Search PubMed⌕ Search

Biomedical subjects

H Li

Publications and source records attributed to H Li.

At least 199 records · Page 11Linked to original sources
PubMed2002

Restriction fragment length polymorphism assessment of the heterogeneous nature of maize population GT-MAS:gk and field evaluation of resistance to aflatoxin production by Aspergillus flavus.

Aflatoxin, produced by Aspergillus flavus, is one of the most toxic and carcinogenic substances known and contaminates many agricultural commodities such as corn, peanuts, cottonseed, and tree nuts. The challenge to breeders/plant pathologists is to identify lines that have resistance to aflatoxin production. Maize population GT-MAS:gk has been identified and released as a germplasm with resistance to aflatoxin contamination. In the present study, we assessed genetic divergence in the GT-MAS:gk population using restriction fragment length polymorphism (RFLP) DNA markers to survey 11 selfed inbred lines and conducted field evaluations for the dissimilarities in aflatoxin production among these inbred lines in comparison with a sister population, GT-MAS:pw.nf. The 11 selfed inbred lines were assayed for DNA polymorphism using 113 RFLP markers in 10 linkage groups covering 1,518.2 centimorgans (cM; unit of gene or chromosome size). Considerable variation among the inbreds was detected with RFLP markers, of which 42 probe-enzyme combinations gave 102 polymorphic bands. Cluster analysis based on genetic similarities revealed associations and variations among the tested lines. Three polymorphic groups were distinguished by cluster analysis. Two years of field evaluation data showed that aflatoxin concentrations among the lines were significantly different in both years (P < 0.001). Maturity data were also different. Thus, this study demonstrates that the maize population GT-MAS:gk is heterogeneous and that individuals may be different in resistance to A. flavus infection and aflatoxin production. Therefore, the most resistant lines should be inbred to increase homogeneity, and resistance should be confirmed through progeny testing.

Aflatoxins↗
PubMed2002

[Effects of Lewis Y oligosaccharide on secretion and gene expression of EGF and EGF-R in mouse embryos].

Implantation is a complicated developmental process. Some hormones and cytokines are involved in the regulation of the implantation by regulating functions of the endometrium and the embryo. Oligosaccharide antigen Lewis Y is specifically expressed on embryo surface and plays an important role in implantation. In this study, effects of Lewis Y on secretion and gene expression of EGF and EGF receptor of the embryo were investigated. Embryos were pre-incubated with Le(Y) specific antibody AH6 for 3 h, then antibody was removed, immuno-dot blots and RT-PCR were used to analyze the secretion of EGF and EGF receptor and their gene expression in the embryo at different times after pre-incubation. The results showed that, when blocked by AH6 antibody for 1.5 h, the secretion and expression of EGF in the embryo were significantly declined, and the alteration was continued to over 6 h; and those of EGF-R were slightly decreased after blocking. The results suggest that Lewis Y oligosaccharide on the surface of embryo may be involved in the regulation of embryo development and implantation, by affecting the expression and secretion of EGF in embryo.

Animals↗
PubMed2001

[New type pathogenic mycoplasmas isolated from female patients with genital infection in Nanjing, China].

OBJECTIVE: To study if infection of new type pathogenic mycoplasmas, Mycoplasma penetrans (Mpe), Mycoplasma fermentans (Mf), and Mycoplasma pirum (Mpi), exists in the genital tract of gynecologic patients with genital infection in China so as to provide information for clinical diagnosis and therapy. METHODS: Cervical secretions from 172 patients with infectious diaseses of gentital tract and 172 healthy controls were collected and inoculated in improved SP-4 culture medium. Biochemical reaction, coagglutination test, metabolism-inhibition test, polymerase chain reaction (PCR) assay, and DNA sequencing were employed to identify the isolated microorganisms. RESULTS: One strain of Mycoplasma penetrans (0.58%) and two strains of Mycoplasma fermentans (1.16%) were isolated from the cervical secretions of patients, but none was found in healthy controls. CONCLUSION: Mpe infection and Mf infection exist in female patients with genital infection in Nanjing.

