Biomedical subjects

R Renne

Publications and source records attributed to R Renne.

At least 19 recordsLinked to original sources

PubMed2004

Experimental transmission of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) to SIV-positive and SIV-negative rhesus macaques.

Kaposi's sarcoma-associated herpesvirus (KSHV) is a gamma-herpesvirus associated with Kaposi's sarcoma (KS) and two lymphoproliferative diseases, primary effusion lymphoma (PEL) and multicentric Castleman's disease. Studies on the biology and pathogenesis of KSHV have been limited by lack of efficient cell culture systems and lack of a suitable animal model for KS. Here we report on the experimental inoculation of SIV-positive and SIV-negative rhesus macaques with KSHV-infected PEL cells or KSHV preparations derived from PEL cells. Low levels of viral DNA could be detected in cultivated peripheral blood mononuclear cell of all animals, as well as in the bone marrow of one monkey that died from SAIDS. However, we were not able to detect KSHV-specific antibodies or transcripts, nor did we observe any symptoms clearly related to KSHV infection (e.g. KS or lympho-proliferative disease). Hence, although KSHV replicates in rhesus macaques at very low levels, this non-human primate host is unlikely to provide a useful animal model for disease.

Animals↗

PubMed2001

Modulation of cellular and viral gene expression by the latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV), also called human herpesvirus 8 (HHV-8), is the likely etiological agent of Kaposi's sarcoma and primary effusion lymphoma. Common to these malignancies is that tumor cells are latently infected with KSHV. Viral gene expression is limited to a few genes, one of which is the latency-associated nuclear antigen (LANA), the product of ORF73. Examination of the primary sequence of LANA reveals some structural features reminiscent of transcription factors, leading us to hypothesize that LANA may regulate viral and cellular transcription during latency. In reporter gene-based transient transfection assays, we found that LANA can have either positive or negative effects on gene expression. While expression of a reporter gene from several synthetic promoters was increased in the presence of LANA, expression from the human immunodeficiency virus (HIV) long terminal repeat (LTR)-and from NF-kappaB-dependent reporter genes-was reduced by LANA expression. In addition, the promoter of KSHV ORF73 itself is activated up to 5.5-fold by LANA. This autoregulation may be important in tumorigenesis, because two other genes (v-cyclin and v-FLIP) with likely roles in cell growth and survival are also controlled by this element. To identify cellular genes influenced by LANA, we employed cDNA array-based expression profiling. Six known genes (and nine expressed sequence tags) were found to be upregulated in LANA-expressing cell lines. One of these, Staf-50, is known to inhibit expression from the HIV LTR; most of the other known genes are interferon inducible, although the interferon genes themselves were not induced by LANA. These data demonstrate that LANA expression has effects on cellular and viral gene expression. We suggest that, whether direct or indirect in origin, these effects may play important roles in the pathobiology of KSHV infection.

Animals↗

PubMed2001

DNA binding and modulation of gene expression by the latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. The latency-associated nuclear antigen (LANA) is highly expressed in these malignancies and has been shown to play an important role in episomal maintenance, presumably by binding to a putative oriP. In addition, LANA modulates cellular and viral gene expression and interacts with the cellular tumor suppressors p53 and retinoblastoma suppressor protein. Many of these features are reminiscent of Epstein-Barr virus nuclear antigens (EBNAs), a family of six proteins expressed during latency. EBNA-1 is required for episome maintenance, binds to oriP, and strongly activates transcription from two promoters, including its own. We have previously shown that LANA can transactivate its own promoter and therefore asked whether LANA, like EBNA-1, activates transcription by direct binding to DNA. By using recombinant LANA expressed from vaccinia virus vectors for electrophoretic mobility shift assays, we found that LANA does not bind to its own promoter. In contrast, LANA binds specifically to sequences containing an imperfect 20-bp palindrome in the terminal repeat (TR) of KSHV. We further show that the C-terminal domain of LANA is sufficient for site-specific DNA binding. Unlike EBNA-1, which activates transcription through binding of oriP, we found that LANA inhibits transcription from a single TR binding site. A multimerized TR as found in the viral genome results in strong transcriptional suppression when linked to a heterologous promoter. These data suggest that LANA, although fulfilling functions similar to those of EBNA-1, does so by very different mechanisms.

