Search for virus specific DNA sequences and viral particles in mitochondria of avian leukemic myeloblasts

The intracellular localization of the avian myeloblastosis virus (AMV) genome was studied. Nuclear and mitochondrial DNAs from myeloblasts were examined by hybridization with 32P labeled AMV-RNA of high molecular weight for the presence of virus specific DNA sequences. Nuclear DNA (nDNA) from myeloblasts specifically hybridized with viral RNA, whereas purified closed circular mitochondrial DNA (mtDNA) did not hybridize with viral RNA. It was therefore concluded that viral genome was present in nuclear DNA and not in mitochondrial DNA. Likewise, in normal chick cells, nDNA but not mtDNA hybridized with viral RNA.

RNA viruses and cancer: Lucy Wortham James Lecture (Basic Science)

Some animal viruses that contain RNA replicate through a DNA intermediate. The molecular details of the replication of these viruses, which are called ribodenoxyviruses, are starting to be known. The ribodenoxyviruses belonging to a single species may either cause sarcomas, leukemia or no disease. The viruses belonging to a single species differ only in whether or not they contain genes for disease formation. In the case of Rous sarcoma virus, the virus causes sarcomas by adding a gene for sarcoma formation to the genome of infected cells. Ribodeoxyviruses appear to undergo different kinds of genetic changes at extraordinarily high rates. In addition, nucleotide sequences related to ribodeoxyvirus RNA are present in the DNA of many uninfected cells. These nucleotide sequences may represent a virus precursor, and ribodeoxyviruses are hypothesized to have evolved from these nucleotide sequences in uninfected cells. These data have led us to hypothesis that non-viral carcinogens act to mutate a cellular gene(s) that is involved in the same types of information transfer and genetic variation as ribodeoxyviruses and thus give rise to the formation of cancer gene(s).

Oncornavirus-induced sarcoma formation obscured by rapid development of lethal leukemia

Injection i.v. of avian erythroblastosis virus (AEV) strain ES4 causes a high incidence of leukemia and the death of most of the inoculated chicks within 2 weeks. As found earlier, the virus is defective for replication and transforms bone marrow cultures in vitro, and surprisingly, also chick embryo fibroblasts. Inoculation of transformed AEV cells negative for virus production into newborn chicks induced the formation of sarcomas only, whereas cells superinfected with helper virus induced the formation of erythroblastosis in addition to sarcomas. The helper virus alone caused neither sarcomas nor erythroblastosis during the experimental period. These findings were explained by the hypothesis that AEV-induced erythroblastosis develops more rapidly than do AEV-induced sarcomas and that animals receiving i.v. injections die of the leukemia before sarcomas become detectable. The observation that animals receiving i.m. injections of AEV developed sarcomas at the site of injection strongly supports this concept. Most of the animals that received i.m. injections also developed an erythroblastosis that was delayed, however, in comparison to the animals receiving i.v. injections. Our data also suggest that the erythroblastosis induced by AEV does not suppress the formation of sarcomas in the same animal.

Cell surface changes observed in MC-29 virus-infected chicken-embryo fibroblast (CEC) cultures

By transmission and scanning electron microscopic studies of MC-29 virus-infected CEC cultures, C-type virus particles were detected in the medium of infected cultures, in infected cells and in intracellular vacuoles. Virus budding was also observed. In the scanning electron microscope (SEM) so-called blebs appeared on the surfaces of the infected cells, in a number proportional to the concentration of the virus preparation. On the basis of the size of the blebs, it could be considered that virus formation was taking place in their center. In control cells, neither viruses nor blebs were observed. This method will presumably be suitable for the titration of virus preparations.

Hypergammaglobulinemia in chickens congenitally infected with an avian leukosis virus

Significantly elevated (2- to 5-fold higher than controls) serum levels of IgG were found in chickens congenitally infected with F42 strain of avian leukosis (ALV-F42) a subgroup A avian leukosis virus (ALV). A further increase in IgG levels in congenitally infected birds was found to be induced by injection of influenza virus in complete Freund's adjuvant(CFA). Serum immunoglobulin M (IgM) levels were not significantly elevated in ALV congenitally infected chickens except in those animals that had been injected with influenza virus in CFA. Hypergammaglobulinemia in ALV infected birds resulted only after congenital infection and not after infection of immunologically competent birds. Therefore this phenomenon appeared to have striking parallels with other persistent or chronic viral infections that have been previously described in mammals.

