Special Issue "Recent Progress in Foamy Virus (FV) Research"

Lead Guest Editor
Dr. Arifa S. Khan
Senior Investigator, Laboratory of Retroviruses, Division of Viral Products, Office of Vaccines Research and Review, Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, 8800 Rockville Pike, HFM-454, Bldg 29B, Room 4NN10, Bethesda, MD 20892 USA
Website: http://fdazilla.com/fda/directory/employee/arifa.khan@fda.hhs.gov
E-Mail: arifa.khan@fda.hhs.gov
Phone: +301 827 0791
Fax: +301 496 1810

Co-Guest Editor
Prof. Dr. Martin Löchelt
Group Leader, German Cancer Research Center (DKFZ), Research Program Infection Center, Department Genome Modifications and Carcinogenesis (F020), Im Neuenheimer Feld 242, D-69120 Heidelberg, Germany
Website: http://www.dkfz.de/de/f020/groups/loechelt/people.html
E-Mail: m.loechelt@dkfz.de
Phone: +49 6221 42 4933
Fax: +49 6221 42 4932

Co-Guest Editor
Prof. Dr. Axel Rethwilm
Professor and Chair, Universität Würzburg, Institut für Virologie und Immunbiologie, Versbacher Str. 7, 97078 Wurzburg, Germany
Website: http://www.virologie.uni-wuerzburg.de/
E-Mail: Rethwilm@vim.uni-wuerzburg.de
Phone: +49 931 201 49555
Fax: +49 931 201 49553

Dear Colleagues,

Foamy viruses are ancient retroviruses that naturally occur in non-human primate species and in a variety of other animal species including bovine, equine, and feline. However, human foamy virus infections have been shown to be due to cross-species transmission from infected non-human primates. Although there is no evidence thus far of FV pathogenesis in any species, human exposure should be minimized since infectious foamy virus can stably persist life-long. Studies of virus replication and latency, virus prevalence in the natural host, and human infections can contribute to evaluating  the potential risks of FV infection in humans. Based upon several unique properties of these ancient retroviruses and the lack of known pathogenicity, foamy viruses are being developed as novel vectors for targeted gene delivery and vaccination, with recent improvements for new applications in experimental systems and medicine.

The main focus of this special issue is to review the current knowledge of FVs and present an update of FV research. The topics will include, but not limited to:

• Simian and non-simian FVs: Overview
• Natural infections
• Zoonoses
• Evolution
• Molecular Biology and Replication
• Viral proteins
• FV vectors
• Restriction factors
• Antivirals
• Virus detection assays
• Management of potential sources of exposure and infection

Dr. Arifa S. Khan
Prof. Dr. Martin Löchelt
Prof. Dr. Axel Rethwilm
Guest Editors

Submission

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Grant D. Trobridge, Peter A. Horn, Brian C. Beard and Hans-Peter Kiem Review: Large Animal Models for Foamy Virus Vector Gene Therapy Viruses 2012, 4(12), 3572-3588; doi:10.3390/v4123572 Received: 15 October 2012; in revised form: 19 November 2012 / Accepted: 28 November 2012 / Published: 7 December 2012 Show/Hide Abstract | Download PDF Full-text (229 KB) | Download XML Full-text Abstract: Foamy virus (FV) vectors have shown great promise for hematopoietic stem cell (HSC) gene therapy. Their ability to efficiently deliver transgenes to multi-lineage long-term repopulating cells in large animal models suggests they will be effective for several human hematopoietic diseases. Here, we review FV vector studies in large animal models, including the use of FV vectors with the mutant O6-methylguanine-DNA methyltransferase, MGMTP140K to increase the number of genetically modified cells after transplantation. In these studies, FV vectors have mediated efficient gene transfer to polyclonal repopulating cells using short ex vivo transduction protocols designed to minimize the negative effects of ex vivo culture on stem cell engraftment. In this regard, FV vectors appear superior to gammaretroviral vectors, which require longer ex vivo culture to effect efficient transduction. FV vectors have also compared favorably with lentiviral vectors when directly compared in the dog model. FV vectors have corrected leukocyte adhesion deficiency and pyruvate kinase deficiency in the dog large animal model. FV vectors also appear safer than gammaretroviral vectors based on a reduced frequency of integrants near promoters and also near proto-oncogenes in canine repopulating cells. Together, these studies suggest that FV vectors should be highly effective for several human hematopoietic diseases, including those that will require relatively high percentages of gene-modified cells to achieve clinical benefit.

