Reactivation of feline foamy virus from a chronically infected feline renal cell line by trichostatin A

Genetic and biological characterization of feline foamy virus isolated from a leopard cat (Prionailurus bengalensis) in Vietnam

Foamy viruses have been isolated from various mammals and show long-term co-speciation with their hosts. However, the frequent inter-species transmission of feline foamy viruses (FFVs) from domestic cats to wild cats across genera has been reported. Because infectious molecular clones of FFVs derived from wild cats have not been available, whether there are specific characteristics enabling FFVs to adapt to the new host species is still unknown. Here, we obtained the complete genome sequences of two FFV isolates (strains NV138 and SV201) from leopard cats (Prionailurus bengalensis) in Vietnam and constructed an infectious molecular clone, named pLC960, from strain NV138. The growth kinetics of the virus derived from pLC960 were comparable to those of other FFVs derived from domestic cats. Phylogenetic analysis revealed that these two FFVs from leopard cats are clustered in the same clade as FFVs from domestic cats in Vietnam. Comparisons of the amino acid sequences of Env and Bet proteins showed more than 97% identity among samples and no specific amino acid substitutions between FFVs from domestic cats and ones from leopard cats. These results indicate the absence of genetic constraint of FFVs for interspecies transmission from domestic cats to leopard cats.

Frequent cross-species transmissions of foamy virus between domestic and wild felids

Emerging viral outbreaks resulting from host switching is an area of continued scientific interest. Such events can result in disease epidemics or in some cases, clinically silent outcomes. These occurrences are likely relatively common and can serve as tools to better understand disease dynamics, and may result in changes in behavior, fecundity, and, ultimately survival of the host. Feline foamy virus (FFV) is a common retrovirus infecting domestic cats globally, which has also been documented in the North American puma (Puma concolor). The prevalent nature of FFV in domestic cats and its ability to infect wild felids, including puma, provides an ideal system to study cross-species transmission across trophic levels (positions in the food chain), and evolution of pathogens transmitted between individuals following direct contact. Here we present findings from an extensive molecular analysis of FFV in pumas, focused on two locations in Colorado, and in relation to FFV recovered from domestic cats in this and previous studies. Prevalence of FFV in puma was high across the two regions, ∼77 per cent (urban interface site) and ∼48 per cent (rural site). Comparison of FFV from pumas living across three states; Colorado, Florida, and California, indicates FFV is widely distributed across North America. FFV isolated from domestic cats and pumas was not distinguishable at the host level, with FFV sequences sharing >93 per cent nucleotide similarity. Phylogenetic, Bayesian, and recombination analyses of FFV across the two species supports frequent cross-species spillover from domestic cat to puma during the last century, as well as frequent puma-to-puma intraspecific transmission in Colorado, USA. Two FFV variants, distinguished by significant difference in the surface unit of the envelope protein, were commonly found in both hosts. This trait is also shared by simian foamy virus and may represent variation in cell tropism or a unique immune evasion mechanism. This study elucidates evolutionary and cross-species transmission dynamics of a highly prevalent multi-host adapted virus, a system which can further be applied to model spillover and transmission of pathogenic viruses resulting in widespread infection in the new host.

Feline foamy virus adversely affects feline mesenchymal stem cell culture and expansion: implications for animal model development

