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MicroRNAs (miRNAs) play regulatory roles in diverse processes in both eukaryotic hosts and their viruses, yet fundamental questions remain about which viruses code for miRNAs and the functions that they serve. Simian foamy viruses (SFVs) of Old World monkeys and apes can zoonotically infect humans and, by ill-defined mechanisms, take up lifelong infections in their hosts. Here, we report that SFVs encode multiple miRNAs via a noncanonical mode of biogenesis. The primary SFV miRNA transcripts (pri-miRNAs) are transcribed by RNA polymerase III (RNAP III) and take multiple forms, including some that are cleaved by Drosha. However, these miRNAs are generated in a context-dependent fashion, as longer RNAP II transcripts spanning this region are resistant to Drosha cleavage. This suggests that the virus may avoid any fitness penalty that could be associated with viral genome/transcript cleavage. Two SFV miRNAs share sequence similarity and functionality with notable host miRNAs, the lymphoproliferative miRNA miR-155 and the innate immunity suppressor miR-132. These results have important implications regarding foamy virus biology, viral miRNAs, and the development of retroviral-based vectors. IMPORTANCE Fundamental questions remain about which viruses encode miRNAs and their associated functions. Currently, few natural viruses with RNA genomes have been reported to encode miRNAs. Simian foamy viruses are retroviruses that are prevalent in nonhuman host populations, and some can zoonotically infect humans who hunt primates or work as animal caretakers. We identify a cluster of miRNAs encoded by SFV. Characterization of these miRNAs reveals evolutionarily conserved, unconventional mechanisms to generate small RNAs. Several SFV miRNAs share sequence similarity and functionality with host miRNAs, including the oncogenic miRNA miR-155 and innate immunity suppressor miR-132. Strikingly, unrelated herpesviruses also tap into one or both of these same regulatory pathways, implying relevance to a broad range of viruses. These findings provide new insights with respect to foamy virus biology and vectorology.
Spuma- or foamy viruses (FV), endemic in most non-human primates, cats, cattle and horses, comprise a special type of retrovirus that has developed a replication strategy combining features of both retroviruses and hepadnaviruses. Unique features of FVs include an apparent apathogenicity in natural hosts as well as zoonotically infected humans, a reverse transcription of the packaged viral RNA genome late during viral replication resulting in an infectious DNA genome in released FV particles and a special particle release strategy depending capsid and glycoprotein coexpression and specific interaction between both components. In addition, particular features with respect to the integration profile into the host genomic DNA discriminate FV from orthoretroviruses. It appears that some inherent properties of FV vectors set them favorably apart from orthoretroviral vectors and ask for additional basic research on the viruses as well as on the application in Gene Therapy. This review will summarize the current knowledge of FV biology and the development as a gene transfer system.
Characterization of the env gene and of two novel coding regions of the human spumaretrovirus
(1988)
Recombinant clones harboring retroviral DNA were established. The nucleotide sequence of the central and 3' region of the genome of the human spumaretrovirus was determined. The 5' end of the deduced protein sequence was homologaus to the endonuclease domain of retroviral reverse transcriptases. A small intergenic region is followed by a lang open reading frame of 985 aminoacid residues that according to its genomic location and structural features is a typical retroviral env gene. Surprisingly, the postenv region contains two open reading frames that encodes two novel retroviral genes, termed bel-l and bel-2. The 3' LTR is 963 nucleotides lang and contains the signal sequences characteristic for transcriptional regulation of retrovirus genomes.
Transcription factor AP-1 modulates the activity of the human foamy virus long terminal repeat
(1991)
The human foamy virus (HFV) contains within the UJ region of its long terminal repeat (L TR) three perfect consensus sequences for the binding of the inducible transcription factor AP-1. Results of DNase I footprint protection and gel retardation assays demonstrated that proteins in extracts of HeLa and BHK-21 cells as weil as bacterially expressed Jun and Fos proteins bind to these AP-1 sites. By conducting transient expression assays using chloramphenicol acetyltransferase plasmids carrying LTR sequences with point-mutated AP-1 sites it was found that the three AP-1 sites contribute to the optimal activity ofthe HFV promoter. It is shown that lnduction of the HFV L TR by 12-O-tetradecanoylphorbol-13-acetate (TPA) and serum factors is mediated through the AP-1 sites.
