Primate and murine type-C viral nucleic acid association kinetics: analysis of model systems and natural tissues

Cis-acting transcriptional regulatory sequences in the gibbon ape leukemia virus (GALV) long terminal repeat

Gibbon ape leukemia viruses (GALV) are a group of retroviruses which have been associated with hematopoietic neoplasms in primates. Two of the viruses, GALV-SEATO and GALV-San Francisco (GALV-SF), are associated with myeloid and lymphocytic leukemias, respectively, in apes. Using an assay based on the transient expression of the bacterial gene chloramphenicol acetyltransferase (CAT), we examined the transcriptional activity of GALV-SEATO and GALV-SF. The results suggest that high level expression of GALV is due primarily to cis-acting enhancer sequences. Sequence delineation analysis of GALV-SEATO showed the GALV-SEATO enhancer sequences to be located within a 45-bp tandem repeat in GALV-SEATO. GALV-SF, which has two- to fivefold lower transcriptional activity, contains only a single copy of the 45-bp element with 6-bp differences from those in the GALV-SEATO enhancer element. This 45-bp element is highly homologous to sequences within the LTRs of several murine leukemia viruses but has not been examined for enhancer function in these retroviruses. Expression of GALV was not restricted to hematopoietic cells but was extraordinarily high in MLA 144 cells, a gibbon ape T-cell line known to be infected with GALV-SF. However, expression of constructs containing the CAT gene directed by GALV-SEATO LTR sequences was similar in uninfected and GALV-infected fibroblasts, indicating the lack of virally encoded or virally induced trans-activating factors capable of increasing expression in these cells.

Nucleotide sequence of the large terminal repeat of two different strains of gibbon ape leukemia virus

Gibbon ape leukemia virus, SEATO strain (GaLV-SEATO), a virus that induces myeloid leukemia in gibbon apes, and GaLV, San Francisco strain (GaLV-SF), a virus associated etiologically with lymphocytic leukemia in gibbon apes, have been molecularly cloned. The complete nucleotide sequence of the large terminal repeats (LTRs) of both viruses are reported and compared to the previously published nucleotide sequence of the LTR of another member of the same virus group, the simian sarcoma virus (SSV). Substantial homology is evident among all three LTR sequences. The most striking feature of the GaLV-SEATO LTR is the presence of a 45-bp tandem direct repeat in the U3 region, an area likely to contain transcriptional enhancers. Both GaLV-SEATO and GaLV-SF contain a deletion in U3 when compared to SSV. Each of the three LTRs differ from the other two by short deletions in R-U5 and short additions in U3, as well as by numerous point mutations. The possibility that the structural changes observed in the LTR contribute to the differences in the pathogenic effects of these viruses is discussed.

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.

Conserved sequence related to the 3'-terminal region of retrovirus RNA'S In normal cellular DNAs

The nucleotide sequences related to the 3'-terminal protion of retrovirus genomic RNA have been detected in the DNA of animals, including humans. The DNA complementary to the 400 to 700 nucleotides from the 3'-terminal end of retrovirus RNA (cDNA3'), which contains the enriched conserved region, was hybridized with DNA from a variety of animal cells. Under the conditions of annealing in 0.72 M NaCl at 67 degrees C and hydroxyapatite chromatography at 55 degrees C, 20 to 50% of the radioactivity of the cDNA3' prepared from two retroviruses, a murine Rauscher virus (RLV) and a baboon virus (M7), annealed with normal cellular DNA of animals, including human tissue. The thermal denaturation profile revealed considerable mismatching between the duplex of the cDNA3' and human DNA, cDNA3' of retroviruses is most homologous to cellular DNA of the host species of origin and is less homologous to cellular DNA of species that are distant in the phylogeny of the host species. The conservation and evolution of nucleotide sequences related to the 3' end of retrovirus genomes in animal DNAs, including humans, suggest that the sequences may have important functions.

Number and location of mouse mammary tumor virus proviral DNA in mouse DNA of normal tissue and of mammary tumors

The Southern DNA filter transfer technique was used to characterize the genomic location of the mouse mammary tumor proviral DNA in different inbred strains of mice. Two of the strains (C3H and CBA) arose from a cross of a Bagg albino (BALB/c) mouse and a DBA mouse. The mouse mammary tumor virus-containing restriction enzyme DNA fragments of these strains had similar patterns, suggesting that the proviruses of these mice are in similar genomic locations. Conversely, the pattern arising from the DNA of the GR mouse, a strain genetically unrelated to the others, appeared different, suggesting that its mouse mammary tumor proviruses are located in different genomic sites. The structure of another gene, that coding for beta-globin, was also compared. The mice strains which we studied can be categorized into two classes, expressing either one or two beta-globin proteins. The macroenvironment of the beta-globin gene appeared similar among the mice strains belonging to one genetic class. Female mice of the C3H strain exogenously transmit mouse mammary tumor virus via the milk, and their offspring have a high incidence of mammary tumor occurrence. DNA isolated from individual mammary tumors taken from C3H mice or from BALB/c mice foster nursed on C3H mothers was analyzed by the DNA filter transfer technique. Additional mouse mammary tumor virus-containing fragments were found in the DNA isolated from each mammary tumor. These proviral sequences were integrated into different genomic sites in each tumor.

