Delineation of functional determinants in the transforming protein of Fujinami sarcoma virus

We analyzed linker insertion mutations throughout the 3' region of the v-fps gene of Fujinami sarcoma virus to identify tyrosine kinase transforming protein (P130gag-fps) determinants that are important for catalysis and transforming activity and, in particular, to define residues that participate in substrate selection. Mutations that encode kinase-active, transformation-defective v-fps alleles were recovered, defining sites in the transforming protein that may normally facilitate kinase-substrate interaction. Additionally, one region within the catalytic domain of the transforming protein (amino acid residues 1012 to 1020) that tolerates peptide insertions without loss of transforming activity was discovered, although the insertion mutations in this region of v-fps exhibited qualitatively abnormal transforming function. Transformed rat cell lines that express these mutations displayed unusual phenotypes, including giant cells and cells with an extremely fusiform shape. Furthermore, the insertion mutations in this region were temperature sensitive, transformed cells assumed a flat morphology, cellular protein phosphotyrosine was reduced, and the kinase activity of the transforming protein was decreased when cells were incubated at 40.5 degrees C. Point mutations that specify the ancestral chicken c-fps sequence in the insertion-tolerant region were also introduced into v-fps. These back mutations led to a modest decrease in kinase activity, decreased tumorigenic potential in chickens, and an unexpected increase in transforming activity in rat cells. These results indicate that the insertion-tolerant region of P130gag-fps influences the biologic activity and thermostability of the kinase.

Severity of arthritis is predicted by antibody response to gp135 in chronic infection with caprine arthritis-encephalitis virus

Antibody titers to caprine arthritis-encephalitis virus surface glycoprotein gp135 and core protein p28 in synovial fluid and serum from 35 goats infected for 3 years were compared with the histologic severity of arthritis in these animals. Anti-gp135 antibody titers in synovial fluid and serum directly reflect the severity of carpal arthritis in chronically infected goats.

An in-vivo infectivity assay for cloned retroviruses lacking a susceptible cell culture

The lymphoproliferative disease virus (LPDV) of turkeys is the retroviral agent of etiology of a rapidly developing, naturally occurring, lymphoproliferative process. Recently we have molecularly cloned the viral genome. The lack of a susceptible cell culture which can sustain LPDV replication hampered the analysis of the infectious capability of the cloned genome. Based on the efficient in-vivo replication of LPDV we have developed a sensitive in-vivo approach aimed at establishing the infectious capability of the cloned provirus. According to this approach, peripheral leukocytes withdrawn from 3-week-old turkeys were transfected with the cloned DNA and the transfected leukocytes were re-injected into the turkey from which they had been obtained. The injected leukocytes enabled the efficient expression of the viral genome and the release into the blood stream of LPDV virions, which thereafter could travel to their appropriate in-vivo target lymphoid cells and start multiple replication cycles, resulting in the development of a detectable viremia. The applicability of this in-vivo assay for other cloned viral genomes is discussed.

Retroviral expression in mononuclear blood cells isolated from a patient with osteopetrosis (Albers-Schönberg disease)

We report the presence of reverse transcriptase activity in the supernatant of long-term culture of mononuclear blood cells (monocytes and lymphocytes) isolated from a 27-year-old patient suffering from benign osteopetrosis. The enzyme was purified to homogeneity according to the technique of Chandra and Steel, by chromatography, first on DEAE-cellulose (DE 52) and then on phosphocellulose (P11). After purification, the enzyme was characterized biochemically for its template specificity and ionic requirements. The purified enzyme was able to transcribe poly(rA).(dT)12-18 and poly(rC).(dG)12-18 very efficiently and had a marked preference for Mg2+ ions over Mn2+ ions. The pattern of ionic dependency for this enzyme is similar to that of reverse transcriptases purified from human lymphotropic viruses. The patient was tested and found sero-negative for HIV-1, HIV-2, and HTLV-I and seropositive (immunoglobulin G) for cytomegalovirus. Epstein-Barr virus nuclear antigens (EBNA) were detected in the patient's B lymphocytes. Since reverse transcriptase is the hallmark of retroviruses, we suggest that a retrovirus may be involved in the etiology of osteopetrosis.

Pathogenesis of caprine arthritis encephalitis virus. Cellular localization of viral transcripts in tissues of infected goats

Pathologic specimens of 18 goats with classical lesions of caprine arthritis-encephalitis (CAE) virus infection were examined morphologically and by in situ hybridization using molecularly cloned CAEV deoxyribonucleic acid (DNA) to determine which tissues and cells of naturally infected goats supported virus replication. Large numbers of cells with viral transcripts were detected in inflamed brain, spinal cord, lung, joints, and mammary gland. These cells were morphologically compatible with macrophages. Fewer cells with viral transcripts were seen in noninflamed tissues. Viral RNA was identified in macrophagelike cells in lung, liver, spleen, and lymph nodes, in cells lining the vessels of brain and synovium, and in epithelial cells of intestinal crypts, renal tubules, and thyroid follicles. These data suggest that the cell tropism of lentiviruses may extend beyond the narrow boundaries of lymphocytes and macrophages.