Rhesus monkeys (M. mulatta) were i. v. infected with SIV mac251. Three phases of lymph node changes were observed. 1: physiological follicular hyperplasia (3 and 6 weeks p.i.). 2: Alterations of germinal centers: loss of follicular mantle zone, fragmentation or sclerosis (12 and 24 weeks p.i.). 3: Partial depletion of T-lymphocytes, accumulation of plasma cells, increased numbers of syncytial giant cells, hemophgocytosis in the sinuses (about 1 year p.i.). The thymus of the juvenile animals showed first changes 12 and 24 weeks after infection with focalloss of immature (and Ki-67 positive) cortical thymocytes, leading to severe accidental involution of the thymuses one year after infection and reduced numbers of Hassalls corpuscles. These investigations show the value of this animal model for the study of morphology and pathogenesis of AIDS.
The thymus in SIV infection
(1993)
no abstract available
Rhesus monkeys (M. mulatta) were i.v. infected with SIV mac251. Three phases of lymph node changes were observed. 1: physiological follicular hyperplasia (3 and 6 weeks p.i.). 2: Alterations of germinal centers: loss of follicular mande zone, fragmentation or sclerosis (12 and 24 weeks p.i.). 3: Partial depletion of T-lymphocytes, accumulation of plasma cells, increased numbers of syncytial giant cells, hemophgocytosis in the sinuses (ab out 1 year p.i.). The thymus of the juvenile animals showed first changes 12 and 24 weeks after infection with focalloss of immature (and Ki-67 positive) cortical thymocytes, leading to severe accidental involution of the thymuses one year after infection and reduced numbers of Hassalls corpuscles. These investigations show the value of this animal model for the study of morphology and pathogenesis of AIDS.
We have identified the major immunogenic structural proteins of the human foamy virus (HFV), a distinct member of the foamy virus subfamily of Retroviridae. Radiolabelied viral proteins were immunoprecipitated from HFV -infected cells by foamy virus antisera of human and non-human primate origin. Precipitated viral proteins were in the range of 31 K to 170K. Labelling of proteins with [\(^{14}\)C]glucosamine or with [\(^{35}\)S]methionine in the presence oftunicamycin, as well as endo-ß-N-acetylglycosaminidase Hand F treatment of [\(^{35}\)S]methionine-labelled proteins, revealed three viral glycoproteins of approximately 170K, 130K and 47K, most likely representing the env gene-encoded precursor, the surface glycoprotein and the transmembrane protein of HFV, respectively.
Human foamy viruspol gene fragments were molecularly cloned into a procaryotic expression vector. The expression pattern of the cloned fragments and nucleotide sequence analysis of the 5' pol gene region revealed that in HFV the protease (PR) is located in the pol open reading frame. Purified recombinant proteins were used to generate antibodies in rats. ln immunoblot assay, using infected cells as antigen, a precursor protein with an apparent molecular mass (M,) of 127K was identified by antibodies directed against the reverse transcriptase (RT), RNaseH, or integrase (IN) domeins of pol. With concentrated virus as antigen, the RT and RNaseH antibodies recognized a protein of 80K, the IN antiserum recognized a protein of 40K, and the PR antiserum detected a protein of approximately 10K.
A virus derived from cells of a Iymphoblastoid line originating from the lymph node of a healthy African green monkey was characterized as a typical member of the foamy virus subgroup of rctroviridac by its morphological, physicochemical, biological and biochemical properties (reverse transcriptase actvity). Besides the usual host range of foamy viruses, the isolated strain revealed a remarkable T -lymphotropism, distinguishing it from the prototypes of foamy viruses previously isolated from African green monkeys. Two foamy virus infectious are demonstrated in human contacts of the African green monkey colony, with the animal barbauring the isolate.
To study the activation of HIV by human spumaretrovirus (HSRV) the long terminal repeats (LTRs) of HSRV, HIVl and HIV2 were examined with respect to their ability to function as transcriptional promoters in virus infected and uninfected cells. Transient transfections using plasmids in which the L TRs of the three viruses were coupled to the bacterial chloramphenicol acetyltransferase (CA T) gene revealed (i) the level of cat gene expression directed by the HSRV LTR was markedly increased in HSRV infected cells compared to uninfected cells, (ii) cat gene expression driven by the HIV1 LTR, but not by the HIV2 LTR could be enhanced upon HSRV infection, whereas (iii) neither in HIV1 nor in HIV2 infected cells an effect on HSRV LTR driven cat geneexpression was detected.
