Biomedical subjects

S Zhao

Publications and source records attributed to S Zhao.

At least 217 records · Page 12Linked to original sources

PubMed1999

Cloning and mapping of the XRN2 gene to human chromosome 20p11.1-p11.2.

The Dhm1 gene is the mouse homologue of the dhp1(+) gene of Schizosaccharomyces pombe, which is involved in homologous recombination and RNA metabolism, such as RNA synthesis and RNA trafficking, in S. pombe. Complementation analysis showed the Dhm1 gene on a multicopy plasmid can rescue the temperature-sensitivity mutation of dhp1(ts) and the lethality of the dhp1 null mutation. This finding suggests that Dhm1 has a function in mouse similar to that of dhp1(+). The human homologue of this gene, XRN2, has been identified. A 3.6-kb transcript of XRN2 was detected in 16 tissues examined and was more abundant in testis. By radiation hybrid panel mapping, the XRN2 gene was localized to chromosome 20p11.1-p11.2 between markers D20S180 and D20S871.

Adult↗

PubMed1999

Mechanism of transfer of the methyl group from (6S)-methyltetrahydrofolate to the corrinoid/iron-sulfur protein catalyzed by the methyltransferase from Clostridium thermoaceticum: a key step in the Wood-Ljungdahl pathway of acetyl-CoA synthesis.

The methyltetrahydrofolate:corrinoid/iron-sulfur protein methyltransferase (MeTr) from Clostridium thermoaceticum catalyzes transfer of the N5-methyl group from (6S)-methyltetrahydrofolate (CH3-H4folate) to the cobalt center of a corrinoid/iron-sulfur protein (CFeSP), forming methylcob(III)amide and H4folate. This reaction initiates the unusual biological organometallic reaction sequence that constitutes the Wood-Ljungdahl or reductive acetyl-CoA pathway. The present paper describes the use of steady-state, product inhibition, single-turnover, and kinetic simulation experiments to elucidate the mechanism of the MeTr-catalyzed reaction. These experiments complement those presented in the companion paper in which binding and protonation of CH3-H4folate are studied by spectroscopic methods [Seravalli, J., Shoemaker, R. K., Sudbeck, M. J., and Ragsdale, S. W. (1999) Biochemistry 38, 5736-5745]. Our results indicate that a pH-dependent conformational change is required for methyl transfer in the forward and reverse directions; however, this step is not rate-limiting. CH3-H4folate and the CFeSP [in the cob(I)amide state] bind randomly and independently to form a ternary complex. Kinetic simulation studies indicate that CH3-H4folate binds to MeTr in the unprotonated form and then undergoes rapid protonation. This protonation enhances the electrophilicity of the methyl group, in agreement with a 10-fold increase in the pKa at N5 of CH3-H4folate. Next, the Co(I)-CFeSP attacks the methyl group in a rate-limiting SN2 reaction to form methylcob(III)amide. Finally, the products randomly dissociate. The following steady-state constants were obtained: kcat = 14.7 +/- 1.7 s-1, Km of the CFeSP = 12 +/- 4 microM, and Km of (6S)-CH3-H4folate = 2.0 +/- 0.3 microM. We assigned the rate constants for the elementary reaction steps by performing steady-state and pre-steady-state kinetic studies at different pH values and by kinetic simulations.

Acetyl Coenzyme A↗

PubMed1999

[Study of NAIP gene in spinal muscular atrophy]

OBJECTIVE: Investigating the correlation between the genotype and spinal muscular atrophy(SMA) clinical phenotype. METHODS: Neuronal apoptosis inhibitory protein(NAIP) gene analysis was performed by PCR amplification of exon 5 in 13 unrelated SMA patients with deletions of SMN gene. RESULTS: Two Type-I patients(2/5, 40%) lacked the NAIP exon 5. CONCLUSION: The results suggest a possible correlation between NAIP gene deletion and the disease severity of SMA.

Journal Article↗

PubMed1999

Phosphorylase phosphatase: new horizons for an old enzyme.

