Detection of feline leukemia virus RNA in saliva from naturally infected cats and correlation of PCR results with those of current diagnostic methods

A novel diagnostic test for feline leukemia virus (FeLV) RNA in saliva from naturally infected cats is described in this study. We evaluated different diagnostic tests and compared them with the widely used enzyme-linked immunosorbent assay (ELISA) for the detection of p27 in the diagnosis of FeLV. Blood samples from 445 cats were tested for the presence of provirus by real-time PCR and plasma and saliva specimens from those cats were tested for the presence of viral RNA by real-time reverse transcription (RT)-PCR and for the presence of p27 by ELISA. In comparison to conventional ELISA, the diagnostic sensitivity and specificity of the detection of salivary FeLV RNA by real-time RT-PCR were found to be 98.1 and 99.2%, respectively. Detection of viral RNA in saliva had a positive predictive value of 94.6% and a negative predictive value of 99.7%. The kappa value was 0.96, demonstrating an almost perfect agreement between both tests. Furthermore, we confirmed previous results showing that a number of cats which tested negative for the presence of p27 in plasma were in fact positive for the presence of DNA provirus in blood specimens (5.4%). However, 96.4% of these latently infected cats did not shed viral RNA in saliva; therefore, we assume that these cats are of relatively low clinical importance at the time of testing. This study shows considerable diagnostic value of the detection of saliva FeLV RNA in naturally infected cats. This new diagnostic method has advantages over the conventional ELISA, such as less invasive sample collection and no requirement for trained personnel.

Widely varying SIV prevalence rates in naturally infected primate species from Cameroon

Although it is now well established that a substantial proportion of wild-living primates in sub-Saharan Africa harbor SIV, no study to date has examined to what extent the various species are naturally infected. In this study, we first describe the development and validation of sensitive and specific SIV antibody detection assays representing all major known primate lentiviral lineages on a panel of 207 sera from 11 different primate species with known infection status. The newly developed assays were then used to determine SIV prevalence rates in nine primate species native to Cameroon. Analysis of 722 sera revealed widely varying prevalence rates, ranging from an apparent absence of SIV infection in crested mona (0/70), grey cheeked (0/36) and agile mangabeys (0/92), to prevalence rates of 3%, 4%, 11%, 27%, 39% and 52% for mustached (6/203), greater spot-nosed (8/193), northern talapoin (3/26), mantled guereza (14/52), De Brazza's (9/23) and mandrill (14/27) monkeys, respectively. The epidemiology of naturally occurring SIV infections is thus more complex than previously appreciated and the various non-human primate hosts seem to differ in their susceptibility to SIV infection. The newly developed assays should now permit to define with greater accuracy existing SIV reservoirs and associated human zoonotic risk.

An HIV-1 encoded peptide mimics the DNA binding loop of NF-kappaB and binds thioredoxin with high affinity

Pro-fs is a human immunodeficiency virus type 1 (HIV-l)-encoded putative selenoprotein, predicted by a theoretical analysis of the viral genome; it is potentially expressed by a -1 frameshift from the protease coding region. Pro-fs has significant sequence similarity to the DNA binding loop of nuclear factor kappa B (NF-kappaB), which is known to bind thioredoxin (Trx). We hypothesize that the putative HIV-1 pro-fs gene product functions by mimicry of NF-kappaB via binding to Trx. The hypothesis was tested in vitro by co-immunoprecipitation and GST-pull down assays, using a purified mutant pro-fs protein, in which the two potential selenocysteine residues were mutated to cysteines, in order to permit expression in bacteria. Both experiments showed that pro-fs binds to human wild type Trx (Trx-wt) with high affinity. Mutation of the two conserved cysteine residues in the Trx active site redox center to serine (Ser) (Trx-CS) weakened but failed to abolish the interaction. In pro-fs-transfected 293T cells, using confocal microscopy and fluorescence resonance energy transfer (FRET), we have observed that pro-fs localizes in cell nuclei and forms oligomers. Upon stimulation by phorbol 12-myristate 13-acetate (PMA), Trx translocates into cell nuclei. Significant FRET efficiency was detected in the nuclei of PMA-stimulated 293T cells co-expressing fluorescence-tagged pro-fs and Trx-wt or Trx-CS. These results indicate that in living cells the double cysteine mutant of pro-fs binds to both Trx and Trx-CS with high affinity, suggesting that Trx-pro-fs binding is a structurally-specific interaction, involving more of the Trx molecule than just its active site cysteine residues. These results establish the capacity for functional mimicry of the Trx binding ability of the NF-kappaB/Rel family of transcription factors by the putative HIV-1 pro-fs protein.

A single amino acid change in gp41 is linked to the macrophage-only replication phenotype of a molecular clone of simian immunodeficiency virus derived from the brain of a macaque with neuropathogenic infection

Simian immunodeficiency virus (SIV)-related neuropathogenesis has been observed in 90% of pig-tailed macaques infected with strain SIVsmmFGb, making it an excellent system for studying human immunodeficiency virus (HIV)-associated neurological disease. To investigate the genetics of SIV neurovirulence, infectious molecular clones were generated from the brain of a SIVsmmFGb-infected pig-tailed macaque. One clone, BPZm.12, displayed a macrophage-restricted phenotype not previously described; this clone replicated to high levels in macrophages, but did not replicate in peripheral blood mononuclear cells (PBMC) until at least 21 days postinfection. Sequence analysis of the env gene of BPZm.12 revealed the substitution of a serine residue for a highly conserved proline residue at position 629 in gp41. A mutant clone, which contained the conserved proline to serine (BPZm.12-629P), was able to replicate in both macrophages and PBMC without delay. A mutant of an unrelated dual tropic molecular clone PBj6.6, substituting proline for serine (PBj6.6-629S), replicated to high levels in macrophages, but did not replicate in PBMC at any time point. These data indicated that a single determinant in gp41 of an SIV clone changed its phenotype from macrophage tropic to dual tropic.