Adult↗
PubMed2001

Photochemical reactions of substituted cyclopropenium salts.

Photochemical reactions of triphenylcyclopropenium tetrakis(pentafluorophenyl)gallate (TPCPGa) and diphenyl-(2-methoxy-1-naphthyl)-cyclopropenium tetrakis(pentafluorophenyl)gallate (DPMNCPGa) (Chart 1) have been investigated in acetonitrile. Traces of water were required for the photochemical reactions to proceed. The disappearance of both TPCPGa and DPMNCPGa obeys zero-order kinetics with rate constants (k) having a linear dependence on the concentration of water. Electron-transfer from water to the cyclopropenium cation is proposed as the primary process in the formation of the cyclopropenyl radical. The latter dimerizes leading to the photoproducts.

Journal Article↗
PubMed2001

Immunization with a portion of rickettsial outer membrane protein A stimulates protective immunity against spotted fever rickettsiosis.

Two approaches for presentation of a part of the rickettsial outer membrane protein A (OmpA) of Rickettsia rickettsii, namely (1) recombinant Mycobacterium vaccae (rMV) or (2) recombinant DNA vaccine, stimulated protective immunity against a lethal challenge with the closely related bacterium, R. conorii, in mice. After primary immunization with rMV and booster immunization with homologous recombinant protein, 67 and 55% of mice were protected against challenge in two experiments. DNA vaccination with booster recombinant protein immunization protected six out of eight animals from a lethal challenge. Production of IFN-gamma by antigen-exposed T-lymphocytes of DNA vaccine recipients indicated that cellular immunity had been stimulated.

Animals↗
PubMed2001

Hormone-dependent, CARM1-directed, arginine-specific methylation of histone H3 on a steroid-regulated promoter.

Activation of gene transcription involves chromatin remodeling by coactivator proteins that are recruited by DNA-bound transcription factors. Local modification of chromatin structure at specific gene promoters by ATP-dependent processes and by posttranslational modifications of histone N-terminal tails provides access to RNA polymerase II and its accompanying transcription initiation complex. While the roles of lysine acetylation, serine phosphorylation, and lysine methylation of histones in chromatin remodeling are beginning to emerge, low levels of arginine methylation of histones have only recently been documented, and its physiological role is unknown. The coactivator CARM1 methylates histone H3 at Arg17 and Arg26 in vitro and cooperates synergistically with p160-type coactivators (e.g., GRIP1, SRC-1, ACTR) and coactivators with histone acetyltransferase activity (e.g., p300, CBP) to enhance gene activation by steroid and nuclear hormone receptors (NR) in transient transfection assays. In the current study, CARM1 cooperated with GRIP1 to enhance steroid hormone-dependent activation of stably integrated mouse mammary tumor virus (MMTV) promoters, and this coactivator function required the methyltransferase activity of CARM1. Chromatin immunoprecipitation assays and immunofluorescence studies indicated that CARM1 and the CARM1-methylated form of histone H3 specifically associated with a large tandem array of MMTV promoters in a hormone-dependent manner. Thus, arginine-specific histone methylation by CARM1 is an important part of the transcriptional activation process.

Acetylation↗
PubMed2001

Human immunodeficiency virus type 1-mediated syncytium formation is compatible with adenovirus replication and facilitates efficient dispersion of viral gene products and de novo-synthesized virus particles.

