Sequence homology between the RNA of Mason-Pfizer monkey virus and the RNA of human malignant breast tumors

Virus-like particles and macromolecules in human milk and breast tumors

Relevant data pertaining to present evidence for virus-like particles and virus-related macromolecules in human milk and breast tumors are presented. A critical review and discussion of reported observations concerning virus-related macromolecules will include RNA-directed DNA polymerase, viral antigens, and RNA related to murine mammary tumor virus and/or Mason-Pfizer monkey virus. From the standpoint of clinical applications, the finding of viral-related antigens in human breast tumors and evidence for specific host immune responses to one or more of these antigens may be especially pertinent. The latter data, therefore, will be discussed in depth as to possible employment of these parameters in diagnosis, prognosis and possible management of the human disease.

The association of viruses with urveal melanoma

Electron microscopic examination of 57 ocular melanomas (54 human, two feline and one canine) revealed the presence of viral particles in six specimens. Herpesviruses particles were observed in one human specimen and were passed in human fibroblasts (WI-38), where they gave rise to intranuclear inclusions. A-type oncornavirus particles (oncogenic RNA virus) were observed in a second case, both in cells of tumor directly removed from an enucleated eye as well as in cells grown in tissue culture. In three human specimens and one feline specimen, togavirus particles were observed. Rubella is a member of this group, and the possibility that the presence of togavirus in these tumors is the result of latent ocular infection by rubella virus is raised. Herpes virus and RNA tumor viruses are widely considered as having a possible etiologic role for certain human cancers. The observation of togavirus is unexpected, as this virus has not been previously implicated in human or animal tumors. Injection of an RNA tumor virus (Gardner strain feline sarcoma virus) into the anterior chamber of newborn kittens resulted in the development of iris and ciliary body melanomas, many of which showed invasion and, in one instance, metastasis. This is the first animal model of a viral-induced uveal melanoma, and the histology and ultrastructure are described. These results emphasize the need for the continued investigation of the role of these viruses in uveal melanoma.

Detection in human breast carcinomas of an antigen immunologically related to a group-specific antigen of mouse mammary tumor virus

An antigen immunologically related to a group-specific antigen (gp52, a 52,000-dalton glycoprotein) of the mouse mammary tumor virus has been identified in paraffin sections of human breast cancers by means of the indirect immunoperoxidase technique. The specificity of the reaction with antibody against mouse mammary tumor virus was examined by absorption of the IgG with the following: (a) purified gp52; (b) a number of virus preparations (mouse mammary tumor virus, Rauscher leukemia virus, simian sarcoma virus, baboon endogenous virus, and Mason-Pfizer monkey virus); (c) normal plasma, leukocytes, breast tissue, milk, actin, collagen, and hyaluronic acid, all of human origin; (d) sheep erythrocytes and mucin. Only mouse mammary tumor virus (from C(3)H or Paris RIII strains and grown in either murine or feline cells) and purified gp52 eliminated the immunohistochemical reaction in the human breast tumors. Positive reactions were seen in 51 of 131 (39%) breast carcinomas of various histologic types, a minimal estimate in view of the limited number of sections from each tumor that could be examined. Negative reactions were obtained in all 119 benign breast lesions (cystic disease, fibroadenoma, papilloma, gynecomastia) and in all 18 normal breast tissues. With one exception, 99 carcinomas from 13 organs other than breast and 8 cystosarcomas were all negative.