An infectious molecular clone (pHSRV) of the human Spumaretrovirus (HSRV) was constructed using viral DNA and cDNA clones. The infectivity of pHSRV was proven by transfection of cell cultures and subsequent infection of susceptible cultures with cell free transfection derlved virus. pHSRV derived virus produced foamy virus typical cytopathic effects in susceptible cultures. lnfected cells could be stained specifically with foamy virus antisera by means of indirect immunofluorescence. Radiolmmunoprecipltatlon revealed the presence of characteristic HSRV structural proteins in pHSRV infected cultures. By cotransfection of pHSRV and an indicator plasmid it was found that pHSRV is able to transactivate the viral L TR. Viral transcripts were found to be approximately 200 bases Ionger in pHSRV infected cultures compared to wildtype infected cultures. This difference is most likely due to an Insertion of DNA of non-viral origin ln the U3 region of the 3'L TR of the infectious clone.
DNA ofhuman spumaretrovirus (HSRV) was cloned from both cDNA and from viral DNA into phage A and bacterial plasmid vectors. The recombinant plasm.ids harboring viral DNA were characterized by Southern blot hybridization and restriction mapping. Physical maps were constructed from cDNA and found to be colinear with the restriction maps obtained from viral DNA. The recombinant clones isolated contained viral DNA inserts which rangein size from 2.2 kb to 15.4 kb. The recombinant clones allowed to construct a physical map of the complete HSRV provirus of 12.2 kb.
The human foamy virus (HFV) genome possesses three open reading frames (bel I, 2, and 3) located between env and the 3' long terminal repeat. By analogy to other human retroviruses this region was selected as the most Iikely candidate to encode the viral transactivator. ResuIts presented here confirmed this and showed further that a deletion introduced only into the bell open reading frame of a plasmid derived from an infectious molecular clone of HFV abolished transactivation. In contrast, deletions in bel 2 and bel 3 had only minor effects on the ability to transactivate. The role of the bel I genomic region as a transactivator was further investigated by eukaryotic expression of a genome fragment of HFV spanning the bel I open reading frame. A construct expressing bell under control of a heterologous promoter was found to transactivate the HFV long terminal repeat in a dose-dependent fashion. Furthermore, it is shown that the U3 region of the HFV long terminal repeat is sufficient to respond to the HFV transactivator.
The long terminal repeat (LTR) of the human spumaretrovirus (HSRV) was examined with respect to its ability to function as transcriptional promotor in virus-infected and uninfected cells. Transient transfections using a plasmid in which the 3' L TR of HSRV was coupled to the bacterial chloramphenicol cetyltransferase (cat) gene revealed that the Ievei of HSRV LTR-directed cat gene expression was markedly increased in HSRV-infected cells compared to uninfected cells. Northern blot analysis of cat mRNA from transfected cultures suggests that transactivation of HSRVdirected gene expression occurs at the transcriptionallevel.
All foamy viruses give rise to a strong nuclear staining when infected cells are reacted with sera from infected hosts. This nuclear ftuorescence distinguishes foamy viruses from all other retroviruses. The experiments reported here indicate that the foamy virus Gag precursor protein is transiently located in the nuclei of infected cells and this is the likely reason for the typical foamy virus nuclear fluorescence. By using the vaccinia virus expression system, a conserved basic sequence motif in the nucleocapsid domain of foamy virus Cag proteins was identified to be responsible for the nuclear transport of the gag precursor molecule. Tbis motif was also found to be able to direct a heterologous protein, the Gag protein of human immunodeficiency virus, into the nucleus.
Retroviral vectors are potent tools for gene delivery and various biomedical applications. To accomplish a gene transfer task successfully, retroviral vectors must effectively transduce diverse cell cultures at different phases of a cell cycle. However, very promising retroviral vectors based on the foamy viral (FV) backbone lack the capacity to efficiently transduce quiescent cells. It is hypothesized that this phenomenon might be explained as the inability of foamy viruses to form a pre-integration complex (PIC) with nuclear import activity in growth-arrested cells, which is the characteristic for lentiviruses (HIV-1). In this process, the HIV-1 central polypurine tract (cPPT) serves as a primer for plus-strand synthesis to produce a “flap” element and is believed to be crucial for the subsequent double-stranded cDNA formation of all retroviral RNA genomes. In this study, the effects of the lentiviral cPPT element on the FV transduction potential in dividing and growth-arrested (G1/S phase) adenocarcinomic human alveolar basal epithelial (A549) cells are investigated by experimental and theoretical methods. The results indicated that the HIV-1 cPPT element in a foamy viral vector background will lead to a significant reduction of the FV transduction and viral titre in growth-arrested cells due to the absence of PICs with nuclear import activity.