Protein phosphatase-1, originally studied as phosphorylase phosphatase, is one of the major ser/thr protein phosphatases. It has a long history and a complex enzymology. It consists of a catalytic subunit of 37 kDa, which is bound to a number of different regulatory or targeting subunits. These are believed to restrict its activity to its immediate microenvironment and thus define its specificity, as well as acting to regulate phosphatase activity. The existence of multiple protein phosphatase-1 binding proteins provides the mechanism whereby phosphatase-1 activity can be involved in a diverse range of cellular functions, and reflects a novel strategy for its evolutionary development.

Amino Acid Sequence↗

PubMed1999

Expression and function of leptin receptor isoforms in myeloid leukemia and myelodysplastic syndromes: proliferative and anti-apoptotic activities.

The receptor for the gene product of the obesity gene, leptin, was recently reported to be expressed on murine and human hematopoietic progenitor cells. Therefore, we studied the expression of the leptin receptor, OB-R, in normal myeloid precursors, human leukemia cell lines, and primary leukemic cells using reverse-transcriptase polymerase chain reaction. In normal hematopoiesis, OB-R was expressed in CD34(+) cells. Normal promyelocytes (CD34(-)33(+) and CD34(-)13(+)) expressed only very low levels of the short, presumably nonsignaling isoform. Both the long and short isoforms of OB-R were expressed in 10 of 22 samples from patients with newly diagnosed primary or secondary acute myeloid leukemia (AML), with a higher incidence of the long isoform in primary AML (87.6% v 28.6%; P =.01). The incidence of OB-R expression was higher in recurrent than in newly diagnosed AML (P <.001), and samples from four patients with refractory AML showed strong expression of both isoforms. Both OB-R isoforms were also expressed in newly diagnosed and recurrent acute promyelocytic leukemia cells but were essentially absent in samples of chronic or acute lymphocytic leukemia. In vitro growth of myeloid leukemic cell lines and of blasts from 14 primary AMLs demonstrated that recombinant human leptin alone induced low level proliferation, significantly (P <.05) increased proliferation induced by recombinant human granulocyte colony-stimulating factor, interleukin 3, and stem cell factor in a subset of AML and increased colony formation (P <.005). Also, leptin reduced apoptosis induced by cytokine withdrawal in MO7E and TF-1 cells. Serum leptin levels correlated only with body mass index (P <. 001) and gender (P =.03). Results confirm the reported expression of leptin receptor in normal CD34(+) cells and demonstrate the frequent expression of leptin receptors in AML blasts. While normal promyelocytes lack receptor expression, leukemic promyelocytes express both isoforms. We also demonstrate proliferative effects of leptin alone and in combination with other physiologic cytokines, and anti-apoptotic properties of leptin. These findings could have implications for the pathophysiology of AML.

Apoptosis↗

PubMed1999

[A DNA probe suitable for the detection of chromosome 21 copy number in human interphase nuclei by fluorescence in situ hybridization].

OBJECTIVE: To prepare DNA probe which can be used to accurately detect chromosome 21 copy number in human interphase nuclei by fluorescence in situ hybridization (FISH). METHODS: A probe was produced by universal primer PCR from YAC clone 881D2 and characterized by FISH to metaphases and interphase nuclei of peripheral lymphocytes from 8 normal individuals and 5 patients suffering from trisomy 21. RESULTS: A DNA probe was produced and its characteristics were :(1) Most of the probes ranged in size from 350bp to 750bp; (2) The hybridization signals of the probes were located near centromere on long arm of human chromosome 21; (3) In 1524 metaphases scored, about 99.95% of hybridization signals were located on chromosome 21; (4) The signals were very bright and recognizable easily in both metaphases and interphases nuclei; (5) The expected copy number of chromosome 21 was detected by FISH with the probe in more than 98.40% of interphase nuclei and 99.60% of metaphases. CONCLUSION: The DNA probe reported here is suitable for the detection of chromosome 21 copy number in interphase nuclei and for the study of segregation of chromosome 21 during mitoses of human lymphocytes in culture.

Cell Nucleus↗

PubMed1999

Isolated operator binding and ligand response domains of the TyrR protein of Haemophilus influenzae associate to reconstitute functional repressor.