Animals↗

PubMed2000

Inflammatory cytokines and the reactivation of Kaposi's sarcoma-associated herpesvirus lytic replication.

Kaposi's sarcoma (KS) is a complex proliferative lesion long suspected of being dependent on exogenous paracrine signaling molecules to stimulate its proliferative, angiogenic, and inflammatory components. In particular, both clinical and experimental observations have pointed to a potential role for inflammatory cytokines as permissive factors for KS development, but KS pathogenesis is also critically dependent on infection by an exogenous herpesvirus, the KS-associated herpesvirus (KSHV). To examine the possible links between inflammatory cytokines and KSHV replication, we tested for the ability of such cytokines to induce lytic viral reactivation in the latently infected BCBL-1 cell line. Interferon-gamma consistently activated KSHV replication, whereas tumor necrosis factor, interleukin-1, interleukin-2, interleukin-6, granulocyte-macrophage colony stimulating factor, and basic fibroblast growth factor did not. Glucocorticoids also failed to induce lytic KSHV growth in these cells, but ionomycin, a calcium ionophore, induced replication and strongly augmented the known inductive effects of phorbol esters. Interferon-alpha had a dose-dependent inhibitory effect on KSHV induction by ionomycin. The identification of interferon-gamma as an activator and interferon-alpha as an inhibitor of KSHV induction in vitro correlates well with in vivo observations and demonstrates for the first time that inflammatory cytokines can directly modulate KSHV replication.

Cytokines↗

PubMed2000

Human herpesvirus 8 glycoprotein K8.1: expression, post-translational modification and localization analyzed by monoclonal antibody.

BACKGROUND: The genome of human herpesvirus 8 (HHV-8) contains at least 84 open reading frames, including the highly immunogenic K8.1. Other studies have determined that K8.1 gene generates at least two spliced transcripts in the HHV-8 infected BCBL-1 cells, termed as glycoprotein (gp)K8.1A and gpK8.1B. OBJECTIVE: To analyze the expression, post-translational modification and localization of HHV-8 gpK8.1 by monoclonal antibody (mAb). STUDY DESIGN: Mabs to HHV-8 produced by conventional hybridization and several clones identified. A mAb was used by various immunological assays to analyze HHV-8 K8.1 proteins in BCBL-1- and Sf9 insect cells. RESULTS: MAb clone 19B4 identified a 0.75-kb insert from the lambdaZAP cDNA expression library of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced BCBL-1 cells. Sequence analysis revealed that the cDNA insert corresponds to the published spliced ORF K8.1 mRNA of HHV-8. By immunofluorescence assay, the mAb stained the cell membrane, cytoplasm and perinuclear region of TPA induced BCBL-1 cells and showed no cross-reactivity with other herpesviruses. By immunoblotting assay, mAb 19B4 reacted with two species polypeptides giving a diffuse band with rMW from 42 to 64 kDa (gpK8.1A) and two closely migrating polypeptides of rMW 35/37 kDa (gpK8.1B). Both species were labeled by [14C]glucosamine, indicating that they are glycosylated and only gpK8.1A was detected in the virions. Expression of the full length K8.1 derived from cDNA in baculovirus system confirmed that these two glycoproteins are encoded by K8.1 gene. Enzymatic deglycosylation with endoF/peptide-N-glycosidase F, led to the reduction of rMW of both polypeptides whereas deglycosylation with O-glycosidase led only the reduction of rMW of K8.1A. CONCLUSION: The mAb 19B4 reacts specifically with BCBL-1 and Sf9 cells infected with recombinant baculovirus containing HHV-8 K8.1 gene. In several assays the mAb reacts with gpK8.1A and gpK8.1B. Only the mature spliced gpK8.1A is incorporated into virion. Enzymatic deglacosylation determined that gpK8.1A is N- and O-glycosylated, whereas gpK8.1B may lack O-glycosylation.

Alternative Splicing↗

PubMed1999

Experimental transmission of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) to SCID-hu Thy/Liv mice.

Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) is a novel human lymphotropic herpesvirus linked to several human neoplasms. To date, no animal model for infection by this virus has been described. We have examined the susceptibility of C.B-17 scid/scid mice implanted with human fetal thymus and liver grafts (SCID-hu Thy/Liv mice) to KSHV infection. KSHV virions were inoculated directly into the implants, and viral DNA and mRNA production was assayed using real-time quantitative polymerase chain reaction. This revealed a biphasic infection, with an early phase of lytic replication accompanied and followed by sustained latency. Ultraviolet irradiation of the inoculum abolished all DNA- and mRNA-derived signals, and infection was inhibited by ganciclovir. Viral gene expression was most abundant in CD19(+) B lymphocytes, suggesting that this model faithfully mimics the natural tropism of this virus. Short-term coinfection with HIV-1 did not alter the course of KSHV replication, nor did KSHV alter levels of HIV-1 p24 during the acute phase of the infection. Although no disease was evident in infected animals, SCID-hu Thy/Liv mice should allow the detailed study of KSHV tropism, latency, and drug susceptibility.

Animals↗

PubMed1999

A complex translational program generates multiple novel proteins from the latently expressed kaposin (K12) locus of Kaposi's sarcoma-associated herpesvirus.

The most abundantly expressed latent transcripts encoded by the Kaposi's sarcoma (KS)-associated herpesvirus derive from the genomic region surrounding open reading frame (ORF) K12 (kaposin A). Here we show that these transcripts, initially described as limited to ORF K12 itself, more frequently encompass upstream sequences spanning two sets of 23-nucleotide GC-rich direct repeats (DRs) (DR1 and DR2). Although the DRs lack AUG codons and were previously presumed to be noncoding, a monoclonal antibody raised to infected cells detected multiple polypeptides encoded by this region. These proteins are expressed during latency and upon induction of lytic viral replication in both primary effusion lymphoma (PEL) cell lines and KS tumors. Biochemical and genetic analyses reveal that these proteins are derived from variant translational initiation at CUG codons. The predominant translation product in the PEL cell line BCBL-1 derives from the 5'-most CUG codon in the transcript, resulting in a protein (termed kaposin B) which is encoded largely by the repeats themselves and which does not include K12 sequences. Other non-AUG codons in alternate reading frames are also used at lower efficiency, including one that initiates translation of a DR-K12 fusion protein (kaposin C) that is predicted to sort to a different subcellular locale than kaposin B. Thus, the products of the K12 region, which is the most abundantly transcribed region in latency, are surprisingly complex and may encompass multiple biological functions.

3T3 Cells↗

PubMed1998

Reactivation of Kaposi's sarcoma-associated herpesvirus infection from latency by expression of the ORF 50 transactivator, a homolog of the EBV R protein.

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV), or human herpesvirus 8, is a lymphotropic virus strongly linked to several AIDS-related neoplasms. The primary reservoir of infection consists of latently infected B lymphocytes and possibly other mononuclear cells. Viral reactivation from latency and spread from this lymphoid reservoir is presumably required for development of nonlymphoid tumors like KS. Here we show that deregulated expression of a single viral gene, ORF 50, which encodes a transactivator able to selectively upregulate delayed-early viral genes, suffices to disrupt latency and induce the lytic gene cascade in latently infected B cells. The identification of this gene opens the way to studies of the physiologic mechanisms controlling reactvation of KSHV from latency.

B-Lymphocytes↗

PubMed1998

A cluster of latently expressed genes in Kaposi's sarcoma-associated herpesvirus.

Infection with Kaposi's sarcoma-associated herpesvirus (KSHV) is closely associated with Kaposi's sarcoma (KS) and primary effusion lymphoma, with viral genomes present in a latent state in the majority of tumor cells. Here we describe a cluster of latently expressed viral genes whose mRNAs are generated from a common promoter. Two mRNAs in this region encode the latency-associated nuclear antigen, the product of open reading frame 73 (ORF73). The larger RNA, of 5.8 kb, is an unspliced transcript that includes ORF72 and -71 at its 3' end; it initiates at nucleotides (nt) 127880 to 127886 from a promoter lacking recognizable TATA elements. A less abundant mRNA, of 5.4 kb, is a variant of this transcript, in which 336 nt of 5' noncoding information has been removed by RNA splicing. A third, more abundant RNA is generated from the same promoter region via splicing from the common splice donor at nt 127813 to an acceptor 5' to ORF72; this transcript is the presumed mRNA for ORF72, which encodes the viral cyclin D homolog. All three RNAs are 3' coterminal. In situ hybridization analysis with probes that can detect all three transcripts shows that the RNAs are detectable in a large fraction of BCBL-1 cells prior to lytic induction and in >70% of KS spindle cells in primary KS tumors. This confirms that these transcripts are indeed latent RNAs and suggests a role for their products in viral persistence and/or KSHV-associated proliferation.