Autoantibodies and CD4 T cells target a cell retroviral envelope protein in non-obese diabetic mice

We determined that, over a biologic time interval, from 4 to 8 weeks of age, female non-obese diabetic (NOD) mice develop antibodies against pancreatic beta-cell-surface antigens depending upon the presence of both the MHC class II susceptibility allele, I-A(g7), and other NOD background genes. We generated a mAb from a pre-diabetic NOD mouse that binds to the surface of insulinoma cells and isolated mouse beta cells, and identified the target as a retroviral envelope glycoprotein expressed on pancreatic beta cells. The cloned and expressed sequence for this protein was recognized by the mAb. The antibody as well as sera from pre-diabetic NOD mice recognized the recombinant protein. Spontaneous T cell reactivity against a peptide from the cloned protein was found in NOD mice. In conclusion, a beta cell retroviral envelope protein is a target antigen that is selected by the NOD mouse immune system early in the pathogenesis of autoimmune diabetes.

Expression, purification, and characterization of recombinant HIV gp140. The gp41 ectodomain of HIV or simian immunodeficiency virus is sufficient to maintain the retroviral envelope glycoprotein as a trimer

Efforts to understand the molecular basis of human immunodeficiency virus (HIV) envelope glycoprotein function have been hampered by the inability to generate sufficient quantities of homogeneous material. We now report on the high level expression, purification, and characterization of soluble HIV gp140 ectodomain proteins in Chinese hamster ovary-Lec3.2.8.1 cells. Gel filtration and analytical ultracentrifugation show that the uncleaved ADA strain-derived gp140 proteins are trimeric without further modification required to maintain oligomers. These spike proteins are native as judged by soluble CD4 (sCD4) (K(D) = 1-2 nm) and monoclonal antibody binding studies using surface plasmon resonance. CD4 ligation induces conformational change in the trimer, exposing the chemokine receptor binding site as assessed by 17b monoclonal antibody reactivity. Lack of anti-cooperativity in sCD4-ADA trimer interaction distinct from that observed with sCD4-SIV mac32H implies quaternary structural differences in ground states of their respective spike proteins.

Evidence for a retroviral trigger in Graves' disease

An apparently high frequency of Graves' disease encountered in New Orleans, Louisiana, prompted an investigation for a possible infectious agent that might be triggering the disease in genetically susceptible individuals. We studied 40 patients with Graves' disease, and compared them to the following groups of controls: age and gender matched healthy subjects; patients with multinodular goiter (non-autoimmune thyroid controls); patients with chronic lymphocytic thyroiditis (autoimmune thyroid disease controls) and additional organ or tissue specific autoimmune controls exclusive of thyroid autoimmunity, including patients with Type I diabetes and other endocrine autoimmune complex disorders. Serum antibodies against a prototypic strain of a human intracisternal A-type retroviral particle type 1 (HIAP-1) were detected by a sensitive and specific immunoblotting assay. In 87.5% (35/40) of the Graves' disease patients there was a positive reaction against several HIAP-1-associated proteins, predominantly 97 Kd and 80 Kd, with only 5 showing no reactivity to any. In contrast, 2% (2/105) of sera from normal controls showed positive reactivity. Furthermore, only 10% (1/10) of sera from multinodular goiter control patients and 10% (1/10) of Hashimoto's patients showed reactivity (p < 0.0005). Sera from 3 of 20 (15%) of Type I diabetic patients none of whom had Graves' disease, showed reactivity but there was no reactivity in 9 other patients with one or more of the endocrine autoimmune complex disorders, including Addison's disease, vitiligo, myasthenia gravis and pernicious anemia. In addition we studied two individuals with Graves' disease from each of two families residing outside Louisiana, all of whom were positive for these antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

A set of beta-galactosidase gene fusion cassettes demonstrates usefulness in expressing HIV-1 genes in Escherichia coli

Heterologous expression in Escherichia coli is often limited by yield and solubility of the foreign protein in the bacterial cytoplasm. In many cases, overexpression also results in growth inhibition. In order to produce retroviral proteins that are especially difficult to overexpress in E. coli, we designed a set of beta-galactosidase fusion cassettes. Fusions with beta-galactosidase increase significantly both yield and solubility of the foreign proteins, thus making purification much easier. These cassettes allow for N- or C-terminal fusions, and the retroviral proteins can be released from the fusion by automaturation in vivo for the HIV-1 protease or cleavage by thrombine for Tat. More generally, any synthetic sequence coding for a given cleavage site can be introduced 5' or 3' to the lacZ gene through a convenient set of unique restriction sites, making these fusion cassettes highly versatile.

Identification and characterization of the Bel 3 protein of human foamy virus

The human foamy virus (HFV) is a complex retrovirus that contains several regulatory and auxiliary bel genes besides the gag, pol, and env genes. In contrast to the gene products of bel 1 and bel 2/bet that were identified previously, the Bel 3 protein has not been described to date. Here we report the identification of Bel 3 in HFV-infected cells by immunoprecipitation, indirect immunofluorescence, and expression cloning under the control of a strong heterologous promoter. Bel 3 was immunoprecipitated with an antiserum directed against a bacterially expressed and purified form of recombinant Bel 3 antigen. Bel 3 was found to be expressed in low amounts in the cytoplasm of HFV-infected cells and to migrate with an apparent molecular mass of 19.4 kDa on electrophoresis in SDS-polyacrylamide gels, consistent with the calculated value of 18.2 kDa. Radioimmunoprecipitation of HFV-infected cell lysates with the hyperimmune serum against Bel 3 revealed at least two additional immunoreactive bands of 15.5 and 10.6 kDa. The results indicate that Bel 3 was labile, because it was partially degraded even at early time points after infection. On transfection and expression in transfected COS cells, recombinant Bel 3 was immunoprecipitated and migrated in three polypeptide bands of 18.7, 14.8, and 9.3 kDa under denaturing conditions. In the absence of reducing agents, the bacterially expressed and purified recombinant Bel 3 protein of 16.1 kDa can form homodimers of 30 kDa.

