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Expression of foreign proteins by poliovirus polyprotein fusion: analysis of genetic stability reveals rapid deletions and formation of cardioviruslike open reading frames.

Using a strategy developed by R. Andino, D. Silvera, S. D. Suggett, P. I. Achacoso, C. J. Miller, D. Baltimore, and M. B. Feinberg (Science 265:1448-1451, 1994), we constructed recombinant polioviruses by fusing the open reading frame (ORF) of the green fluorescent protein gene (gfp) of Aequorea victoria or the gag gene (encoding p17-p24) of human immunodeficiency virus type 1 (HIV-1) to the N terminus of the poliovirus polyprotein. All poliovirus expression vectors constructed by us and those obtained from Andino et al. were found to be severely impaired in viral replication and genetically unstable. Upon replication, inserted sequences were rapidly deleted as early as the first growth cycle in HeLa cells. However, the vector viruses did not readily revert to the wild-type sequence but rather retained some of the insert plus the artificial 3Cpro/3CDpro cleavage site, engineered between the heterologous sequence and the poliovirus polyprotein, to give rise to genotypes reminiscent of cardioviruses. These virus variants that carry a small leader polypeptide were now relatively stable, and they grew better than their progenitor strains. Reverse transcription followed by PCR and sequence analysis of the genomic RNAs reproducibly revealed a few preferred genotypes among the isolated deletion variants. The remaining truncated inserts were retained through subsequent passages. In the immediate vicinity of the deletion borders, we observed short direct sequence repeats that we propose are involved in aligning RNA strands for illegitimate (nonhomologous) RNA recombination during minus-strand synthesis. On the basis of our results, which are at variance with published data, the utility of poliovirus vectors to express proteins > 10 kDa in size through fusion with the polyprotein needs to be reevaluated.

Amino Acid Sequence↗

Induction of an antitumor immunological response by an intratumoral injection of dendritic cells pulsed with genetically engineered Semliki Forest virus to produce interleukin-18 combined with the systemic administration of interleukin-12.

OBJECT: The aim of this study was to investigate further immunogene treatment of malignant brain tumor to improve its therapeutic efficacy. METHODS: Intratumoral dendritic cells pulsed with Semliki Forest virus (SFV)-interleukin-18 (IL-18) and/or systemic IL-12 were injected into mice bearing the B16 brain tumor. To study the immune mechanisms involved in tumor regression, we monitored the growth of implanted B16 brain tumor cells in T cell-depleted mice and IFNgamma-neutralized mice. To analyze the protective immunity created by tumor inoculation, B16 cells were injected into the left thighs of mice that had received an inoculation, and tumor growth was monitored. The local delivery of dendritic cells pulsed with IL-18 bound by SFV combined with the systemic administration of IL-12 enhanced the induction of the T helper type 1 response from tumor-specific CD4+ and CD8+ T cells and natural killer cells as well as antitumor immunity. Interferon-gamma is partly responsible for this IL-18-mediated antitumor immunity. Furthermore, the protective immunity is mediated mainly by CD8+ T cells. CONCLUSIONS: Immunogene therapy that combines the local administration of dendritic cells pulsed with IL-18 bound by SFV and the systemic administration of IL-12 may be an excellent candidate for the development of a new treatment protocol. A self-replicating SFV system may therefore open a novel approach for the treatment of malignant brain tumor.

Animals↗

[Interleukin-12 gene transfection into murine B16 melanoma cells suppresses tumorigenicity and decreases metastatic potential].

