Relationships between intracisternal type A and extracellular oncornavirus-like particles produced in murine MOPC-460 myeloma cells

Characterization of infectious oncornaviruses from MOPC-460 plasmacytomas: their relation to A-type particles

MOPC-460 mouse plasmacytoma cells produce intracellular A-type particles and extracellular oncornavirus-like particles ("myeloma-associated virus," abbreviated MAV). The genomes of these two particles are closely related. During attempts to establish infections with MOPC-460 extracellular particles, we isolated ecotropic and xenotropic infectious forms of murine leukemia virus. We have investigated the relation of these isolates to A-type particles and to MAV by nucleic acid hybridization. Using complementary DNA probes prepared from the two isolates, we found that these infectious murine leukemia viruses differ from A-type particles and from MAV. Moreover, we found that MAV is the predominant extracellular component: the ecotropic and xenotropic forms of murine leukemia virus were present at only low levels (less than 5%) in MAV preparations. Neither the SC-1 cells infected with ectropic murine leukemia virus nor the mink cells infected with xenotropic murine leukemia virus showed any A-type particles in their cytoplasm when examined by electron microscopy. Our inability to demonstrate infection by the A-type particle-related component, MAV, suggests that these may be defective.

Characterization of the proteins of intracisternal type A and extracellular oncornavirus-like particles produced by MOPC-460 myeloma cells

The mouse plasmacytoma cell line, MOPC-460, produces both intracisternal and intracytoplasmic A-type particles when grown as a solid tumor. When these cells are grown either as an ascites tumor or in tissue culture, a third type of particle is produced extracellularly. This particle, the "myeloma-associated virus," is closely related to, and probably an alternate form of, the intracisternal A-type particle. The proteins present in these two types of particles were compared by tryptic peptide mapping. Both types of particles were found to contain essentially the same major proteins of 76,000 (p76), 68,000 to 70,000 (p68-70), and 45,000 (p45) daltons, in addition to varying amounts of smaller proteins. The relative proportions of all these proteins varied from preparation to preparation in an unpredictable way. The p45, p68, and p70 proteins all contained sequences found in p76, suggesting precursor-product relationships of p76 leads to p70 leads to p45 for solid tumor A-type particles and p76 leads to p68 leads to p45 for extracellular myeloma-associated virus. In addition, immune precipitation experiments have established that p76 contains at least some of the antigenic determinants characteristic of murine leukemia virus p30. This confirms earlier nucleic acid hybridization studies which indicated a moderate degree of relatedness between MOPC-460 A-type particles and several standard murine leukemia and sarcoma viruses. Taken together, our results provide evidence supporting the concept that MOPC-460 A-type particles may represent aberrant forms of C-type murine viruses.

Type C virus and immunoglobulin A production by murine myeloma MOPC-315: two independent activities

The suspected correlation between cessation of type C virus production and halt in immunoglobulin secretion by murine myeloma cells was studied. Employing two variants of the murine myeloma MOPC-315, immunoglobulin A-producing and nonproducing cells, we demonstrated that the two myelomas release similar levels of type C viruses which share common nucleotide sequences and that the viral genomes are equally expressed within the cells. Thus, the suggested relation between these two activities does not apply for MOPC-315 cells and probably for other murine myelomas also.

Genetic individuality of intracisternal A-particles of Mus musculus

The nucleic acid sequence relationship between mouse intracisternal type A-particles and type C and B viruses was examined by reciprocal complementary DNA-RNA hybridization; complementary DNAs prepared from the RNAs of intracisternal A-particles were hybridized with high-molecular-weight RNAs from a variety of murine tumor viruses, and complementary DNAs representing a variety of RNA tumor virus genomes were hybridized with the high-molecular-weight RNAs from A-particles. The criterion for homology between two types of virus was that the heterologous hybridization reaction occurs over the same RNA concentration range as the homologous reacton. The results of these hybridizations indicate that there are no major sequence homologies between the RNA of intracisternal A-particles and the RNA of representative members of type B and C viruses of Mus musculus.

Nucleotide sequence relationship between intracisternal type A particles of Mus musculus and an endogenous retrovirus (M432) of Mus cervicolor

Intracisternal type A particles are retrovirus-like structures found in embryonic cells and many tumors of Mus musculus but having no clear relationship with other retroviruses of this mouse species. We have observed a partial nucleotide sequence homology between the high-molecular-weight (32S and 35S) RNA components of intracisternal A-particles from a neuroblastoma cell line and the 70S RNA fraction from M432, a type of retrovirus endogenous to the Asian mouse Mus cervicolor. M432 complementary DNA (cDNA) was hybridized to the extent of 30% by the A-particle RNAs. The hybrids showed a lower thermal stability (DeltaT(m), 7 degrees C) than those formed with homologous RNA. The reaction was commensurate with that found between M432 cDNA and divergent sequences in the M. musculus genome. The capacity to hybridize M432 cDNA was closely correlated with the concentration of A-particle sequences in the cytoplasmic RNA of several M. musculus cell types. The major RNA fraction of M432 virus showed a reciprocal partial reaction with the A-particle cDNA's; the virus, which was grown in NIH/3T3 (M. musculus) cells, also contained a small proportion of apparently authentic A-particle nucleotide sequences. A subset of A-particle sequences seemed to be almost totally lacking in the main M432 RNA. The A-particle cDNA's hybridized extensively with divergent sequences in M. cervicolor cellular DNA, indicating that this mouse species may contain not only the partially homologous M432 virogene, but also a more complete genetic equivalent of the intracisternal A-particle.

