weeks after CCl4 induction. Hepatocyte apoptosis was rarely seen in control rat liver. The hepatocyte apoptosis was obviously increased 72 h after treatment. Fifteen weeks after treatment, the apoptosis was still more obvious in treatment group than that in controls. PCNA was constantly expressed in CCl4 group, with highest level at middle phase. C-fos was positive 7 and 11 weeks after CCl4 treatment. The results suggest that: 1) apoptosis is involved in rat liver damage at the early phase in CCl4-induced injury, and the process can alleviate nodule reconstruction or eradicate potentially mutational hepatocytes at the later phase; 2) hepatocytes constantly proliferate in CCl4-induced rat liver cirrhosis, especially at the middle phase; 3) c-fos might modulate hepatocyte proliferation in CCl4-induced rat liver cirrhosis.

Animals↗

PubMed1999

Estimation of the transition/transversion rate bias and species sampling.

The transition/transversion (ti/tv) rate ratios are estimated by pairwise sequence comparison and joint likelihood analysis using mitochondrial cytochrome b genes of 28 primate species, representing both the Strepsirrhini (lemurs and lories) and the Anthropoidea (monkeys, apes, and humans). Pairwise comparison reveals a strong negative correlation between estimates of the ti/tv ratio and the sequence distance, even when both are corrected for multiple substitutions. The maximum-likelihood estimate of the ti/tv ratio changes with the species included in the analysis. The ti/tv bias within the lemuriform taxa is found to be as strong as in the anthropoids, in contradiction to an earlier study which sampled only one lemuriform. Simulations show the surprising result that both the pairwise correction method and the joint likelihood analysis tend to overcorrect for multiple substitutions and overestimate the ti/tv ratio, especially at low sequence divergence. The bias, however, is not large enough to account for the observed patterns. Nucleotide frequency biases, variation of substitution rates among sites, and different evolutionary dynamics at the three codon positions can be ruled out as possible causes. The likelihood-ratio test suggests that the ti/tv rate ratios may be variable among evolutionary lineages. Without any biological evidence for such a variation, however, we are left with no plausible explanations for the observed patterns other than a possible saturation effect due to the unrealistic nature of the model assumed.

Algorithms↗

PubMed1999

Molecular cloning and characterization of Ct-PKAR, a gene encoding the regulatory subunit of cAMP-dependent protein kinase in Colletotrichum trifolii.

Colletotrichum trifolii is a plant pathogenic fungus causing alfalfa anthracnose. Prepenetration development, including conidial germination and appressorial formation, are requisite for successful infection. Pharmacological data from our laboratory indicated a role for a cAMP-dependent protein kinase (PKA) pathway during these early morphogenic transitions. Thus, the cloning and characterization of the genes for PKA catalytic and regulatory subunits were undertaken to more precisely determine the function of PKA during C. trifolii pathogenic growth and development. In this report, the cloning, sequencing, and partial characterization of the gene encoding the regulatory subunit of cAMP-dependent protein kinase (Ct-PKAR) is described. An open reading frame of 1,212 bp containing 404 predicted amino acid residues was identified. Database analysis revealed that the deduced amino acid sequence of Ct-PKAR shares considerable similarity with that of PKA regulatory subunits in other organisms, particularly in the conserved regions. Furthermore, the Ct-PKAR protein is classified as a type II regulatory subunit based on the presence of the hall-mark autophosphorylation site. Southern blot analysis indicated that Ct-PKAR is a single-copy gene. Northern blot analysis showed that the expression of Ct-PKAR is developmentally regulated. Ct-PKAR was shown to be a functional regulatory subunit of PKA by complementating the Neurospora crassa mcb mutant, which has a temperature-sensitive mutation in the regulatory subunit of PKA.

Amino Acid Sequence↗

PubMed1999

Effects of early eschar excision en masse at one operation for prevention and treatment of organ dysfunction in severely burned patients.

