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Biomedical subjects

Z Zhao

Publications and source records attributed to Z Zhao.

At least 217 records · Page 12Linked to original sources
PubMed1997

Identification of increased protein tyrosine phosphatase activity in polycythemia vera erythroid progenitor cells.

Polycythemia vera (PV) is a clonal hematologic disease characterized by hyperplasia of the three major bone marrow lineages. PV erythroid progenitor cells display hypersensitivity to several growth factors, which might be caused by an abnormality of tyrosine phosphorylation. In the present study, we have investigated protein tyrosine phosphatase (PTP) activity in highly purified erythroid progenitor cells and found that the total PTP activity in the PV cells was twofold to threefold higher than that in normal cells. Protein separation on anion-exchange and gel-filtration columns showed that the increased activity was due to a major PTP eluted at approximately 170 kD. This enzyme was sensitive to PTP inhibitors and it did not cross-react with antibodies to SHP-1, SHP-2, or CD45. Subcellular fractionation showed that the PTP localized with the membrane fraction, where its activity was increased by threefold in PV erythroid progenitors when compared with normal cells. As the erythroid progenitors progressively matured, activity of the PTP declined rapidly in the normal cells but at a much slower rate in the PV cells. These studies suggest that a potentially novel membrane or membrane-associated PTP, representing a major PTP activity, may have an important role in proliferation and/or survival of human erythroid progenitors and that its hyperactivation in PV erythroid progenitors might be responsible for the increased erythropoiesis in PV patients.

Adult↗
PubMed1997

Role of the Arg123-Tyr166 paired helix of apolipoprotein A-I in lecithin:cholesterol acyltransferase activation.

The Arg123-Tyr166 central and Ala190-Gln243 carboxyl-terminal pairs of helices of apoA-I were substituted with the pair of helices of apoA-II, resulting in the apoA-I(Delta(Arg123-Tyr166), nablaA-II(Ser12-Ala75)) and apoA-I(Delta(Ala190-Gln243), nablaA-II(Ser12-Gln77)) chimeras, respectively. The structures of these chimeras in aqueous solution and in reconstituted high density lipoproteins (rHDL) and the lecithin:cholesterol acyltransferase (LCAT) activation properties of the rHDL were studied. Recombinant human apoA-I and the chimeras were expressed in Escherichia coli and purified from the periplasmic space. Binding of the apolipoproteins with palmitoyloleoylphosphatidylcholine was associated with a similar shift of Trp fluorescence maxima from 337 to 332 nm, from 339 to 334 nm, and from 337 to 333 nm, respectively. All rHDL had a Stokes radius of 4.8 nm and contained 2 apolipoprotein molecules/particle. Circular dichroism measurements revealed eight alpha-helices per apoA-I and per chimera molecule. The catalytic efficiencies of LCAT activation were 1.5 +/- 0.33 (mean +/- S.D.; n = 3), 0.054 +/- 0.009 (p < 0.001 versus apoA-I), and 1.3 +/- 0.32 (p = not significant versus apoA-I) nmol of cholesteryl ester/h/microM, respectively. The lower LCAT activity of the central domain chimera was due to a 27-fold reduced Vmax with unaltered Km. Binding of radiolabeled LCAT to rHDL of apoA-I and apoA-I(Delta(Arg123-Tyr166), nablaA-II(Ser12-Ala75)) was very similar. In conclusion, although substitution of the Arg123-Tyr166 central or Ala190-Gln243 carboxyl-terminal pair of helices of apoA-I with the pair of helices of apoA-II yields chimeras with structure similar to that of native apoA-I, exchange of the central domain (but not the carboxyl-terminal domain) of apoA-I reduces the rate of LCAT activity that is independent of binding to rHDL.

Apolipoprotein A-I↗
PubMed1997

Phosphatidylinositol-specific phospholipase C: kinetic and stereochemical evidence for an interaction between arginine-69 and the phosphate group of phosphatidylinositol.

