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PubMed1975

Different hematological diseases induced by type C viruses chemically activated from embryo cells of different mouse strains.

Type C RNA viruses can be induced by certain chemicals from cells of many mouse strains. Both C58 and BALB/c cells have been shown to contain endogenous viruses that are designated N-tropic because they grow preferentially in cells of NIH Swiss mouse origin. While demonstrating many similar biological and immunological properties, the C58-induced virus is around 10-fold more infectious per physical particle than the N-tropic virus of BALB/c cells. In the present studies, inoculation of these viruses into newborn NIH Swiss mice led to the development of diseases associated with splenomegaly and lymphadenopathy at similar frequency in each group. The disease induced by C58-MuLV was histophathologically diagnosed as lymphoblastic leukemia and was highly malignant following transplantation into newborn mice. The histopathological appearance of spleens from BALB/c virus-affected animals was distinguishable, demonstrating instead myeloid metaplasia or myelogenous leukemia. These findings provide evidence that different endogenous mouse type C viruses can induce distinct diseases in the same mouse strain. Furthermore, they implicate the N-tropic virus endogenous to C58 cells as a major factor in the development of lymphoblastic leukemia that occurs at high frequency in that strain.

Animals↗
PubMed1975

Effect of glucocorticoids on activation of leukemia virus in AKR mouse embryo cells.

The effect of glucocorticoids on activation and replication of leukemia virus in AKR mouse embryo cells was analyzed. The number of cells detected as positive by fluorescent antibody techniques as well as the virus production in cells chronically producing virus was doubled at optimal concentrations of glucocorticoids. The effect of the hormones in activated cells was found to be not on the process of activation per se but rather on synthesis of the viral components after activation has occurred. Intracellular reverse transcriptase levels were not changed by hormone treatment. The stimulation of virus synthesis by glucocorticoids requires binding of the steroid to a cytoplasmic receptor protein.

Animals↗
PubMedDate not supplied

Search for C-type particles in human neoplasia.

The salient biologic and morphologic characteristics of RNA tumor (oncornavirus) virus are reviewed. The ultrastructure of replicating oncornaviruses is illustrated in detail. C-type particles wide spread in at least three orders of animals were sighted in human sarcomas and leukemias. One case, an infantile fibrosarcoma, is presented from our cases surveyed for the presence of C-type particles. Tissue cultures derived from this tumor contained viral particles and had an elevated reverse transcriptase activity associated with the presence of 70 S RNA. The particles were larger (125 to 150nm) than those of the murine or avian Type C particles.

Animals↗
PubMed1975

Microanalytical system for determination of picogram quantities of metals in metalloenzymes, as illustrated with zinc-containing enzymes.

Microwave-induced emission spectrometry combined with gel-exclusion chromatography provides a microanalytical system capable of precisely measuring 10 minus 10 to 10 minus 13 g of metal in microgram amounts of enzyme. Such sensitivity greatly exceeds that of other, more conventional methods. Metal quenching agents and low-molecular-weight protein contaminants were removed from the enzyme by Sephadex G-100 chromatography in microbore columns (0.03 times 25 cm). Droplet fractions were analyzed for zinc by the present method, for enzyme activity, and for protein content. With this analytical system we could demonstrate that stoichiometric amounts of zinc are present in the RNA-dependent DNA polymerase, the reverse transcriptase, from wooly monkey type C RNA tumor virus. The precision of the method for zinc was demonstrated by the coefficient of variation of 4.4 percent for 10 mug of zinc per liter. Validity and accuracy of the method were established by determining zinc in a series of zinc metalloenzymes of known metal content and stoichiometry.

Animals↗
PubMed1975

Mammary tumor virus induction by glucocorticoids. Characterization of specific transcriptional regulation.

Dexamethasone (1,4-pregnadiene-9-fluor-16alpha-methyl-11beta,17alpha,21-triol-3,20-dione), a potent synthetic glucocorticoid, stimulates mouse mammary tumor virus expression 10- to 20-fold in tissue culture cells. This hormone effect was observed at concentrations as low as 1 times 10-10 M and was maximal at 10-7 to 10-8 M. The time course of induction indicated that detectable increases in extracellular viral DNA polymerase were first noted 18 to 24 hours following the addition of dexamethasone, and cells produced the highest polymerase levels at the time monolayers approached confluence. Steroid responsiveness was associated with specific increases in type B murine mammary tumor virus structural polypeptide (gp52(sl) expression and murine mammary tumor virus RNA that quantitatively paralleled the increase in extracellular virus production as measured by electron microscopy and supernatant RNA-dependent DNA polymerase activity. Another virally transformed murine cell line, KA 31, did not contain detectable levels of murine mammary tumor virus gp52(sl) or RNA before or after dexamethasone stimulation; thus induction was noted only in murine cells with pre-existing murine mammary tumor virus expression. No increase in basal levels of type C murine leukemia viral proteins or RNA was detected in dexamethasone-treated mammary cell lines which were producing increased levels of murine mammary tumor virus. Therefore, increases in murine mammary tumor virus gene products are specific for murine mammary tumor virus DNA sequences under these conditions.