Conditionally replicative adenovirus (CRAd) vectors are designed for specific oncolytic replication in tumor tissues with concomitant sparing of normal cells. As such, CRAds offer an unprecedented level of anticancer potential for malignancies that have been refractory to previous cancer gene therapy interventions. CRAd efficacy may, however, be compromised by inefficient dispersion of the replicating vector within the tumor tissue. To address this issue, we evaluated the utility of a fusogenic membrane glycoprotein (FMG), which induces the fusion of neighboring cellular membranes to form multinucleated syncytia. We hypothesized that the FMG-mediated syncytia would facilitate dispersion of the adenovirus (Ad) gene products and viral progeny. To test this, human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins, which induce syncytia in the presence of CD4+ target cells, were expressed by an Ad (Ad5HIVenv) in permissive (CD4-positive) and nonpermissive (CD4-negative) cell lines. After validating this Ad-FMG model, the efficiency of Ad replication in the presence or absence of syncytia was evaluated. The results demonstrated that syncytium formation was compatible with Ad replication and dramatically increased the dispersion of virus gene products within the cytoplasm of the syncytia as well as viral particles in the nuclei of the syncytial mass. Moreover, progeny virions were released more efficiently from syncytia compared with nonsyncytial cells. These data demonstrate the utility of FMGs as a dispersion agent and suggest that FMGs can improve the efficacy of CRAd gene therapy.

Adenoviruses, Human↗
PubMed2001

Phylogenetic comparison of classical swine fever virus in China.

An N-terminal fragment of the E2 gene of classical swine fever (CSF) virus encoding major immunogenic sites was amplified by RT-PCR directly from 110 clinical specimens representing 109 epizootic sites during the last decade in China. Phylogenetic relationships between these viruses as well as 20 reference strains were determined by comparison of their nucleotide sequences. A phylogenetic tree showed that 103 of the 110 field viruses (93.6%) were clustered within group 2 and subdivided into three subgroups, while the remaining seven viruses (6.4%), along with two Chinese reference strains, Shimen and HCLV (attenuated vaccine strain), were clustered into subgroup 1.1 within group 1. However, none of the Chinese CSF viruses were members of subgroup 1.2 (represented by reference strain Brescia). This is the first report on the distribution of CSF virus genotypes in China. Results indicated that CSF viruses predominating in recent epizootics within China are genetically divergent from the reference strain Shimen and the vaccine strain HCLV.

Animals↗
PubMed2001

Calreticulin and calnexin in the endoplasmic reticulum are important for phagocytosis.

Calreticulin and calnexin are Ca2+-binding proteins with chaperone activity in the endoplasmic reticulum. These proteins have been eliminated by gene replacement in Dictyostelium, the only microorganism known to harbor both proteins; family members in Dictyostelium are located at the base of phylogenetic trees. A dramatic decline in the rate of phagocytosis was observed in double mutants lacking calreticulin and calnexin, whereas only mild changes occurred in single mutants. Dictyostelium cells are professional phagocytes, capable of internalizing particles by a sequence of activities: adhesion of the particle to the cell surface, actin-dependent outgrowth of a phagocytic cup, and separation of the phagosome from the plasma membrane. In the double-null mutants, particles still adhered to the cell surface, but the outgrowth of phagocytic cups was compromised. Green fluorescent protein-tagged calreticulin and calnexin, expressed in wild-type cells, revealed a direct link of the endoplasmic reticulum to the phagocytic cup enclosing a particle, such that the Ca2+ storage capacity of calreticulin and calnexin might directly modulate activities of the actin system during particle uptake.

Animals↗
PubMed2001

Persistent expression of Hlxb9 in the pancreatic epithelium impairs pancreatic development.

The homebox gene Hlxb9, encoding Hb9, exhibits a dual expression profile during pancreatic development. The early expression in the dorsal and ventral pancreatic epithelium is transient and spans from embryonic day (e) 8 to e9-e10, whereas the later expression is confined to differentiating beta-cells as they appear. We previously showed that Hlxb9 is critically required for the initiation of the dorsal, but not the ventral, pancreatic program. Here, we demonstrate the requirement for a stringent temporal regulation of Hlxb9 expression during early stages of pancreatic development. In transgenic mice, where Hlxb9 expression, under control of the Ipf1/Pdx1 promoter, was extended beyond e9-e10, the development of the pancreas was drastically perturbed. Morphological analyses showed that the growth and morphogenesis of the pancreatic epithelium was impaired. Moreover, differentiation of pancreatic endocrine and exocrine cells was diminished and instead the pancreatic epithelium with its adjacent mesenchyme adopted an intestinal-like differentiation program. Together, these data point to a need for a tight temporal regulation of Hlxb9 expression. Thus, a total loss of Hlxb9 expression results in a block of the initiation of the dorsal pancreatic program, while a temporally extended expression of Hlxb9 results in a complete impairment of pancreatic development.