A new substrate analogue, (2R)-1,2-dipalmitoyloxypropanethiophospho-1-D-myo-inositol (DPsPI), has been used in a new, continuous assay for phosphatidylinositol-specific phospholipase C (PI-PLC). DPsPI is superior to other substrate analogs that have been used for assaying PI-PLC since it is synthesized as a pure diastereomer and maintains both acyl chains of the natural substrate, dipalmitoylphosphatidylinositol (DPPI). The assay that has been developed using this new analogue has allowed us to elucidate detailed kinetic data so far lacking in the field. In addition, several mutants of PI-PLC were constructed and assayed. The results show that Arg-69 is essential for catalysis, since mutations at this position led to a 10(3)- 10(4)-fold decrease in activity with respect that of to the wild-type (WT) enzyme. An alanine mutant of Asp-67, a residue also found at the active site, displays activity similar to that of WT. We have also used nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy to analyze the structural integrity and conformational stability of the mutants. The results show that the overall global conformation of the enzyme is not perturbed by the mutants. The 15N-1H HSQC NMR spectrum of WT PI-PLC is also reported at 600 MHz. The stereoselectivity of the reaction toward the stereoisomers of another analogue, 1,2-dipalmitoyl-sn-glycero-3-thiophospho-1-myo-inositol (DPPsI), was used to probe whether Arg-69 interacts with the phosphate moiety of the substrate. We have calculated that the WT enzyme shows a stereoselectivity ratio of 160000:1 in favor of the Rp isomer versus the Sp isomer. The R69K mutant displayed a significant 10(4)-fold relaxation of stereoselectivity. Our data support the role of Arg-69 in stabilizing the negative charge on the pentacoordinate phosphate in the transition state during catalysis.

Arginine↗
PubMed1997

Identification of a new phosphorylation site in cardiac muscle phosphofructokinase.

The novel phosphorylation site (Ser376) that we discovered during in vitro studies of the troponin C- or calmodulin-induced phosphorylation of rabbit muscle phosphofructokinase [Zhao, Z., Malencik, D.A., and Anderson, S. R. (1991) Biochemistry 30, 2204] also undergoes phosphorylation in the epinephrine-stimulated rabbit heart. Reversed-phase HPLC and/or iron chelate affinity chromatography performed on CNBr digests of phosphofructokinase that had been isolated from epinephrine-treated hearts yields a largely phosphorylated peptide corresponding to amino acid residues 371-378 of the enzyme. Mass spectrometry, gas phase sequencing, and amino acid analyses establish the structure and phosphorylation state of the peptide.

Animals↗
PubMed1997

Developmental acquisition of enhancer function requires a unique coactivator activity.

Enhancers are believed to stimulate promoters by relieving chromatin-mediated repression. However, injection of plasmid-encoded genes into mouse oocytes and embryos revealed that enhancers failed to stimulate promoters prior to formation of a two-cell embryo, even though the promoter was repressed in the maternal nucleus of both oocytes and one-cell embryos. The absence of enhancer function was not due to the absence of a required sequence-specific enhancer activation protein, because enhancer function was not elicited even when these proteins either were provided by an expression vector (GAL4:VP16) or were present as an endogenous transcription factor (TEF-1) and shown to be active in stimulating promoters. Instead, enhancer function in vivo required a unique coactivator activity in addition to enhancer-specific DNA binding proteins and promoter repression. This coactivator activity first appeared during mouse development in two- to four-cell embryos, concurrent with the major onset of zygotic gene expression. Competition between various enhancers was observed in these embryos, but not competition between enhancers and promoters, and competition between enhancers was absent in one-cell embryos. Moreover, enhancer function in oocytes could be partially restored by pre-injecting mRNA from cells in which enhancers were active, the same mRNA did not affect enhancer function in two- to four-cell embryos.

Animals↗
PubMed1997

Dinuclear center of ferritin: studies of iron binding and oxidation show differences in the two iron sites.