The Bel1 protein of human foamy virus contains one positive and two negative control regions which regulate a distinct activation domain of 30 amino acids

The Bel1 transactivator is essential for the replication of human foamy virus (HFV). To define the functional domains of HFV Bel1, we generated random missense mutations throughout the entire coding sequence of Bel1. Functional analyses of 24 missense mutations have revealed the presence of at least two functional domains in Bel1. One domain corresponds to a basic amino acid-rich motif which acts as a bipartite nuclear targeting sequence. A second, central domain corresponds to a presumed effector region which, when mutated, leads to dominant-negative mutants and/or lacks transactivating ability. In addition, deletion analyses and domain-swapping experiments further showed that Bel1 protein contains a strong carboxy-terminal activation domain. The activating region is also capable of functioning as a transcription-activating domain in yeast cells, although it does not bear any significant sequence homology to the well-characterized acidic activation domain which is known to function only in yeast and mammalian cells. We also demonstrated that the regions of Bel1 from residues 1 to 76 and from residues 153 to 225 repressed transcriptional activation exerted by the Bel1 activation domain. In contrast, the region from residues 82 to 150 appears to overcome an inhibitory effect. These results indicate that Bel1 contains one positive and two negative regulatory domains that modulate a distinct activation domain of Bel1. These regulatory domains of Bel1 cannot affect the function of the VP16 activation domain, suggesting that these domains specifically regulate the activation domain of Bel1. Furthermore, in vivo competition experiments showed that the positive regulatory domain acts in trans. Thus, our results demonstrate that Bel1-mediated transactivation appears to undergo a complex regulatory pathway which provides a novel mode of regulation for a transcriptional activation domain.

Expression, characterization and purification of simian immunodeficiency virus soluble, oligomerized gp160 from mammalian cells

The envelope glycoprotein, gp160, of human (HIV) and simian (SIV) immunodeficiency viruses mediates virus-host cell binding followed by fusion of the viral and plasma membranes. The envelope proteins are known to exist as non-covalently associated oligomers on the virus surface. The production of permanent mammalian cell lines that constitutively secrete relatively high levels of soluble forms of SIV gp160 is described and we show that these proteins are secreted predominantly as tetramers with lower levels of dimer forms. Oligomeric forms were purified to greater than 90% purity using a simple gel filtration method. The purified proteins bind CD4 suggesting that they remain in their native conformation. The purified oligomeric proteins provide the basis for more relevant structural, functional and immunological studies than recombinant gp120 as they more closely resemble the envelope protein oligomer.

A defective human foamy provirus generated by pregenome splicing

Foamy viruses are a group of retroviruses of complex structure which were thought to be non-pathogenic. The recent demonstration of neurological diseases in mice transgenic for human foamy virus (HFV) and the high prevalence of HFV sequences in Graves' disease question this idea. By PCR, we have detected HFV sequences with a non-random deletion in the bel1 transactivator gene in other autoimmune conditions. Sequence analysis revealed that this deleted area corresponds to the excision of a known intron in bet, one of HFV's regulatory genes. The same phenomenon was observed in both acute and chronic infections, in vitro or in vivo, although the deleted forms were distinctly more abundant in chronic states. The viral DNA containing the bel1 deletion is apparently part of an otherwise complete genome, strongly suggesting that this provirus derives from the reverse transcription of a spliced pregenomic RNA. Bel1-spliced provirus was shown to be defective when transfected into permissive cells. However, co-expression with the Bel1 transactivator led to functional trans-complementation and formation of viral particles. Splicing of the genome may be an important factor in HFV biology: genomes with the deletion may either interfere with wild-type virus expression or alter host cell functions through background expression of viral regulatory proteins.

Enhanced incorporation of transgenic DNA into zebrafish chromosomes by a retroviral integration protein

Manufacture of lines of fish containing specific transgenes is difficult because most fish that hatch from embryos injected with foreign DNA are mosaic; few have the transgenic DNA integrated in germ-line cells. To determine whether the process of integration of exogenously supplied DNA into fish genomes could be accelerated, we examined the ability of the Moloney murine leukemia virus (MoMLV) integration protein (IN) to function in embryonic zebrafish cells. We used partially purified IN from a baculovirus/insect cell expression system and unpurified IN from extracts of psi-2 mouse cells that carry a MoMLV provirus. Both forms of IN were able to enhance expression in zebrafish 10 days after fertilization. At day 14 of development, fish injected with IN had higher levels of transgenic DNA than control fish. The ability of IN to enhance integration of transgenic constructs was demonstrated by a ligation-mediated polymerase chain reaction procedure, which was employed to detect junction fragments of foreign and host genomic DNA, generated by IN-mediated integration.

Human foamy virus polypeptides: identification of env and bel gene products

Human foamy virus (HFV) proteins were identified in human cells cultured in vitro by immunoprecipitation and immunoblotting with specific antisera. Among several viral polypeptides, four glycoproteins of approximately 160, 130, 70, and 48 kDa were identified in HFV-infected cells. gp130 was shown to represent the intracellular env precursor, and gp70 and gp48 were shown to represent the external and transmembrane env proteins, respectively. The nature of gp160, which shares sequences with the env, bel1, and bel2 proteins, is not yet resolved. In addition, a p62 identified with bel1- and bel2-specific antisera likely corresponds to the bet gene product.

Breast cancer and T-cell-mediated immunity to proteins of the mouse mammary tumour virus (MMTV)

We have previously reported that breast cancer patients and some healthy subjects show positive T-cell-mediated immune responses to a semi-purified mouse mammary tumour viral pool (MMTV). We have now used Western blotting to analyse the specificity of the response and to determine the target polypeptides. Two types of T-cell response to the viral antigens were examined, proliferation and MIF release, the latter implies a DTH status in vivo where primed lymphocytes are involved. Two viral fractions were used, one containing a glycoprotein, the 52 kD major virus envelope, and the other containing the 28 kD main virus core protein. We analysed both patients and healthy subjects whose T-cells proliferated to the MMTV total extract (viral pool). The T-cell response in the patients was shown to be viral specific since both the T-cell proliferation (21/25) and MIF release (17/19) were directed against viral components of the pool (gp 52 and/or p 28). The T-cell response in the healthy control subjects was shown to be mostly directed against a species-specific albumin component of the extract. In addition, the monocyte integrity required for the MIF response was altered in the breast cancer patients. The monocytes from one patient out of three failed to respond to MIF, even though the lymphokine was released normally by the patients' activated T-cells.