Endogenous RNA tumor viruses are activated during chemical induction of murine plasmacytomas

Plasmacytomas are induced in BALB/c mice by the intraperitoneal injection of pristane (2,6,10,14-tetra-methylpentadecane) after a latent period of six months and more [Anderson, P. N. & Potter, M. (1969) Nature 222, 994-995]. Spleen cells mesenteric lymph node cells, thoracic lymph node cells, and peritoneal exudate cells were prepared from pristane-treated and control uninjected BALB/c mice during the course of a 10-month period, and these cell suspensions were tested for the release of infectious murine leukemia viruses. Endogenous ecotropic and xenotropic murine leukemia viruses were expressed in pristane-treated mice during the latter part of the tumor induction period, in those cell populations in which transformed plasma cells appear, namely, peritoneal exudate cells and thoracic lymph node cells. The significance of preferential expression of both ecotropic and xenotropic murine leukemia virus in target cell populations following the administration of a carcinogen is discussed in terms of the possible formation of an oncogenic variant virus.

Specificity of interferon action in protein synthesis

Inhibitors of elongation steps in protein synthesis such as cycloheximide and anisomycin mimic interferon treatment in that they specifically inhibit the synthesis of certain viral proteins. These specific effects are seen only at very low concentrations of the antibiotics, under conditions where host cellular protein synthesis, as well as cell viability, are not severely reduced. A qualitatively as well as quantitatively close correlation between the effects of the two types of agents has been established for encephalomyocarditis virus, vesicular stomatitis virus and murine leukemia virus protein synthesis. It is concluded that one of the primary mechanisms of interferon action may be a nonspecific retardation of one or more elongation steps, and that this may be sufficient to account for its effects on the replication of certain viruses such as encephalomyocarditis and vesicular stomatitis viruses.

RNA associated with murine intracisternal type A particles codes for the main particle protein

Intracisternal type A particles were isolated from MOPC-104E myeloma grown subcutaneously and from N 4 neuroblastoma cells in culture. Polyadenylated RNA was prepared from the particles and tested in a cell-free translation system derived from rabbit reticulocytes. RNA from the two sources directed the synthesis of multiple polypeptides with similar distributions of electrophoretic mobilities in sodium dodecyl sulfate-containing polyacrylamide gels, including one conponent of the same size as the major A-particle structural protein (73,000 daltons). Analysis of the RNAs by electrophoresis in methyl mercury-containing agarose gels revealed a 35S component common to A-particles from both cell types. This was a major component of the N4 preparations, whereas a 28S species predominated in the case of MOPC-104E. These two RNAs (35S from N4 cells and 28S from MOPC-104E), when isolated on isokinetic sucrose gradients, each directed the synthesis of a 73,000-molecular-weight polypeptide that comigrated on gels with authentic A-particle structural protein. Idnetity of the cell-free product was confirmed by two-dimensional analysis of the [35S]methionine-labeled tryptic peptides. The N4 RNA preparations also contained a major32S component which did not code effectively for the A-particle structural protein.

Purification and characterization of DNA polymerases from the plasmacytoma MOPC 104E and Abelson murine leukemia viruses

RNA-dependent DNA polymerases of intracisternal A particles from the mouse plasma cell tumor MOPC 104E and of Abelson murine leukemia virus (A-MuLV) were isolated from particle preparations by Nonidet P40 and ultrasonic treatment and purified by column chromatography on DEAE-cellulose and phosphocellulose, followed by centrifugation in linear sucrose gradients. Both DNA polymerases were very similar in their elution patterns from phospho and DEAE-cellulose, template specificities, requirements for optimum activity and inactivation by anti-(reverse transcriptase) antiserum. They are associated with ribonuclease H activity. For molecular weight determinations, antibody-precipitated enzymes were bound to staphylococcal-protein-A-Sepharose, solubilized and run on dodecylsulfate/polyacrylamide gels. Their apparent molecular weight was estimated to be 80000.

Sequences associated with intracisternal A particles are reiterated in the mouse genome

Using a 3H-cDNA for RNA sequences specifically associated with murine intracisternal type A particles, we have found multiple copies of this information in high molecular weight nuclear DNA from tissues of both Mus muscules (BALB/c, NIH Swiss, A/Jax and feral) and Mus cervicolor. Reiteration frequencies varied from 1050-1800 per haploid genome, except that fewer copies (450) were found in BALB/3T3 cells. In the series studied, the reiteration frequencies in the DNA of A particle-rich tumor cells (myeloma and neuroblastoma) were not higher than those in normal tissues (liver and sperm). Multiple copies were retained when cellular DNAs were sedimented through alkaline sucrose gradients, indicating that the sequences are integrated in the mouse genome. In situ hybridization with cDNA showed that the sequences were associated with many chromosomes and were concentrated over certain regions of some chromosomes. Only low levels of homologous sequences were detected in rat, hamster and guinea pig DNA under stringent conditions of hybridization. The presence of reiterated sequence transcripts in poly(A) RNA from a neuroblastoma A particle fraction was confirmed by direct hybridization of the RNA with cellular DNA.