The ferroxidase activity of human ferritin has previously been associated with a diiron site situated centrally within the four-helix bundle of H-type chains (HuHF). However, direct information about the site of Fe(II) binding has been lacking, and events between Fe(II) binding and its oxidation have not previously been studied. A sequential stopped-flow assay has now been developed to enable the dissection of binding and oxidation. It depends on the ability of 1,10-phenanthroline to complex protein-bound Fe(II) and to distinguish it from the more immediately available free Fe(II). This approach, aided by the use of site-directed variants, indicates that in HuHF and the non-heme ferritin of Escherichia coli the first 48 Fe(II) atoms/molecule added are bound and oxidized at the dinuclear centers. At a constant iron concentration, the rate of Fe(II) oxidation was maximal for additions of 2 Fe(II) atoms/subunit, consistent with a two-electron oxidation of the Fe(II) pair. Although, at low Fe(II)/protein ratios, no cooperativity in Fe(II) binding was observed; a preferred order of binding was deduced [Fe(II) binding first at site A and then at site B]. Binding of Fe(II) at both sites was essential for fast oxidation. Modification of site A ligands resulted in slow iron binding and slow oxidation. Modification of site B did not prevent Fe(II) binding at site A but greatly reduced its oxidation rate. These differences may mean that dioxygen is initially bound to Fe(II) at site B.

Binding Sites↗
PubMed1997

Patterning of the mammalian dentition in development and evolution.

The mammalian dentition is a segmented organ system with shape differences among its serially homologous elements (individual teeth). It is believed to have evolved from simpler precursors with greater similarities in shape among teeth, and a wealth of descriptive data exist on changes to the dentition that have occurred within mammals. Recent progress has been made in determining the genetic basis of the processes that form an individual tooth, but patterning of the dentition as a whole (i.e. the number, location and shape of the teeth) is less well understood. In contrast to similarly organized systems, such as the vertebral column and limb, Hox genes are not involved in specifying differences among elements. Nevertheless, recent work on a variety of systems is providing clues to the transcription factors and extracellular signalling molecules involved.

Animals↗
PubMed1997

Expression, purification, and crystallization of the catalytic domain of protein tyrosine phosphatase SHP-1.

The catalytic domain of SHP-1, a SH2-domain containing protein tyrosine phosphatase, has been crystallized by the vapor diffusion method using polyethylene glycol as the precipitant. The crystals belong to the monoclinic space group P21 with unit cell dimensions a = 42.12 A, b = 87.94 A, c = 43.22 A, alpha = 90.0 degrees, beta = 120.12 degrees, and gamma = 90.0 degrees. There is one catalytic domain of SHP-1 per asymmetric unit. X-ray was diffracted to at least 2.5 A and the crystals are appropriate for high-resolution structure determination.

Binding Sites↗
PubMed1997

An A3-subtype adenosine receptor is highly expressed in rat vascular smooth muscle cells: its role in attenuating adenosine-induced increase in cAMP.

Adenosine analogs are known to induce changes in the steady-state concentration of cAMP via binding to adenylyl cyclase-inhibitory or -stimulatory adenosine receptors. Although adenosine has been found to increase cAMP in vascular smooth muscle cells (VSMC), we found by the polymerase chain reaction of reverse-transcribed RNA and subsequently by Northern blot analysis that rat VSMC express high levels of an A3-subtype adenosine receptor cDNA which encodes an adenylyl cyclase-inhibitory adenosine receptor. The A3-specific agonist, N6-(3-iodobenzyl) adenosine-5'-N-mehylcarboxamide (IB-MECA) indeed decreases cAMP levels in VSMC cultured in the presence of forskolin. Antisense oligomers to the A3 adenosine receptor significantly reduce the level of this receptor in VSMC and potentiate endogenous adenosine- or 5'-N-ethylcarboxamido adenosine-induced increases in cAMP and of the proto-oncogene c-fos. Abrogating the expression of the A3 adenosine receptor also largely abolishes IB-MECA-induced inhibition of adenylyl cyclase. The level of A3 adenosine receptor mRNA and the extent of changes in cAMP in response to IB-MECA were lower in cultures of VSMC derived from adult rats, compared to VSMC from neonatal rats. The expression of a functional A3 adenosine receptor was also confirmed in preparations of isolated aortas. Our findings thus indicate that: (a) the A3-type receptor is a functional inhibitory adenosine receptor in VSMC; and (b) the regulation of expression of the A3 receptor is critical in determining effects of adenosine on the steady-state concentration of cAMP.