Alternative Splicing↗

PubMed1998

Limited transmission of Kaposi's sarcoma-associated herpesvirus in cultured cells.

Kaposi's sarcoma-associated herpesvirus (KSHV) (also called human herpesvirus 8) is a novel gammaherpesvirus strongly implicated in the pathogenesis of Kaposi's sarcoma. Although virions can be produced in high yield from latently infected B-cell lines treated with phorbol esters, little is known about the infectivity of such virus, and efficient serial propagation of KSHV has been problematic. Here we report on the infectivity of KSHV produced from phorbol-induced BCBL-1 cells, employing an assay based on the detection of a spliced late mRNA by a sensitive reverse transcriptase PCR (RT-PCR) method. The results of this study confirm previous observations that 293 cells are susceptible to viral infection; however, infection with BCBL-1-derived virus is inefficient and the pattern of viral gene expression in infected cells may not fully reproduce that of authentic lytic infection. In keeping with this finding, serial propagation of BCBL-1-derived virus could not be demonstrated on 293 cells. Eleven of 38 other cell lines tested also supported KSHV infection, as judged by this RT-PCR assay, including cells of B-cell, endothelial, epithelial, and fibroblastic origin; however, in all cases, infection proceeded at or below the levels observed in 293 cells.

Gene Expression Regulation, Viral↗

PubMed1997

Identification of the gene encoding the major latency-associated nuclear antigen of the Kaposi's sarcoma-associated herpesvirus.

Over 85% of patients with Kaposi's sarcoma (KS) are seropositive for antibodies to the latency-associated nuclear antigen (LANA) expressed in B cell lines infected with Kaposi's sarcoma-associated herpesvirus (KSHV). The presence of antibodies to LANA strongly correlates with the risk of developing the disease. However, the identity of the protein(s) comprising LANA and the corresponding gene(s) has remained unclear. To identify potential latent gene candidates for LANA, we probed total RNA extracted from BCBL-1 cells (a B cell line latently infected with KSHV) using lambda clones that span the KSHV genome. One region encoding latent transcripts spanned KSHV open reading frames (orfs) 71 (K13), 72 (v-cyclin), and 73. Among these, however, only orf 73, when expressed in heterologous mammalian cell systems, reacted with KSHV antibody-positive human sera, resulting in a punctate nuclear staining pattern reminiscent of LANA in BCBL-1 cells. Furthermore, extracts from cells expressing the orf 73 protein product specifically blocked the binding of KS patient antibodies to LANA. Finally, seroreactivity with recombinant orf 73 protein exactly paralleled reactivity with classical LANA as expressed in BCBL-1 cells, both in KS patients and in other groups. Together, these data support the identification of KSHV orf 73 as the gene encoding the dominant immunogenic component of LANA.

Animals↗

PubMed1997

Kaposi's sarcoma-associated herpesvirus gene expression in endothelial (spindle) tumor cells.

The recent discovery of DNA sequences of a new human herpesvirus in Kaposi's sarcoma (KS) has fueled speculation that this virus might cause KS. The mere presence, however, of a virus in a complex multicellular tumor like KS could just as well be construed as evidence of a passenger agent. We sought stronger evidence linking the KS-associated herpesvirus (KSHV) to tumor formation by using in situ hybridization to investigate the specificity, constancy, and timing of KSHV gene expression in KS tumor cells. Here we document expression of a 700-nucleotide viral RNA in every KS tumor examined, from the earliest histologically recognizable stage to advanced tumors in which the vast majority of identifiable spindle tumor cells contain this transcript. Two other KSHV RNAs were also detected in a smaller fraction of the tumor cells in all but the earliest lesion. These viral RNAs were expressed to relatively low levels in this subset; because one of these RNAs encodes a major viral capsid protein, these cells may be producing KSHV. We did not find these KSHV genes expressed in a variety of other tumors and proliferative processes, but we did detect viral gene expression in prostatic tissue, supporting a possible mechanism for sexual transmission of KSHV. The close relationship between KS and KSHV gene expression is consistent with the hypothesis that KSHV is directly involved in the etiology and pathogenesis of KS.