Mouse mammary tumor virus (MMTV) antigen(s) are present on B lymphocytes of BALB/c mice

Immunofluorescence studies using a polyvalent anti-MMTV serum revealed the presence of MMTV antigen(s) on the surface of spleen cells from the low mammary tumor incidence mouse strain BALB/cCrgl. Upon separation of the splenocytes on nylon-wool columns the populations of cells exhibiting positive fluorescence were nylon-adherent. These cells were considered to be B lymphocytes by the following criteria: presence of surface immunoglobulin (Slg), absence of Thy-1 antigens, enhanced responses to B-cell mitogens and decreased reactivity to T-cell mitogens. In order to ascertain the specificity of the cell surface immunofluorescence reaction, blocking studies were performed. Immunofluorescence was blocked by preincubation of the antiserum or with purified MMTV, but not by R-MuLV. Non-specific binding of the anti-MMTV to Fc receptors present on B lymphocytes was ruled out by the use of Fab'2 fragments of IgG from the various sera. Double label immunofluorescent studies with rhodamine-conjugated anti-mouse Slg Fab'2 fragments and rabbit anti-MMTV Fab'2 with fluorescein-conjugated goat anti-rabbit Fab'2 showed the simultaneous appearance of both labels in the nylon-adherent splenocytes. These results suggest the expression of viral polypeptide(s) encoded by an endogenous MMTV on the surface of B-type splenocytes in mice devoid of intact viral particles.

Conserved region of mammalian retrovirus RNA

The viral RNAs of various mammalian retroviruses contain highly conserved sequences close to their 3' ends. This was demonstrated by interviral molecular hybridization between fractionated viral complementary DNA (cDNA) and RNA. cDNA near the 3' end (cDNA(3')) from a rat virus (RPL strain) was fractionated by size and mixed with mouse virus RNA (Rauscher leukemia virus). No hybridization occurred with total cDNA (cDNA(total)), in agreement with previous results, but a cross-reacting sequence was found with the fractionated cDNA(3'). The sequences between 50 to 400 nucleotides from the 3' terminus of heteropolymeric RNA were most hybridizable. The rat viral cDNA(3') hybridized with mouse virus RNA more extensively than with RNA of remotely related retroviruses. The related viral sequence of the rodent viruses (mouse and rat) showed as much divergence in heteroduplex thermal denaturation profiles as did the unique sequence DNA of these two rodents. This suggests that over a period of time, rodent viruses have preserved a sequence with changes correlated to phylogenetic distance of hosts. The cross-reacting sequence of replication-competent retroviruses was conserved even in the genome of the replication-defective sarcoma virus and was also located in these genomes near the 3' end of 30S RNA. A fraction of RD114 cDNA(3'), corresponding to the conserved region, cross-hybridized extensively with RNA of a baboon endogenous virus (M7). Fractions of similar size prepared from cDNA(3') of MPMV, a primate type D virus, hybridized with M7 RNA to a lesser extent. Hybridization was not observed between Mason-Pfizer monkey virus and M7 if total cDNA's were incubated with viral RNAs. The degree of cross-reaction of the shared sequence appeared to be influenced by viral ancestral relatedness and host cell phylogenetic relationships. Thus, the strikingly high extent of cross-reaction at the conserved region between rodent viruses and simian sarcoma virus and between baboon virus and RD114 virus may reflect ancestral relatedness of the viruses. Slight cross-reaction at the site between type B and C viruses of rodents (mouse mammary tumor virus and RPL virus, 58-2T) or type C and D viruses of primates (M7, RD114, and Mason-Pfizer monkey virus) may have arisen at the conserved region through a mechanism that depends more on the phylogenetic relatedness of the host cells than on the viral type or origin. Determining the sequence of the conserved region may help elucidate this mechanism. The conserved sequences in retroviruses described here may be an important functional unit for the life cycle of many retroviruses.