Analysis of a temperature-sensitive mutation affecting the integration protein of Moloney murine leukemia virus

We have previously described a series of mutations in the 3' terminus of the pol gene of Moloney murine leukemia virus which adversely affect the establishment of an integrated provirus (Roth, M. J., Schwartzberg, P., Tanese, N., and Goff, S. P., J. Virol. 64, 4709-4717, 1990). While most of the mutations were unconditionally lethal for virus replication, we now demonstrate that one mutation, in6161-12, a 12-base pair linker insertion into the 3' end of the pol gene, causes a temperature-sensitive phenotype. This mutant virus is temperature-sensitive for IN protein function as well as viral replication.

Purification and biochemical characterization of recombinant simian immunodeficiency virus protease and comparison to human immunodeficiency virus type 1 protease

Simian immunodeficiency virus protease (SIV-PR) was produced in Escherichia coli with a recombinant expression system in which the mature enzyme autoprocessed from a precursor form. Recombinant SIV and HIV-1 (human immunodeficiency virus, type 1) proteases were purified from bacterial cell lysates by use of sequential steps of ammonium sulfate precipitation and size-exclusion and ion-exchange chromatography. The amino acid composition, amino-terminal sequence, and molecular weight (monomer) of the recombinant SIV-PR were in accord with that of the 99 amino acid polypeptide predicted from the SIVMac-PR nucleotide sequence. The active form of SIV-PR was shown to be dimeric by gel filtration chromatography. Inhibition by pepstatin A, time-dependent inactivation by 1,2-epoxy-3-(4-nitrophenoxy)propane, and pH rate profiles using oligopeptide substrates demonstrated that SIV-PR behaves as an aspartic protease. Recombinant HIV-1 Pr55gag precursor was processed in vitro by SIV-PR and HIV-1 PR with indistinguishable proteolytic patterns upon NaDodSO4-polyacrylamide gel electrophoresis. Oligopeptide substrates for HIV-1 PR were found to be suitable substrates for recombinant SIV-PR with the exception of a peptide containing the site identified for p66/p51 cleavage (Phe*Tyr) within HIV-1 reverse transcriptase (RT). Several synthetic peptide analogue inhibitors of HIV-1 PR were also potent inhibitors of SIV-PR, indicating that SIV infection in macaques and rhesus monkeys should be useful models for the preclinical evaluation of acquired immunodeficiency syndrome (AIDS) therapeutics targeted towards the virally encoded HIV-1 protease.

Antibody response to reverse transcriptase in cats infected with feline immunodeficiency virus

The antibody response in cats to feline immunodeficiency virus (FIV) reverse transcriptase (RT) was followed for 3 years. Eight of the nine cats used in this study produced reverse transcriptase-inhibiting (RTI) antibodies. Relative inhibitory means of 2.9%, 18.4%, 33%, and 47% were found 6, 12, 24, and 36 months, respectively, after infection with FIV. The enzyme activity was suppressed by greater than or equal to 78% with the use of 100 micrograms of FIV-associated IgG. The RTI antibodies were FIV-specific, as they did not inhibit other mammalian retroviral polymerases, including feline leukemia virus RT. An RT-inhibition assay with sera in the presence of protein A and immunoblot analysis showed that antibody binding to FIV RT protein p62 is independent of antibody ability to block enzyme activity. Viral RT released by detergent-treated virus was stable for more than 6 weeks at 4 degrees C, whereas its activity was reduced by 50% after 2 weeks at 37 degrees C. Because significant concentrations of RTI antibodies are detected only at 1 to 2 years after infection, they can be used to determine the approximate time of virus infection and as a marker for disease progression.

Immunoprecipitation of human immunodeficiency virus type 2 glycoproteins by sera positive for human immunodeficiency virus type 1

Analysis by radioimmunoprecipitation of serum samples from 27 different human immunodeficiency virus type 1 (HIV-1)-infected individuals residing in Chile showed that the sera of 26% of these individuals also react with glycoprotein gp125 of HIV type 2 (HIV-2). This cross-reaction seems to reflect a qualitative difference among infected individuals, because the titer of antibodies against gp120 of HIV-1 in the cross-reacting samples did not differ significantly from that in the non-cross-reacting samples. Most of the HIV-1-seropositive sera, including many that did not react with gp125 of HIV-2, reacted with gp140, the precursor of HIV-2 glycoproteins. The observed cross-reactions allowed us to distinguish three groups of HIV-1-infected individuals: (i) those whose sera react with both gp140 and gp125, (ii) those whose sera react with gp140, and (iii) those whose sera react with neither of these glycoproteins. The possible cause and significance of these differences is under study.

Purification and characterization of P47gag-crk expressed in insect cells

The crk oncogene product, P47gag-crk, was expressed and purified using a baculovirus expression system. Approximately 2-10 mg of P47gag-crk was produced in 10(9) insect cells infected with a recombinant baculovirus. Partially purified P47gag-crk was obtained by precipitation in a low salt buffer and gel filtration. A better purification of P47gag-crk was achieved by immunoaffinity chromatography, resulting in a single band by Coomassie Blue staining. The insect cells expressing P47gag-crk showed an increase in protein-phosphotyrosine content, which is a characteristic feature of crk-transformed cells. Moreover, like P47gag-crk produced in chicken or rat cells, P47gag-crk produced in insect cells associated in vitro with a tyrosine kinase and its substrates from Crk-3Y1 cells. Peptide mapping of P47gag-crk expressed in insect, rat, and chicken cells showed that similar sites were phosphorylated in these proteins. These data suggest that P47gag-crk expressed in insect cells is functional and will be useful for the further analysis of this protein.