Animals↗
PubMed2001

Heat shock and heat shock protein 70i enhance the oncolytic effect of replicative adenovirus.

Replication-competent viruses are currently being evaluated for their cancer cell-killing properties. These vectors are designed to induce tumor regression after selective viral propagation within the tumor. However, replication-competent viruses have not resulted heretofore in complete tumor eradication in the clinical setting. Recently, heat shock has been reported to partially alleviate replication restriction on an avian adenovirus (Ad) in a human lung cancer cell line. Therefore, we hypothesized that heat shock and overexpression of heat shock protein (hsp) would support the oncolytic effect of a replication-competent human Ad. To this end, we tested the oncolytic and burst kinetics of a replication-competent Ad after exposure to heat shock or to inducible hsp 70 overexpression by a replication-deficient Ad (Adhsp 70i). Heat-shock resulted in augmentation of Ad burst and oncolysis while decreasing total intracellular Ad DNA. Overexpression of hsp 70i also enhanced Ad-mediated oncolysis but did not decrease intracellular Ad DNA levels. We conclude that heat shock and Adhsp 70i enhance the Ad cell-killing potential via distinct mechanisms. A potential therapeutic implication would be the use of local hyperthermia to augment oncolysis by increasing the burst of replication-competent Ad. The role of hsp in Ad-mediated oncolysis should be additionally explored.

Adenoviruses, Human↗
PubMed2001

Hypoxia down-regulates endostatin production by human microvascular endothelial cells and pericytes.

Endostatin is a potent anti-angiogenic factor derived from the C-terminal region of collagen XVIII and is implicated in the regulation of physiological and pathological angiogenesis. In this study, reverse transcription-polymerase chain reaction analysis of poly(A+) RNA demonstrated the presence of mRNA for collagen XVIII in human endothelial cells (EC) and pericytes, the very constituents of microvessels wherein angiogenesis takes place. Enzyme immunoassay revealed that both cell types liberated endostatin into culture media and that the endostatin levels were decreased by hypoxia, the principal cause of angiogenesis. Northern and Western blot analyses revealed that while the collagen XVIII/endostatin mRNA levels were invariant between hypoxic and normoxic conditions, the collagen XVIII protein levels in EC and pericytes decreased by hypoxia. Further, exogenously administered intact endostatin was significantly decreased when it was incubated with hypoxic conditioned media of endothelial cells or pericytes, but not with normoxic media. The results suggest that the reduction of autocrine endostatin may take an active part in hypoxia-driven angiogenesis.

Angiogenesis Inhibitors↗
PubMed2001

Novel synthesis of 4,5-diarylphenanthrenes via C2-C6 cyclization of benzannulated enyne-allenes.

A new synthetic pathway to the 4,5-diarylphenanthrenes 8 having a helical twist in their structures was developed. The synthetic sequence involves condensation of the diketone 5 with 2 equiv of the lithium acetylides derived from the diacetylenes 4 followed by protonation to produce the propargylic alcohols 6. Reduction of 6 with triethylsilane in the presence of trifluoroacetic acid furnished the tetraacetylenic hydrocarbons 7 in nearly quantitative yields. Treatment of 7 with potassium tert-butoxide under refluxing toluene at 110 degrees C for up to 10 h then furnished the 4,5-diarylphenanthrenes 8. Apparently, the transformation from 7 to 8 involves initial prototropic isomerizations to form the benzannulated enyne-allenes 9. Two subsequent formal intramolecular Diels-Alder reactions via the biradicals 10 and 12 derived from the C(2)-C(6) cyclizations then led to 13, which in turn underwent tautomerizations to give 8. The structure of 8a was established by the X-ray structure analysis, showing that the two phenyl substituents are bent away from each other and the central aromatic system is severely distorted with a helical twist. The existence of a helical twist in 8 imposed by the aryl groups at the 4- and 5-positions was also revealed with a set of AB (1)H NMR signals for the diastereotopic methylene hydrogens on the five-membered rings.