Neurodegenerative disease induced by the wild mouse ecotropic retrovirus is markedly accelerated by long terminal repeat and gag-pol sequences from nondefective Friend murine leukemia virus

The wild mouse ecotropic retrovirus (WM-E) induces a spongiform neurodegenerative disease in mice after a variable incubation period of 2 months to as long as 1 year. We isolated a molecular clone of WM-E (15-1) which was weakly neurovirulent (incidence, 8%) but was highly leukemogenic (incidence, 45%). Both lymphoid and granulocytic leukemias were observed, and these leukemias were often neuroinvasive. A chimeric virus was constructed containing the env and 3' pol sequences of 15-1 and long terminal repeat (LTR), gag, and 5' pol sequences from a clone of Friend murine leukemia virus (FB29). FB29 has been shown previously to replicate to high levels in the central nervous system (CNS) but is not itself neurovirulent. This finding was confirmed at the DNA level in the current study. Surprisingly, intraperitoneal inoculation of neonatal IRW mice with the chimeric virus (FrCasE) caused an accelerated neurodegenerative disease with an incubation period of only 16 days and was uniformly fatal by 23 days postinoculation. Introduction of the LTR of 15-1 into the FrCasE genome yielded a virus (FrCasEL) with a degree of neurovirulence intermediate between those of 15-1 and FrCasE. No differences were found in the levels of viremia or the relative levels of viral DNA in the spleens of mice inoculated with 15-1, FrCasE, or FrCasEL. However, the levels of viral DNA in the CNS correlated with the relative degrees of neurovirulence of the respective viruses (FrCasE greater than FrCasEL greater than 15-1). Thus, the env and 3' pol sequences of WM-E (15-1) were required for neurovirulence, but elements within the LTR and gag-pol regions of FB29 had a profound influence on the level of CNS infection and the rate of development of neurodegeneration.

[Viruses and malignant hemopathies]

Review on general problems raised by the role of some viruses: parvoviruses, herpes viruses, retroviruses, in the physiopathology of human malignant blood diseases.

Immunodeficiency and clonal growth of target cells induced by helper-free defective retrovirus

The murine acquired immunodeficiency syndrome is induced by a defective retrovirus. To study the role of virus replication in this disease, helper-free stocks of defective Duplan virus were produced. These stocks were highly pathogenic in absence of detectable replicating murine leukemia viruses (MuLVs) other than xenotropic MuLV. They induced expansion of the infected cell population (over 1000-fold), and this cell expansion was oligoclonal in origin and, most likely, arose through cell division. These results suggest that this defective virus is oncogenic, inducing a primary neoplasia associated with an acquired immunodeficiency syndrome as a paraneoplastic syndrome. These data emphasize the need to determine whether virus replication is necessary for the progression of other immunodeficiency diseases, including acquired immunodeficiency syndrome, and whether these diseases also represent paraneoplastic syndromes.

Progression to development of lymphoma in the thymus of AKR mice treated neonatally with SL 3-3 virus

All AKR mice develop thymic lymphoma between 60 and 90 days of age after neonatal treatment with the oncogenic retrovirus SL 3-3. At 40-50 days of age, in the normal-sized thymus of virus-treated mice, cells appear that produce lymphoma when inoculated intrathymically but not when inoculated s.c. These cells are designated as thymus-dependent (TD) lymphoma cells. TD cells progress to cells that form tumors after both intrathymic and s.c. inoculation; these are designated as thymus-independent (TI) lymphoma cells. In this report, we show that the TD and TI cells can be distinguished as two distinct cell populations. Experiments show that the TD cells reside within the immature CD4- CD8- thymocyte population of the virus-treated mice. In addition, we also show that CD4- CD8- thymocytes from SL 3-3 virus-treated mice do not mature in fetal thymic stromal rudiments. Using three-color flow cytometry to trace maturation of CD4- CD8- thymocytes after intrathymic inoculation into irradiated syngeneic hosts, disregulated thymocyte maturation of this population from virus-treated mice is demonstrated. Thus, altered maturation of and the appearance of TD lymphoma cells in, the most immature population of thymocytes appears to be a first step in a multistep process of thymic lymphomagenesis caused by SL 3-3 virus.

Prediction of the virulencies of some enveloped viruses from the structure of the cleavage recognition site of viral glycoproteins essential for infectivity. I. Calculation of interaction energy

Some evidences have been found that virulency in paramyxoviruses depends on the sensitivity of the cleavage recognition site of the F glycoprotein to serine type proteases. In this report, the interaction energies between the active site of trypsin and the cleavage recognition sites in paramyxoviruses are calculated. Results show that van der Waals energy and electrostatic energy contribute to the sensitivity. The virulencies of some myxo- and retro-viruses are then predicted on the basis of the two calculated interaction energy values.