Expression and biochemical characterization of human immunodeficiency virus type 1 nef gene product

nef genes from human immunodeficiency virus type 1 isolates BH10 and LAV1 (lymphadenopathy-associated virus type 1) were expressed in Escherichia coli under the deo operon promoter. The two proteins found in the soluble compartment of the bacterial lysate were purified by ion-exchange column chromatography to apparent homogeneity. Determination of the amino-terminal sequence revealed glycine as the first amino acid in the Nef protein, indicating removal of the initiator methionine during expression in E. coli. Under native conditions, the recombinant Nef protein is a monomer of 23 kilodaltons. In denaturing polyacrylamide gels, however, BH10 and LAV1 Nef proteins migrate as 28 and 26 kilodaltons, respectively. GTP binding and GTPase activity were monitored during Nef protein purification. These activities did not copurify with the recombinant Nef protein from either the BH10 or the LAV1 isolate. Purified recombinant BH10 Nef protein was used as an immunogen to elicit mouse monoclonal antibodies. A series of monoclonal antibodies were obtained which reacted with sequences at either the amino or carboxy terminus of Nef. In addition, a conformational epitope reacting with native BH10, but not LAV1, Nef was isolated.

Human immunodeficiency virus vpr product is a virion-associated regulatory protein

The vpr product of the human immunodeficiency virus type 1 (HIV-1) acts in trans to accelerate virus replication and cytopathic effect in T cells. Here it is shown that the HIV-1 viral particle contains multiple copies of the vpr protein. The vpr product is the first regulatory protein of HIV-1 to be found in the virus particle. This observation raises the possibility that vpr acts to facilitate the early steps of infection before de novo viral protein synthesis occurs.

Serological responses of cats to feline immunodeficiency virus

The proteins of feline immunodeficiency virus (FIV) were identified by sodium dodecylsulphate poly-acrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Purified [35S]methionine/cysteine-labelled virus contained proteins of Mr 120, 24, 17, and 10kD, of which the most prominent were p24 and p17, and minor components of 62, 54, 52, 41 and 32kD. Sera from FIV-infected cats precipitated two glycoproteins (gp) of Mr 120kD (gp120) and 41kD (gp41) from lysates of [14C]glucosamine-labelled infected cells. Purified virus contained very little or no detectable glycoproteins. The serological response to individual viral proteins was followed in experimentally infected cats by immunoblotting. Since purified virus was a poor source of gp120, a method using FIV-infected cell lysates was developed. Cats produced antibodies to gp120, p55, p24 and p17. (The p55 was presumed to be a precursor of p24 and p17.) Following infection, antibodies developed first to p24 and subsequently to p17, p55 and gp120. Sera from cats infected with three separate isolates of FIV, two from the UK and one from the USA, had cross-reacting antibodies to all of these viral proteins. The criteria for identification of seropositive cats were defined. The minimum requirement for a positive immunoblot was antibody to gp120 or to at least three core proteins (p55, p24 and p17). Comparison of two commercial enzyme-linked immunosorbent assay (ELISA) kits and immunoblotting indicated that false-positive results occurred as a result of non-specific reactions in the ELISA systems.

Normal fibroblasts responding to anoxia exhibit features of the malignant phenotype

Cancer has two fundamental features: neoplasia, representing the aberrant expression of a normal cell proliferation response, and malignancy, an ability to penetrate normal tissue boundaries. Although the role of oncogenes in neoplastic transformation is becoming clearer, malignancy remains far less well understood. Normal rat fibroblasts exhibit a staged response to anoxia which, if expressed in an uncontrolled fashion, may contribute vital aspects to the malignant phenotype. The response begins with induction of retrotransposon-like VL30 element transcription, progresses through induction of several intracellular proteins, and is followed by secretion of three major proteins including the protease cathepsin L. The induced VL30 element RNA encodes a 61-kDa secretory protein of unknown function. The response of fibroblasts to anoxia is evidently not a survival response. Instead, the response represents a close match to the role of fibroblasts during the early stages of wound healing where they are active under near-anoxic conditions. Malignant cancer cells are known to exhibit several of the characteristics we find induced in fibroblasts by anoxia. Conversion to the malignant phenotype may represent coordinate loss of control of this normal cellular response.

Functional alterations of herpes simplex virus-specific CD4+ multifunctional T cell clones following infection with human T lymphotropic virus type I

In an attempt to understand the mechanisms of immunodeficiency induced by human T lymphotropic virus type I (HTLV-I), HSV-specific CD4+ human multifunctional T cell clones were infected with HTLV-I in vitro. Early after HTLV-I infection, when their growth was still IL-2-dependent, clones were found to have almost completely lost their cytotoxic activity. At that time, their HSV-Ag-induced proliferative response and helper function for anti-HSV antibody production by B cells were only partially impaired. After this initial phase, the HTLV-I-infected clone became IL-2-independent, and the helper function was also completely lost. IL-2-dependent HTLV-I-infected clones showed degrees of proliferative response and elevation of intracellular free Ca2+ concentration induced by anti-CD3 mAb equivalent to those of HTLV-I-uninfected clones. On the other hand, during the IL-2-independent stage, expression of CD3-TCR complex on the cell surface was markedly decreased, and no significant elevation of intracellular free Ca2+ concentration was detected in response to anti-CD3 mAb. These data indicated that the loss of cytotoxic activity of HSV-specific T cell clones observed early after HTLV-I infection was not the result of impaired antigen recognition via the CD3-TCR complex, but might be due to dysfunction in the effector phase. On the other hand, the dysfunction of helper activity found late after HTLV-I infection might have mainly occurred in the recognition phase due to the decreased expression of CD3-TCR complex. The present data appear to suggest certain aspects of the pathogenesis of the immunodeficiency occurring in HTLV-I infection.

Expression and immunogenicity of the extracellular domain of the human immunodeficiency virus type 1 envelope glycoprotein, gp160

The envelope glycoprotein of human immunodeficiency virus type 1 is synthesized as a precursor, gp160, that subsequently is cleaved to yield mature gp120 and gp41. In these studies, the gene encoding gp160 was mutagenized so as direct the synthesis of a truncated protein consisting of the extracellular domains of both gp120 and gp41. The variant protein, termed sgp160, consisted of 458 amino acids of gp120 and 172 amino acids of gp41. To facilitate protein purification, the normal polyglycoprotein processing site between gp120 and gp41 was deleted through the use of site-directed mutagenesis. This allowed for the synthesis of a molecule that could be purified by affinity chromatography, using acid elution, without dissociation of the gp120 polypeptide from the gp41 polypeptide. The conformation of the sgp160 variant appeared to be functionally relevant, as reflected by its ability to bind to CD4 with an affinity comparable to that of the variant rgp120. The structure of the sgp160-containing polypeptide differed from that of rgp120 in that it tended to form high-molecular-weight aggregates that could be dissociated to monomers and dimers in the presence of reducing agents. Antibodies against the sgp160 protein reacted with authentic virus-derived gp160, gp120, and gp41; neutralized viral infectivity; and inhibited the binding of rgp120 to CD4. Rabbit antibodies to the sgp160 protein differed from those raised against rgp120 in that they were enriched for populations that blocked CD4 binding but did not prevent human immunodeficiency virus type 1-induced syncytium formation.