Mesenchymal stem cells (MSCs) are a promising therapeutic option for various immune-mediated and inflammatory disorders due to their potent immunomodulatory and trophic properties. Naturally occurring diseases in large animal species may serve as surrogate animal models of human disease, as they may better reflect the complex genetic, environmental, and physiologic variation present in outbred populations. We work with naturally occurring diseases in large animal species to better understand how MSCs work and to facilitate optimal translation of MSC-based therapies. We are investigating the use of MSC therapy for a chronic oral inflammatory disease in cats. During our efforts to expand fat-derived feline MSCs (fMSCs), we observed that∼50% of the cell lines developed giant foamy multinucleated cells in later passages. These morphologic alterations were associated with proliferation arrest. We hypothesized that the cytopathic effects were caused by infection with a retrovirus, feline foamy virus (FFV). Using transmission electron microscopy, polymerase chain reaction, and in vitro assays, we determined that syncytial cell formation and proliferation arrest in fMSCs were caused by FFV strains that were highly homologous to previously reported FFV strains. We determined that the antiretroviral drug, tenofovir, may be used to support ex vivo expansion and salvage of FFV-infected fMSC lines. MSC lines derived from specific pathogen-free cats do not appear to be infected with FFV and may be a source of allogeneic fMSCs for clinical application. FFV infection of fMSC lines may hinder large-scale expansion of autologous MSC for therapeutic use in feline patients.

Non-simian foamy viruses: molecular virology, tropism and prevalence and zoonotic/interspecies transmission

Within the field of retrovirus, our knowledge of foamy viruses (FV) is still limited. Their unique replication strategy and mechanism of viral persistency needs further research to gain understanding of the virus-host interactions, especially in the light of the recent findings suggesting their ancient origin and long co-evolution with their nonhuman hosts. Unquestionably, the most studied member is the primate/prototype foamy virus (PFV) which was originally isolated from a human (designated as human foamy virus, HFV), but later identified as chimpanzee origin; phylogenetic analysis clearly places it among other Old World primates. Additionally, the study of non-simian animal FVs can contribute to a deeper understanding of FV-host interactions and development of other animal models. The review aims at highlighting areas of special interest regarding the structure, biology, virus-host interactions and interspecies transmission potential of primate as well as non-primate foamy viruses for gaining new insights into FV biology.

HIV-1 nef suppression by virally encoded microRNA

BACKGROUND

MicroRNAs (miRNAs) are 21 to approximately 25-nucleotides (nt) long and interact with mRNAs to trigger either translational repression or RNA cleavage through RNA interference (RNAi), depending on the degree of complementarity with the target mRNAs. Our recent study has shown that HIV-1 nef dsRNA from AIDS patients who are long-term non-progressors (LTNPs) inhibited the transcription of HIV-1.

RESULTS

Here, we show the possibility that nef-derived miRNAs are produced in HIV-1 persistently infected cells. Furthermore, nef short hairpin RNA (shRNA) that corresponded to a predicted nef miRNA (approximately 25 nt, miR-N367) can block HIV-1 Nef expression in vitro and the suppression by shRNA/miR-N367 would be related with low viremia in an LTNP (15-2-2). In the 15-2-2 model mice, the weight loss, which may be rendered by nef was also inhibited by shRNA/miR-N367 corresponding to suppression of nef expression in vivo.

CONCLUSIONS

These data suggest that nef/U3 miRNAs produced in HIV-1-infected cells may suppress both Nef function and HIV-1 virulence through the RNAi pathway.

Overlapping CRE and E box motifs in the enhancer sequences of the bovine leukemia virus 5' long terminal repeat are critical for basal and acetylation-dependent transcriptional activity of the viral promoter: implications for viral latency