OBJECTIVE: To study the tumorigenicity and metastasis of poorly immunogenic murine B16 melanoma cells transfected with murine interleukin-12 (IL-12) gene. METHODS: Two recombinant vectors containing the full length cDNA of p40 or p35 subunit of IL-12 were constructed. They were cotransfected into B16 melanoma cells by LipofectAMIN method. The expressions of p40 and p35 mRNAs were analyzed by means of reverse transcription polymerase chain reaction (RT-PCR). The secretion of bioactive IL-12 was detected by bioassay (measuring the proliferative response of PMA-activated murine splenocytes). To determine the effects of IL-12 secreted by genetically engineered B16 cells (B16T-IL12) on tumorigenesis and metastasis, the cells were inoculated s.c. or i.v. into C57BL/6 mice. RESULTS: B16T-IL12 cells expressed both p40 and p35 mRNAs, also produced bioactive IL-12. Only 70% of the mice injected with B16T-IL12 cells developed palpable tumors. The emergence of palpable tumors in the mice inoculated with B16T-IL12 cells was significantly delayed (P < 0.01), the growth rate of the tumors was obviously decreased (P < 0.01), and the survival time of tumor-bearing mice was prolonged substantially (P < 0.01), compared with the control B16 or B16Tneo cells. The incidence of experimental pulmonary metastasis of B16T-IL12 cells was inhibited, and the number of pulmonary metastases was reduced markedly, in contrast to the i.v. inoculation of B16 cells (P < 0.01). CONCLUSION: Transfection of IL-12 gene into B16 cells results in the inhibition of tumorigenesis and in the suppression of experimental pulmonary metastasis.

Animals↗

Ligand-regulated internalization and recycling of human beta 2-adrenergic receptors between the plasma membrane and endosomes containing transferrin receptors.

Agonist-regulated redistribution of human beta 2-adrenergic receptors was examined in 293 cells. A specific antiserum recognizing the carboxyl-terminal hydrophilic domain of the receptor was developed, characterized, and used for immunocytochemical localization of receptors in fixed cells by conventional fluorescence and confocal fluorescence microscopy. The beta-adrenergic agonist isoproterenol induced redistribution of receptors from the surface of cells into small (less than 1 micron diameter) punctuate accumulations which were detected in cells within 2 min of agonist addition. The time course of receptor redistribution paralleled that of receptor sequestration measured by ligand binding, and receptor redistribution was reversible in the presence of the beta-adrenergic antagonist alprenolol. Optical sections imaged through cells by confocal microscopy localized receptor accumulations within the cytoplasm. To address the question of receptor internalization further, a mutant receptor possessing an engineered antigenic epitope in the amino-terminal hydrophilic domain was constructed, transfected into cells, and localized using both a monoclonal antibody recognizing the epitope tag (receptor ectodomain) and an antiserum recognizing the carboxyl terminus (receptor endodomain). In untreated cells most receptor antigen was detected at the cell surface, as assessed by accessibility to ectodomain antibodies in unpermeabilized specimens. In isoproterenol-treated cells, however, little receptor antigen was detected at the cell surface. Punctate receptor accumulations present in isoproterenol-treated cells were labeled by antibodies only following permeabilization of cells, as expected if these receptor accumulations were intracellular. Finally, internalized beta-adrenergic receptors colocalized with transferrin receptors, which are markers of endosomal membranes. These data provide several lines of evidence establishing that beta-adrenergic receptors undergo ligand-regulated internalization, they suggest that internalized receptors may be recycled back to the cell surface, and they provide the first direct indication that these processes involve the same endosomal membrane system passaged by constitutively recycling receptors.

Alprenolol↗

Recombinant human hepatitis B virus reverse transcriptase is active in the absence of the nucleocapsid or the viral replication origin, DR1.

The double-stranded DNA genome of hepatitis B virus (HBV) is reverse transcribed from the viral pregenome RNA template by a virally encoded reverse transcriptase enzyme (RT) that possesses both priming and elongation activities. Prior efforts have failed to express an active form of HBV RT outside the nucleocapsid in animal cells or to release it from viral nucleocapsids, thus restricting the characterization of this important enzyme. Here, we have engineered epitope-tagged HBV RT proteins and expressed them in Xenopus oocytes via a synthetic RT mRNA which does not include the viral capsid protein or the known initiation site for viral DNA synthesis, DR1. We demonstrate the production of an immunoprecipitable 96-kDa HBV RT protein and show, using a simple in vitro RT assay, that oocyte lysates containing this protein possess an activity that (i) catalyzes an RNA-dependent deoxynucleotide triphosphate polymerization reaction by using an as-yet-unidentified RNA template and (ii) is sensitive to the RT inhibitors actinomycin D and phosphonoformate. Experiments with the chain terminator ddATP suggest that a significant amount of chain elongation occurs in our in vitro reaction. Electrophoretic analysis reveals a heterogeneous array of RT reaction products with sizes ranging from about 100 bases to far larger than that of the input RT mRNA. These products appear to contain covalently bound protein, consistent with the notion that the RT protein may have primed their synthesis. We conclude that HBV RT activity can be uncoupled from both the nucleocapsid and the replication origin, DR1. Our results raise the possibility that unless HBV employs novel mechanisms to regulate its constitutively active RT, cellular RNAs may be reverse transcribed during HBV infection, with potential implications for the development of HBV-related liver cancer. The use of the oocyte system should facilitate studies of HBV RT, including the development of HBV RT inhibitors for antiviral therapy.