We sought to determine whether early eschar excision en masse (EEE) at one operation would be effective in the prevention and treatment of postburn organ dysfunction (OD) and multiple organ dysfunction syndrome (MODS). A total of 60 patients, with total body surface burned area over 35% and a third degree burn area over 20% were studied and divided into two groups, the EEE group (35 cases) and the group treated with repeated escharectomies by stages (repeated escharectomy group, 25 cases). Other than the different operations undertaken, the patients in both groups received identical conventional treatment. Before, during, and after operation the hemodynamic and blood gas indices, plasma levels of endotoxin and tumor necrosis factor (TNF), and the injurious effects of burn patients' sera on endothelial cells in vitro were determined in patients of the EEE group. The incidence of OD and MODS was decreased significantly (11.4%) in patients of the EEE group, and the cure rate increased greatly (85.7%). The cardiac output dropped to 77.8% of its preoperative level at the end of escharectomy but began to rise at 2 hours and returned to its baseline levels at 24 hours after operation. Plasma levels of endotoxin and TNF and levels of lactic dehydrogenase and 6-keto-prostaglandin F(1|ga) in the endothelial cell culture media were all reduced profoundly. The cultured endothelial cells maintained their original morphology. The findings substantiate the hypothesis that eschar excision en masse at one operation is feasible and effective in preventing and treating early postburn OD and MODS, mainly by alleviating systemic inflammatory response syndrome and endothelial cell injury.

Adult↗

PubMed1999

Small peripheral carcinomas of the lung: thin-section CT and pathologic correlation.

The aim of this study was to clarify the thin-section CT features of small peripheral carcinomas of the lung on the basis of pathologic findings of tumor growth patterns. Thin-section CT and pathologic correlation was evaluated in 19 patients with surgically verified small peripheral carcinomas of the lung ( < 20 mm in size) that had been detected in a screening trial for lung cancer using spiral CT. Four thin-section CT types of nodules were observed: (a) type L1 (4 of 19, 21 %), a fairly well-defined nodule with ground-glass attenuation, corresponding to tumor lepidic growth without alveolar collapse; (b) type L2 (4 of 19, 21 %), a partly lobulated nodule with a low but inhomogeneous attenuation, corresponding to tumor lepidic growth with scattered foci of alveolar collapse; (c) type L3 (4 of 19, 21 %), an ill-defined nodule with an irregularly shaped higher-density central zone in a ground-glass attenuation peripheral zone, accompanied by convergence of the bronchovascular structures from the surrounding lung parenchyma, which corresponded to desmoplastic response in the central zone and to tumor lepidic growth in the peripheral zone; and (d) type H (7 of 19, 37 %), a well-defined nodule with a solid homogeneous attenuation, corresponding to tumor hilic growth. Thin-section CT features of small peripheral carcinomas of the lung can be classified into four types, based on the density distribution of the tumor, which reflect the histologic findings.

Adenocarcinoma↗

PubMed1999

The influence of the paraventricular nucleus on baroreceptor dependent caudal ventrolateral medullary neurones of the rat.

The question of whether neurones in the paraventricular nucleus (PVN) of the hypothalamus have an influence on barosensitive vasomotor neurones of the caudal ventrolateral medulla (CVL) was addressed in this study using anaesthetised rats. Extracellular microelectrode recordings were made from 27 vasomotor neurones in the CVL, identified by their cardiac cycle-related probability of discharge, by the increase in activity in response to an increase in arterial blood pressure produced by i.v. phenylephrine and by the decrease in activity in response to a decrease in blood pressure produced by i.v. nitroprusside. Activation of neurones at different sites in the PVN with a microinjection of d,l-homocysteic acid (DLH) activated 12 CVL neurones and inhibited 6 CVL neurones. In four CVL units single-shock electrical stimulation at a PVN pressor site, first identified with DLH, elicited a synaptic action potential with a latency of 29+/-0.3 ms. It is concluded that PVN neurones can influence the CVL vasomotor neurones directly. This could be one means by which PVN-depressor and sympatho-inhibitory effects are produced.