Bovine leukemia virus (BLV) infection is characterized by viral latency in a large proportion of cells containing an integrated provirus. In this study, we postulated that mechanisms directing the recruitment of deacetylases to the BLV 5' long terminal repeat (LTR) could explain the transcriptional repression of viral expression in vivo. Accordingly, we showed that BLV promoter activity was induced by several deacetylase inhibitors (such as trichostatin A [TSA]) in the context of episomal LTR constructs and in the context of an integrated BLV provirus. Moreover, treatment of BLV-infected cells with TSA increased H4 acetylation at the viral promoter, showing a close correlation between the level of histone acetylation and transcriptional activation of the BLV LTR. Among the known cis-regulatory DNA elements located in the 5' LTR, three E box motifs overlapping cyclic AMP responsive elements (CREs) in U3 were shown to be involved in transcriptional repression of BLV basal gene expression. Importantly, the combined mutations of these three E box motifs markedly reduced the inducibility of the BLV promoter by TSA. E boxes are susceptible to recognition by transcriptional repressors such as Max-Mad-mSin3 complexes that repress transcription by recruiting deacetylases. However, our in vitro binding studies failed to reveal the presence of Mad-Max proteins in the BLV LTR E box-specific complexes. Remarkably, TSA increased the occupancy of the CREs by CREB/ATF. Therefore, we postulated that the E box-specific complexes exerted their negative cooperative effect on BLV transcription by steric hindrance with the activators CREB/ATF and/or their transcriptional coactivators possessing acetyltransferase activities. Our results thus suggest that the overlapping CRE and E box elements in the BLV LTR were selected during evolution as a novel strategy for BLV to allow better silencing of viral transcription and to escape from the host immune response.

Feline foamy virus Tas protein is a DNA-binding transactivator

Foamy viruses (FVs) harbour a transcriptional transactivator (Tas) and two Tas-responsive promoter regions, one in the 5′ long terminal repeat (LTR) and the other an internal promoter (IP) in the envelope gene. To analyse the mechanism of transactivation of the FVs, the specificity of feline FV (FFV) Tas protein, which is more distantly related to the respective proteins of non-human primate origin, were investigated. FFV Tas has been shown specifically to activate gene expression from the cognate promoters. No cross-transactivation was noted of the prototype foamy virus and human immunodeficiency virus type 1 LTR. The putative transactivation response element of FFV Tas was mapped to the 5′ LTR U3 region (approximately nt −228 to −195). FFV Tas binds to this element in addition to a previously described sequence (position −66 to −51). It is therefore concluded that FFV Tas is a DNA-binding transactivator that interacts with at least two regions in the virus LTR.

A potential live vector, foamy virus, directed intra-cellular expression of ovine interferon-tau exhibited the resistance to HIV infection

Interferon-tau (IFN-tau), produced by the embryonic trophectoderm, is a member of type I IFNs required for the establishment of pregnancy in the ruminant ungulates. Although this IFN possesses antiviral activity similar to other type I IFNs, the effectiveness of IFN-tau as an antiviral agent has not been well characterized. To investigate possible antiviral effects of ovine IFN-tau (oIFN-tau), oIFN-tau-GST fusion protein was expressed in E. coli BL21, from which the purified protein isolated possessed anti-viral activity. An apathogenic human foamy virus (hFV) was then used to establish a potential recombinant live vector consisting of oIFN-tau cDNA sense (+) or antisense (-) sequence, oIFN-tau(+)/hFV or oIFN-tau(-)/hFV, respectively. Human hematopoietic and other mammalian cell lines that had been transduced with hFV vector consisting of no oIFN-tau, oIFN-tau(+)/hFV or oIFN-tau(-)/hFV construct were cultured initially for 12 days, and three of cell lines were then maintained for up to 90 days. These cells with oIFN-tau expression directed by hFV exhibited the in vitro cytopathic effect minimally. Transduced cell lines that had been cultured for 90 days were subjected to studies on human immunodeficiency virus type-1 (HIV-1) infection, which was measured with infectivity of viral particles resulted from the GFP inserted T-cell tropic HIV SF2 or macrophage tropic HIV SF162: the number of HIV-1 positive cells was reduced by the hFV driven-intra-cellular oIFN-tau expression. Since oIFN-tau/hFV transduced cells exhibited the resistance to HIV-1 infection and/or replication, oIFN-tau could be considered as one of effective antiviral agents against HIV-1. These results suggest that the hFV genome could be an effective recombinant live vector for the expression of a targeted gene in various cell types.

