UMLS:C0023418 - FACTA Search

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Query: UMLS:C0023418 (leukemia)
93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The GIX antigen, which is expressed on the surface of thymocytes of certain mouse strains, is an antigenic determinant of the major envelope glycoprotein of murine leukemia virus (gp70). Although GIX is expressed in some mouse strains that appear to be free of virus, the antigen can also be induced in GIX- mice by infection with particular murine leukemia viruses (termed GIX+). We have investigated the envelope gene products from two closely related viruses that differ in their GIX phenotype. Analysis of the envelope protein precursors by polyacrylamide gel electrophoresis and endoglycosidase treatment indicated that the GIX+ viral protein contained six oligosaccharide chains, whereas the GIX- viral protein contained seven. The observed differences in gel electrophoretic mobilities and glycopeptide profiles of the respective glycosylated envelope gene cleavage products (gp70) may be accounted for by the presence of an additional oligosaccharide chain on the gp70 of the GIX- virus. No differences between the apparent molecular weights of the nonglycosylated product of the envelope gene (p15E) were detected. These results suggest that the GIX- virus codes for an extra glycosylation site relative to the GIX+ virus, and this oligosaccharide chain is present both on the envelope gene precursor (Prenv) and on the major cleavage product (gp70). Recent nucleotide sequence analyses of selected RNase T1 oligonucleotides from the genomes of viruses that differ in GIX phenotype have similarly suggested that there may be a correlation between the GIX- phenotype and an extra glycosylation site [Donis-Keller, H., Rommelaere, J., Ellis, R. W. & Hopkins, N. (1980) Proc. Natl. Acad. Sci. USA 77, 1642-1645]. The results of these two different approaches raise the possibility that the presence of an additional oligosaccharide chain on gp70 may, either directly or indirectly, mask the expression of the GIX antigen on the surfaces of thymocytes and virus-infected cells.
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PMID:Relationship of GIX antigen expression to the glycosylation of murine leukemia virus glycoprotein. 693 56

Erythroleukemia cell lines HFL/d and HFL/b, derived from tumors induced in vivo in BALB/c (H-2d) and congenic BALB.B (H-2b) mice, respectively, by a polycythemia-inducing strain of Friend virus, produced both spleen focus-forming virus (SFFV) and its native NB-tropic helper virus (Friend murine leukemia virus [FMuLV]) during early-passage generations in culture. Eventually each line ceased production of both infectious viruses but retained its tumorigenic potential in syngeneic hosts. Virus-producer and -nonproducer clones of these cell lines were examined for expression of proteins encoded by the SFFV or FMuLV genomes. Lysates of labeled cells were treated with various antiviral sera, and the precipitates were examined by gel electrophoresis. Expression of the FMuLV env gene-encoded precursor protein, gPr84env, was observed in all producer and most nonproducer clones, but the FMuLV gag and pol gene products, Pr65gag and Pr200gag-pol, were uniformly undetectable in nonproducer clones. All HFL/d and HFL/b clones expressed appreciable amounts of the SFFV-encoded envelope protein, gp52, including one exceptional clone which had ceased to express any FMuLV-encoded proteins. The molecular weight of this SFFV-encoded envelope protein was consistently smaller in all HFL/b clones than in HFL/d clones, regardless of their producer or nonproducer status. The virus-nonproducer phenotype thus appears to be due to shutdown of expression of the 5' portion of the FMuLV genome in two independent cell lines.
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PMID:Viral protein expression in producer and nonproducer clones of friend erythroleukemia cell lines. 693 35

The T cell responses of Moloney leukemia virus (MoLV)-infected preleukemic BALB/c mice were examined. The major in vitro response detectable was T cell blastogenesis in response to the major viral envelope protein MoLV gp71 and an internal viral protein p12. The majority of the preleukemic mice had readily detectable responses to gp71, whereas the presence of a response to p12 was less consistent. With both antigens, T cell blastogenesis showed typical antigen response characteristics similar to those detected in other immune responses to C-type viruses. Proliferation was dependent on a Thy-1+, Lyt-1+, 2- population and was macrophage-independent. In contrast to most immune responses to C-type viruses, which are temporally restricted, T cell blastogenesis was detectable throughout the preleukemic period of 4 to 16 wk of age. During this period neither gp71-specific T cells nor PHA-responsive T cells were found to express viral antigens. The correlations between T cells responding to gp71 and leukemia were examined. Under conditions in which MoLV inoculation of BALB/c mice does not induce leukemia, no T cell responses were deectable. These results suggest a causal relationship between the presence of antigen-specific T cells and the ability of MoLV to induce leukemia. The results are discussed with reference to the possible role of chronic immune stimulation in virus-induced leukemogenesis.
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PMID:Mechanisms in T cell leukemogenesis. II. T cell responses of preleukemic BALB/c mice to Moloney leukemia virus antigens. 696 59