Biological and electron microscopic studies on the phenotypic mixing of the thermolabile mutant of vesicular stomatitis virus, tl-17, with avian RNA tumor viruses

A thermolabile as well as thermosensitive mutant of vesicular stomatitis virus, VSV-tl-17, could be thermostabilized by phenotypic mixing with avian RNA tumor viruses (ATV). Biological, immunological and morphological studies revealed that this effect is due to a replacement of the thermolabile projections of the VSV by the avian tumor viral projections. The arrangement of projections of VSV and ATV on phenotypically mixed viria was studied by electron microscopy. A-type particles were detected in chick embryo cells which were doubly infected by ATV and VSV. Their intracytoplasmic appearance seemed to be the result of a disturbed maturation of ATV due to the relative deficiency of envelope proteins which were depleted by VSV maturation in the course of phenotypic mixing.

Neutral protease activity of Rous sarcoma (RSV) transformed chick embryo fibroblasts

The proteolytic activities of normal, Schmidt-Ruppin Rous sarcoma virus (SR-RSV) transformed, and infected (RAV) chick embryo fibroblasts (CEF) have been measured by a highly sensitive technique using 3H-acetylated haemoglobin as a substrate.When all 3 types of CEF cells were maintained in serumless media, no differences were detected in the amount of pH 3–4 protease activity released into the media over a 24-h period, and only negligible amounts of pH 7-6 proteolytic activity were found. When normal, transformed, and infected cells were maintained in serumless media and later incubated with 3H-acetylate haemoglobin, a significant proteolysis of the haemoglobin, a 6-fold increase compared to the normal CEF cells, was associated only with plates containing SR-RSV-CEF cells. A fluorescent assay for peptides confirmed that SR-RSV-CEF cells have increased cell-associated proteolytic activity. The net surface charge of the transformed CEF cells was unchanged by maintenance in serumless media but the net surface negativity of the normal and RAV-CEF cells was significantly increased by incubation in media minus serum for 24 h. This suggests that normal CEF cells, maintained in media plus serum, have a substance masking their surface charge which is absent from the surface of transformed cells, possibly because of proteolytic degradation.

The DNA provirus hypothesis

I have discussed the observations and experiments that led to the formulation and establishment of the provirus hypothesis and the DNA provirus hypothesis, which includes RNA-directed DNA synthesis for the formation of the provirus. I have also discussed some aspects of the present status of our knowledge of the mechanism of formation of the DNA provirus both to point out the work remaining to be done and to illustrate hypotheses for the origins of ribodeoxyviruses and the origins of other animal enveloped RNA viruses and of animal small DNA viruses. Finally, I have indicated that I do not believe that infectious viruses cause most human cancers, but I do believe that viruses provide models of the processes involved in the etiology of human cancer.

Anorexia as the probable cause of plasma alpha-lipoprotein changes seen in avian erythroblastosis

The plasma alpha-lipoprotein bands seen on starch-gel electrophoresis are progressively split and retarded as avian erythroblastosis progresses. Similar changes may be produced in normal birds by starvation, and by pair-feeding methods. Anorexia appears to be a major cause, if not the total cause, of the plasma alpha-lipoprotein changes seen in erythroblastosis.

Lymphoproliferative diseases of fowl: chromosome breaks caused in lymphocytes by JM-V herpesvirus

Chromosome preparations were made of bone marrow cells and peripheral lymphocytes isolated from chicks that developed leukemia following infection with JM-V herpes-virus. Karyotypic analysis revealed a high frequency of chromosome breaks and aneuploidy, as well as some pulverization of chromosomes. The number of chromosome breaks began to increase at 2-3 days post infection, and by 5 days post infection it reached 12.7% of bone marrow cells and 17.2% of peripheral lymphocytes. Similarly, the number of aneuploid metaphase figures increased rapidly and reached 12% of bone marrow cells and 19% of peripheral lymphocytes at 5 days post infection. Some specificity was observed in the chromosomes that were affected.