Purification and characterization of human immunodeficiency virus (HIV) core precursor (p55) expressed in Saccharomyces cerevisiae

The core structure of retroviruses, including the human immunodeficiency virus (HIV), consists of proteins that are initially synthesized as polyprotein precursors and then processed by a virally encoded protease yielding the mature core polypeptides. To obtain sufficient quantities of the purified HIV core precursor p55 for detailed studies, a segment of HIV DNA encoding the full length core precursor polyprotein p55 was expressed in Saccharomyces cerevisiae using a plasmid containing a constitutive galactose promoter. The expression of this DNA produced a protein with an estimated molecular size of 55,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE); this protein was immunoreactive to anti-HIV p24 antisera. Following cell lysis, freezing, and thawing, the expressed protein was an insoluble aggregate that served as the starting material for the purification process. Solubilization of the insoluble p55 with guanidine HCl followed by phenyl-Sepharose column chromatography and high performance liquid chromatography resulted in a preparation of p55 that was greater than 95% pure by SDS-PAGE, immunoreactive to anti-HIV core protein antibodies, and completely soluble in aqueous solution. The expressed p55 appeared to be myristoylated as evidenced by the incorporation of radiolabel following incubation of recombinant yeast cells with [3H]myristic acid; in addition the amino terminus of the final purified protein was blocked. Proteolytic digestion of purified p55 with synthetic HIV protease yielded the predicted amino- and carboxyl-terminal products; these were confirmed by amino acid sequence analysis. In contrast, digestion of purified p55 by the protease derived from the avian myeloblastosis virus resulted in fragments that were different in size from those produced by the HIV protease. The availability of the purified, full length water-soluble HIV core precursor will be useful in identifying agents that inhibit its processing by the HIV protease.

Expression and purification of biologically active v-sis/platelet-derived growth factor B protein by using a baculovirus vector system

Malignant transformation induced by simian sarcoma virus is mediated by its v-sis protein, the monkey homolog of the platelet-derived growth factor (PDGF) B chain. By use of an appropriately engineered baculovirus expression vector, the v-sis protein was expressed in the insect cell line Spodoptera frugiperda (Sf9) at a level 50- to 100-fold higher than that observed with overexpression in mammalian-cell transfectants. The sis protein produced by Sf9 cells underwent processing similar to that observed in mammalian cells, including efficient disulfide-linked dimer formation. Moreover, the recombinant sis protein was capable of binding PDGF receptors and inducing DNA synthesis as efficiently as PDGF-B synthesized by mammalian cells. A significant fraction of sis protein was released from Sf9 cells, which made possible a one-step immunoaffinity purification to near homogeneity with a 40% recovery of biological activity. These results demonstrate that a protein whose normal processing requires both intrachain and interchain disulfide-bridge formation can be efficiently expressed in a biologically active form in insect cells by using a baculovirus vector system.

Analysis of gag proteins from mouse mammary tumor virus

Structural proteins designated p10gag, p21gag, p8gag, p3gag, p27gag, and p14gag from the C3H strain of mouse mammary tumor virus (MMTV) were purified by reversed-phase high-pressure liquid chromatography. The N- and C-terminal amino acid sequences and amino acid composition of each protein were determined and compared with the amino acids encoded by the proviral DNA sequences for the MMTV gag gene. The results show that each of the purified proteins is a proteolytic cleavage product derived from the predicted primary translational product of the gag gene (Pr77gag) and that their order in Pr77gag is p10-pp21-p8-p3-n-p27-p14 (where n represents 17 predicted residues that were not identified among the purified proteins). Purified p10gag lacks the initiator methionine and has a myristoyl group attached in amide linkage to the N-terminal glycine residue predicted by the second codon of the gag gene. The cleavage products are contiguous in the sequence of Pr77gag, and the C-terminal residue of p14gag is encoded by the last codon of the gag gene. By analogy with other retrovirus, p14gag is the viral nucleocapsid protein, p10gag is the matrix protein, and p27gag is the capsid protein of mature MMTV. Proteolytic cleavage sites in MMTV Pr77gag bear a striking resemblance to cleavage sites in the gag precursors of D-type retroviruses, suggesting that these viral proteases have similar specificities.

Human cell lines stably expressing HIV env and tat gene products

A DNA fragment containing the tat, rev and env genes of the human immunodeficiency virus type 1 was inserted into the retroviral vector pZIPneoAU3. The resulting plasmid penvAU3 was transfected into HeLa and psi CRIP cells. Resulting recombinant retroviruses were used to infect HeLa and Jurkat cells. Immunoprecipitation analysis of stable transformants showed the expression of HIV env glycoproteins gp160, gp120 and gp41. Transactivation assays with a plasmid containing the gene for chloramphenicol acetyltransferase linked to HIV promoter-enhancer sequences demonstrated the expression of functional tat. These cells constitute virus-free tools for functional and structural studies of native env and tat.

elk, tissue-specific ets-related genes on chromosomes X and 14 near translocation breakpoints

The myb-ets-containing acute leukemia virus, E26, transforms myeloblasts and erythroblasts in culture and causes a mixed erythroid and myeloid leukemia in chicks. Genes (ets-1, ets-2, and erg) with variable relatedness to the v-ets oncogene of the E26 virus have been identified, cloned, and characterized in several species. Two new members (elk-1 and elk-2) of the ets oncogene superfamily have now been identified. Nucleotide sequence analysis of the elk-1 cDNA clone revealed that this gene encodes a 428-residue protein whose predicted amino acid sequence showed 82% similarity to the 3' region of v-ets. The elk or related sequences appear to be transcriptionally active in testis and lung. The elk cDNA probe detects two loci in the human genome, elk-1 and elk-2, which map to chromosome regions Xp11.2 and 14q32.3, respectively. These loci are near the translocation breakpoint seen in the t(X;18) (p11.2;q11.2), which is characteristic of synovial sarcoma, and the chromosome 14q32 breakpoints seen in ataxia telangiectasia and other T cell malignancies. This suggests the possibility that rearrangements of elk loci may be involved in pathogenesis of certain tumors.

