Immunological cross reactivity of Mason-Pfizer monkey virus with type C RNA viruses endogenous to primates

Importance of p12 protein in Mason-Pfizer monkey virus assembly and infectivity

Mason-Pfizer monkey virus (M-PMV) represents the prototype type D retrovirus, characterized by the assembly of intracytoplasmic A-type particles within the infected-cell cytoplasm. These immature particles migrate to the plasma membrane, where they are released by budding. The gag gene of M-PMV encodes a novel protein, p12, just 5' of the major capsid protein (CA) p27 on the polyprotein precursor. The function of p12 is not known, but an equivalent protein is found in mouse mammary tumor virus and is absent from the type C retroviruses. In order to determine whether the p12 protein plays a role in the intracytoplasmic assembly of capsids, a series of in-frame deletion mutations were constructed in the p12 coding domain. The mutant gag genes were expressed by a recombinant vaccinia virus-T7 polymerase-based system in CV-1 cells or in the context of the viral genome in COS-1 cells. In both of these high-level expression systems, mutant Gag precursors were competent to assemble but were not infectious. In contrast, when stable transfectant HeLa cell lines were established, assembly of the mutant precursors into capsids was drastically reduced. Instead, the polyprotein precursors remained predominantly soluble in the cytoplasm. These results show that while p12 is not required for the intracytoplasmic assembly of M-PMV capsids, under the conditions of low-level protein biosynthesis seen in virus-infected cells, it may assist in the stable association of polyprotein precursors for capsid assembly. Moreover, the presence of the p12 coding domain is absolutely required for the infectivity of M-PMV virions.

Localization of the receptor gene for type D simian retroviruses on human chromosome 19

Simian retrovirus (SRV) serotypes 1 to 5 are exogenous type D viruses causing immune suppression in macaque monkeys. These viruses exhibit receptor interference with each other, with two endogenous type D viruses of the langur (PO-1-Lu) and squirrel monkey, and with two type C retroviruses, feline endogenous virus (RD114/CCC) and baboon endogenous virus (BaEV), indicating that each utilizes the same cell surface receptor (M. A. Sommerfelt and R. A. Weiss, Virology 176:58-69, 1990). Vesicular stomatitis virus pseudotype particles bearing envelope glycoproteins of RD114, BaEV, and the seven SRV strains were employed to detect receptors expressed in human-rodent somatic cell hybrids segregating human chromosomes. The only human chromosome common to all the susceptible hybrids was chromosome 19. By using hybrids retaining different fragments of chromosome 19, a provisional subchromosomal localization of the receptor gene was made to 19q13.1-13.2. Antibodies previously reported to be specific to a BaEV receptor (L. Thiry, J. Cogniaux-Leclerc, R. Olislager, S. Sprecher-Goldberger, and P. Burkens, J. Virol. 48:697-708, 1983) did not block BaEV, RD114, or SRV pseudotypes or syncytia. Antibodies to known surface markers determined by genes mapped to chromosome 19 did not block virus-receptor interaction. The identity of the receptor remains to be determined.

Molecular cloning of the Mason-Pfizer monkey virus genome: biological characterization of genome length clones and molecular comparisons to other retroviruses

The molecular cloning of the DNA provirus of Mason-Pfizer monkey virus (M-PMV) is described. Fourteen independent clones of integrated M-PMV proviruses were isolated from a human embryo kidney cell line that had been previously derived from a single cell clone infected with M-PMV. Characterization of these clones for size of insert, restriction pattern of flanking DNA, and presence of repetitive DNA in the flanking sequences revealed that 10 of the isolates were identical while the four remaining clones were unique. Three independent clones of unintegrated M-PMV proviruses containing a single copy of the long terminal repeat (LTR) were cloned from acutely infected human embryo kidney cells, Transfection assays revealed that 13 of 14 integrated proviruses and 2 of 3 unintegrated proviruses were capable of producing infectious virus. One of the integrated provirus clones (clone 6A) produced consistently higher titers of virus than all of the other clones in all assays used and in two different cell lines, indicating that it contained a mutation that enhances virus replication. The virus recovered after transfection was shown to be capable of inducing cell fusion in nontransformed cell lines, confirming that this property is associated with M-PMV. One of the clones was hybridized under conditions of varying stringency, to molecular clones of type B, C, and D retroviruses. These studies revealed M-PMV to be most closely related to squirrel monkey retrovirus (D-type virus) and more distantly related to mouse mammary tumor virus (B-type virus). Hybridization was also detected with clones from the pol gene region of a family of human endogenous sequences. No homology was detected with Rous sarcoma virus or most mammalian C-type viruses tested. The exceptions were baboon endogenous virus and RD114 in which previously identified homology in the env gene was confirmed. These results suggest that the type D and type B viruses can be linked together in a group of viruses of similar ancestral origin analogous to that recently proposed for the human T-cell leukemia viruses and bovine leukemia virus.