Anesthesia↗

PubMed1999

Chromosome 9 monosomy by fluorescence in situ hybridization of bladder irrigation specimens is predictive of tumor recurrence.

PURPOSE: Bladder irrigation specimens are effective for sampling the urothelium for detection of recurrent bladder cancer. These specimens can be evaluated by cytology or quantitative techniques. Proliferation and ploidy changes are readily detected using deoxyribonucleic acid (DNA) cytometry. Tumor associated chromosomal aberrations can be assayed using fluorescence in situ hybridization (FISH). The prognostic values of DNA cytometry, and chromosome 9 and 9p21 FISH on exfoliated cells from bladder irrigation specimens from 61 bladder cancer patients were evaluated. MATERIALS AND METHODS: A total of 61 consecutive bladder irrigation specimens were obtained during cystoscopy. DNA cytometry was performed by image analysis. FISH was performed using a centromeric chromosome 9 probe and a cosmid contig (COSp16) probe to the CDKN2A/p16 tumor suppressor region of 9p21. Proportional hazards regression analysis was performed with statistical software to test the predictor variables of initial patient status (presence of tumor), COSp16 fraction (the proportion of COSp16 signals relative to centromeric probe signals), monosomic and hyperdisomic fractions of the chromosome 9 probe, and hyperdiploid fraction from DNA cytometry. Median time to recurrence was calculated using statistical software survival analysis. RESULTS: Initial patient status and monosomy of chromosome 9 were predictive of bladder cancer recurrence (p <0.0001 and p = 0.0073, respectively). The 11 patients with chromosome 9 monosomy fractions greater than 15% and a visible tumor had a median time to recurrence of 105 days. In contrast, only 8 of the 25 patients with chromosome 9 monosomy fractions less than 15% and no visible tumor had recurrence within 560 days. Median time to recurrence was 185 days for 6 patients with chromosome 9 monosomy fractions greater than 15% and no visible tumor, and 225 for 19 with chromosome 9 monosomy fractions less than 15% and a visible tumor. Hyperdiploid fraction was suggestive but not predictive of bladder cancer recurrence (p = 0.078). COSp16 and hyperdisomic fractions were not predictive of bladder tumor recurrence (p = 0.11 and p = 0.30, respectively). CONCLUSIONS: Chromosome 9 monosomy by FISH was predictive of bladder tumor recurrence. Furthermore, our findings support the hypothesis that losses of tumor suppressor genes on chromosome 9 are critical, perhaps initiating genetic events in bladder cancer.

Adult↗

PubMed1999

Hydrogen peroxide-induced endothelium-dependent relaxation of rat aorta involvement of Ca2+ and other cellular metabolites.

In phenylephrine-precontracted rings, H2O2 produced an endothelium-dependent relaxation at concentrations of 4.4 x 10(-7) to approximately 4.4 x 10(-5) M. Removal of extracellular Ca2+ ([Ca2+]0) markedly attenuated the relaxant effects of H2O2. Complete inhibition of the H2O2 relaxant action was obtained after buffering intracellular Ca2+ ([Ca2+]i) in endothelial cells, with 10 microM acetyl methyl ester of bis (o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). These relaxant effects of H2O2 were nearly abolished by 15 x 10(-5)M N(G)-monomethyl-arginine (L-NMMA) or 5 x 10(-5) M N(G)-nitro-L-arginine (L-NAME) and were attenuated markedly by the presence of either 10(-6) M Fe2+, 10(-6) M Fe3+, or 5 x 10(-6) M methylene blue. These inhibitory effects of L-NMMA or L-NAME could be reversed partly by 5 x 10(-5) M L-arginine. These Fe(2+)- and Fe(3+)-induced inhibitions of H2O2-stimulated relaxation were reduced significantly by either 1.0 mM deferoxamine (a Fe2+ chelator) or 100 microM dimethyl sulfoxide (DMSO). In addition, 17-octadecynoic acid (2.5 microM) or proadifen (10 microM) (both antagonists of cytochrome P450 metabolism of fatty acids) markedly decreased the H2O2 relaxant effects. Proadifen (10 microM) produced concentration-dependent impairment of vasorelaxation to acetylcholine. A variety of amine antagonists and a cyclo-oxygenase inhibitor all fail to interfere with or attenuate the H2O2-induced relaxations. Our observations suggest that, at suitable pathophysiologic concentrations, H2O2 could induce release of an endothelium-derived relaxing factor, probably nitric oxide, from endothelial cells. The H2O2 relaxant effects are clearly Ca(2+)-dependent and require formation of cyclic guanosine monophosphate (cGMP). These vasorelaxing effects of H2O2 appear to be induced by H2O2 itself. Hydrogen peroxide may stimulate production of some unknown metabolites metabolized by cytochrome P450-dependent enzymes.