5'-terminal nucleotide sequences of the Rauscher leukemia virus and gibbon ape leukemia virus genomes exhibit a high degree of correspondence

The 5'-terminal regions of gibbon ape leukemia virus-Hall's Island and Rauscher murine leukemia virus have been completely sequenced. The chain length for the 5'-terminal region of Rauscher murine leukemia virus is 140 nucleotides, and that for gibbon ape leukemia virus-Hall's Island is 144 nucleotides. An alignment of the sequences maximizing the number of ocrrespondences with the minimum introduction of gaps shows 81% nucleotide matches. From the complementary RNA, secondary structures of this region have been proposed. These data demonstrate the conservation of the 5'-terminal genetic sequences of these viruses and strongly reinforce the concept that viruses of murine origin and viruses of the gibbon ape leukemia virus-Simian sarcoma-associated virus group are closely related.

Structural analysis of the genomes of gibbon ape and woolly monkey leukosis viruses

Infectious retroviruses have been isolated from gibbon apes and a woolly monkey. Previous studies have shown that these isolates share some antigenic determinants and that they exhibit partial nucleic acid homology. To further define the relationships in this group of viruses, we compared the RNAs of the viruses of the woolly monkey-gibbon ape class 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 the fingerprint patterns and in some cases by partial sequence analysis of individual oligonucleotides. This technique permitted us to determine the degree of sequence identity in related RNA species. These studies showed that as much as 80% of the genomes of gibbon ape leukosis virus-Halls' Island and gibbon ape leukosis virus-brain could be identical. The other viruses, simian sarcoma-associated virus, gibbon ape leukosis virus-Thailand, and gibbon ape leukosis virus-San Francisco, showed an extensive but somewhat lower degree of sequence identity (between 40 to 60% of the genomes.

Characterization of a type-C virus produced by co-cultures of human leukemic bone-marrow and fetal canine thymus cells

The putative human helper virus SKA-21/A204V, isolated by Nooter et al. in 1977 from human leukemic bone-marrow cells following co-culture with normal fetal canine thymus cells, Cf2th, has been characterized with respect to its major viral core protein, reverse transcriptase, and nucleic acid sequences. The results of these analyses show that this virus is not distinguishable from the woolly monkey type-C virus, SSAV-1, by the techniques employed.

Avian reticuloendotheliosis viruses: evolutionary linkage with mammalian type C retroviruses

Reticuloendotheliosis viruses have been shown to be causative of tumors in a variety of avian species. The major structural protein of these non-genetically transmitted viruses is demonstrated to possess antigenic determinants common to those of all known mammalian type C viruses. These findings establish a mammalian origin for this oncogenic avian retrovirus group. None of the known mammalian type C virus groups demonstrated a closer immunological relationship to avian reticuloendotheliosis viruses. These results suggest that reticuloendotheliosis viruses have been non-genetically transmitted for a long period of evolution or that these viruses may have arisen by relatively recent infection of birds with an as yet undiscovered mammalian type C retrovirus.

Gibbon ape leukemia virus-Hall's Island: new strain of gibbon ape leukemia virus

Gibbon ape leukemia virus-Hall's Island (GaLV-H), a type C virus related to previous isolates of GaLV and simian sarcoma virus, was isolated from a gibbon ape with lymphocytic leukemia from a small colony of free-ranging gibbon apes on Hall's Island near Bermuda. We show here by molecular hybridization experiments that GaLV-H is approximately 60% related to three previous isolates of GaLV (GaLV-SF, GaLV-SEATO, and GaLV-Br) and is less closely related to simian sarcoma virus. The oligopyrimidine pattern of a transcript of the terminal 135 +/- 5 nucleotides of the viral RNA of GaLV-H is similar to that of GALV-Br but distinct from that of GaLV-SF and simian sarcoma virus. GaLV-H thus represents a fifth distinct strain of the infectious primate type C viruses, which among the previously described isolates of GaLV is most closely related to GaLV-Br.

Antigenic characterization of a new gibbon ape leukemia virus isolate: seroepidemiologic assessment of an outbreak of gibbon leukemia

A type-C virus recently isolated from a leukemic gibbon in a colony located on Hall's Island, Bermuda, was characterized with respect to the antigenic properties of its gag and env gene-coded proteins. This virus, designated GaLV-H, was found to be closely related immunologically to type-C viruses previously isolated from gibbons (GaLV-SF, GaLV-SEATO, GaLV-Br) and from woolly monkey (SSAV). However, GaLV-H was readily differentiated from these isolates in a radioimmunoassay for its env gene product, gp70. Seroepidemiology established that GaLV-H was horizontally transmitted among gibbons within the colony. There was no evidence of exposure leading to an immune response to the virus or viral antigenemia in humans working in association with these animals.