An altered v-raf is required in addition to v-myc in J3V1 virus for acceleration of murine plasmacytomagenesis

We have isolated and molecularly cloned a highly pathogenic virus variant, J3V1, from murine plasmacytomas induced by a combination of pristane and the weakly transforming recombinant retrovirus J3. J3 virus is a derivative of the v-raf/v-myc-carrying J2 virus that was generated by a frameshifting deletion inactivating v-raf in J2. J3V1 contains an additional deletion of 334 base paris in gag, which restores the correct reading frame for v-raf and results in the expression of a p57 gag-raf fusion protein. Reactivation of v-raf in J3 is required for efficient plasmacytoma acceleration in pristane-conditioned BALB/cAn mice.

The BLV-induced leukemia--lymphosarcoma complex in sheep

Sheep are highly susceptible to BLV infection and can be infected via several different means (routes). In all inoculated animals, specific anti-BLV antibodies can be demonstrated 1 to 3 months post-inoculation (p.i.). Between 10 and 13 months p.i., a moderate but persistent lymphocytosis (PL) may be detected in about 50% of the infected animals. This hematological disorder may be, but is not necessarily, associated with the development of a lymphosarcoma and can (might) be interpreted as a true lymphoid leukemia. According to findings revealed by immunolabelling and mitogen stimulation of peripheral blood lymphocytes, BLV-induced PL appears to be a B-cell disorder. Induced lymphosarcoma appears in about 40% of infected sheep during the 6 years p.i. It too is of B-lymphocyte lineage. In vitro studies demonstrate that BLV antigen is expressed exclusively in B-lymphocytes. Yet, BLV expression is greatly stimulated in whole lymphocyte culture by the addition of T-cell mitogen. This same phenomenon occurs when the supernatant of stimulated T-lymphocyte cultures is added to isolated BLV-infected B-lymphocytes. This observation supports the hypothesis that, as is the case with other retroviruses such as HIV, BLV is able to use the regular activation machinery of the immune system for its own replication and transmission. It seems, therefore, that the leukemia-lymphoma complex in sheep may serve as an accurate experimental model for the study of the biological properties of retroviruses.

Transgenic approach for the study of pathogenesis induced by human viruses

An understanding of the pathogenesis of human viral diseases has been hampered by the lack of suitable animal models. However, with the advent in the last decade of transgenic technology, it is now possible to introduce one or more viral genes into the germ-line of animals. Thus, transgenic technology allows for the study of viral gene expression and function in the context of the whole animal. The focus of this review is to define the advantages and disadvantages of the transgenic approach in studies of viral pathogenesis. Studies involving a human DNA tumor virus (JCV) and a human retrovirus (HIV) will be described to illustrate these points.

Human retroviruses: their role in neoplasia and immunodeficiency

Human retroviruses (HTLVs and HIVs) infect the cells of the immune system and cause mild-to-severe immune dysfunction. They are directly or indirectly responsible for associated neoplasia and central nervous system disorders. The study of these viruses is of great importance, not only because they cause grave illnesses like AIDS, neoplasias, and CNS disease, but also because they have the ability to exert such fine levels of gene regulatory control in their replication and expression. These studies will ultimately shed light on fundamental mechanisms of genetic control in human cells in their normal state and the alterations of these controls in neoplastic or immunologically aberrant states.

[Retroviruses and their importance in neurology]

Retroviruses comprise spumaviruses, lentiviruses and oncoviruses. After these taxonomic remarks neurologic-psychiatric-syndromes (multifocal leucencephalopathy, dementia-complex, vacuolar myelopathy and others) are described, that could be observed as manifestations of the "acquired immune deficiency syndrome". Some therapeutic measures are discussed, especially the administration of Zidovudine that shows good temporary results. Essentially Zidovudine works by misleading the Reserve Transkriptase by offering a "Fake-thymidine"--so misleading replication. Lastly the hypotheses concerning multiple sclerosis are put in relation to lentiviruses. Some animal variants of the viruses and their neurotropic features are described. This discovery has lead to those speculations--however, these speculations remain unsecure.

Potential human health risks associated with animal retroviruses: some hypotheses

Several studies have demonstrated the existence of morphological, biological, genetic and antigenic correlations between human and animal retroviruses. Furthermore, some agents of bovine and feline origin can also be considered useful comparative models for the pathogenetic study of human diseases such as leukaemia, acquired immunodeficiency syndrome (AIDS) and multiple sclerosis (MS). In spite of the existence of data suggesting a possible role of some animal retroviruses (e.g. the bovine leukosis virus, BLV) in the etiology and epidemiology of human leukaemia and MS, the true zoonotic potential of such agents remains unknown, but their genetic and antigenic linkages with some human lentiviruses (such as the human immunodeficiency virus-1, HIV 1) can make them hypothetically responsible for a certain number of false-positive serological reactions in man, especially in those subjects who are professionally exposed to animal lentiviruses. In the present paper particular reference is made to this last hypothesis which, if confirmed, would suggest a larger scale-utilization of more specific diagnostic tests for HIV infection in man, such as the immunoblotting techniques.

[Ultrastructural analysis of the action of centrophenoxine on retrovirus-transformed cells]

The ultrastructure of hybridoma cells cultured with 5.10(-4) centrophenoxine (CP) has been studied. It is shown that CP effects hybridomas and prevents retrovirus exocytosis. The effect of CP on Ca-calmodulin system associated with cytoskeleton is suggested.