A glycoprotein associated with the non-A, non-B hepatitis agent(s): isolation and immunoreactivity

A glycoprotein was isolated and purified to homogeneity from the serum of a patient with chronic non-A, non-B hepatitis. NaDodSO4/PAGE of the glycoprotein revealed a single major band at Mr approximately 77,000. Antibodies to this glycoprotein were shown to possess the following immunoreactivity: (i) they reacted by radioimmunoassay with sera obtained at the time of diagnosis from 17 of 42 patients with non-A, non-B hepatitis and with only 2 of 58 sera from either matched controls or patients with hepatitis A or hepatitis B, (ii) they reacted with sucrose gradient fractions from a proven infectious non-A, non-B hepatitis serum at a peak density of 1.14 g/ml and in the soluble protein fractions on top of the gradient, and (iii) they reacted in ELISA with disrupted human T-cell lymphocytotropic virus type III (HTLV-III), and (iv) they reacted in immunoblots with a protein of Mr 74,000 derived from HTLV-III.

Major pol gene progenitors in the evolution of oncoviruses

The genetic relationships among molecularly cloned prototype viruses representing all of the major oncovirus genera were investigated by molecular hybridization and nucleotide sequence analysis. One of the major progenitors of the pol genes of such viruses gives rise to mammalian type C viruses and another gives rise to type A, B, D, and avian type C oncoviruses. Evidence of unusual patterns of homology among the env genes of mammalian type C and D oncoviruses illustrates that genetic interactions between their progenitors contributed to the evolution of oncoviruses.

Molecular cloning of the unintegrated squirrel monkey retrovirus genome: organization and distribution of related sequences in primate DNAs

The closed circular form of the endogenous squirrel monkey type D retrovirus (SMRV) was molecularly cloned in a bacteriophage vector. The restriction map of the biologically active clone was determined and found to be identical to that of the parental SMRV linear DNA except for the deletion of one long terminal repeat. Restriction enzyme analysis and Southern blotting indicated that the SMRV long terminal repeat was approximately 300 base pairs long. The SMRV restriction map was oriented to the viral RNA by using a gene-specific probe from baboon endogenous virus. Restriction enzyme digests of a variety of vertebrate DNAs were analyzed for DNA sequence homology with SMRV by using the cloned SMRV genome as a probe. Consistent with earlier studies, multiple copies of SMRV were detected in squirrel monkey DNA. Related fragments were also detected in the DNAs from other primate species, including humans.

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.

Immunochemistry of the Moloney MuLV gp71 molecule-1. Distribution of antigenic determinants on the products of digestion by Staphylococcus aureus protease

The antigenic characterization of Moloney murine leukemia virus gp71 was carried out by cleavage with Staphylococcus aureus protease. The whole molecule and two fragments of 43,000 and 32,000 daltons were immunoprecipitated with monospecific anti-type, group and interspecies antiserum. The three native molecules were recognized by anti-type antibodies, but only the gp71 and the 32,000-dalton molecule seemed to retain group-specific antigenic determinants. No interspecies determinants were detected on the two products of digestion. A similar pattern of precipitation was found with SDS-denatured antigens. The results suggest that sequential structures contribute to the type-specific antigenic determinants, because they were not destroyed by SDS unfolding or by the change in the protein conformation that follows enzymatic cleavage. Interspecies determinants seem to be mainly conformational, since they disappeared from the whole molecule and the two peptides after the same treatment. Group-specific determinants appear to be intermediate: they disappeared after the conformational change on the native 43K but not on the 32K peptide and the monospecific anti-group antibody showed an intermediate ability to precipitate the SDS-unfolded antigens.

Interaction of viruses with cell surface receptors

This chapter discusses the interaction of viruses with cell surface receptors. The rigorous characterizations of receptor–ligand interactions have been derived from binding studies of radiolabeled ligands in neuropharmacology and endocrinology. The definition of viral recognition sites as receptors involves three major criteria that are derived from models of ligand–receptor interactions: saturability, specificity, and competition. A variety of approaches have been used to study the interaction of viral particles with cell surface receptors or reception sites. A rigorous study of viral–receptor interactions requires the use of more than one technique as different approaches provide complementary information about viral binding. The chapter discusses membrane components that interact with viruses. The identification of the subviral components that are responsible for the binding of viruses to cell surfaces has preceded the structural understanding of the cellular receptors themselves. The chapter summarizes current data concerning the viral attachment protein (VAP) of selected viruses.