Genomic stability of gibbon oncornavirus

The 70S RNAs from several gibbon type C viruses were examined for sequence homology by molecular hybridization using complementary DNA probes. The sequence homology was found to vary with each virus isolate. The genome from one isolate was examined for genomic stability after the virus was experimentally passaged through three unrelated gibbons. The genomic homology remained unchanged after three passages, having greater than 93% homology based on complementary DNA-70S RNA hybridization and melting temperature analysis of the duplex. The genome from another isolate was similarly found to be unchanged after the virus was naturally transmitted in gibbons. The genomic variation found in the various isolates is not the consequence of recent horizontal transmission from a common virus.

A portion of the feline leukaemia virus genome is not endogenous in cat cells

Although viral sequences closely related to feline leukaemia virus are represented in multiple copies in cellular DNA of all domestic cats, a specific fraction was present only in the virus-infected cells. This fraction was detected by viral cDNA enriched by a prior absorption of a total complementary DNA (cDNA) transcript with normal cat liver DNA. The recycled cDNA hybridized well with the cellular DNA of virus-infected cells, but to a lesser extent with DNA from uninfected cat cells. The probe was used to differentiate virus-positive from virus-negative tumour tissues of cats. The same approach with cDNA of another endogenous feline virus, RD114, failed to show any difference between a virus-infected cell line and normal cells, including both virus-inducible and non-inducible lines.

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.

Primate retroviruses: envelope glycoproteins of endogenous type C and type D viruses possess common interspecies antigenic determinants

The major 70,000- to 80,000-molecular-weight envelope glycoproteins of the squirrel monkey retrovirus, Mason-Pfizer monkey virus, and M7 baboon virus and the related endogenous feline virus, RD114, were isolated and immunologically characterized. Immunoprecipitation and competition immunoassay analysis revealed these viral envelope glycoproteins to possess several distinct classes of immunological determinants. These include species-specific determinants, group-specific antigenic determinants unique to endogenous primate type C viruses, and group-specific determinants for type D viruses such as Mason-Pfizer monkey virus and squirrel monkey retrovirus. In addition, a class of broadly reactive antigenic determinants shared by envelope glycoproteins of both type C viruses of the baboon/RD114 group and type D viruses of the Mason-Pfizer monkey virus/squirrel monkey virus group are described. Other mammalian oncornaviruses tested, including isolates of nonprimate origin and representative type B viruses, lacked these determinants. The demonstration of antigenic determinants specific to envelope glycoproteins of type C and type D primate viruses indicates either that these viruses are evolutionarily related or that genetic recombination occurred between their progenitors. Alternatively, endogenous type D oncornaviruses may be replication defective, and acquisition of endogenous type C viral genetic sequences coding for envelope glycoprotein determinants may be necessary for their isolation as infectious virus.

Molecular mechanisms involved in the differential expression of gag gene products by clonal isolates of a primate sarcoma virus

Clonal isolates of an early passage stock of woolly monkey sarcoma virus (WSV) have been shown to code for different numbers of woolly monkey helper leukemia virus gag gene products. In the present report, the molecular mechanisms responsible for their differential expression of gag gene products have been analyzed. Three WSV RNA genomes were shown to possess sedimentation coefficients consistent with the differences demonstrated in their allotments of helper viral sequences. The WSV variant (WSV clone 9) that expressed no detectable proteins was shown to contain the largest amount of helper viral information. Moreover, there was no additive hybridization of the WLV complementary DNA probe by RNA of this WSV clone and that of a WSV clone coding for several gag gene products. These results suggest that the lack of expression of gag gene products by WSV clone 9 is not due to a major deletion of helper viral gag gene sequences. Similar levels of WLV-specific RNA were demonstrated in cells nonproductively transformed by each WSV clone, arguing that the ability to express gag gene proteins was not related to the magnitude of viral RNA transcription. Taken together, the results are most consistent with a mechanism by which small deletions or point mutations in the genomes of some WSV variants result in premature termination of translation or synthesis of immunologically nonreactive gag gene proteins. The present findings have implications concerning the effects of evolutionary selective pressures on helper viral genetic information in mammalian transforming viruses.

