Reverse transcriptases of primate viruses as immunological markers

Immunological and chemotherapeutic prevention and control of oncogenic viruses

Computed tomographic (CT) and surgical findings were correlated retrospectively in 51 patients with preoperative diagnoses of prolactin-secreting pituitary microadenomas. Twenty-four had microadenomas at surgery. Twenty-eight had identifiable discrete lesions. Of these, 18 had microadenomas and 10 did not; these two groups could not be distinguished reliably. Six patients with proven microadenomas had normal CT scans. Focal hypodense lesions, sellar floor erosion, infundibulum displacement, gland height greater than 8 mm, and an abnormal diaphragma sellae configuration are neither sensitive nor specific findings of microadenoma. A significant number of patients with proven microadenomas had few or none of these abnormalities. Thus, recognition of prolactin microadenoma is seldom possible by CT alone, even with high-resolution direct coronal imaging.

DNA sequence relationship of the baboon endogenous virus genome to the genomes of other type C and type D retroviruses

Baboon endogenous virus (BaEV) is a type C retrovirus present in multiple proviral copies in the DNA of baboons. Although interspecies antigenic determinants present on reverse transcriptase and gag proteins are shared among all mammalian type C viruses, no nucleic acid homology between BaEV and other type C viruses (except RD-114) has been found in conventional liquid hybridization experiments. In this study, we used restriction fragments of cloned BaEV DNA immobilized on nitrocellulose to test for relatedness with [(32)P]cDNA's of various type C and type D viruses. We detected the following distant relationships previously found only through immunological and protein sequencing techniques: (i) eight type C viral cDNA's (the endogenous virus of rhesus monkeys, feline leukemia virus, simian sarcoma virus, gibbon ape leukemia virus, Rauscher murine leukemia virus, BALB-2, NZB, and RD-114) and two type D viral cDNA's (Mason-Pfizer monkey virus and squirrel monkey retrovirus) were able to hybridize with cloned BaEV DNA; (ii) the eight type C probes hybridized to restriction fragments spanning most of the BaEV genome, but only RD-114 hybridized to fragments within the 1.9 kilobases at the 3' end of the genome; (iii) the two type D probes hybridized primarily to fragments within the 1.9 kilobases at the 3' terminus and weakly or not at all elsewhere; and (iv) [(32)P]cDNA's of several other oncornaviruses (mouse mammary tumor virus, equine infectious anemia virus, bovine leukemia virus, and reticuloendotheliosis virus) exhibited no homology with BaEV DNA. DNA sequence analysis has allowed us to orient the BaEV restriction map with the genetic map at both ends of the genome. Homologies between retroviral cDNA's and BaEV clone restriction fragments could thus be related to specific BaEV genes. Whereas type C cDNA's hybridized to fragments from gag, pol, and the pol-env junction, squirrel monkey retrovirus cDNA hybridized only to a fragment coding for the p15E portion of env. Mason-Pfizer monkey virus cDNA also hybridized within the p15E region, but exhibited homology to the 3' half of gp70 as well. These results are discussed relative to previously reported antigenic relatedness of retroviral proteins. The data suggest that BaEV represents an important link in oncornavirus evolution.

Biochemical and immunological properties of the DNA polymerase and RNAase H activities of purified feline leukemia virus reverse transcriptase

Feline leukemia virus DNA polymerase was purified by ion-exchange and nucleic acid affinity chromatographies. The enzyme consists of a single polypeptide chain of mol. wt. approx. 72,000 as determined by both glycerol density gradient centrifugation and SDS-polyacrylamide gel electrophoresis. The preferred divalent cation for DNA synthesis is Mn2+ on a variety of template-primers, and its optimum concentration appears to be significantly lower than reported results of other mammalian type-C viral enzymes. The purified enzyme also contained RNAase H activity. Both DNA polymerase and RNAase H activities appear to reside on the same molecule as demonstrated by the copurification of both activities through various purification steps. The divalent cation requirement for maximum activity of RNAase H is also similar to that of the DNA polymerase. RNAase H without detectable polymerase activity was generated by a limited chymotrypsin digestion of the purified reverse transcriptase. This RNAase H activity was inhibited equally effectively as RNAase H in the intact reverse transcriptase by antisera prepared against reverse transcriptase of feline leukemia virus. These results indicate that the RNAase H catalytic activity of reverse transcriptase is distinct from the polymerase portion of the molecule. Since the RNAase H activity appears to be more stable, the measurement of RNAase H activity with a proper antibody might be useful for assaying tumor cells for the presence of the viral enzyme.