Amino Acid Sequence↗

Manipulation of gene expression by an ecdysone-inducible gene switch in tumor xenografts.

BACKGROUND: Rapid, robust and reversible induction of transgene expression would significantly facilitate cancer gene therapy as well as allow the in vivo functional study of newly discovered genes in tumor formation and progression. The popularity of the ecdysone inducible gene switch system has led us to investigate whether such a system can successfully regulate gene expression in a syngeneic tumor system in vivo. RESULTS: MBT-2 and Panc02 carcinoma cells were transfected with components of a modification of the ecdysone switch system driving firefly luciferase (F-Luc). In vitro luciferase expression +/- ecdysone analog GS-E indicated a robust induction with minimal baseline activity and complete decay after 24 hours without drug. In vitro selection of MBT-2 transfected cell clones which had complete absence of F-Luc expression in the absence of stimulation but which expressed this gene at high levels in response to GS-E were chosen for in vivo evaluation. Tumors from engineered MBT-2 cells were grown to 5 mm in diameter prior to GS-E administration, animals euthanized and tumors removed at 6, 12 and 24 hours after GS-E administration and assayed for F-Luc activity. GS-E resulted in a maximal induction of F-Luc activity at 6 hours in tumor tissue with almost complete reversion to control levels by 12 hours. CONCLUSIONS: This study is the first demonstration that robust and reversible transgene expression in tumors is feasible using the ecdysone system, allowing future rapid in vivo functional characterization of gene function or gene therapy applications.

Animals↗

[Stimulation of insulin-like growth factor-I to chondrogenesis of engineering cartilage tissue].

OBJECTIVE: To explore the ability of insulin-like growth factor-I (IGF-I) and hyaluracan acid in prompting chondrogenesis of engineering cartilage tissue. METHODS: Human articular chondrocytes were isolated and cultured in DMEM plus 10% fetal bovine serum. They were divided into three groups: hyaluracan acid + chondrocytes + IGF-I group (IGF-I group), hyaluracan acid + chondrocytes group (cell group), hyaluracan acid group (control group). The ability of chondrogenesis was investigated by HE and toluidine blue staining, human collagen II immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). RESULTS: Both cell group and IGF-I group could develop into cartilage tissue in the sixth week while control group could not. The number of cartilage lacuna in IGF-I group were more than that in cell group. Human collagen II immunohistochemistry showed that there were stronger positive cell in IGF-I group than in cell group, collagen II mRNA expression was more higher and collagen I mRNA expression was lower in IGF-I group than in cell group. CONCLUSION: Insulin growth factor-I can prompt chondrogenesis of engineering cartilage tissue and ameliorate the quality of engineering cartilage tissue in vitro.

Cartilage, Articular↗

Transition-state stabilization in the mechanism of tyrosyl-tRNA synthetase revealed by protein engineering.

The principal catalytic factor in the activation of tyrosine by the tyrosyl-tRNA synthetase is found to be improved binding of ATP in the transition state. The activation reaction involves the attack of the tyrosyl carboxylate on the alpha-phosphate group of ATP to generate a pentacoordinate transition state. Model building of this complex located a binding site for the gamma-phosphate group of ATP, consisting of hydrogen bonds with the side chains of Thr-40 and His-45. Removal of these groups by protein engineering shows that they contribute no binding energy with unreacted ATP but put all of their binding energy into stabilizing the [tyrosine-ATP] transition state [the mutant tyrosyl-tRNA synthetase (Thr-40----Ala-40; His-45----Gly-45) has the rate of formation of tyrosyl adenylate lowered by 3.2 X 10(5) but KS for ATP is lowered by only a factor of 5]. The side chains of these residues also provide a binding site for pyrophosphate in the reverse reaction. Thus, catalysis is accomplished by stabilization of the transition state by improved binding of a group on the substrate that is distant from the seat of reaction.