Chemical and Immunological characterization of the major structural protein (p28) of MMC-1, a rhesus monkey endogenous type C virus: homology with the major structural protein of avian reticuloendotheliosis virus

The major core protein (p28) of MMC-1, an endogenous type C virus of the rhesus monkey (Macaca mulatta), was purified and subjected to structural and immunological analyses. The NH2-terminal amino acid sequence of MMC-1 p28 showed extensive homology to the sequences of the major structural proteins (p30) of known mammalian type C viruses. Similarly, interspecies antigenic determinants shared by all the above viral proteins were detected in MMC-1 p28. Competition radioimmunoassays together with the results of statistical analysis of the primary structure data provided evidence that MMC-1 p28 is not more closely related to primate type C viruses of the Papio genus than to those isolated from rodents, cats, or New World monkeys. MMC-1 p28 was found to be closely related structurally to the p30 protein of the avian reticuloendotheliosis virus (REV-A), a horizontally transmitted type C virus of putative mammalian origin. In addition, MMC-1 p28 and REV-A p30 shared a specific subset of antigenic determinants not present in any of the other avian or mammalian type C viruses studied. These findings suggest that MMC-1 and REV may have a common evolutionary origin.

Detection and cloning of murine leukemia virus-related sequences from African green monkey liver DNA

By using low-stringency nucleic acid hybridization conditions and specific subgenomic segments of the AKR ecotropic provirus as probes, murine leukemia virus (MuLV)-related sequences were detected in African green monkey (AGM) liver DNA. The MuLV-reactive segments present in restricted AGM DNA ranged from 1.9 kilobases (kb) to greater than 10 kb in size. On the basis of this finding, a 17-kb segment was cloned from a partial EcoRI AGM library in lambda Charon 4A which shared nearly 5 kb of homology with AKR ecotropic MuLV DNA. The MuLV-related sequences detected in restricted preparations of AGM DNA or present in the cloned monkey DNA reacted with probes mapping 2.0 to 7.0 kb from the 5' terminus of the AKR ecotropic provirus. The AGM clone also contained repeated sequences that flanked the MuLV-related segment. Labeled, subgenomic, MuLV-reactive segments of the monkey clone hybridized to multiple restriction fragments of AGM liver DNA, indicating the presence of several copies of the MuLV-related sequences.

Humans have antibodies capable of recognizing oncoviral glycoproteins: demonstration that these antibodies are formed in response to cellular modification of glycoproteins rather than as consequence of exposure to virus

There is controversy in the literature concerning the presence in humans of antibodies directed against the envelope glycoproteins of known oncoviruses. In the present report, we show that antibodies capable of precipitating a wide variety of oncoviral glycoproteins can be demonstrated under certain assay conditions. Substances as diverse as normal components of serum, extracts of bacteria, and even nonprotein molecules such as glycogen also shared the oncoviral glycoprotein determinants recognized by normal human sera. It was found that immunoprecipitation of a given viral glycoprotein by human sera was entirely dependent upon the cell in which the virus was grown. Human sera specifically did not recognize glycoproteins purified from oncoviruses grown in human or higher primate cells. These findings not only demonstrate that the antibodies were directed against cellular rather than the virus-coded antigenic determinants but also exclude the possibility that this immune response was elicited as a consequence of oncovirus exposure.

Major structural proteins of type B, type C, and type D oncoviruses share interspecies antigenic determinants

Interspecies antigenic determinants have been used as markers to study the evolution of oncoviruses. By radioimmunologic techniques, it has been possible to detect crossreactivities among the major structural proteins of prototype viruses representing each of the three major Oncovirinae genera. Two different subsets of interspecies antigenic determinants were demonstrated. One encompasses known type B and type D viruses; the other is shared by type D and mammalian type C viruses. Such determinants were also demonstrated in certain as yet unclassified oncoviruses. These findings provide experimental evidence supporting the concept of an evolutionary relationship among the three major oncovirus genera.

A new virion precipitation test for oncovirus envelope antigens which detects common antigenic determinants in mammalian type-C viruses and Mason-Pfizer monkey virus

A method for the study of oncovirus envelope antigens was developed, bases on the precipitation of intact virions by a double antibody technique. The amount of precipitated virus was then measured as reverse transcriptase activity. The method was designated the virion precipitation test (VPT). It has been used for titration of antibodies to envelope antigens of oncoviruses. The study of envelop antigens of 11 different oncoviruses permitted their differentiation into the following groups: (1) murine type-C viruses: (2) feline type-C viruses; (3) simian type-C viruses; (4) the RD-114/BEV group; (5) Mason-Pfizer monkey virus (M-PMV); (6) bovine leukemia virus; (7) avian type-C viruses; (8) mouse mammary tumor virus. No common antigenic determinants were detected in the last three groups. Mammalian type-C viruses (RD-114, NIH-MuLV, G-MuLV) had common antigenic determinants in the envelope, as demonstrated with an anti-RD-114 serum. Mammalian type-C viruses also shared antigenic determinants with M-PMV. The relationship of type-C viruses to M-PMV decreased in the following order: RD-114--NIH-MuLV--G-MuLV. It was also shown that the endogenous xenotropic feline RD-114 virus was more closely related to xenotropic NIH-MuLV than to ecotropic G-MuLV. The nature of the common antigenic determinants, as demonstrated by VPT on the surface of mammalian type-C viruses and M-PMV, and their significance for the concept of oncovirus evolution are discussed.

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.