Journal Article↗
PubMed2001

Crystal structure of nitric oxide synthase bound to nitro indazole reveals a novel inactivation mechanism.

Nitric oxide is generated under normal and pathophysiological conditions by three distinct isoforms of nitric oxide synthase (NOS). A small-molecule inhibitor of NOS (3-Br-7-nitroindazole, 7-NIBr) is profoundly neuroprotective in mouse models of stroke and Parkinson's disease. We report the crystal structure of the catalytic heme domain of endothelial NOS complexed with 7-NIBr at 1.65 A resolution. Critical to the binding of 7-NIBr at the substrate site is the adoption by eNOS of an altered conformation, in which a key glutamate residue swings out toward one of the heme propionate groups. Perturbation of the heme propionate ensues and eliminates the cofactor tetrahydrobiopterin-heme interaction. We also present three crystal structures that reveal how alterations at the substrate site facilitate 7-NIBr and structurally dissimilar ligands to occupy the cofactor site.

Binding Sites↗
PubMed2001

Refined structure of alpha beta-tubulin at 3.5 A resolution.

We present a refined model of the alpha beta-tubulin dimer to 3.5 A resolution. An improved experimental density for the zinc-induced tubulin sheets was obtained by adding 114 electron diffraction patterns at 40-60 degrees tilt and increasing the completeness of structure factor amplitudes to 84.7 %. The refined structure was obtained using maximum-likelihood including phase information from experimental images, and simulated annealing Cartesian refinement to an R-factor of 23.2 and free R-factor of 29.7. The current model includes residues alpha:2-34, alpha:61-439, beta:2-437, one molecule of GTP, one of GDP, and one of taxol, as well as one magnesium ion at the non-exchangeable nucleotide site, and one putative zinc ion near the M-loop in the alpha-tubulin subunit. The acidic C-terminal tails could not be traced accurately, neither could the N-terminal loop including residues 35-60 in the alpha-subunit. There are no major changes in the overall fold of tubulin with respect to the previous structure, testifying to the quality of the initial experimental phases. The overall geometry of the model is, however, greatly improved, and the position of side-chains, especially those of exposed polar/charged groups, is much better defined. Three short protein sequence frame shifts were detected with respect to the non-refined structure. In light of the new model we discuss details of the tubulin structure such as nucleotide and taxol binding sites, lateral contacts in zinc-sheets, and the significance of the location of highly conserved residues.

Amino Acid Sequence↗
PubMed2001

Huntingtin aggregate-associated axonal degeneration is an early pathological event in Huntington's disease mice.

Huntington's disease (HD) is characterized by the selective loss of striatal projection neurons. In early stages of HD, neurodegeneration preferentially occurs in the lateral globus pallidus (LGP) and substantia nigra (SN), two regions in which the axons of striatal neurons terminate. Here we report that in mice expressing full-length mutant huntingtin and modeling early stages of HD, neuropil aggregates form preferentially in the LGP and SN. The progressive formation of these neuropil aggregates follows intranuclear accumulation of mutant huntingtin and becomes prominent from 11 to 27 months after birth. Neuropil aggregates, but no intranuclear inclusions, were observed in the LGP and SN, suggesting that huntingtin aggregates are formed in the axons of striatal projection neurons. In the LGP and SN, we observed degenerated axons in which huntingtin aggregates were associated with dark, swollen organelles that resemble degenerated mitochondria. Neuritic aggregates also form in cultured striatal neurons expressing mutant huntingtin, block protein transport in neurites, and cause neuritic degeneration before nuclear DNA fragmentation occurs. These findings suggest that the early neuropathology of HD originates from axonal dysfunction and degeneration associated with huntingtin aggregates.

Aging↗