Adenosine Triphosphate↗

Virus replication begins in dendritic cells during the transmission of HIV-1 from mature dendritic cells to T cells.

BACKGROUND: To initiate immunity, dendritic cells (DCs) capture antigens or viruses at body surfaces, undergo maturation to express T-cell costimulatory molecules, and then migrate to lymphoid organs. DCs at body surfaces can capture human immunodeficiency virus 1 (HIV-1), but mature DCs do not support replication of the virus unless T cells are added. The initial site for HIV-1 replication remains unknown and it is unclear whether replication can take place in DCs or whether the virus must first be transmitted from DCs to T cells. RESULTS: We generated mature DCs from monocyte precursors. Upon infection with HIV-1, reverse transcription was completed only when T cells were added. When the reverse transcriptase inhibitor azidothymidine was added to the DCs during exposure to HIV-1, the DCs remained fully infectious, as long as the drug was removed just before culturing the DCs with T cells. HIV-1 variants that were engineered to undergo only one cycle of replication were able to infect DCs and replicate once in these cells. When T cells were added, newly produced HIV-1 Gag protein was exclusively localized to the DCs. With wild-type virus, subsequent rounds of replication took place in T cells. Soluble CD40 ligand (CD40L) and CD40L-transfected fibroblasts stimulated HIV-1 replication in purified mature DCs. CONCLUSIONS: Mature DCs provide a drug-resistant reservoir for HIV-1. This reservoir is activated within DCs by CD40L and upon interaction with T cells, and the virus then spreads rapidly to other T cells.

Anti-HIV Agents↗

Intravenous administration of replication-incompetent adenovirus to rhesus monkeys induces thrombocytopenia by increasing in vivo platelet clearance.

A replication-incompetent adenovirus vector was administered to rhesus macaques at 1, 3 and 6 x 1012 particles/kg doses to investigate its toxicity. Platelet count decrements of 28%, 82% and 90%, respectively, were observed, with corresponding platelet half-lives of 69.0, 25.2 and 22.2 h (compared with 111 h in untreated animals). The platelet decline was equivalent for all three doses for 8 h, and platelet count recovery began as early as 8 h after infusion for low-dose recipients, or as late as 24 h for the medium and high dose recipients. These observations suggest that thrombocytopenia is a saturable, reversible consumptive process.

Adenoviridae↗

Molecular characterization of a flagellar export locus of Helicobacter pylori.

Motility of Helicobacter species has been shown to be essential for successful colonization of the host. We have investigated the organization of a flagellar export locus in Helicobacter pylori. A 7-kb fragment of the H. pylori CCUG 17874 genome was cloned and sequenced, revealing an operon comprising an open reading frame of unknown function (ORF03), essential housekeeping genes (ileS and murB), flagellar export genes (fliI and fliQ), and a homolog to a gene implicated in virulence factor transport in other pathogens (virB11). A promoter for this operon, showing similarity to the Escherichia coli sigma70 consensus, was identified by primer extension. Cotranscription of the genes in the operon was demonstrated by reverse transcription-PCR, and transcription of virB11, fliI, fliQ, and murB was detected in human or mouse biopsies obtained from infected hosts. The genetic organization of this locus was conserved in a panel of H. pylori clinical isolates. Engineered fliI and fliQ mutant strains were completely aflagellate and nonmotile, whereas a virB11 mutant still produced flagella. The fliI and fliQ mutant strains produced reduced levels of flagellin and the hook protein FlgE. Production of OMP4, a member of the outer membrane protein family identified in H. pylori 26695, was reduced in both the virB11 mutant and the fliI mutant, suggesting related functions of the virulence factor export protein (VirB11) and the flagellar export component (FliI).

Animals↗

Analysis of a human immunodeficiency virus type 1 gag mutant with an engineered 110-amino-acid insertion in the matrix protein domain.