Squirrel monkey retrovirus: an endogenous virus of a new world primate

Squirrel monkey retrovirus (SMRV) was isolated by cocultivation of squirrel monkey lung cells with canine cells. 3H-labeled 60-70S SMRV RNA, isolated from virus grown in canine cells, hybridized to the same extent and to the same Cot1/2 value to the DNA of all tissues of all squirrel monkeys tested; Cot1/2 values show that SMRV proviral sequences are present in the low repetitive range. No SMRV proviral sequences were detected in tissues from a variety of other New World monkeys, Old World monkeys, or apes. Murine, feline, bovine, and canine cells also contain no detectable SMRV proviral sequences. Competitive molecular hybridization studies revealed no detectable sequence homology between the 60-70S RNAs of SMRV and Mason-Pfizer virus (MPV). The virion-associated DNA polymerase of SMRV is similar to that of MPV in that it has a molecular weight of approximately 80,000 and prefers magnesium as a divalent cation using oligo(dG)-poly(rC) as primer-template. The virion-associated DNA polymerase of SMRV can be clearly distinguished from those of MPV and the mouse mammary tumor viruses, however, by its preference for manganese as a divalent cation in the presence of high salt.

Antigenic relatedness of the DNA polymerase of human breast cancer particles to the enzyme of the Mason-Pfizer monkey virus

We have previously reported [(Ohno, T., Sweet, R.W., Hu, R., DeJak, D. & Spiegelman, S. (1977) Proc. Natl. Acad. Sci. USA 74, 764-768)] on the purification and characterization of the DNA polymerase from human breast cancer particles. Its preference for certain synthetic templates and its ability to use a viral RNA to fashion a faithful DNA transcript identify it as a reverse transcriptase similar to that found in the mouse mammary tumor virus and in the Mason-Pfizer monkey virus (MPMV). We report here that the human breast cancer enzyme crossreacts immunologically with the reverse transcriptase of MPMV. The crossreactivity was shown both by inhibition of enzyme activity and by complex formation between purified enzyme and isolated IgG against MPMV polymerase. No such interactions were observed with other oncornavirus reverse transcriptases of avian, murine, feline, or simian origin. Further, the IgG failed to neutralize the reverse transcriptases from human mesenchymal neoplasias (leukemias and lymphomas) or the activities of normal cellular DNA polymerases (alpha, beta, gamma).

Radioimmunoassay for the major structural protein of Mason-Pfizer monkey virus: Attempts to detect the presence of antigen or antibody in humans

The 25,000 dalton protein of Mason-Pfizer monkey virus (MPMV) was isolated by gel filtration chromatography. In agreement with results from other laboratories, antisera to type-C and the non-type-C bovine leukemia and equine infectious anemia viruses did not precipitate 125I-labelled MPMV p25. In addition, these viruses did not cross-react in a competition radioimmunoassay for MPMV p25. Twenty-one human tissues (15 breast carcinomas, 2 normal breasts, 3 acute myelogenous leukemias and 1 sarcoma) were fractionated by detergent solubilization, ammonium sulfate precipitation, and DE-52 anion exchange chromatography. These methods were shown to be highly effective for purification of MPMV p25. Under assay conditions which minimized incubation damage to the 125I-MPMV p25, all tissues failed to react in the competition radioimmunoassay (RIAT). Two hundred and two human sera or plasma specimens, including those from patients with breast cancer and 33 age-matched controls, from 50 patients with hematologic malignancies, from 12 patients with amyotrophic lateral sclerosis, and from 14 patients with systemic lupus erythematosis, were examined for antibodies to MPMV p25. With the exception of two multiple myeloma plasma which produced artifactual false positive reactions based on hypergammaglobulinemia, a known complication of salt precipitation radioimmunoassays, the remainder of the specimens were negative for evidence of MPMV p25 antibodies.