AIDS-Related Opportunistic Infections↗

PubMed1996

Transactivation of the two promoters of SFV-3 by different mechanisms.

Simian foamy virus type 3 (SFV-3), a member of the spumavirus genus of retroviruses, has a complex genome organization and encodes two open reading frames (ORFs), in addition to the structural genes gag, pol, and env. ORF-1 encodes a viral transcriptional transactivator designated Taf (transactivator of foamy viruses) which augments transcription from the viral long terminal repeat (LTR). It was recently shown that human foamy virus, as well as the simian viruses SFV-1 and SFV-3, contains a second internal transcriptional promoter in the transmembrane domain of the env gene; this promoter also is transactivated by Taf. Here we report the characterization of the internal promoter of SFV-3. The transcriptional start site of this promoter has been mapped in two different SFV-3-infected cell lines to nt position 9761 in the proviral genome of SFV-3. All cis-regulatory elements required for transactivation by Taf are located between -202 and -32 (+1 representing the transcription initiation site in the internal promoter). Analysis of hybrid promoter constructs and deletion mutants in transient expression assays revealed that this region contains two elements which are independently responsive to Taf. In addition, we employed an in vivo DNA competition assay to determine whether the transactivation mechanisms of both SFV-3 promoters are similar or different. The differences observed utilizing this competition assay suggest that Taf transactivates the internal promoter and the LTR through different cellular transcription factors.

Animals↗

PubMed1996

Lytic growth of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) in culture.

Kaposi's sarcoma (KS) is the leading neoplasm of AIDS patients, and HIV infection is known to be a major risk factor for its development. However, KS can occur in the absence of HIV infection and the risk of KS development varies widely even among HIV-infected patients, with homosexual men with AIDS being 20 times more likely to develop KS than AIDS-afflicted children or hemophiliacs. These and other data strongly suggest that a sexually transmitted agent or co-factor may be involved in KS pathogenesis. Recently, DNA sequences corresponding to the genome of a novel member of the herpesvirus family have been identified within AIDS-KS biopsies, and several reports indicate that these sequences are also present in all forms of HIV-negative KS. These and other findings suggest this new agent, referred to as KS-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV8), as a candidate for the putative etiologic cofactor. However, the role of this agent in KS remains hotly debated. Further progress in understanding its biology has been severely hampered by the lack of a cell culture system for virus growth. Here we report the development of a system for the lytic growth of this virus in a latently infected B cell line and present the first ultrastructural visualization of the virus. This system will facilitate the detailed study of the molecular biology of viral replication, the testing of antiviral drugs and the development of diagnostic tests for viral infection.

Acquired Immunodeficiency Syndrome↗

PubMed1996

The size and conformation of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) DNA in infected cells and virions.

The genome of a novel human herpesvirus has been detected in specimens of Kaposi's sarcoma (KS) and in several AIDS-related lymphoproliferative disorders. Here we examine the size and genomic conformation of the DNA of this virus (known as KS-associated herpesvirus or human herpesvirus 8) in latently and lytically infected cells and in virions. Pulsed-field gel electrophoresis of viral DNA shows that the viral genome is similar in size to those of other gammaherpesviruses (160 to 170 kb). As with Epstein-Barr virus, KS-associated herpesvirus DNA is stably maintained in latently infected B cells as episomal monomer circles and induction from latency is associated with the selective accumulation of linear genomic forms.

Cell Line↗

PubMed1994

Isolation, cloning, and sequencing of simian foamy viruses from chimpanzees (SFVcpz): high homology to human foamy virus (HFV).