Feline malignant mammary tumors. III. Presence of C-particles and intracisternal A-particles and their relationship with feline leukemia virus antigens and RD-114 virus antigens

Thirty-six feline mammary tumors were examined by the electron microscope, and by the indirect immunofluorescence (IFA) test with anti-FeLV and anti-RD-114 serum. In 11 (30.6%) tumors intracisternal A-particles (IAP) were found. One of these tumors contained a few particles with an electron-dense nucleoid in the cisternae of the endoplasmic reticulum. In 7 (19.4%) other tumors C-particles were found and in the remaining 18 (50.0%) no particles at all could be detected. In 11 (30.6%) tumors FeLV antigens and in 20 (55.5%) tumors RD-114 virus antigens were present. In 9 (25%) tumors we found a high (greater than 1/64) and in 11 (30.6%) tumors a low (greater than 1/16 less than or equal to 1/64) titer. There was a good correlation between the presence of C-particles and the demonstration of FeLV-antigen but none between IAP and FeLV antigens. No correlation was found between RD-114 virus antigens and any type of particle. Morphologically, the IAP found in feline mammary tumors were indistinguishable from the IAP present in mammary tumors of some inbred mice strains. The IAP in feline mammary tumors possibly represent an endogenous virus, different from RD-114 virus. The role of these viruses in the etiology of feline mammary tumors is discussed.

Transcription of specific genes in isolated nuclei by exogenous RNA polymerases

Mouse plasmacytoma (MOPC) 460 cells contain two chromatographic forms of RNA polymerase III (IIIA and IIIB) in addition to the major class I and II RNA polymerases. Nuclei isolated from these cells actively synthesize RNA. Among the discrete transcription products observed are the 5S and 4.5S RNAs and additional low molecular weight RNA species (approximately 5.8S, 6.3S, and 6.6S in size). The 4.5S RNAs appear to be tRNA precursors since they can be converted in vitro to 4S RNAs. Studies with alpha-amanitin have shown that the synthesis of these discrete RNA species, and other uncharacterized transcripts somewhat larger in size, is mediated by an endogenous RNA polymerase III activity(ies). Nuclear RNA synthesis is stimulated by exogenous purified RNA polymerases. Exogenous MOPC class III RNA polymerases stimulate the synthesis of each of the distinct low molecular weight species (including 5S and 4.5S RNAs) about 3-6 fold. The hybridization of nuclear transcripts to purified 5S genes (5S DNA) confirms that exogenous class III RNA polymerases stimulate (approximately 4 fold) the synthesis of ribosomal 5S RNA. The 5S RNA genes in nuclei are transcribed asymmetrically by both the endogenous and the exogenous class III enzymes. Exogenous RNA polymerase III from Xenopus laevis ovaries stimulates 4.5S and 5S RNA synthesis in MOPC nuclei as effectively as do the MOPC class III RNA polymerases. However, exogenous MOPC class I and II RNA polymerases do not stimulate 4.5S and 5S RNA synthesis, suggesting that this effect is specific for the structurally similar class III RNA polymerases.

DNA polymerases from intracisternal A-type particles on the mouse plasmacytoma MPC 11

Intracisternal A particles from mouse plasma cell tumors were isolated from microsomal vesiclels by detergent treatment and separated in linear sucrose gradients. Four peaks of DNA polymerase activities banding at densities of 1.30, 1.24, 1.20--1.22 and 1.13 g/cm3 were observed assaying on poly(rA).oligo(dT). Solubolized DNA polymerases of the 1.30 g/cm3...

Viral protein synthesis in Friend erythroleukemia cell lines

Viral protein synthesis was studied in two Friend virus-induced erythroleukemia cell lines (Ostertag cell lines FSD1-F4 and B8) by the technique of immuno-precipitation with monospecific antisera to the major envelope glycoprotein gp70 and major core protein p30. One of the cell lines (F4) releases active Friend virus complex to the growth medium, where release of virus from the other cell line (B8) is barely or nondetectable. It was found that in the nonproducer cell line B8, a large-molecular-weight protein of about 65,000 containing p30 antigenic determinants is synthesized, yet no p30 is produced upon prolonged incubation and chase, suggesting that this might be the actual lesion that prevents mature virus production by these cells. In both cell lines, the predominant protein species that is immunoprecipitated with monospecific anti-gp70 serum is a protein of 55,000 to 60,000 daltons that is labeled with glucosamine to a much lesser extent that gp70 and appears to become heterogeneous with time. Large amounts of gp70 can be detected in the cell-free medium, but none of the unstable species of 55,00 to 60,000 molecular weight.