Adenocarcinoma↗
PubMed1975

Biochemical properties of a hamster syncytium-forming ("foamy") virus.

A hamster syncytium-forming ("foamy") virus (HFV) was characterized. The HFV sedimented in isopyknic sucrose density gradients at 1.16-1.165 g/ml. It had RNA but no DNA, its replication was inhibited by actinomycin D, and it contained virion-associated, RNA-dependent DNA polymerase. Analysis of the RNA from purified virus showed several species: 62S, 40S, 28-30S, 18-20S, and 4-7S.

Animals↗
PubMedDate not supplied

[Reproduction of leukovirus RD-114 in diploid and heteroploid human cells].

The capacity of leukovirus RD-114 to replicate in human embryo lung diploid cell cultures and continuous human angiosarcoma cell cultures (AS and 709 lines). Differences in the capacity to support the virus reproduction were observed in the two strains of human embryo lung cells (HEL-1 and HEL-3) and the two continuous angiosarcoma cell lines. No virus reporduction was observed in mouse and rat cell cultures. No cytopathic or transformation changes were caused by the virus in any of the systems examined.

Animals↗
PubMed1975

Acute myelogenous leukemia of the Wistar/Furth rat: establishment of a continuous tissue culture line producing lysozyme in vitro and in vivo.

A transplantable myelogenous leukemia of an inbred Wistar/Furth rat has been established in tissue culture and cloned. The resulting transplantable leukemia line demonstrates in vitro doubling time of 20 hr, colony-forming efficiency of 5% in liquid and methylcellulos-containing medium, and a saturation density of 3.0 x 106 cells/sq cm in liquid medium. Following intraperitoneal inoculation, newborn rats developed solid tumors, ascities, and leukemia with ld50 of5 x 103 cells and mean latency of 60 days. The tumor cell morphology was consistent with that of acute myelogenous leukemia. Histochemical staining for myeloid enzymes revealed no evidence of myeloperoxidase, esterase, or leukocyte alkaline phosphatase; however, fluorescent antibody staining for lysozyme was markedly positive. Serum, urine, and ascitic fluid from rats with transplanted leukemia also contained elevated levels of lysozyme. There was no detectable type-CRNA virus production by this cell line after as long as 100 days in vitro. This inbred rat myelogenous leukemia should provide a useful model for studies of chemotherapy and immunoltherapy of human acute myelogenous leukemia.

Animals↗
PubMed1975

Possible association of oncornavirus type D with some forms of human cancer.

The method of molecular hybridization of nucleic acids of oncornavirus type D produced by HEp2 cells with cellular nucleic acids was applied. No sequences homologous to the viral nucleic acids were found in normal human embryo cells as well as in bovine, porcine, murine, and chicken cells. No such sequences were found in tissues of malignant lymphomas. Sequences homologous to the viral nucleic acids were found in some cancer cells, predominantly in hormone-associated tumors of females.

Animals↗
PubMed1975

Molecular hybridization study of cells producing oncornaviruses type D.

Five human cell lines producing oncornaviruses type D were studied by the method of molecular hybridization of viral and cellular nucleic acids. Repeated sequences of viral genome equivalents were found in nuclear DNA and numerous copies of viral genome were found in the cytoplasm. The viruses produced by the cell lines were found to be identical or closely related as regards nucleotide sequences of their genomes.

Animals↗
PubMed1975

Effects of nitrosocarbaryl on BALB/3T3 cells.