Foamy virus transactivation and gene expression

An overview of the pattern and mechanisms of spuma or foamy virus (FV) gene expression is presented. FVs are complex retroviruses with respect to their genetic outfit and the elements used to control and regulate expression of the viral genome. The increased insight into transcriptional and posttranscriptional mechanisms has revealed that the FVs are distinct, unconventional retroviruses clearly apart from the orthoretroviruses. Although less characterized than the orthoretroviruses, FVs have several unique features that are important for construction and assembly of FV-based vectors for targeted gene delivery and vaccination purposes. Some of these distinguishing features are directly related to the FV-specific mechanisms of gene expression and include (1) the presence of an internal, functional active second transcription unit for expression of the nonstructural genes, (2) the utilization of a subgenomic, spliced transcript for Pol protein expression, and (3) distinct but not yet understood mechanisms for the nuclear exit of defined transcripts and thus an additional level of posttranscriptional control of gene expression. Finally, the interactions of the viral transactivator not only with both viral promoters but also with regulatory elements controlling the expression of defined cellular genes are an important issue with respect to vector development and the apparent apathogenicity of FVs in their natural hosts.

Histone deacetylase 1 inactivation by an adenovirus early gene product

Gam1 is an early gene product of the avian adenovirus CELO and is essential for viral replication. Gam1 has no homology to any known proteins; however, its early expression and nuclear localization suggest that the protein functions to influence transcription in the infected cell. A determinant of eukaryotic gene expression is the acetylation state of chromosomal histones and other nuclear proteins. We find that Gam1 expression increases the level of transcription from a variety of eukaryotic promoters, similar to the effect of treating cells with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA ). We show that Gam1 can effectively inhibit histone deacetylation by HDAC1 and that Gam1 binds to HDAC1 both in vitro and in vivo. A CELO virus lacking Gam1 (CELOdG) is replication defective, but the defect can be overcome by either expressing an interfering HDAC1 mutant or by treating infected cells with TSA. The identification of a viral early gene product having the specific function of binding and inactivating HDAC suggests that deacetylase complexes play an important role in limiting early gene expression from invading viruses.

Isolation and sequencing of infectious clones of feline foamy virus and a human/feline foamy virus Env chimera

Full-length DNAs of the Coleman and S7801 strains (pSKY3.0, pSKY5.0) of infectious feline foamy viruses (FFVs) were cloned and sequenced. Parental viruses, designated SKY3.0 and SKY5.0, were secreted following transfection of Crandell feline kidney (CRFK) cells. Production of the rescued parental viruses was enhanced in the presence of trichostatin A. Amino acid sequence similarities between FFV and human foamy virus (HFV) are extremely low for the envelope protein and capsid antigen, as predicted from the two clones. However, a chimeric FFV clone was constructed with the HFV Env substituted for the FFV Env. The chimeric virus (HFFV, SKY4.0) was able to infect and replicate in CRFK cells as well as in peripheral blood mononuclear cells of cats in vivo. Consequently, the chimeric HFFV may be useful for the creation of FV vectors for gene transfer strategies.

Genetic analyses of feline foamy virus isolates from domestic and wild feline species in geographically distinct areas

To know the genetic diversities and phylogenetic relationship among feline foamy virus (FeFV) isolates from domestic cats (Felis catus) and FeFV-related viruses from the Iriomote cats (Felis iriomotensis) and leopard cats (Felis bengalensis) in geographically distinct areas, we sequenced a partial gag-pol region of 17 strains and a partial env region of nine strains, and the U3 region of long terminal repeat of three strains of the viruses. FeFV-related viruses from the feral cats were quite similar to the FeFV from domestic cats in the sequenced regions. In the partial gag region, the identities of nucleotide sequences among the isolates were from 94 to 99%. In the partial env gene, the isolates were divided into two distinct genotypes (F17- and FUV-types) as reported by Winkler et al. (Virology 247 (1999) 144-151). More than 94% nucleotide identities were observed in the env region within a particular env genotype and about 75% nucleotide identities were noted between the two genotypes.