Rapid purification of squirrel monkey retrovirus-H major gag protein by high performance liquid chromatography

The major gag protein (p34) of squirrel monkey retrovirus-H was purified in one chromatographic step by anion-exchange high performance liquid chromatography. The virus in a crude fraction was disrupted with Brij 35 in the presence of three kinds of protease inhibitors. The soluble virus lysate was injected into a Polyanion SI column, and p34 was eluted with a linear salt gradient. The recovery of the protein was about 60%. The purified p34 was nearly homogenous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining.

Large-scale production and purification of a vaccinia recombinant-derived HIV-1 gp160 and analysis of its immunogenicity

The human immunodeficiency virus (HIV-1) envelope gene was expressed in large-scale microcarrier cultures of Vero cells using a system involving coinfection with two recombinant vaccinia viruses. One recombinant contained the bacteriophage T7 RNA polymerase gene under control of a vaccinia virus promoter. The second contained the HIV-1 gp160 gene flanked by T7 promoter and termination sequences. The protein was expressed on the surface of infected cells, and it was shown to have a molecular weight of 160 kD and to react with gp41 and gp120 specific monoclonal antibodies. After purification by successive affinity and ion-exchange chromatography, the protein was demonstrated to be present in a particulate form with a diameter in the range of 15-30 nm. When injected into goats a high-titer gp160 specific antibody response was elicited and group-specific neutralizing activity could be demonstrated in vitro. The immunogenicity of the protein was also studied in conjunction with a number of adjuvant formulations, and the highest potency in mice was obtained using a preparation with 0.2% Al(OH)3 and 0.25% deoxycholate.

Phosphatidylinositol kinase activity associates with viral p60src protein

Immunoprecipitates of p60v-src proteins from chicken embryo fibroblasts infected with Rous sarcoma virus were assayed for phosphatidylinositol (PI) kinase activity in the absence of detergents. The product of the PI kinase reaction, phosphatidylinositol monophosphate (PIP), migrated slightly slower than did the authentic phosphatidylinositol-4-monophosphate marker in thin-layer chromatography and was indistinguishable from phosphatidylinositol-3-monophosphate produced by PI kinase type I. Furthermore, the deacylated product comigrated with glycerophosphoinositol-3-phosphate in high-performance liquid chromatography. Both sucrose gradient fractionation and the heat stability of PI kinase activity from cells infected with temperature-sensitive mutants suggest that the PI kinase activity is not intrinsic to p60v-src but is a property of another molecule complexed with p60v-src. All transforming variants of p60src were associated with PI kinase activity, whereas this enzyme activity was hardly detectable in immunoprecipitates from cells infected with nontransforming viruses encoding p60c-src or an enzymatically inactive variant. However, PI kinase activity was found in p60src immunoprecipitates from cells infected with nonmyristylated, nontransforming mutants as well as temperature-sensitive mutants at the nonpermissive temperature, which indicated that simple association of PI kinase activity with p60src is not sufficient for cell transformation.

Free gp70 from FeLV: enrichment from cell culture fluid by ferric oxide-agarose chromatography

A new chromatographic material based on beads of macroporous crosslinked agarose containing ferric oxide particles was used for enrichment of gp70--the envelope glycoprotein of feline leukemia virus (FeLV). Free gp70 was purified from cell culture fluid in one step with a recovery of 50 to 60% and a purification of about 60 times. The described procedure is a suitable first step for the purification of gp70 from large volumes of cell culture fluid.

Concentration and purification of feline leukaemia virus (FeLV) and its outer envelope protein gp70 by aqueous two-phase systems

The major protective antigens of retroviruses are considered to be their glycosylated envelope proteins. However, the methods commonly employed to enrich and purify virus from culture media such as pelleting and density-gradient centrifugation result in a low recovery of the viral external glycoproteins. This is an obvious drawback when the virus is intended for use in a vaccine. In search for alternative methods to concentrate and purify FeLV, we have attempted extraction in two-phase systems based on water-soluble polymers (Albertsson PA., Biochem Biophys Acta 1958; 27: 378-395). A variety of polymer systems was tested. Some of them seem attractive for a large-scale concentration of the virus and/or its glycoprotein. The distribution between the phases of two FeLV proteins, the outer envelope protein, gp70, and the gag protein, p27, was determined. With a system composed of dextran sulfate and polyvinyl alcohol both the glycoprotein and the gag protein were almost completely recovered in the lower phase which constitutes about 3% of the total system in weight. The two proteins were more than 40-fold purified as calculated on protein basis. The proteins can be extracted readily.

Mapping of immunogenic regions of human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins with env-encoded synthetic peptides and a monoclonal antibody to gp46

Antigenic sites on human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins that are immunogenic in man were studied with envelope gene (env)-encoded synthetic peptides and a mAb to HTLV-I gp46 envelope glycoprotein. Antibodies in 78% of sera from HTLV-I seropositive subjects reacted with synthetic peptide 4A (amino acids 190 to 209) from a central region of HTLV-I gp46. Human anti-HTLV-I antibodies also bound to synthetic peptides 6 (29% of sera) and 7 (18% of sera) from a C-terminal region of gp46 (amino acids 296 to 312) and an N-terminal region of gp21 (amino acids 374 to 392), respectively. mAb 1C11 raised to affinity-purified HTLV-I gp46 reacted with gp46 external envelope glycoprotein and gp63 envelope precursor in immunoblot assay and also bound to the surface of HTLV-I+ cells lines HUT-102 and MT-2. Antibody 1C11 did not react with HTLV-II or HIV-infected cells or with a broad panel of normal human tissues or cell lines. In competitive RIA, anti-gp46 antibody 1C11 was inhibited from binding to gp46 either by antibodies from HTLV-I seropositive subjects or by HTLV-I env-encoded synthetic peptide 4A, indicating that 1C11 bound to or near a site on gp46 within amino acids 190 to 209 also recognized by antibodies from HTLV-I-seropositive individuals. When tested in syncytium inhibition assay, mAb 1C11 did not neutralize the infectivity of HTLV-I. Thus, HTLV-I infection in man is associated with a major antibody response to a region of gp46 within amino acids 190 to 209 that is on the surface of virus-infected cells.