Carbaryl(N-methyl-1-naphthylcarbamate) and its nitrosated product, N-nitrosocarbaryl, were tested for their effects of BALB/3T3 (clone A31) cells in culture. Nitrosocarbaryl, but not carbaryl, caused transformation of the BALB/3T3 fibroblasts, but neither chemical induced the complete expression of endogenous murine leukemia virus. Transformed cells differed from the parental control cells by loss of contact inhibition, change in morphology, growth in soft agar, growth to higher saturation densities, and tumorigenicity in normal newborn and irradiated weanling mice and athymic (nude) mice. Transformed clones were found to be negative for expression of RNA tumor virus antigens, viral reverse transcriptase, and infectious virus. Thus, it appears that nitrosocarbaryl can transform BALB/3T3 cells to tumorigenic cells with altered biological properties but without complete activation of RNA tumor viruses in the transformed cells. Expression of viral antigen in the transformed cells was inducible by iododeoxyuridine, indicating that the endogenous viral genome was retained in an unexpressed state.

Animals↗
PubMed1975

Partial characterization of C-type particles in a cell line (WR-9) derived from a rat epidermoid carcinoma of spontaneous origin.

A C-type virus continuously released from a cell line (WR-9) derived from a spontaneous epidermoid carcinoma was purified by means of large-scale tissue culture techniques and high-volume zonal centrifuges. With the use of relatively pure virus concentrates, partial characterization of the virus has been accomplished. Up to 60 liters of spent culture medium from relatively low virus-yielding cultures were processed at a time through the Model K ultracentrifuge in order to obtain quantities of virus sufficient for convenient Tween-ether extraction of the major polypeptide (30,000 daltons). This structural protein having group-specific reactivity was purified and isolated by isoelectric-focusing techniques. A UV absorption peak (A280) was found to be coincident with a major peak of radioacticity at pH 8.6, the isoelectric point (pI) for rat virus gs antigen previously reported by other investigators. Because species-specific (gs-1) and cross-reactive (gs-3) determinants coexist on this protein, fractions containing the group-specific antigen were identified on the basis of the mammalian interspecies determinant (gs-3), using antiserum prepared against Tween-ether-disrupted feline leukemia virus. At the same time, reactivity to the gs-1 determinants in identical fractions was observed in complement fixation and gel diffusion assays, using guinea pig antiserum known to contain principally antibodies to rat gs-1 determinants. Presently, the principal source of rat type C viral gs antigen is rat cell line MSB, which continuously releases a rat leukemia virus pseudotype of murine sarcoma virus. The WR-9 rat virus line may be of use in providing an additional source of C-type particles that are capable of yielding good gs reagents.

Animals↗
PubMed1975

An endogenous oncornavirus of guinea pigs: its expression in leukemic cells.

Guinea pigs do not have any known infectious oncornaviruses. We have recently activated an endogenous oncornavirus (GPV) from cultured guinea pig cells after bromodeoxyuridine riboside (BUdR) treatment. GPV is noninfectious for guinea pig cells and is inducible from any guinea pig cell in culture. Although the morphogenesis of the activated virus is unique, it has the morphology and density (1.16 g/ml) of type C oncornaviruses. It contains an oncornavirus specific reverse transcriptase and a high molecular weight RNA (70S) which dissociates into 36S following denaturation. GPV contains 5 major protein components (mol. wt. 95,000 to 16,000 daltons), 2 of which are glycoproteins. The viral genome which remains repressed in normal cells is expressed in leukemic guinea pig cells. These leukemic cells contain particles which have the morphological and biochemical characteristics of BUdR activated endogenous viruses. Unlike the cells transformed by infectious oncornaviruses, the leukemic cells contain the same amount of virus specific DNA present in normal cells.

Animals↗
PubMed2024

PTGS is dispensable for the initiation of epigenetic silencing of an active transposon in Arabidopsis.

Transposable elements (TEs) are repressed in plants through transcriptional gene silencing (TGS), maintained epigenetic silencing marks such as DNA methylation. However, the mechanisms by which silencing is first installed remain poorly understood in plants. Small interfering (si)RNAs and post-transcriptional gene silencing (PTGS) are believed to mediate the initiation of TGS by guiding the first deposition of DNA methylation. To determine how this silencing installation works, we took advantage of ÉVADÉ (EVD), an endogenous retroelement in Arabidopsis, able to recapitulate true de novo silencing with a sequence of PTGS followed by a TGS. To test whether PTGS is required for TGS, we introduce active EVD into RNA-DEPENDENT-RNA-POLYMERASE-6 (RDR6) mutants, an essential PTGS component. EVD activity and silencing are monitored across several generations. In the absence of PTGS, silencing of EVD is still achieved through installation of RNA-directed DNA methylation (RdDM). Our study shows that PTGS is dispensable for de novo EVD silencing. Although we cannot rule out that PTGS might facilitate TGS, or control TE activity, initiation of epigenetic silencing can take place in its absence.

Arabidopsis↗