Several independent isolates of simian foamy viruses (SFV) were recovered from chimpanzee B-cell lines. One isolate, designated SFVcpz, was molecularly cloned and sequenced. In addition, the genome of SFV type 6 (SFV-6), an independent chimpanzee foamy virus isolate, was partially cloned. The SFVcpz provirus is 13,246 base pairs (bp) long. It is flanked by long terminal repeats (LTRs) and encodes the genes gag, pol, env, the transcriptional transactivator taf, and a second 3' open reading frame (orf-2). DNA sequences of molecular clones derived from the pol, env, and orf-2 genes of SFV-6 are almost identical to those of SFVcpz. DNA and deduced protein sequences of SFVcpz show high homologies to human foamy virus (HFV), whereas both SFV-1 from a rhesus macaque and SFV-3 from an African green monkey are phylogenetically further distant viruses. Amino acid homologies between corresponding genes of SFVcpz and HFV range between 86% for the taf gene and 95% for the pol gene. Comparisons of taf and pol of SFVcpz with SFV-1 and SFV-3 show 40 and 78% homology, respectively. The SFVcpz LTR consists of 1760 bp and is in the same size range as the LTRs of SFV-1 and -3, but significantly larger than the known HFV LTR. These comparisons reveal that a region approximately 500 bp long is missing in the HFV LTR. We also isolated and sequenced an LTR of a wild-type HFV provirus which aligns with high homology to the SFVcpz LTR without major gaps. Based on sequence comparisons in this report, primate foamy viruses may be arranged into different clusters with SFVcpz and HFV forming one cluster and SFV-1 and SFV-3 as prototypes for two unique clusters.

Amino Acid Sequence↗

PubMed1994

Characterization of the internal promoter of simian foamy viruses.

Simian and human foamy viruses (HFV and SFV), genetically related members of the spumavirus genus of retroviruses, have complex genome structures which encode the gag, pol, and env genes for virion proteins as well as additional open reading frames. One of these open reading frames is a viral transactivator, encoded by genes designated taf for SFV and bel-1 for HFV, which augments transcription directed by the long terminal repeat (LTR) through cis-acting targets in the U3 domain of the LTR. Recently, an internal transcriptional promoter has been identified in sequences within the 3' end of the HFV env gene (M. Lochelt, W. Muranyi, and R. M. Flugel, Proc. Natl. Acad. Sci. 90:7317-7321, 1993). We have demonstrated by using transient expression assays in several tissue culture cell lines and by analyzing viral transcripts in infected cells that SFV-1 from a rhesus macaque and SFV-3 from an African green monkey also encode an internal promoter in the env gene. Transcription directed by the internal promoters of SFV-1 and SFV-3 is activated by the taf-1 and taf-3 gene products, respectively, in several cell types. The importance of a TATA box for the SFV-1 internal promoter was established by site-specific mutagenesis, and the 5' ends of transcripts initiating in the internal promoter have been determined. cis-acting sequences in the SFV-1 env gene required for the response to taf-1 are contained within a 121-bp element located 5' to the TATA box in the internal promoter. This taf-1-responsive element in the internal promoter functions in a position- and orientation-independent fashion in a heterologous promoter and thus has the properties of an enhancer which depends on taf-1 activity. Alignments reveal that the SFV-1 internal promoter and the SFV-1 LTR have little sequence relatedness. Cross-transactivation studies show that the transactivators of SFV-1 and HFV function on the internal promoter and LTR of the homologous virus but not on the heterologous virus. In summary, the genomes of simian and human foamy viruses direct viral transcription through both the promoter in the LTR and an internal promoter within the env gene, and each promoter contains unique enhancer-like elements regulated by the viral transactivator.

Animals↗

PubMed1993

Regulatory elements in the long terminal repeat (LTR) of simian foamy virus type 3 (SFV-3).

Simian foamy virus type 3 (SFV-3) is a retrovirus that has a complex genome organization and encodes two open reading frames (ORF-1 and ORF-2) in addition to the genes coding for gag, pol, and env. In this report, we demonstrate that ORF-1 of SFV-3 encodes a transcriptional transactivator designated taf (transactivator of foamy virus) which augments gene expression directed by the viral long terminal repeat (LTR). The taf responsive elements have been mapped to the U3 region of the LTR, between positions -637 and -180 (+1 represents the transcription initiation site). Two regions between -637 and -180 in the LTR are targets for taf transactivation. These target sequences for taf confer responsiveness to a heterologous promoter independent of orientation; thus, they function like conditional enhancers. The R-U5 region of the viral LTR is shown to have an inhibitory effect on gene expression. SFV-1 is a related spumavirus and encodes a taf gene that augments expression directed by the SFV-3 LTR as well as the SFV-1 LTR; however, the taf gene of SFV-3 transactivates the SFV-3 LTR but not the SFV-1 LTR. These data on regulatory elements in the SFV-3 LTR show that the mechanism of foamy virus transactivation is significantly different from lentiviruses as well as from the HTLV group of viruses.

Cell Line↗