Translational products of type-C RNA tumor viruses

T-lymphocyte priming and protection against Friend leukemia by vaccinia-retrovirus env gene recombinant

The current prevalence of the acquired immune deficiency syndrome in humans has provoked renewed interest in methods of protective immunization against retrovirus-induced diseases. In this study, a vaccinia-retrovirus recombinant vector was constructed to study mechanisms of immune protection against Friend virus leukemia in mice. The envelope (env) gene from Friend murine leukemia virus (F-MuLV) was inserted into the genome of a vaccinia virus expression vector. Infected cells synthesized gp85, the glycosylated primary product of the env gene. Processing to gp70 and p15E, and cell surface localization, were similar to that occurring in cells infected with F-MuLV. Mice inoculated with live recombinant vaccinia virus had an envelope-specific T-cell proliferative response and, after challenge with Friend virus complex, developed neutralizing antibody and cytotoxic T cells (CTL) and were protected against leukemia. In contrast, unimmunized and control groups developed a delayed neutralizing antibody response, but no detectable CTL, and succumbed to leukemia. Genes of the major histocompatibility complex influenced protection induced by the vaccinia recombinant but not that induced by attenuated N-tropic Friend virus.

Molecular cloning and characterization of endogenous feline leukemia virus sequences from a cat genomic library

Recombinant bacteriophage lambda clones from a cat genomic library derived from placental DNA of a specific pathogen-free cat were screened to identify endogenous feline leukemia virus (FeLV) sequences. Restriction endonuclease mapping of four different clones indicates that there are a number of similarities among them, notably the presence of a 6.0- to 6.4-kilobase pair (kbp) EcoRI hybridizing fragment containing portions of sequences homologous to the gag, pol, env, and long terminal repeat-like elements of the infectious FeLV. The endogenous FeLV sequences isolated are approximately 4 kbp in length and are significantly shorter than the cloned infectious FeLV isolates, which are 8.5 to 8.7 kbp in length. The endogenous elements have 3.3- to 3.6-kbp deletions in the gag-pol region and approximately 0.7- to 1.0-kbp deletions in the env region. These deletions would render them incapable of encoding an infectious virus and may therefore be related to the non-inducibility of FeLV from uninfected cat cells and the subgenomic expression of these endogenous sequences in placental tissue. It appears that there is conservation in the ordering of restriction sites previously reported in the proviruses of the infectious FeLVs in sequences corresponding to the pol and env boundary as well as the region spanning the env gene of the endogenous clones, whereas a greater divergence occurs among restriction sites mapped to the gag and part of the pol regions of the infectious FeLV. Such deleted, FeLV-related subsets of DNA sequences could have originated either by germ-line integration of a complete ecotropic virus followed by deletion, or by integration of a preexisting, defective, deleted variant of the infectious virus.

Variants of type-C retroviruses from DBA/2 mice: protein-structural and biological properties

Ecotropic murine leukemia viruses isolated from normal and carcinogen-treated DBA/2 mice can be classified into three main groups that differ in structure and biology. Two groups, called Ea and Eb, consist of N-tropic viruses related to the standard endogenous ecotropic virus of AKR mice. Ea viruses replicate with reduced efficiency in cell lines derived from C3H mice, while Eb viruses essentially replicate normally in these cells. As elsewhere reported, Ea viruses appear apathogenic in C3H mice, while Eb viruses cause a moderate incidence of late leukemias. The biological differences are associated with modulations of the fine structure of the gag gene-encoded proteins. A third group of viruses, called Ec, is clearly more diverged. They differ extensively from Ea and Eb viruses in the products of the gag and env gene, and are related to Rauscher leukemia virus. Ec viruses are NB-ecotropic; they replicate efficiently in all mouse cells tested, and induce leukemias in C3H mice with shorter latency periods than Eb viruses. Since published nucleic acid hybridization data indicate that DBA/2 mice only carry one ecotropic provirus, we assume that the DBA/2 viruses represent a developmental series of variants evolving during the life of the animals.