Renal neoplastic response to leukosis virus strains BAI A (avian myeloblastosis virus) and MC29

Previous reports described the induction of avian renal neoplasms by leukosis virus strains BAI A [avian myeloblastosis virus (AMV)] and MC29, and illustrated morphological characteristics of the tumors. Continued studies in this work confirm evidence of the origin of the tumors from embryonal cells residual in the posthatched chick. The work further emphasizes differences in histopathology of the neoplasms caused by the two viruses and reveals differences in the histopathogenesis of the respective growths. Embryonal rests may consist of two types of cells, those of epithelial characteristics and a second element of differentiation between nephroblastema (mesenchyme) and epithelium and designated here as nephromesoblastoma. Infection by AMV induces tumors of epithelial characteristics and, in addition, derivatives of nephromesoblastoma consisting of cartilage, bone, areas of keratinization, and sarcoma. Keratinized structures in the nephroblastoma originate from nephromesoblastoma. In contrast, MC29 virus induces only epithelial growths representing principally aberrant and malformed glomerular and tubular structures with occasional cartilage derived from epithelial cells. MC29 tumors are completely lacking in nephromesoblastoma tissue and contain no bone, sarcoma, or keratinized formations. In MC29 tumors, occasional cartilage was derived from epithelium. Tumors caused by AMV exhibit the complex structure of nephroblastoma with all of the features of the growth in humans (Wilms' tumor). The neoplasms induced by both AMV and MC29 exhibit marked aberration, distortion, and malformation in the differentiation of the cells growing out from the embryonal rests representing rare manifestations of cell genetic influence inherent in the primordial growth of nephroblastema. The results thus illustrate fundamental differences in cellular composition and capacity to respond to etiologically different leukosis viruses.

Experimental models for DNA-RNA viral interactions: a brief review

Evidences that demonstrate or imply the occurrence of DNA-RNA viral interactions in man and animals are reviewed. The concurrent presence of two dissimilar oncogenic viruses influenced responses both in vivo and in vitro. Cell-mediated immune responses to Marek's disease herpesvirus were altered in specific-pathogen-free chickens inoculated as embryos with an avian leukosis virus. The possible roles of immunological factors in the pathogenesis and control of tumor development associated with DNA-RNA viral interactions remain to be investigated.

Tyrosine aminotransferase induction in normal and tumor-bearing chickens

Tyrosine aminotransferase (TAT) induction by glucagon and dexamethasone in the liver of tumor-bearing chickens was studied and compared with induction in healthy animals. The transplantable tumor was caused by inoculation of cells from a cell line induced by MC29 avian leukosis virus. TAT was hardly detectable in tumor tissue of control and dexamethasone-treated chickens, but it was induced by glucagon to levels which were significant although very low when compared to those in host liver or the liver of non-tumor-bearing controls after glucagon treatment. Dexamethasone failed to induce TAT in host liver at 8 A.M. while it significantly indiced TAT in the normal liver at the same time of the day. Similar failure of TAT induction was not detectable when glucagon was used instead of dexamethasone. Furthermore, it was found that diurnal variations in basal and dexamethasone or glucagon-induced TAT levels are considerably mitigated in host liver as compared to those observed in the liver of healthy animals. The possible reasons for these findings are discussed.

In vitro transformation of chicken bone marrow cells with avian erythroblastosis virus

An in vitro transformation of bone marrow cells has been demonstrated for two strains of avian erythroblastosis virus (AEV-R and AEV-ES4). The transformed cells were indistinguishable from in vivo transformed erythroblasts in morphology and staining characteristics and could be propagated to large numbers. The transformation efficiency could be greatly increased by the addition of dimethylsulfoxide (DMSO). The number of foci appearing in the presence of DMSO was proportional to the virus concentration.

Electrophoretic mobilities of RNA tumor viruses. Studies by Doppler-shifted light scattering spectroscopy

We have used laser beat frequency light scattering spectroscopy to measure, at several pH values, the electrophoretic mobilities of purified avian myeloblastosis (AMV), murine leukemia (MuLV), murine mammary tumor (MuMTV), and feline leukemia (FeLV) viruses. The mobilities of these viruses are similar at pH greater than or equal to7 (-2.7 to -3.2 X 10(-4) (cm/sec)/(V/cm). The isoelectric points of MuLV and AMV are apparently less than pH 3, whereas for FeLV the data could be interpreted to indicate an isoelectric point between 3 and 5. Using a Debye-Hückel model to describe the interaction between electrolytes and virus, we show that our values for the mobility of MuMTV, obtained in ionic strength 0.005, are consistent with the values of Sarkar et al. ((1973), Cancer Res. 33, 2283), obtained in ionic strength of 0.10. This model is then used to calculate surface charge densities. In terms of the density of charged groups, the RNA tumor virus envelope is not very different from the erythrocyte membrane.