Highly purified preparations of the TyrR protein of Haemophilus influenzae Rd undergo specific and limited proteolytic cleavage during storage at 4 degreesC to generate two fragments of 28 and 8 kDa. Under nondenaturing conditions, the two fragments remain tightly associated. Nicked TyrR is identical to full-length TyrR in its operator binding characteristics. The 8-kDa fragment containing amino acid residues 258-318 was separated from the 28-kDa fragment (residues 1-257) by gel filtration chromatography in the presence of 4 M urea. Upon renaturation, this fragment bound to operator with an affinity similar to that of full-length TyrR but was unresponsive to ligands that normally modulate operator binding (gamma-S-ATP and L-tyrosine). It was not possible to renature the urea-treated 28-kDa fragment. Highly purified soluble preparations of truncated TyrR containing residues 1-257 were obtained after the overexpression of a shortened form of the tyrR gene via a specific plasmid construct. By several criteria, this species had native secondary and tertiary structure. The 28-kDa fragment was unable to bind to operator but could reconstitute nicked TyrR when added to the renatured 8-kDa fragment, as shown by physical properties and responsiveness to cofactors in operator binding. When either the 28- or 8-kDa species was expressed in vivo, there was no detectable operator binding, as evaluated using a lacZ reporter system driven by the repressible aroF promoter. When the two fragments were co-expressed in a common cytoplasm, an operator-binding species was formed, as demonstrated through partial restoration of repression capability.

Circular Dichroism↗

PubMed1999

NOEY2 (ARHI), an imprinted putative tumor suppressor gene in ovarian and breast carcinomas.

Using differential display PCR, we have identified a gene [NOEY2, ARHI (designation by the Human Gene Nomenclature Committee)] with high homology to ras and rap that is expressed consistently in normal ovarian and breast epithelial cells but not in ovarian and breast cancers. Reexpression of NOEY2 through transfection suppresses clonogenic growth of breast and ovarian cancer cells. Growth suppression was associated with down-regulation of the cyclin D1 promoter activity and induction of p21(WAF1/CIP1). In an effort to identify mechanisms leading to NOEY2 silencing in cancer, we found that the gene is expressed monoallelically and is imprinted maternally. Loss of heterozygosity of the gene was detected in 41% of ovarian and breast cancers. In most of cancer samples with loss of heterozygosity, the nonimprinted functional allele was deleted. Thus, NOEY2 appears to be a putative imprinted tumor suppressor gene whose function is abrogated in ovarian and breast cancers.

Amino Acid Sequence↗

PubMed1999

Myocardial "low reflow" assessed by Dy-DTPA-BMA-enhanced first-pass MR imaging in a dog model.

The aim of this study was to determine whether the use of a magnetic resonance (MR) susceptibility contrast medium, dysprosium diethylenetriamine pentaacetic acid-bismethylamide (Dy DTPA-BMA; Sprodiamide), may characterize myocardial perfusion abnormalities in a dog model of 90 minutes of coronary occlusion followed by 24 hours of reperfusion (no-reflow phenomenon installed). First-pass MR imaging after an intravenous bolus administration of the contrast agent was performed at the end of reperfusion. Signal intensity analysis on MR imaging, planimetry of pathological data, and blood flow determination were obtained by reference methods for comparison. Dogs were separated into two groups according to the level of collateral blood flow level (group I, <22.5 % of the flow in the non-ischemic zone; group II, >22.5 % of the flow in the non-ischemic zone). Signal intensity-time curves in the ischemic and non-ischemic left ventricle walls were extracted. Mean collateral blood flow was lower during occlusion in group I (9.8 +/- 5.4%, n = 5) than in group II (38 +/- 12.5%, n = 7, P < 0.05). Mean infarct size (expressed as a percentage of the area at risk) was significantly larger in group I (low collateral blood flow; 25.3 +/- 14.6%) than in group II (high collateral blood flow; 5.8 +/- 1.1%, P < 0.05). After rapid injection, a transient decrease of signal intensity induced by Dy DTPA-BMA was observed in both remote and ischemic myocardium but more markedly in remote normally perfused myocardium. Hence, during the transit of a susceptibility-type contrast agent, ischemic myocardium after ischemia and reperfusion appeared as a relative high signal intensity area. First-pass MR imaging with susceptibility contrast agent demonstrated the no- or low-reflow phenomenon. However, the behavior of the myocardial signal intensity-time-related curves did not allow distinction between the two groups of dogs.