Isolation and identification of lymphocytic and myelogenous leukemia-specific sequences in genomes of gibbon oncornaviruses

Five gibbon ape leukemia virus substrains (two from gibbons with lymphocytic leukemia and three from gibbons with myelogenous leukemia) were examined for unique genomic sequences specific for each form of leukemia. By using sequential adsorption procedures, the genome from each gibbon ape leukemia virus was fractionated into four sets of distinct nucleotide sequences. Based on their hybridization specificities toward DNAs of leukemic tissues, these sequences were designated as follows: (i) "COM," (ii) "LYM" or "MYE," (iii) "UNI," and (iv) "UND." The COM fraction represented sequences common to all of the viral genomes. The LYM fraction, which was isolated only from gibbon ape leukemia viruses associated with lymphocytic leukemia, represented genomic sequences associated with lymphocytic leukemia since the RNA hybridized at a 4- to 15-fold-higher rate to infected tissue DNA from lymphocytic leukemic gibbons than to infected tissue DNA from myelogenous leukemic gibbons. The MYE fraction, which was isolated only from gibbon ape leukemia viruses associated with myelogenous leukemia, represented genomic sequences associated with myelogenous leukemia since the RNA hybridized at a 5- to 15-fold-higher rate to infected tissue DNA from myelogenous leukemic gibbons than to infected tissue DNA from lymphocytic leukemic gibbons. The UNI fraction contained sequences unique to one virus substrain. The UND fraction contained sequences which varied depending upon the substrains involved in the adsorption procedures. These findings suggest that each gibbon ape leukemia virus examined in this study contains subgenomic sequences that are specifically identifiable only with the form of leukemia from which the virus was isolated.

Relationship of retroviruses isolated from human leukemia tissues to the woolly monkey-gibbon ape leukemia viruses

Retroviruses have been isolated from the tissues of human leukemia patients. Previous studies have shown that these isolates share some antigenic determinants with the family of viruses isolated from the woolly monkey and gibbon ape and that they exhibit partial nuclei acid homology with this same group of viruses. We have compared the RNAs of the viruses by two-dimensional polyacrylamide gel electrophoresis of the large RNase T1-resistant oligonucleotides. The degree of sequence identity between the RNAs was determined by the similarity of their RNase T1-resistant oligonucleotide pattern on gels, fingerprints, and in some cases by partial sequence analysis of individual oligonucleotides. This technique permits us to determine the degree of sequence identity among related RNA species. From our studies we conclude that viruses isolated from the tissues of two human leukemia patients, A1476 and SKA 21-3, as well as some subcultures of a virus isolated from the leukemic tissues of a third patient, HL23V, are closely related to the wooly monkey virus. However, the fingerprints of other HL23 viral isolates are very similar to that of GaLVSF, a gibbon ape leukemia virus isolated from a lymphosarcoma.

Immunologic approaches toward detection of type C viral expression in man

Type C RNA viruses have been isolated from a large number of mammalian species. These agents may be horizontally transmitted as infectious cancer-inducing agents, or vertically transmitted from one generation to the next, often in an unexpressed form, within the host genome. To date, the translational products of three viral genes have been identified. With purified virus-coded proteins as probes, sensitive and highly specific radioimmunologic assays have been developed for the detection of antibodies and antigens related to the known type C viruses. These techniques have proved valuable in sero-epidemiologic studies of the horizontally transmitted oncogenic viruses of cats, cattle, and gibbons, and have been used to detect translational products of endogenous viruses in tissues of species from which complete virus has yet to be isolated. This review describes the application of radioimmunoassays in the search for immunologic evidence of type C virus expression in man.