Animals↗

PubMed1999

Predicting a future lifetime through Box-Cox transformation.

In predicting a future lifetime based on a sample of past lifetimes, the Box-Cox transformation method provides a simple and unified procedure that is shown in this article to meet or often outperform the corresponding frequentist solution in terms of coverage probability and average length of prediction intervals. Kullback-Leibler information and second-order asymptotic expansion are used to justify the Box-Cox procedure. Extensive Monte Carlo simulations are also performed to evaluate the small sample behavior of the procedure. Certain popular lifetime distributions, such as Weibull, inverse Gaussian and Birnbaum-Saunders are served as illustrative examples. One important advantage of the Box-Cox procedure lies in its easy extension to linear model predictions where the exact frequentist solutions are often not available.

Equipment Failure↗

PubMed1999

High throughput fluorescent CE-SSCP SNP genotyping.

Large numbers of single nucleotide polymorphisms (SNPs) are being identified by several laboratories for the purpose of developing dense genetic maps. Single-strand conformation polymorphism (SSCP) analysis has been widely used as a method for detecting novel sequence variations in PCR products. Differences in migration of single-stranded DNA can be used not only to find mutations, but to genotype SNPs in large sample populations. Using PCR with fluorescent labeling and automated capillary electrophoresis SSCP (CE-SSCP), we have developed a panel of 15 functional candidate SNPs. With an automated single capillary instrument, relatively rapid and low cost CE-SSCP SNP genotyping using currently available technology is feasible for 135 000 genotypes per year. With parallel multiple array capillary electrophoresis, more genotypes per year may be attainable.

Automation↗

PubMed1999

Diterpene synthesis in Stevia rebaudiana: recruitment and up-regulation of key enzymes from the gibberellin biosynthetic pathway.

Stevia rebaudiana Bertoni leaves accumulate a mixture of at least eight different glycosides derived from the tetracyclic diterpene steviol. These natural products taste intensely sweet and have similar biosynthetic origins to those of gibberellic acid (GA). The initial steps leading to the formation of GA result from the two-step cyclization of geranylgeranyl diphosphate (GGDP) to (-)-kaurene via the action of two terpene cyclases (-)-copalyl diphosphate synthase (CPS) and (-)-kaurene synthase (KS). Steviol biosynthesis probably uses the same mechanism although the genes and enzymes from S. rebaudiana that are involved in the cyclization of GGDP have not been characterized. We have isolated both the CPS and KS genes from S. rebaudiana and found that recombinant CPS and KS were catalytically active, suggesting that the CPS and KS genes participate in steviol biosynthesis. The genes coding for CPS and KS are usually present in single copies in most plant species and their expression is normally low and limited to rapidly growing tissues. The KS gene has been duplicated in the S. rebaudiana genome and both the KS and CPS genes are highly expressed in mature leaves, a pattern opposite to that found with GA biosynthesis. This pattern may, at least in part, lead to temporal and spatial separation of GA and steviol biosynthesis and probably helps to prevent over-expression from interfering with normal GA metabolism. Our results show that CPS and KS are part of the steviol glycoside biosynthetic pathway and that Stevia rebaudiana has recruited two genes to secondary metabolism from a highly regulated pathway involved in hormone biosynthesis.

Alkyl and Aryl Transferases↗