Animals↗

PubMed1999

Elevation of expression of Smads 2, 3, and 4, decorin and TGF-beta in the chronic phase of myocardial infarct scar healing.

We have previously shown that non-myocytes present in healed 8-week infarct scar overexpress transduction proteins required for initiating the elevated deposition of structural matrix proteins in this tissue. Other work suggests that TGF-beta 1 may be involved in cardiac fibrosis and myocyte hypertrophy. However, the significance of the altered TGF-beta signaling in heart failure in the chronic phase of post-myocardial infarction (MI), particularly in the ongoing remodeling of the infarct scar, remains unexplored. Patterns of cardiac TGF beta 1 and Smad 2, 3, and 4 protein expression were investigated 8 weeks after MI and were compared to relative collagen deposition in border tissues (containing remnent myocytes) and the infarct scar (non-myocytes). Both TGF-beta 1 mRNA abundance and protein levels were significantly increased in the infarct scar v control values, and this trend was positively correlated to increased collagen type I expression. Cardiac Smad 2, 3, and 4 proteins were significantly increased in border and scar tissues v control values. Immunofluorescent studies indicated that Smad proteins localized proximal to the cellular nuclei present in the infarct scar. Decorin mRNA abundance was elevated in border and infarct scar, and the pattern of decorin immunostaining was markedly altered in remote remnant heart and scar v staining patterns of control sections. Expression of T beta RI (53 kDa) protein was significantly reduced in the scar, while the 75 kDa and 110 kDa isoforms of T beta RII were unchanged and significantly increased in scar, respectively. These results indicate that TGF-beta/Smad signaling may be involved in the remodeling of the infarct scar after the completion of wound healing per se, via ongoing stimulation of matrix deposition.

Activin Receptors, Type I↗

PubMed1999

Ultrasound velocity of trabecular cubes reflects mainly bone density and elasticity.

Studies have indicated that quantitative ultrasound (QUS) variables may be influenced by the mechanical properties of bone which in turn are determined by bone's material and structural properties. However, from these studies it is unclear what role density, elasticity, and structure play in determining velocity. Eighteen defatted, 12-mm cubic trabecular bone specimens were cut from cadaveric specimens. Amplitude-dependent speed of sound (SOS) using a single point QUS system was assessed in three orthogonal axes. Magnetic resonance images were obtained, from which measures of apparent trabeuclar structure were derived. The specimens were nondestructively tested in compression along three orthogonal axes defined by the sides of the cubes. The elastic modulus (in the three directions) and the strength (in one direction) were determined. Trabecular BMD was measured by quantitative computed tomography. SOS varied significantly with direction of measurement, with the highest value in the axial direction (axial:1715 m/s, sagittal: 1662 m/second, and coronal: 1676 m/s). SOS of each of the three axes was generally associated with the various mechanical (r = 0.30-0.87), density (r = 0.81-0.93), and bone structural variables (0.3-0.8). However, after adjusting the SOS correlations by density, only the correlation with elasticity remained significant in the coronal direction. BMD alone explained 88-93% of variance in SOS whereas in the multivariate model, BMD plus elasticity and/or anisotropic variables explained 96-98% of the variance in SOS. Variability of SOS is explained mostly by density and to a small extent by elasticity or anisotropy. Since only 2-6% of the variance of the QUS measurement is not explained by density and elasticity, one could conclude that the remaining variance reflects other properties of bone or perhaps simply measurement error. Evidence that these other properties may be structure related is only found in the anisotropy of QUS parameter.

Adult↗

PubMed1999

Positron emission tomography of murine liver metastases and the effects of treatment by combretastatin A-4.