A human immunodeficiency virus (HIV) matrix (MA) protein mutant was constructed by duplication of 107 codons of the HIV-1 MA domain. This MA protein duplication mutant (MAII) still could assemble and process particles, had a wild-type (wt) HIV particle density, and possessed reverse transcriptase activity of about 80% of the wild type virus level. The incorporation of HIV Env and viral RNA genome was not greatly affected. The MAII was noninfectious or poorly infectious, however, when pseudotyped with an amphotropic murine leukemia virus envelope protein or with the HIV envelope protein. Although the MAII mutant displayed an immunofluorescence staining pattern similar to that of the wild type virus, subcellular fractionation studies indicated that the membrane association of MAII Gag precursors was unstable under high-salt conditions. Electron microscopic studies showed that the mutant had a decreased density of particle cores compared with that of the wild type virus, suggesting an altered arrangement of the packed proteins. As this insertion in the MA gene caused no major effects on virus assembly implies that the HIV-1 gag has the potential to adapt large insertions of extra coding sequences without loss of the ability to direct particle assembly and release.

Blotting, Western↗

Trapping HIV-1 reverse transcriptase before and after translocation on DNA.

A disulfide cross-linking strategy was used to covalently trap as a stable complex (complex N) a short-lived, kinetic intermediate in DNA polymerization. This intermediate corresponds to the product of polymerization prior to translocation. We also prepared the trapped complex that corresponds to the product of polymerization after translocation (complex P). The cross-linking method that we used is a variation of a technique developed by the Verdine and Harrison laboratories. It involves disulfide interchange between an engineered sulfhydryl group of the protein (Q258C mutation) and a disulfide-containing tether attached at the N(2) amino group of a modified dG in either the template or the primer strand of the nucleic acid. We report here a highly efficient synthesis of the precursor, bis(3-aminopropyl)disulfide dihydrochloride, used to introduce this substituent into the oligonucleotide. Efficient cross-linking takes place when the base pair containing the substituent is positioned seven registers from the dNTP-binding site (N site) and the N site is occupied. Complex N, but not complex P, is a substrate for the ATP-based excision reaction that unblocks nucleoside reverse transcriptase inhibitor (NRTI)-terminated primers and causes resistance to several NRTIs, confirming predictions that the excision reaction takes place only when the 3'-end of the primer is bound at the N site. These techniques can be used for biochemical and structural studies of the mechanism of DNA polymerization, translocation, and excision-based resistance of RT to NRTIs. They may also be useful in studying other DNA or RNA polymerases or other enzymes.

Adenosine Triphosphate↗

Biocompatible hydrogel supports the growth of respiratory epithelial cells: possibilities in tracheal tissue engineering.

Extensive tracheal defect reconstruction is a major challenge in plastic and reconstructive surgery. The lack of an epithelial lining on the luminal surfaces of tracheal prostheses is among the major causes of their failure. Chitosan-gelatin hydrogels were synthesized for the development of biocompatible, growth-supportive substrata for respiratory epithelial cells. We employed J774 macrophages to test the immunocompatibility of this gel. The hydrogel did not exert a cytotoxic effect on macrophages, as confirmed by tetrazolium reduction and neutral red uptake assay. Flow cytometric analysis of macrophages cultured on the hydrogel showed a comparable expression of activation markers CD11b/CD18, CD45, and CD14 to the control. Semiquantitative RT-PCR results showed an absence of upregulation of interleukin-6 (IL-6) and TNF-alpha in these macrophages with respect to the controls. Primary human respiratory epithelial cells cultured on the hydrogel showed proper attachment, normal morphology, and growth. A small proportion of cells on the hydrogel showed synchronously beating cilia. RT-PCR analysis showed that cells on the hydrogel expressed mucins 2 and 5 and cytokeratin 13, which are markers for secretory goblet and squamous cells, respectively. All these results demonstrate that the hydrogel supports the growth of a mixed population of differentiated epithelial cells. This hydrogel is suitable as a culture substratum for respiratory epithelial cells and could be used as a potential candidate for coating tracheal prostheses.

Biocompatible Materials↗

Development and evaluation of a complementation-dependent gene delivery system based on cucumber mosaic virus.