A method for classification of 5' termini of retroviruses

A new method for the classification of retroviruses is presented. The scheme is based on the length and sequence of a DNA transcript of the 5' end of the genome. The method can be used to detect similarities between distantly related viruses as well as to discriminate between very closely related viruses. The method is applied to viruses isolated from mice, baboons, gibbons, a woolly monkey and chickens.

Purification and characterization of baboon endogenous virus DNA polymerase

An RNA-directed DNA polymerase was purified from baboon endogenous type-C virus by successive column chromatography on DEAE cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 8.0, a Mn2+ optimum of 1 mM, and a KCl optimum of 40 mM. The purified enzyme transcribes heteropolymeric regions of viral 60--70 S RNA isolated from different type-C viruses. The purified enzyme is immunologically related to a similarly purified polymerase from the cat endogenous type-C virus RD114.

[Molecular biology of tumor viruses]

All classes of vertebrates harbor tumor viruses that are capable of inducing either tumors or leukemias. After infection, their genomes become integral parts of the host cell's genetic material (DNA). Many biological functions such as the capacity to code for the synthesis of new proteins and, in particular, the oncogenic property (oncogen) have already been assigned to specific regions (on physical maps) of their DNA.

Reverse transcriptase of foamy virus. Purification of the enzymes and immunological identification

Reverse transcriptase from foamy virus, strain H4188 was estimated and purified. The enzyme has the following characteristics: 1. The reaction utilized preferentially oligo (dT) poly (rA) as a primer-template; however, the synthetic primer-template oligo (dT) poly (dA) could also be used to some extent. 2. The reaction utilized oligo (dG) poly (rC) as a primer-template with very low efficiency. 3. The crude virus preparation had a detectable endogenous reaction using the four deoxyribonucleotides for DNA polymerization. 4. The cation requirement for the enzyme reaction was much more biased for Mn++ than for Mg++ ions. 5. The molecular weight of the partially-purified enzyme was estimated to be about 80,000. Aggregates of 240,000 daltons were also seen. The activity of this enzyme was not inhibited by antisera against the reverse transcriptases of various type C RNA viruses, namely, feline endogenous leukemia virus, RD 114, Woolly simian sarcoma virus (SSV-1) and avian myeloblastosis virus (AMV). Antiserum against Rauscher leukemia virus (RLV) enzyme was marginally active against foamy virus enzyme, perhaps indicating a slight cross-reaction. The biochemical characteristics of foamy virus reverse transcriptase seemed to be very close to those of the type C RNA viruses, but the immunological reaction proved that the foamy virus reverse transcriptase was distinct from the others.

Purification and characterization of gibbon ape leukemia virus DNA polymerase

An RNA directed DNA polymerase was purified over 2500 fold from gibbon ape leukemia virus by successive column chromatography on Sephadex G100, DEAE cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 7.5, a Mn2+ optimum of 0.8 mM, and KCl optimum of 80 mM. The purified enzyme transcribes heteropolymeric regions of viral 60-70 S RNA isolated from avian myeloblastosis virus, Rauscher murine leukemia virus and simian sarcoma virus and it is inhibited by antiserum prepared against either gibbon ape leukemia virus or simian sarcoma virus DNA polymerases.

Isolation of type-C viruses from the Asian feral mouse Mus musculus molossinus

N-tropic and xenotropic type-C viruses have been isolated from the wild Asian mouse subspecies M. musculus molossinus. By host range, morphologic and some immunologic criteria these viruses appear closely related to the previously studied murine type-C viruses isolated from highly inbred laboratory strains of mice.