There are major potential advantages in non-invasive measurement of preclinical tumour biology and therapeutic response in clinically relevant, internal body sites, notably the ability to follow outcome in individual animals rather than averaging results from groups. We have exploited positron emission tomography (PET) to determine the feasibility of detecting liver metastases in B6D2F1 mice using fluorine-18 fluorodeoxyglucose ([18F]FDG) both before and after treatment by the novel cytotoxic agent, combretastatin A-4. The normal distribution of [18F]FDG in the absence of disease was characterised, with the clear delineation of the brain, the heart and the urinary bladder in all studies. In untreated mice with liver metastases, a strong correlation (r2 = 0.98) was found between the quantitative estimates of [18F]FDG uptake obtained by analysis of PET images, and those obtained from ex vivo assay of liver plus metastases excised immediately after imaging. In this first series, the effective limit of resolution was in livers containing a number of small metastases (range 8-14) with a single volume equivalent of approximately 200 mm3. PET image analysis was concordant with histological measurements in showing that single intraperitoneal doses of combretastatin A-4 resulted in an average 30% volume destruction of metastatic mass by 24 h following administration.

Animals↗

PubMed1999

Study of prognostic predictors for non-small cell lung cancer.

BACKGROUND: The outcome of treatment in non-small cell lung cancer (NSCLC) remains poor. One of the reasons is that in many patients its biological behavior does not follow a definite pattern, and can not be accurately predicted prior to treatment. In the present study we have examined the significant prognostic predictors. METHODS: One hundred and fifty-eight patients with NSCLC entered this study. They received surgery alone (95 cases) or combined therapy with postoperative irradiation (63 cases). Three types of data have been collected: (1) clinical characteristics: age, sex, Karnofsky performance status, weight loss, T stage, and N stage; (2) histopathology studies: histological types, tumor differentiation, status of vascular and lymphatic vessel invasions; (3) laboratory measurements by immunohistochemistry assay: oncoprotein overexpression, including pan-ras, c-myc, neu, epidermal growth factor receptor (EGFR) and p53, and tumor cell proliferation by proliferating cell nuclear antigen (PCNA). RESULTS: For the entire group, 5-year actuarial survival, local control and distant metastasis rates were 44, 63 and 40%, respectively. In the univariate analyses, T stage, N stage and lymphatic vessel invasion correlated to survival; T stage and N stage to local control; N stage, lymphatic vessel invasion and pan-ras protein positive stain to distant metastasis. When the index of oncoprotein positive stains was used, the higher index was associated with a higher distant metastasis rate. In the multivariate analyses, T stage, N stage and lymphatic vessel invasion could be independent predictors for survival; T stage for local control; N stage, lymphatic vessel invasion and index of positive oncoprotein stains for distant metastasis. CONCLUSIONS: Late T and N stages, lymphatic vessel invasion and multi-oncoprotein positive stains would predict poor prognoses for NSCLC.

Actuarial Analysis↗

PubMed1999

Radioimmunotherapy of human glioma xenografts in nude mice by indium-111 labelled internalising monoclonal antibody.

The potential of 111Indium (111In)-labelled internalising anti-integrin alpha 3 antibody GA17 in the radioimmunotherapy of human glioblastoma xenografts in nude mice was investigated. A radioisotope retention assay showed a rapid release of radioiodine from the glioblastoma cells after the binding of 125I-GA17, whilst 111In-GA17 was retained in the cells for a longer time period. The glioblastoma xenografts showed a high and prolonged uptake of 111In-GA17, and tumour uptake of 125I-GA17 was lower and decreased with time. In the mice which received two injections of 18.5 MBq of 111In-GA17, the growth of the subcutaneous tumour was significantly suppressed compared with the untreated group and mice injected with an 111In-labelled control antibody. These results indicate that GA17 was internalized into the glioblastoma cells and that 111In was retained within the cancer cells. The injection of a high-dose of 111In-GA17 can suppress the growth of tumour xenografts in nude mice.

Animals↗

PubMed1999

Syntheses of benzoquinolizidine and benzoindolizidine derivatives as anti-amnesic agents.