Specificity studies on cytolytic T lymphocytes directed against murine leukemia virus-induced tumors. Analysis of monoclonal cytolytic T lymphocytes

The specificities of cloned cytolytic T lymphocytes (CTL) were studied for the analysis of CTL populations generated against murine leukemia viruses (MuLV) in H-2 congenic BALB/c (H-2d) and BALB.B (H-2b) mice. In particular, CTL generated in response to tumors induced by Gross MuLV and Friend MuLV were studied; these tumors expressed virus-induced antigens that do not cross-react and that can be distinguished from each other. The systematic study of 92 CTL clones clearly indicated that MuLV-immune CTL were highly heterogeneous with respect to both the intensities of target cell lysis that they mediated and to their specificity of recognition of MuLV-induced tumor target cells. Various categories of CTL clones were identified, ranging from CTL clones tht were tightly H-2 restricted and specific for the immunizing tumor to CTL clones that displayed no discernible patterns of specificity and that attacked a large number of different target cells. In addition, the surface markers of these cloned CTL were defined, and the best conditions for their prolonged maintenance in culture were determined. The present data indicate that future efforts in the definition of target antigens recognized by tumor-specific CTL should be performed with monoclonal lymphocytes.

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.

Characterization of caprine arthritis-encephalitis virus: a retrovirus of goats

A retrovirus isolated from synovial membrane explants of arthritic joints of goats has been characterized with respect to buoyant density. RNA-dependent DNA polymerase, genome structure and protein composition.

Analysis of secondary modifications of mouse mammary tumor virus proteins by two-dimensional gel electrophoresis

The structural proteins of mouse mammary tumor virus (MMTV) were analyzed by two-dimensional electrophoresis on isoelectric focusing and sodium dodecyl sulfate gels. Many of the viral proteins displayed heterogeneity in charge due to variable contents of carbohydrates (in particular, sialic acid) and phosphate residues. Neuraminidase treatment of the virions influenced the isoelectric pattern of the envelope glycoproteins. The glycoproteins of an MMTV variant which was attenuated by replication in feline kidney cells had different isoelectric points. This suggested that the acquisition of an altered carbohydrate configuration had changed the host range of the virus. The major MMTV structural core protein, p27, consisted of two species, which had identical iodinated tryptic peptide compositions but differed in phosphate contents. Another MMTV phosphoprotein, p21, was separated into four different phosphorylated species. Phosphorylation of p21 could be performed in vitro by the MMTV virion-associated protein kinase. This enzyme also has a high affinity for MMTV p30 as a substrate. Possible functions of this enzyme are discussed.

Spontaneous regression of Friend virus-induced erythroleukemia. VI. Structural and antigenic differences between the regressing and conventional strains of virus

The regressing and conventional strains of Friend virus were compared by neutralization assays, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and tryptic peptide mapping of the individual viral components. Neutralization rates of the two viruses differed in the presence of monospecific anti-gp70 antiserum and sera from regressed or immunized mice. Neutralization of regressing Friend virus, but not conventional Friend virus, occurred when the viruses were incubated with anti-p15(E) and complement. Human serum inactivated conventional Friend virus more rapidly than regressing Friend virus, probably as a result of virolysis induced by the reaction of viral p15(E) with human complement component C1. Structural differences between the viruses were detected in their gp70 viral glycoproteins and p15(E) and p12 proteins. Analysis of different stocks and clonal isolates of the viruses showed that the differences between the gp70 and p15(E), but not the p12 proteins, were associated with the regressing phenotype of the regressing strain of Friend virus.

Effect of chemical modification and fragmentation on antigenic determinants of internal protein p30 and surface glycoprotein gp70 of type C retroviruses

The effects of protein modification on the antigenic determinants of p30 and gp70 of type C retroviruses were investigated by using solid-phase competition radioimmunoassays. Proteins were modified by reduction with 2-mercaptoethanol and subsequent carboxymethylation of SH groups with iodoacetamide or by amidination of alpha and epsilon amino groups with methylacetimidate. The type-specific determinants of gp70 were found to be conformational in nature, as they were destroyed by these chemical modifications. Group- and interspecies-specific determinants of gp70 antigens, however, appear to be sequential and do not involve residues susceptible to these chemical reagents. Conformation-dependent type-specific determinants of p30 were affected only by methylacetimidate. Group- and interspecies-specific determinants of p30 are similar to those of gp70 in that they also appear to be sequential antigenic sites. Therefore, the broadly reactive group- and interspecies-specific determinants of gp70 and p30 can be followed into small peptides. Accordingly, a cyanogen bromide cleavage fragment derived from the carboxyl-terminal one-third of Rauscher leukemia virus p30 was found to carry group-specific determinants but no detectable interspecies-specific determinants. In contrast, a peptide obtained by limited trypsin cleavage of p30, which was derived from the NH(2)-terminal region of the protein, contained at least one of the interspecies determinants shared with feline leukemia virus p27.