Type C RNA tumor virus isolated from cultured human acute myelogenous leukemia cells

Previously, type C RNA tumor virus-related components have been described in blood leukocytes from patients with acute myelogenous leukemia. These components, for example, reverse transcriptase, have been shown to be most closely related to those from two oncogenic subhuman primate type C viruses (woolly monkey sarcoma virus and gibbon ape leukemia virus). Now, we report the continuous production of budding type C viruses with the same characteristic reverse transcriptase by three separate culturings of leukocytes from a single bleeding from a patient with acute myelogenous leukemia. These isolations were made possible by the discovery of a source of conditioned media which sustains exponential growth of human myelogenous leukemia cells in liquid suspension culture.

Isolation of a primate type-C virus from a lymphomatous baboon

A type-C RNA virus has been isolated from various tissues of a lymphomatous baboon (sp. P hamadryas). Virus isolations were made by co-cultivating baboon cells from the inguinal and mesenteric lymph nodes, testes, kidneys and spleen with cells of canine or human origin. The isolated virus grew in canine, bat, rhesus, and human cells but not in cells of mouse, rat, cat or rabbit origin. The baboon isolate resemble a type-C virus when infected cells were examined by thin section in the electron microscope. In addition, the virus was capable of providing helper function by rescuing and transmitting the Moloney and Kirsten sarcoma virus genome from non-productively transformed cells. Antibody directed against the RD114 virus reverse transcriptase was very effective in inhibiting the baboon virus polymerase while while anti-mouse and woolly type-C virus polymerase antibodies had no significant inhibitory activity. Further analysis by immunodiffusion and competitive radioimmune assay revealed a close immunological relationship between this virus, RD114 and another type-C virus isolated from the placenta of a different species of baboon. Finally, three different classes of interspecies antigenic determinants have been demonstrated in mammalian type-C virus isolated from the placenta of a different species of baboon. Finally, three different classes of interspecies antigenic determinants have been demonstrated in mammalian type-C viruses.

Isolation and characterization of RNA-directed DNA polymerase from a B-type RNA tumor virus

RNA-directed DNA polymerase was isolated from milk-borne B-type murine mammary tumor virus of the RIII mouse strain. The several hundred-fold-purified enzyme sediments at 5.5 to 5.7S with an average molecular weight of approximately 100,000. The purified enzyme is completely template dependent and responds to RNA, DNA, and synthetic templates. Stability studies indicate differential lability dependent on the exogenous template used to monitor activity.

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.

Specificity of the DNA product of RNA-dependent DNA polymerase in type C viruses. II. Quantitative analysis

A number of mammalian Type C viruses were analyzed for relatedness by the technique of DNA.RNA hybridization. Viral DNAs were prepared in single-stranded form from complexes with 70S viral RNA formed during endogenous polymerase reactions. Extent of hybridization was assayed with the single-strand nuclease (S-1) from Aspergillus oryzae. Results obtained indicated a high degree of viral specificity, with significant cross-reactions being observed only with viruses obtained from within a species, as in the case of mouse and cat viruses, or in the special case of woolly monkey-gibbon comparisons. Comparisons of RD-114 virus, recently determined to be of feline origin, and conventional feline Type C viruses (FeLV), revealed minimal relatedness, especially when feline virus was grown on human cells, thus indicating the possibility of coexistence of greatly disparate Type C viruses within one species. A rat-specific virus, recovered from tumors induced by murine sarcoma virus, was found to contain genetic material common to both the original mouse virus and viruses indigenous to the rat, even though only rat-specific proteins have been detected during infection by this virus.