Synchronized mouse cells (JLS-V9) chronically infected with Rauscher murine leukemia virus were used to study virus production, the synthesis of gag and env precursor proteins, and the expression of env protein on the cell surface during the cell cycle. The amount of virus released into the medium by synchronized cells during a 30-min interval was determined by using the XC plaque assay and by measuring reverse transcriptase activity. The results show that virus production occurs during mitosis. Labeling of the cell surface of synchronized cells with 125I or with fluorescein-conjugated antiserum shows that the amount of gp 70env on the cell surface parallels cellular growth. Therefore, the cell cycle-dependent release of virus is not accompanied by similar variations in the amount of viral envelope protein on the cell surface. Immunoprecipitation of cells labeled with [35S]methionine, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was used to measure viral protein synthesis during the cell cycle. The rate of synthesis of gag precursor proteins show three maximums corresponding to the G1, middle S, and late S to G2 phases of the cell cycle. The rate of synthesis of env precursor proteins does not change, suggesting that in these cells the synthesis of these two gene products is controlled separately.
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PMID:Retrovirus gene expression during the cell cycle. I. Virus production, synthesis, and expression of viral proteins in Rauscher murine leukemia virus-infected mouse cells. 728 18

The murine leukemia virus (MuLV) envelope protein was examined to determine which sequences are responsible for the differences in direct membrane fusion observed with the ecotropic and amphotropic MuLV subtypes. These determinants were studied by utilizing amphotropic-ecotropic chimeric envelope proteins that have switched their host range but retain their original fusion domain (TM subunit). Fusion was tested both in rodent cells and in 293 cells bearing the human homolog of the ecotropic MuLV receptor. The results demonstrate that the amphotropic TM is able to mediate cell-to-cell fusion to an extent equivalent to that mediated by the ecotropic TM, indicating that their fusion domains are equivalent. The "murinized" human homolog of the ecotropic receptor supports syncytium formation as well as the native murine receptor. These findings suggest that interactions between the ecotropic envelope protein and conserved sequences in the ecotropic receptor are the principal determinants of syncytium formation. The relationship of the fusion phenotype to pH-dependent infection and the route of viral entry was examined by studying virions bearing the chimeric envelope proteins. Such virions appear to enter cells via a pathway that is directed by the host range-determining region of their envelope rather than by sequences that confer pH dependence. Therefore, the pH dependence of infection may not reflect the initial steps in viral entry. Thus, it appears that both the syncytium phenotype and the route of viral entry are properties of the viral receptor, the amino-terminal half of the ecotropic envelope protein, or the interaction between the two.
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PMID:The amphotropic and ecotropic murine leukemia virus envelope TM subunits are equivalent mediators of direct membrane fusion: implications for the role of the ecotropic envelope and receptor in syncytium formation and viral entry. 747 42

Since the description of human T-cell leukemia virus type I (HTLV-I) and its simian counterpart, simian T-cell leukemia virus type I (STLV-I), the possible existence of other related simian retroviruses has been raised. Here, we report a new retrovirus, STLV-II, which we have identified in spider monkeys (Ateles fusciceps), a New World primate species. Initially, a recombinant HTLV-II envelope protein (RP-IIB) was used to identify anti-STLV-II antibodies in New World monkeys by Western blot (immunoblot) assays. Subsequently, the virus was characterized by Southern blot hybridization, which showed that STLV-II and HTLV-II have a high degree of nucleotide sequence homology but have different restriction enzyme patterns. Nucleotide sequence analysis of the pX-II region of STLV-II provirus revealed 3% variation with the corresponding region of HTLV-II. Electron micrographic studies revealed HTLV-like, type C retrovirus particles outside the cell membranes of STLV-II-infected cells. This study describes the first link between HTLV-II and a simian reservoir in the New World. Further molecular studies of STLV-II infection in different species of New World monkeys, especially from the wild, may provide valuable information about the origin and intragroup relationships of South American monkeys. Spider monkeys infected with STLV-II may serve as an important animal model for HTLV-II infection in humans.
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PMID:Isolation and characterization of simian T-cell leukemia virus type II from New World monkeys. 750 78