Two distinct endogenous type C viruses isolated from the asian rodent Mus cervicolor: conservation of virogene sequences in related rodent species

The cocultivation of a lung cell line from the Southeast Asian mouse Mus cervicolor with cells from heterologous species has resulted in the isolation of two new distinct type C viruses. Both viruses are endogenous to M. cervicolor and are present in multiple copies in the cellular DNA of these mice. One of the viruses, designated M. cervicolor type CI, replicates readily in the SIRC rabbit cell line and is antigenically related to the infectious primate type C viruses isolated from a woolly monkey (simian sarcoma-associated virus) and gibbon apes (gibbon ape leukemia virus). This virus is also closely related by both immunological and nucleic acid hybridization criteria to a type C virus previously isolated from a second Asian murine species, Mus caroli. The isolation of the M. cervicolor type C I virus thus provides further evidence that the infectious primate type C viruses originated by trans-species infection of primates by an endogenous virus of mice. The second virus, designated M. cervicolor type C II, replicates well in various cell lines derived from the laboratory mouse Mus musculus. While antigenically related to type C viruses derived from M. musculus, the M. cervicolor type C II virus isolate can be readily distinguished from standard murine leukemia viruses. Both new type C viruses from M. cervicolor are unrelated to the previously described retrovirus (M432) isolated from the same Mus species. The DNA of M. cervicolor therefore contains multiple copies of at least three distinct classes of endogenous viral genes. An examination of the cellular DNA of other rodent species for nucleic acid sequences related to the genomes of both M. cervicolor type C I and II reveals that both viruses have been highly conserved evolutionarily, and that other species of rodents, such as laboratory mice and rats, contain endogenous virogenes related to those in the DNA of M. cervicolor.

Detection of human C-type "helper" viruses in human leukemic bone marrow with murine sarcoma virus-transformed human and rat non-producer cells

Bone-marrow cells from two leukemic children were co-cultivated with the leukemic children A 7573. In early passages, C-type oncornaviruses were released as detected by extracellular reverse transcriptase assay. Co-cultivation of the infected canine cells with the non-producing cell lines R-970-5 (human) or K-NRK (rat) both transformed by Kirsten mouse sarcoma virus (MSV) yielded a new pseudotype of MSV that could transform rat embryo, rabbit SIRC and human kidney cells but not mouse embryo cells. The focur formation could be inhibited by an antiserum to the simian sarcoma virus but not by a serum directed against murine leukemia virus. A cell line derived from a focus of transformed cells became a highe virus is related to the simian sarcoma virus. It is concluded that the leukemic bone-marrow cells produce a C-type oncornavirus that can serve as a helper virus to the defective MSV.

Expression of feline type-C virus in normal and tumor tissues of the domestic cat

Tumor and normal tissues from domestic cats were examined for FeLV and RD-114 specific nucleic acids and proteins. Virus-positive tissues showed a 100- to 200-fold higher level of FeLV and a 200- to 400-fold higher level of FeLV p30 than virus-negative tumors and normal cat tissues. In contrast, the levels of RD-114 viral RNA and p30 antigen were comparable in the majority of tumorous and normal tissues examined. When the DNA of these tissues was examined for FeLV-related sequences, the virus-positive tumors were found to contain extra copies of FeLV DNA. Virus-negative tumors contained DNA sequences homologous with FeLV but the copy number of these sequences could not be distinguished from normal tissues. The results indicate that in certain FeLV-induced type-C lymphoproliferative diseases, extra type-C sequences not present in normal tissues can be identified.

Mouse mammary tumor virus in hybrids from strains C57BL and GR: breeding test of backcross segregants

F1 and F2 and first backcross hybrids and second backcross families of the high mammary tumor incidence strain GR and the low incidence strain C57BL were examined for the segregation of mouse mammary tumor viral (MMTV) expression. Although GR has been reported to transmit MMTV as a single dominant gene, several lines of evidence suggest there are multiple genetic factors that influence MMTV expression, MMTV expression as measured by double antibody radioimmunoassay for MMTV p14 segregated in 106 first backcross progeny at a 60:40 ratio, intermediate between what would be expected for either a single or two gene hypothesis. In female second backcross progeny of either male or female first backcross, a heterogeneous pattern of expression was noted that does not fit any simple Mendalian pattern. From an analysis of serial lactations of first backcross and second backcross families, it appears that all hybrid females contain MMTV proviral information that may be expressed either at late lactations or in a variable proportion of progeny mice. These combined results are most consistent with a vertically transmitted genome regulated by multiple factors in these crosses.

Specificity of in vitro binding of primate Type C viral RNA and the homologous viral p12 core protein

The binding of type C viral p12 proteins to purified viral RNA has been examined in vitro with the use of a family of closely related infectious primate type C viruses--the woolly monkey (SSAV) and gibbon (GALV) group. This in vitro protein-RNA binding is type specific. The system should serve as a model for studies of the evolution of nucleic acid binding proteins.