Expression of antigenic crossreactivity to RD114 p 30 protein in a human fibrosarcoma cell line

An antigen crossreacting with the 30,000-molecular-weight protein (p30) of the feline endogenous oncornavirus (RD114) was detected in a well-characterized human fibrosarcoma cell line, HT1080, by indirect immunofluorescence. Three antisera against RD114 p30 gave similar positive results, while two antisera prepared against simian sarcoma virus p30, one antiserum prepared against murine leukemia virus p30, and one antiserum prepared against feline leukemia virus p30 gave no immunofluorescence. The reactivity observed with the antiserum against RD114 p30 was detected in 10-40% of the cells at early passages and was no longer expressed by the forty-first subculture. The reactivity could be removed by adsorption of the antiserum with RD114-infected dog or human cells, but not by uninfected cells or by cells infected with an antigenically unrelated oncornavirus, feline leukemia virus. Neither complete virus particles nor reverse transcriptase (RNA-dependent DNA nucleotidyltransferase) activity was detected in the culture. These experiments suggest that the fibrosarcoma cell line is expressing an antigen related to the p30 protein of RD114 baboon endogenous virus group of oncornaviruses without producing complete virions.

Purification and characterization of the DNA polymerase of human breast cancer particles

Previous studies have identified human breast tumor particles possessing many of the features characteristic of RNA tumor viruses. In addition to the expected size (600 S) and density (1.16 g/ml) these include possession of an outer membrane and an inner one surrounding a "core" containing a DNA polymerase and a large-molecular-weight (70S) RNA possessing detectable homology to the RNAs of the mouse mammary tumor virus (MMTV) and of the Mason-Pfizer monkey virus (MPMV). We report here the purification and characterization of the DNA polymerase from the human breast cancer particles. Its key properties are very similar to those ofthe RNA-dependent DNA nucleotidyltransferase (reverse transcriptase) found in MMTV and MPMV. Thus like these viral enzymes, the purified human breast cancer DNA polymerase exhibits the following three features that together distinguish the known viral reverse transcriptases from normal cellular DNA polymerases: (i) a strong preference for oligo(dT)-poly(rA) over oligo(dT)-poly(dA) as a template for the synthesis of poly(dT); (ii) the acceptance of the highly specific oligo(dG)-poly(rCm) as a template for the formation of poly(dG); (iii) the ability to use a viral RNA (AMV) as a template to fashion a faithful DNA complementary copy; and (iv) its preference for Mg++ over Mn++. In summary, the data described here on the enzyme of the human breast cancer particles add further evidence of similarities to the viral agents associated with the corresponding malignancies in the mouse and monkey models. To date, an enzyme with these properties has not been detected in normal breast tissues or in benign tumors of the breast.

Bovine leukemia virus genes in the DNA of leukemic cattle

Reverse transcripts of the rna genome of the bovine leukemia virus (BLV) as well as 125I-labeled BLV RNA hybridize to the DNA of tissues from leukemic cattle with the adult form of the disease but not to bovine thymic lymphoma or normal bovine tissues.

Mason-Pfizer virus RNA genome: relationship to the RNA of morphologically similar isolates and other oncornaviruses

The 60-70S RNA of Mason-Pfizer virus (MPV) was iodinated in vitro and used in both direct and competitive molecular hybridization studies. MPV proviral sequences are present at a frequency of approximately one to two copies per haploid genome in the DNA of experimentally infected human cells. By nucleic acid competition hybridization, MPV RNA was found to be indistinguishable from the RNA of a virus (X381) isolated from a rhesus mammary gland and from RNA isolated from the cytoplasm of AO cells (Parks et al., 1973) and HeLa cells (Gelderblom et al., 1974), both previously reported to produce MPV-related particles. No homology was observed, however, between MPV RNA and the RNA, or the DNA, from two clones of HeLa cells obtained from the American Type Culture Collection. Hybridization of MPV 60-70S RNA to the DNA of normal tissues of humans and to the DNA of 11 other species revealed that MPV is not an endogenous virus of any of these species. Competition hybridization revealed no detectable sequence homology between the RNA of MPV and the RNAs of simian sarcoma virus, murine mammary tumor virus, murine leukemia virus, BUdR-induced guinea pig virus, or avian myeloblastosis virus. These nucleic acid studies substantiate previous ultrastructural and immunological findings that MPV and morphologically similar isolates constitute a distinct group of oncornavirus.