To study the possible role of immune selection in the in vivo generation of pathogenic recombinant murine leukemia viruses (MuLV), we have constructed recombinant vaccinia viruses (rVV) expressing the envelope genes of three MuLV: AKR623, MCF247, and MCF13. rVV expressing either AKR623 or MCF247 env could prime H-2b mice for anti-AKR/Gross virus CTL responses, and stimulate the in vitro generation of CTL from the spleens of mice immunized with an AKR/Gross virus-positive lymphoma. MC57 (H-2b) cells infected with either 623EnvVac or 247EnvVac could serve as targets for ARK/Gross virus-specific CTL. Cells infected with the rVV expressing MCF13 env, however, were lysed much less efficiently by these CTL. 13EnvVac was also ineffective in priming or stimulating retrovirus-specific CTL. Finally, experiments with synthetic peptides and minigenes suggested that the reduced immunogenicity of the MCF13 envelope protein likely resulted from a single amino acid substitution within an immunodominant epitope of the p15E (TM) protein. The region of MCF13 env that encodes this epitope is derived from an endogenous xenotropic virus, while the allelic sequences in MCF247 are of ecotropic virus origin. These results suggest the potential for recombination within the MuLV envelope gene to allow escape from host cellular immune responses.
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PMID:Cytotoxic T lymphocyte responses to the envelope proteins of endogenous ecotropic and mink cytopathic focus-forming murine leukemia viruses in H-2b mice. 751

Upon infection with the Moloney murine sarcoma virus-murine leukemia virus (MuLV) complex, H-2b C57BL/6 (B6) mice respond with a class I Db-restricted cytotoxic T-lymphocyte (CTL) response, which protects against virus-induced tumorigenesis. In the B6-derived Db mutant B6.CH-2bm13 (bm13) strain, part of the class I Db antigen-presenting groove is shaped by a class I Kb-encoded sequence. Like B6 mice, bm13 mice reject Moloney virus-induced tumors, but the protective CTL response is Kb restricted. In this study we show enhanced levels of Moloney MuLV-specific CTLp with a restriction for Kb in bm13 mice. Through the use of CTL clones from Moloney virus-immunized bm13 mice, the class I Kb-presented CTL epitope was identified. The epitope is located in the Moloney virus gp70 envelope protein region (Moloney envelope, amino acids 189 to 196 [Mol env (189-196)]), SSWDFITV and has the Kb allele-specific binding motif. The Dbm13 molecule does not present the env(189 to 196) epitope to Kb-restricted bm13 CTL. In B6 mice, Mol env(189-196)-specific CTL could be induced by peptide vaccination. B6 mice thus have CTL precursors specific for this epitope but at considerably lower levels than do bm13 mice. We hypothesize that additional positive selection of Kb-restricted CTL on the Dbm13 molecule in bm13 mice explains this difference in precursor frequencies. We examined related strains of MuLV for the presence of Mol env(189-196) sequence equivalents. Rauscher, Friend, and AKV MuLV-encoded Mol env(189-196) epitope equivalents were properly recognized in cytotoxicity assays, both as synthetic and as endogenously expressed (Rauscher MuLV) peptides. In contrast, the mink cell focus-forming virus MuLV-encoded epitope equivalent, lacking a Kb anchor residue, was not presented for CTL recognition and hence can be excluded as an important CTL epitope for mink cell focus-forming viruses.
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PMID:Identification of an H-2 Kb-presented Moloney murine leukemia virus cytotoxic T-lymphocyte epitope that displays enhanced recognition in H-2 Db mutant bm13 mice. 752 98

We explored the feasibility of designing retroviral vectors that can target human breast cancer cells with characteristic receptors via ligand-receptor interaction. The ecotropic Moloney murine leukemia virus envelope was modified by insertion of sequences encoding human heregulin. Ecotropic virus, which normally does not infect human cells, when pseudotyped with the modified envelope protein now crosses species to infect human breast cancer cell lines that overexpress HER-2 (human epidermal growth factor receptor; also called ERBB2) and HER-4 (also called ERBB4), while human breast cancer cell lines expressing low levels of these receptors remain resistant to infection. Since about 20% of human breast cancers overexpress HER-2 and some of breast cancer cell lines overexpress both HER-2 and HER-4, cell-specific targeting of retroviral vectors may provide a different approach for in vivo gene therapy of this type of breast cancer.
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PMID:Ligand-directed retroviral targeting of human breast cancer cells. 756 10

Retroviral vectors are the most efficient tool to introduce genes into vertebrate cells. However, their use is limited by the host range of the retrovirus from which they were derived. To alter the host range of the vector particle, we developed a method to substitute the receptor-binding domain of the envelope protein of a retrovirus with an antigen-binding site of an antibody. To test whether such particles are competent for infection, we established a model system using an antigen-binding site of an antibody against the hapten dinitrophenol (DNP). Retroviral vector particles containing such chimeric envelope proteins were able to bind to and infect cells that were not infectable with wild-type virus after DNP was conjugated to the cell surface. They did not infect such cells without DNP conjugation. Control experiments with chimeric envelope proteins of ecotropic murine leukemia virus (eco-MLV) and spleen necrosis virus (SNV) indicate that the pathway of virus entry of scA-env-containing virus particles was different from that of wild-type virus.
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PMID:Cell targeting with retroviral vector particles containing antibody-envelope fusion proteins. 758 94

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