Adenosine↗
PubMed1997

Demographic systems in historic China: some new findings from recent research.

"Up to the 1980s, studies of Chinese population history were largely confined to the examination of aggregate population figures collected at national or provincial levels. Since then, however, investigations into Chinese demographic history have entered a new stage.... This paper...provides new information on past mortality, fertility and marriage patterns. In the light of these findings, a number of widely held beliefs about the traditional Chinese demographic system are critically examined."

Asia↗
PubMed1997

Long-term mortality patterns in Chinese history: evidence from a recorded clan population.

Human populations have lived on the earth for millions of years, yet the study of population history only began to be established in the mid-twentieth century. In spite of the considerable progress in the study of historical demography which has since been made, there have been hardly any detailed studies of fertility and mortality before the sixteenth century. This study, by analysing a set of Chinese genealogies, examines long-term mortality patterns in a selected clan population over a period of more than 1000 years. The result shows that, in this selected population, mortality fluctuated around a relatively high level and showed no secular change over the very long period studied. The study also provides a comparison between the mortality patterns found in the selected population and those observed in a much larger Chinese lineage population, as well as those recorded among the British elites born between the sixteenth and the early nineteenth century. Based on the findings of this research, the paper presents some tentative suggestions about long-term mortality changes in Chinese history.

China↗
PubMed1997

In vitro metabolic transformations of 2,4-dipyrrolidinylpyrimidine: a chemical probe for P450-mediated oxidation of tirilazad mesylate.

1. We have determined that 2,4-dipyrrolidinylpyrimidine (2,4-DPP), used as a model for studies of the metabolism of therapeutic agents containing this moiety, undergoes three characteristic hydroxylations when incubated with male rat liver microsomes. Analysis of microsomal incubates of stable isotope labelled analogues of 2,4-DPP by particle beam-liquid chromatography-mass spectrometry (LC-PB-MS) has shown that the three metabolites are 4-(3-hydroxypyrrolidinyl)-2-(pyrrolidinyl)-pyrimidine (M1), 4-(2-hydroxypyrrolidinyl)-2-(pyrrolidinyl)-pyrimidine (M2) and 2-(2-hydroxypyrrolidinyl)-4-(pyrrolidinyl)-pyrimidine (M3). 2. We determined that enzymes of the cytochrome P450 family are responsible for the in vitro hydroxylations of 2,4-DPP. 3. We observed that in microsomal incubations carried out in the presence of cyanide, a single cyanide adduct is formed implicating an iminium ion intermediate in the oxidation of the 2-pyrrolidine ring. 4. We also determined the intermolecular deuterium isotope effects for the formation of each of the three products. For M1, kH/kD = 14.55 +/- 0.54; for M2, kH/kD = 6.01 +/- 0.65; and for M3, kH/kD = 5.35 +/- 1.18. 5. We interpret these data as suggesting that M2 and M3 are formed by the same mechanism, probably including the formation of an iminium ion, and that M1 is formed by direct hydrogen abstraction.

Animals↗
PubMed1997

A role for the SHP-2 tyrosine phosphatase in nerve growth-induced PC12 cell differentiation.