To engineer cucumber mosaic virus (CMV-Ix) into a gene vector, genome component RNA 3 of the virus was modified and split into two sub-components, RNA 3A and RNA 3B. In RNA 3A, the open reading frame of the movement protein (MP) was replaced by a reporter gene encoding the green fluorescent protein (GFP), to monitor virus replication and movement. In RNA 3B, the coat protein (CP) gene was eliminated and a multiple cloning site (MCS) was created for foreign gene insertion. Each sub-component alone is defective and relies on its companion sub-component to restore full RNA 3 function. The vector system was evaluated for its ability to deliver and express the bacterial beta-glucuronidase (GUS) gene and a modified bean yellow mosaic virus coat protein (BYMV-CP) gene in Nicotiana benthamiana plants. Results showed that the engineered virus was able to move from cell to cell in the inoculated leaf and enter the minor veins of the inoculated leaf. Foreign gene expression was detected in the inoculated leaves. However, intermolecular recombination between RNA 3A and 3B occurred frequently, preventing efficient systemic expression of the foreign gene(s). Modifications and further evaluations are being undertaken to improve the gene delivery system.

Capsid↗

The effect of fuel composition on the mutagenicity of diesel engine exhaust.

The effect of fuel composition on the mutagenicity of diesel engine emission was investigated. To this end, a fuel matrix comprising fuels with different contents of aromatic and naphthenic compounds was used. Extracts of the organic phase of raw exhausts obtained with different fuels were tested for mutagenicity in bacterial reversion assays. The results obtained demonstrate that the mutagenicity of diesel exhaust is largely dependent on the aromatic content of the fuel. In fact, mutagenicity was greatly reduced when the aromatic content of the fuel was lowered by hydrogen treatment. Conversely, mutagenicity was enhanced when the fuel was enriched with fractions of di- or triaromatic compounds. The addition of di- and trinaphthenic compounds only produced borderline mutagenicity. No clear relationship was observed between sulfur content of the fuel and mutagenicity of the exhaust. Assays in bacterial strains with different sensitivity to nitroaromatic compounds suggest a low contribution of the highly mutagenic dinitropyrenes to the responses observed, and a relatively greater contribution of 1-nitropyrene or other nitroaromatics processed by the same bacterial nitroreductase.

Mutagenicity Tests↗

A smart adhesive joint: entropic control of adhesion at a polymer/metal interface.

The study of adhesion has a long and rich history, with theory, experiments, and applications bridging numerous disciplines, including physics, chemistry, engineering, and medicine. This diverse interest has led to the development of a large number of methods for both enhancing and inhibiting adhesion at specific interfaces of interest. We report herein "smart" adhesion at a polymer/metal (oxide) interface that responds reversibly to changes in temperature by increasing or decreasing in magnitude. The temperature dependence in this system arises from the rubber elasticity of the polymer, 1,4-polybutadiene, and mirrors the interfacial behavior of the same polymer against water. Such systems offer unique opportunities for designing responsive materials whose properties can be actively controlled.

Journal Article↗

Decreased lysosomal storage in the adult MPS VII mouse brain in the vicinity of grafts of retroviral vector-corrected fibroblasts secreting high levels of beta-glucuronidase.

A deficiency of beta-glucuronidase (GUSB) causes the multisystem progressive degenerative syndrome, mucopolysaccharidosis (MPS) type VII (Sly disease), which includes mental retardation. Animal homologues of MPS VII (ref. 3, 4) are models for testing somatic gene transfer approaches to treat the central nervous system in this and other lysosomal storage disorders. Previous attempts to correct murine MPS VII by gene therapy have successfully treated lesions in some organs but not in the brain. Other experimental modalities have forestalled some disease progression in the brain, but only if done at birth, before the onset of severe lesions, when the animals are phenotypically normal. We tested whether therapeutic amounts of GUSB could be delivered to the diseased adult brain by transplanting cells engineered to super-secrete the normal enzyme for export to surrounding neural tissues. Lysosomal distention was cleared from neurons and glial cells in the vicinity of the grafts, showing that the secreted enzyme could reach the diseased cells and reverse lesions in the severely diseased brain. The ability to correct established lesions will be important for the treatment of many lysosomal storage diseases affecting the brain, because most patients are not diagnosed until lesions are advanced enough to affect phenotype or developmental milestones in early childhood, and some forms of the diseases do not become apparent until later in life.

Animals↗