Mapping of a small phosphopeptide at the carboxyterminus of the viral myb protein by monoclonal antibodies

Several myb-specific monoclonal antibodies were produced and their antigen recognition sites characterized using a series of bacterially expressed truncated myb proteins. The monoclonal antibodies were used for analysing the in vivo phosphorylation site of the oncogene protein from avian myeloblastosis virus (AMV), p48v-myb. The p48v-myb protein labeled metabolically with [32P]orthophosphate was isolated from the AMV-transformed chicken myeloblast cell line BM-2 by immunoaffinity chromatography. Phosphoamino acid analysis indicated that it was phosphorylated mainly on serine and to a lesser extent (less than 5%) on threonine residues. Indirect immunoprecipitation of phosphopeptides from trypsin-digested [32P]-labeled purified p48v-myb protein by use of the myb-specific monoclonal antibodies allowed the mapping of a small phosphopeptide at the carboxyterminus of p48v-myb.

Identification of two novel members of erbA superfamily by molecular cloning: the gene products of the two are highly related to each other

Two v-erbA-related genes, named ear-2 and ear-3, have been identified in the human genome and characterized by cDNA cloning. These genes are predicted to encode proteins that are very similar in primary structure to receptors for steroid hormones or thyroid hormone (T3). In addition, amino acid sequences of the ear-2 and ear-3 gene products are very similar each other especially at the DNA binding domain (86% homology) and at the putative ligand binding domain (76% homology). Northern hybridization with ear DNA probes of RNAs from various tissues of a human fetus reveals that the expression of ear-2 is high in the liver whereas the expression of ear-3 is relatively ubiquitous. Hybridization analysis of DNAs from sorted chromosomes shows that the ear-2 gene is located on chromosome 19 and ear-3 on chromosome 5, indicating that the two genes are clearly different from each other.

Expression and purification of protein segments encoded by the envelope and 3'-orf genes of human immunodeficiency virus type 1

The pJL6 expression vector and its derivatives, pJLA16 and pANH-1, have been used for the synthesis and high-level expression in Escherichia coli of restriction enzyme fragments derived from the envelope and 3'-orf genes of the BH10 and BH8 clones, respectively, of the human immunodeficiency virus (HIV-1). These bacterially expressed proteins have been purified to apparent homogeneity by sequential detergent extraction, gel filtration, and reverse-phase high-performance liquid chromatography. The recombinant proteins have been used for the production of polyclonal and monoclonal antibodies, and the fusion proteins from the envelope gene are currently being evaluated for use as immunodiagnostic assay reagants.

Enzyme-linked immunosorbent assays (ELISAs) for the determination of contaminants resulting from the immunoaffinity purification of recombinant proteins

Two immunoassays have been developed for the quantitation of part-per-million levels of contaminants likely to co-purify with monoclonal antibodies produced in tissue culture and purified by protein A affinity chromatography. These contaminants are bovine IgG originating from the fetal bovine serum used in cell culture, and protein A. Mouse IgG was shown not to interfere in the bovine IgG assay, where contamination levels of 0.2-0.7% bovine IgG were measured in the lots of monoclonal antibody tested. The protein A ELISA was developed with monoclonal antibody included in the standard, and in the preparations of monoclonal antibody tested, 64 parts per million (ppm) or less of protein A were demonstrated. An additional immunoassay was developed to quantitate monoclonal antibody contamination of two recombinant proteins, rHBsAg and rgp 120 from HIV, purified by affinity chromatography with such antibodies. Possible interference of monoclonal antibody quantitation by the respective antigens was examined in this ELISA, and contamination levels of less than 56 ppm of antibody were determined in the purified recombinant proteins. The three immunoassays were shown to be specific for the major protein contaminants in either monoclonal antibodies or the recombinant proteins and were necessary in demonstrating their purity.

Isolation and characterization of HIV-2 from an AIDS patient in Ghana

This report describes the isolation and characterization of a retrovirus of the HIV-2 group from a Ghanaian AIDS patient which has different restriction patterns from previously reported HIV-2 viruses. The virus was morphologically very similar to HIV-1 and HIV-2, and had Mg2+-dependent reverse transcriptase. Like previous HIV isolates, it induced severe cytopathic effects in CD4-positive human lymphoid cell lines. Its major proteins were shown to be gp110, p66, p55, p41, gp32, p30 and p26 by Western blot analysis. In dot-blot hybridization experiments, the virus hybridized with a HIV-2 DNA probe, but not with HIV-1 and SIVagm probes in stringent conditions. These data indicate that this Ghanaian virus is a HIV-2 group virus. However, in a Southern blot hybridization experiment, the restriction patterns of this virus, designated HIV-2 [GH-1], were quite different from those of previously reported HIV-2 viruses from West Africa isolated at the Pasteur Institute.

A unique human immunodeficiency virus culture secreting soluble gp160

A clone of the HUT78 cell line, chronically infected with the HIV-1 isolate HTLV-III451, has been demonstrated to secrete unprocessed HIV-1 envelope precursor protein gp160 as well as mature gp120. Further, when grown in serum-free defined medium these cells released approximately five times the amount of virus compared with cultures in normal medium. These proteins corresponded in their immunologic reactivities with the respective envelope proteins of the HTLV-IIIB isolate. They formed high-affinity soluble complexes with the CD4 antigen and inhibited the syncytium formation induced by HTLV-IIIB on CD4-positive cells. This is the first description of an HIV-1 culture system capable of shedding into the medium native gp160 that is soluble in the absence of detergents.