Neoplastic response of the avian liver to host infection with strain Mc29 leukosis verus

Studies were made on the oncogenic response of 3086 young chicks to i.v. inoculation of MC29 avian leukosis virus from blood plasma of previous-passage birds or the supernatant fluid of cultures of chick embryo cells infected with strain MC29. Among the large variety of neoplasms of other tissues previously described, there occurred a high incidence of primary growths of the liver. Pathomorphology of the growths frequently differed greatly in both different hosts and the same bird, but some uniformity of the types of neoplasms was evident in many animals. Despite much variation in histopathology, the large proportion of growths could be grouped in several distinctive categories. Examinations by light and electron microscopy provided evidence of derivation of the tumors by alteration of hepatocytes originating principally in the portal regions as indicated by forms transitional from the parenchymal cells to the cells of the different types of growths. Neoplastic aspects of the growths were evident by infiltration and invasion of adjacent tissues, penetration of blood vessels, transplantability to other avian hosts (described in another report), and metastasis to distant organs including the lung, kidney, and spleen. There was no evidence of tumors arising from the biliary system, and growths of cells resembling the biliary type could be traced to altered hepatocytes. None of the findings suggested conversion of biliary-type cells to hepatocytes. Continued growth resulted in anaplastic and metaplastic changes in cell morphology and structural organization and in the formation of cartilage, osteoid, and sarcoma-like spindle-cell tumors of probable epithelial origin. Development of the growths wasnot associated with cirrhosis, and necrosis was limited to infrequent disseminated, essentially unicellular changes or necrobiosis of small groups of cells. The marked variations in the type of virus-induced growths demonstrated the remarkable capacity of cells morphologically inidistinguishable from the hepatocytes for the most diverse alterations in cell structure and tissue organization. This neoplastic response of hepatocytes to the MC29 strain constitutes the only demonstration thus far of the specific hepatocarcinogenic activity of an avian tumor virus.

Ability of tryptophan tRNA to hybridize with 35S RNA of avian myeloblastosis virus and to prime reverse transcription in vitro

Selected species of 4S RNA of chick embryo cells will hybridize in vitro with 35S RNA of avian myeloblastosis virus. A major tRNA component of the hybridizable 4S RNA is tryptophan tRNA. A hybrid prepared from purified tryptophan tRAN and 35S RNA of avian myeloblastosis virus in vitro is an efficient templateprimer for DNA synthesis catalyzed by reverse transcriptase (RNA-dependent DNA polymerase).

Interspersion of sequences in avian myeloblastosis virus rna that rapidly hybridize with leukemic chicken cell DNA

Liquid hybridization of progressively smaller fragments (35S, 27S, 15.5S, 12.5S, and 8S) of poly(A)-selected avian myeloblastosis virus RNA with excess DNA from leukemic chicken myeloblasts revealed that all sizes of RNA contained sequences complementary to both slowly and rapidly hybridizing cellular DNA sequences. Apparently, the RNA sequences which hybridize rapidly with excesses of cellular DNA are not restricted to any one region of the avian myeloblastosis virus 35S RNA. Instead, they appear to be randomly distributed over the entire 35S avian myeloblastosis virus RNA molecule with some positioned within 200 nucleotides of the poly(A) tract at the 3' end of the RNA.

Radiolabeling of proteins and viruses in vitro by acetylation with radioactive acetic anhydride

We describe a convenient, rapid, and reproducible method for labeling proteins in vitro by acetylation with [3H] or [14-C]acetic anhydride dissolved in small amounts of anhydrous dioxane. The reaction is carried out at neutral pH and does not require the use of detergents, water-immiscible organic solvents, oxidizing, or reducing agents. Thus undesirable solvent-induced alterations in protein structure and biological activity are minimized. A method for calculating the specific activity of the protein and the efficiency of acetylation at known concentrations of protein and acetic anhydride is presented. Radioacetylated proteins were shown to be suitable for use as molecular weight calibration standards and as protein markers in polyacrylamide gel electrophoresis, gel filtration, and enzyme studies. Acetic anhydride was used to label intact oncornaviruses, which consist of a complex ribonucleo-protein core within a lipid envelope. Some of the viral lipid and all of the viral proteins, including the internal ones, were labeled without detectable alterations in viral morphology or buoyant density. This result suggests that acetic anhydride, evidently by virtue of its small size and neutral charge, penetrates freely throughout the viral membrane and core structures. The reactivity of RNA with acetic anhydride was less than 1% that of protein under similar reaction conditions.