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Biomedical subjects

J R Stephenson

Publications and source records attributed to J R Stephenson.

At least 235 records · Page 13Linked to original sources
PubMed1974

Cellular replication and the persistence of inducible RNA type C viruses.

Cells of mouse and rat origin contain endogenous type C viruses. There are intrinsic regulatory factors which restrict the ability of different classes of these inducible viruses to persist in cells after chemical activation. The cellular block to certain viruses is shown to be overcome under conditions in which the virus-activated cells are allowed continued exponential growth. These findings may help to explain the high frequency at which replicating type C viruses are detectable in naturally occurring tumors of some species.

Animals↗
PubMed1974

Immunological properties of two polypeptides of Mason-Pfizer monkey virus.

Two polypeptides were isolated from the Mason-Pfizer monkey virus (MP-MV). The polypeptides, designated MP-MV p26 and MP-MV p15, were 26,000 and 15,000 molecular weight, respectively, based on gel filtration chromatography in the presence of 6 M guanidine hydrochloride. Radioimmunoassays developed for MP-MV p26 and p15 were, respectively, 10 and 100 times more sensitive than immunodiffusion and 1 and 10 times more sensitive than micro-complement fixation for the detection of MP-MV. Antigens of other reverse transcriptase-containing RNA viruses did not cross-react in either MP-MV radioimmunoassay. Further, antisera against these other viruses did not react with the radioiodine-labeled MP-MV polypeptides. The MP-MV radioimmunoassays should be useful in studying the natural occurrence of this virus and its relationship to primate tumors.

Animals↗
PubMed1974

Temperature-sensitive mutants of murine leukemia virus. IV. Further physiological characterization and evidence for genetic recombination.

Several temperature-sensitive mutants of the Rauscher strain of murine leukemia virus representing three distinct physiological groups have been further characterized. Genetic recombination between different pairs of these mutants has been demonstrated. Several representative genetic recombinants were isolated and shown to replicate equally well at the permissive (31 C) and nonpermissive (38 C) temperatures and to have serological characteristics of the wild-type parental virus. Alternative models for the mechanisms involved in recombination between type C RNA viruses are discussed.

Animals↗
PubMed1973

Segregation of loci for C-type virus induction in strains of mice with high and low incidence of leukemia.

Multiple genetic loci for induction of murine leukemia viruses are demonstrated in cells of the high leukemic incidence C58 mouse strain. The biologic properties of viruses at C58 inducibility loci are clearly distinguishable from those of viruses activated from mouse cells containing a locus for virus induction of the low leukemia incidence BALB/c strain. These findings are consistent with the hypothesis that the genes for virus induction in normal mouse embryo cells represent viral structural information.

Animals↗
PubMed1973

Demonstration of a cell-surface antigen associated with murine sarcoma virus by immunoelectron microscopy.

Cells transformed by murine sarcoma virus have been examined for the presence of a new virus-associated cell-surface antigen by immunoelectron microscopy. A common antigen has been detected on the surface of nonproductively transformed cells that were induced by two different strains of murine sarcoma virus, Kirsten and Moloney. This antigen shows crossreaction with cell lines transformed by murine sarcoma virus that were produced in two different mammalian species, rats and mice. Further, this antigen is distinct from previously described antigens on the surfaces of cells infected by murine leukemia virus, on the viral envelope, and on the surfaces of spontaneously transformed cell lines or cell lines transformed by x-irradiation.

Animals↗
PubMed1973

Independent segregation of loci for activation of biologically distinguishable RNA C-type viruses in mouse cells.

Two genetic loci for induction of RNA C-type virus in BALB/c mouse embryo cells segregate independently in backcross embryo cell lines. The viruses at these loci are shown to be biologically distinguishable. The first, described previously, codes for activation of a virus that grows preferentially in NIH Swiss embryo cells. The newly detected locus codes for activation of a virus that grows poorly, if at all, in NIH Swiss or BALB/c cells, but replicates well in a rat cell line. Its serologic properties are different from those of viruses of the two major serologic subgroups of murine leukemia virus. The present findings provide support for the hypothesis that the loci for virus induction in BALB/c cells represent genetic information for C-type viruses and that the endogenous viruses are subject to different cellular genetic controls.

Animals↗
PubMed1973

Characterization of morphologic revertants of murine and avian sarcoma virus-transformed cells.

Morphologic revertants which contain avian or murine sarcoma viruses have previously been isolated at low frequency from clonal lines of transformed mammalian cells. In the present study, these lines have been further characterized. They are indistinguishable from nontransformed parent cell lines with respect to parameters such as saturation density and colony formation in depleted medium or on monolayers of contact-inhibited cells. The rate of glucose uptake had also reverted to normal. The malignant potential of one of the revertant lines was examined and found to be markedly reduced compared to that of the corresponding transformed cells. The differences in the susceptibilities of revertant cells to retransformation by the same or other oncogenic viruses suggest that different cellular genes may be involved in expression of transformation by various tumor viruses.