Homology between type-C viruses of various species as determined by molecular hybridization

Two strains of feline leukemia virus, two endogenous feline type-C viruses (RD/CCC group), several endogenous and laboratory strains of murine "leukemia" virus, two rat viruses, two primate viruses (woolly monkey and gibbon ape), as well as hamster, pig, and avian type-C viruses were examined for their relatedness to one another by molecular hybridization. The extent of nucleic-acid homology was determined by hybridization of the various viral RNAs to a [(3)H]DNA product synthesized from each virus. Among the murine type-C viruses (Rauscher, Kirsten, AT-124, and endogenous BALB/c virus) a high degree of homology is observed, although the viruses are not identical. The two primate viruses are also closely related to one another. The feline, rat, hamster, and pig endogenous viruses can be readily distinguished from one another and from the murine and primate viruses since their DNA products share very little or no nucleic-acid homology. However, the murine and primate type-C virus groups possess a surprising degree of relatedness. Feline type-C viruses fall into two distinct groups, the feline leukemia virus group and the RD-114/CCC group, with little detectable nucleic-acid homology between them. Infection of feline or rat cells with type-C virus results in production of the endogenous type-C virus of the species along with the infecting virus.

Mason-Pfizer virus characterization: a similar virus in a human amniotic cell line

Mason-Pfizer monkey virus (MP-MV) is a RNA virus with an RNA-instructed DNA polymerase first isolated from a rhesus monkey mammary adenocarcinoma in 1970. Until recently, there have been no other isolates. A continuous human amnion cell line, AO, was found to be producing a virus indistinguishable or closely related to the Mason-Pfizer virus as measured by morphological, immunological, and biochemical methods. By thin-section electron microscopy, the extracellular virus particle in AO line is 115 to 130 nm in diameter and has a preformed nucleoid (80 to 90 nm) before budding, properties which are also characteristic of MP-MV. Two proteins of the virus from the AO line were studied. By immunodiffusion, sera which react specifically with MP-MV give a line of identity with virus from the AO line. The AO viral RNA-instructed DNA polymerase purified by phosphocellulose chromatography was specifically inhibited by anti-MP-MV polymerase sera, and the AO cells contained both DNA and RNA sequences related to MP-MV (3)H-DNA. Viruses thus far indistinguishable from MP-MV have also recently been found by others in different human lines, raising again the question of the species of origin of MP-MV. Because the virus in the AO cells cannot be differentiated from MP-MV, we attempted to determine the origin of MP-MV virus by measuring DNA sequences related to MP-MV (3)H-DNA in uninfected human and rhesus monkey cells. The quantity of MP-MV-like DNA sequences in uninfected primate tissues was found to be much lower than the amount of DNA sequences of murine type-B or type-C viruses in uninfected murine tissues. Thus, it was not possible to determine whether the virus produced by AO cells or MP-MV was of human or monkey origin, or both.

Structural characteristics and nucleotide sequence analysis of genomic RNA from RD-114 virus and feline RNA tumor viruses

The results of molecular hybridization experiments have demonstrated that the RNA genome of RD-114 virus has extensive nucleotide sequence homology with the RNA genome of Crandell virus, an endogenous type C virus of cats, but only limited homology with the RNA genomes of feline sarcoma virus and feline leukemia virus. The genomic RNAs of RD-114 virus and Crandell virus also had identical sedimentation coefficients of 50S. A structural rearrangement of genomic RNA did not exist within released RD-114 virions, whereas a structural rearrangement of genomic RNA did occur within feline sarcoma virions and feline leukemia virions after release from virus-producing cells.

RD 114 virus-specific sequences in feline cellular RNA: detection and characterization

RNA extracted from cat cells contains sequences homologous to RD-114 viral RNA. The sequences are measured by molecular hybridization with a single-stranded DNA probe synthesized by the virion polymerase using the endogenous viral RNA as template. Viral-specific RNA has been detected in all cells of cat origin tested thus far, but not in cells of other animals, except for the virus-producing human rhabdomyosarcoma cell, RD-114. The extent of hybridization of the DNA probe to cellular RNA was equivalent to that obtained with viral 70S RNA indicating that an equal extent of viral specific sequences is present in all cat cells as well as in RD-114 cells. The amounts of this viral RNA reach approximately 100 copies per cell in cat cells, while virus-producing RD-114 cells contain about 1,000 copies per cell. The viral RNA is present in cat cells in two distinct sizes of about 35S and 18S, whereas in RD-114 cells virus-specific RNA is quite heterogeneous in size.