SHP-1 and SHP-2 are intracellular protein tyrosine phosphatases containing two adjacent src homology 2 domains that target these phosphatases to cell surface receptor signaling complexes and play a role in receptor signal transduction. In this report the PC12 cell system was used to investigate the potential roles of SHP-1 and SHP-2 in the induction of neuronal differentiation by nerve growth factor (NGF). By using neurite outgrowth as a marker for differentiation, the effects of transfected constructs of SHP-1 and SHP-2 were assessed. Overexpression of a catalytically inactive SHP-2, but not a catalytically inactive SHP-1, blocked NGF-stimulated neurite outgrowth. The mitogen-activated protein kinase (MAPK) signaling cascade is important for the morphological differentiation in PC12 cells, and both SHP-1 and SHP-2 have been implicated to act upstream of MAPK in other receptor signaling systems. A positive role for SHP-2 but not SHP-1 in the activation of MAPK by NGF was demonstrated by introduction of the SHP-2 phosphatase mutants along with hemagglutinin-tagged MAPK. Coexpression studies with the SHP-2 mutant along with mutant forms of MAPK kinase suggested that SHP-2 functions upstream of MAPK kinase and MAPK in NGF-induced neurite outgrowth.

Animals↗
PubMed1997

Introduction of HIV into drug injector networks outside AIDS epicentres.

Injection drug users (IDUs) continue to be at risk for HIV infection despite high levels of knowledge about how human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) is transmitted. Yet, among not-in-treatment injection drug users, the chances of becoming infected with HIV vary substantially. Information regarding the factors that facilitate the introduction of HIV into networks of drug injectors in low HIV seroprevalence cities is urgently needed. This study examines the factors related to HIV seroprevalence in a large (n=9492), multi-site sample of IDUs recruited in 11 low seroprevalence cities. Univariate and multivariate associations between drug injection and sexual behaviours and travel to an AIDS epicentre were examined. Results show that, next to male-to-male sexual contact, having sex at least twice in an AIDS epicentre was the strongest predictor of HIV infection. Also associated with higher odds of being HIV-positive were racial/ethnic characteristics, daily drug injection, and injecting drugs in an AIDS epicentre. These results confirm that travelling to an AIDS epicentre and having sex or injecting drugs play a large role in the introduction of HIV into drug injector networks in low seroprevalence cities.

Adult↗
PubMed1997

[Transposition of the pedicled gluteus maximum myocutaneous flap for the repair of huge sacral pressure sores].

From 1986 to 1992, the authors repaired huge sacral pressure sores in 14 cases using the pedicled gluteus maximum myocutaneous flap. The treatment was completed in one stage and the results were satisfactory in all the cases during the follow-up period of 6 months to 7 years. No recurrence occurred. The authors concluded that the method is a good treatment for persistent sacral pressure sores.

Adolescent↗
PubMed1997

[Micrometastasis of colorectal carcinoma in bone marrow with immunohistochemical staining].

From April 1994 to April 1996, immunohistochemical technique was used to detect micrometastasis of patients with colorectal carcinoma with monoclonal antibody to epithelial membrane antigen (anti EMA). Positive cells were found in their bone marrow in 23 of 57 cases, including 14 in 34 patients with colonic carcinoma (positive rate 41%) and 9 in 23 patients with rectal carcinoma (positive rate 39.1%). The positive rate was 40.4%. Statistical analysis showed that the modified Dukes stage of the cancer, the pathological type of carcinoma and the age of the patients were correlated with the positive rate, but the primary locations of the cancer were not. This method can be used to identify the extent of the cancer and direct clinical comprehensive treatment for colorectal carcinoma.

Adenocarcinoma↗
PubMed1997

[Identification of the anti-rIL-1ra McAb].

Using dot-immuno-blot and Western blotting techniques, we have identified the specificity of anti-rIL-1ra McAbs. The results showed that the anti-rIL-1ra McAb 2E4 specifically reacted with rIL-1ra, from which the recognizing signal of dot-immunoblot was significantly positive (+2) and a single rIL-1ra protein band (20 kd) was clearly recognized by Western blotting. The control results of PcAb recognization have further proved the high sensitivity of Western blotting and high specificity of rIL-1ra McAb 2E4. The successful identification of rIL-1ra McAb 2E4 will be helpful to further understand the biologic effects, especially the pro-inflammatory properties, to study the change of rIL-1ra level during inflammation, and to instruct the clinical use of rIL-1ra.

Animals↗