Alpharetrovirus↗
PubMed1973

Radioimmunoassay for avian C-type virus group-specific antigen: detection in normal and virus-transformed cells.

A radioimmunoassay has been developed for detection of avian C-type virus (30,000 mol wt) group-specific (gs) antigen. The method is 10- to 1,000-fold more sensitive than immunological methods previously available. By the radioimmunoassay technique, normal chicken embryo cells, which have previously been classified as gs negative or weakly gs positive, contain clearly detectable amounts of gs antigen. The assay has been used to study the effect of chemical induction and superinfection by mammalian C-type viruses on the expression of avian gs antigen in mammalian cells nonproductively transformed by avian sarcoma viruses.

Alpharetrovirus↗
PubMed1973

Expression of endogenous RNA C-type virus group-specific antigens in mammalian cells.

Highly sensitive and specific radioimmunoassays are described for quantitation of the intraspecies determinants of several mammalian C-type viral group-specific (gs) antigens. An interspecies (gs-3) immunoassay has been developed which has both the broad reactivity and great sensitivity necessary for detection of C-type viruses where intraspecies gs assays are not available. By using these immunoassays, the expression of endogenous virus-specified gs antigens in mammalian cells of different species has been studied. Whereas mouse gs antigen was clearly detectable in tissue culture cells of several mouse strains, the respective gs antigens of rat, cat, Chinese hamster, woolly monkey, and gibbon ape were not detectable in cells of those species, using assays of comparable sensitivity. Thus, differences exist in the level of endogenous virus expression in cells of different mammalian species.

Animals↗
PubMed1972

Genetic factors influencing C-type RNA virus induction.

Genetic factors were studied which affect the inducibility of C-type RNA viruses from embyro cultures of mouse strains with high and low incidence of spontaneous leukemia. Virus was inducible by chemical treatment from secondary embryo cultures of several inbred strains. Both virus inducibility and the capacity of the virus to persist in cells from which it was activated were found to be inherited as dominant genetic characteristics. The results show that the factors controlling virus activation and persistence in culture also play an important role in spontaneous virus expression in the animal.

Animals↗
PubMed1972

Antigenic properties of murine sarcoma virus-transformed BALB-3T3 nonproducer cells.

The isolation of clonal lines of murine sarcoma virus-transformed, non-producer BALB/3T3 cells has provided a model system for determining whether RNA tumor virus-transformed cells possess virus-specific transplantation antigens. MSV nonproducer cells (K-234) were clonally derived from an inbred mouse cell line, BALB/3T3. A parallel virus-producing cell line was obtained by infection of the MSV nonproducer cells with Rauscher leukemia virus. K-234 was much more tumorigenic than K-234(R). Preimmunization of syngeneic mice with either K-234(R) or with UV-inactivated Rauscher leukemia virus induced transplantation resistance to subsequent challenge with K-234(R), but not with K-234. In contrast, mice preimmunized with nonproducer cells were not made resistant to subsequent challenge with the homologous cells. Antisera prepared from mice immunized with K-234(R) were specifically cytotoxic and positive by fluorescent antibody staining for K-234(R) target cells, but not to either BALB/3T3 or K-234. The results show that MSV nonproducer cells lack detectable transplantation antigens and suggest that the transplantation resistance to the producing cells is attributable to maturing virus at the cell surface.

Animals↗
PubMed1972

A genetic locus for inducibility of C-type in BALB-c cells: the effect of a nonlinked regulatory gene on detection of virus after chemical activation.

Previous studies have shown that chemicals can transiently activate endogenous C-type viruses from embryo cells of the BALB/c mouse strain, but not from cells of another mouse strain, NIH Swiss. The number of genetic loci for inducibility of endogenous virus in BALB/c cells was investigated with cell lines derived from appropriate, F(1), F(2)-hybrid, and backcross generation embryos of these strains. A single genetic locus responsible for inducibility of virus in BALB/c cells was detected, and tentatively designated Ind. A second locus, previously described in studies of mouse-cell susceptibility to exogenous virus infection, Fv-1, was found to be genetically nonlinked to Ind. This regulatory gene plays an important role in determining whether the induced viruses of BALB/c cells can persist after chemical activation.

Animals↗
PubMed1972

Isolation of temperature-sensitive mutants of murine sarcoma virus.

Three separate murine sarcoma virus nonproducer cell lines have been isolated which are temperature sensitive for the maintenance of transformation. In each case, a viral rather than a cellular genetic mutation is the reason for the temperature-sensitive effect. Superinfection of one of the mutants with murine leukemia virus overcomes the temperature-sensitive change in the transformed state.

Animals↗