Tacrine, one of the drugs available for Alzheimer's disease based on the cholinergic approach, suffers from considerable toxicity. Many analogues of tacrine have been prepared which retain the pharmacologically rich aminopyridine or aminoquinoline motifs. The current research was undertaken to produce an acetylcholinesterase inhibitor by employing 11-aminobenzoquinolizidines (4) and 10-aminobenzoindolizidines (5) as templates. Thus, we aimed to achieve three goals relative to tacrine: eliminate the pyridine and quinoline moieties and render the molecule less flat. Overall, the compounds we prepared were poorer inhibitors of acetylcholinesterase compared to tacrine. The single exception was compound 6f which exhibited an effect comparable to that of tacrine, but only at a dose of the order of 10(-3) M. However, despite the poor acetylcholinesterase inhibition by 6b, this compound proved to be an effective anti-amnesic agent at 45 mg/kg dose.

Animals↗

PubMed1999

Syntheses of 1,2-diamino and 1,2-aminoalcohol derivatives in the piperidine and pyrrolidine series as anti-amnesic agents.

Tacrine, one of the drugs available for Alzheimer's disease based on the cholinergic approach, suffers from considerable toxicity. Many analogues of tacrine has been prepared which retain the pharmacologically rich aminopyridine or aminoquinoline motifs. The current research is a continuation of our efforts in the area of 11-aminobenzoquinolizidines (4) and 10-aminobenzoindolizidines (5) (cf. ref9). A serendipitous discovery led us to the biologically active open chain analogue 9, and we proceeded to elaborate on this molecule. Overall, the compounds we prepared were poor inhibitors of acetylcholinesterase as compared to tacrine. The single exception was compound 20 which exhibited an effect comparable to that of tacrine, but only at a dose in the order of 10(-3) M. However, despite the poor acetylcholinesterase inhibition by 9, this compound was found to be an effective antiamnesic agent.

Alcohols↗

PubMed1999

Five new triterpene saponins from Pulsatilla patens var. multifida.

Five new oleanane-type glycosides (1-5), along with two known triterpene saponins, were isolated from the roots of Pulsatilla patens var. multifida (Ranunculaceae). The structures of the new triterpene saponins were elucidated as 3-O-beta-D-glucopyranosyl(1-->2)-beta-D-galactopyranosyl hederagenin 28-O-beta-D-glucopyranosyl ester (1), hederagenin 3-O-[beta-D-glucopyranosyl(1-->2)][beta-D-glucopyranosyl(1-->6)]-beta -D-galactopyranoside (2), 3-O-beta-D-glucopyranosyl bayogenin 28-O-alpha-L-rhamnopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->6)-beta -D-glucopyranosyl ester (3), 3-O-beta-D-glucopyranosyl(1-->2)-beta-D-galactopyranosyl oleanolic acid 28-O-alpha-L-rhamnopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->6)-beta -D-glucopyranosyl ester (4), and 3-O-[beta-D-glucopyranosyl(1-->2)][beta-D-glucopyranosyl(1-->6)]-beta -D-galactopyranosyl hederagenin 28-O-alpha-L-rhamnopyranosyl(1-->4)-beta-D-glucopyranosyl(1-->6)-beta -D-glucopyranosyl ester (5). Structure elucidation was accomplished by 1D and 2D NMR (HMQC, HMBC, and ROESY) methods, FABMS, and hydrolysis.

Carbohydrate Sequence↗

PubMed1999

Cloning and tissue expressional characterization of a full-length cDNA encoding human neuronal protein P17.3.

A full-length cDNA of 595 bp was isolated from a human fetal brain cDNA library. It contains an open reading frame encoding 153 amino acids, with an 18-bp 5'UTR and a 118-bp 3'UTR in which there is an atypical polyadenylation signal (ATTAAA). The calculated molecular weight of the deduced protein is 17.3 kU. The predicted isoelectric point is 4.89. On account of its high homology to mouse neuronal protein NP15.6 (81.2% identity), the deduced protein was named neuronal protein 17.3 (NP17.3). When its secondary structure was examined by the GGBSM program of PCGENE software, it was found that 32.6 and 15.0% of its amino acids are involved in forming alpha-helices and beta-sheets, respectively. Examined with the PESTFIND program, a typical PEST region found in rapidly degraded proteins was found between residue 48 and residue 68.

5' Untranslated Regions↗