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Eun-Gyung Lee, Carolyn R. Stenbak and Maxine L. Linial Review: Foamy Virus Assembly with Emphasis on Pol Encapsidation Viruses 2013, 5(3), 886-900; doi:10.3390/v5030886 Received: 31 January 2013; in revised form: 11 March 2013 / Accepted: 14 March 2013 / Published: 20 March 2013 Show/Hide Abstract | Download PDF Full-text (306 KB) | Download XML Full-text Abstract: Foamy viruses (FVs) differ from all other genera of retroviruses (orthoretroviruses) in many aspects of viral replication. In this review, we discuss FV assembly, with special emphasis on Pol incorporation. FV assembly takes place intracellularly, near the pericentriolar region, at a site similar to that used by betaretroviruses. The regions of Gag, Pol and genomic RNA required for viral assembly are described. In contrast to orthoretroviral Pol, which is synthesized as a Gag-Pol fusion protein and packaged through Gag-Gag interactions, FV Pol is synthesized from a spliced mRNA lacking all Gag sequences. Thus, encapsidation of FV Pol requires a different mechanism. We detail how WT Pol lacking Gag sequences is incorporated into virus particles. In addition, a mutant in which Pol is expressed as an orthoretroviral-like Gag-Pol fusion protein is discussed. We also discuss temporal regulation of the protease, reverse transcriptase and integrase activities of WT FV Pol.

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Erik Müllers Review: The Foamy Virus Gag Proteins: What Makes Them Different? Viruses 2013, 5(4), 1023-1041; doi:10.3390/v5041023 Received: 25 January 2013; in revised form: 15 March 2013 / Accepted: 20 March 2013 / Published: 26 March 2013 Show/Hide Abstract | Download PDF Full-text (846 KB) | Download XML Full-text Abstract: Gag proteins play an important role in many stages of the retroviral replication cycle. They orchestrate viral assembly, interact with numerous host cell proteins, engage in regulation of viral gene expression, and provide the main driving force for virus intracellular trafficking and budding. Foamy Viruses (FV), also known as spumaviruses, display a number of unique features among retroviruses. Many of these features can be attributed to their Gag proteins. FV Gag proteins lack characteristic orthoretroviral domains like membrane-binding domains (M domains), the major homology region (MHR), and the hallmark Cys-His motifs. In contrast, they contain several distinct domains such as the essential Gag-Env interaction domain and the glycine and arginine rich boxes (GR boxes). Furthermore, FV Gag only undergoes limited maturation and follows an unusual pathway for nuclear translocation. This review summarizes the known FV Gag domains and motifs and their functions. In particular, it provides an overview of the unique structural and functional properties that distinguish FV Gag proteins from orthoretroviral Gag proteins.

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Ursula Berka, Martin Volker Hamann and Dirk Lindemann Review: Early Events in Foamy Virus—Host Interaction and Intracellular Trafficking Viruses 2013, 5(4), 1055-1074; doi:10.3390/v5041055 Received: 27 February 2013; in revised form: 28 March 2013 / Accepted: 29 March 2013 / Published: 8 April 2013 Show/Hide Abstract | Download PDF Full-text (1445 KB) | Download XML Full-text Abstract: Here we review viral and cellular requirements for entry and intracellular trafficking of foamy viruses (FVs) resulting in integration of viral sequences into the host cell genome. The virus encoded glycoprotein harbors all essential viral determinants, which are involved in absorption to the host membrane and triggering the uptake of virus particles. However, only recently light was shed on some details of FV’s interaction with its host cell receptor(s). Latest studies indicate glycosaminoglycans of cellular proteoglycans, particularly heparan sulfate, to be of utmost importance. In a species-specific manner FVs encounter endogenous machineries of the target cell, which are in some cases exploited for fusion and further egress into the cytosol. Mostly triggered by pH-dependent endocytosis, viral and cellular membranes fuse and release naked FV capsids into the cytoplasm. Intact FV capsids are then shuttled along microtubules and are found to accumulate nearby the centrosome where they can remain in a latent state for extended time periods. Depending on the host cell cycle status, FV capsids finally disassemble and, by still poorly characterized mechanisms, the preintegration complex gets access to the host cell chromatin. Host cell mitosis finally allows for viral genome integration, ultimately starting a new round of viral replication.

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Sylvia Hütter, Irena Zurnic and Dirk Lindemann Review: Foamy Virus Budding and Release Viruses 2013, 5(4), 1075-1098; doi:10.3390/v5041075 Received: 4 February 2013; in revised form: 25 March 2013 / Accepted: 29 March 2013 / Published: 10 April 2013 Show/Hide Abstract | Download PDF Full-text (815 KB) | Download XML Full-text Abstract: Like all other viruses, a successful egress of functional particles from infected cells is a prerequisite for foamy virus (FV) spread within the host. The budding process of FVs involves steps, which are shared by other retroviruses, such as interaction of the capsid protein with components of cellular vacuolar protein sorting (Vps) machinery via late domains identified in some FV capsid proteins. Additionally, there are features of the FV budding strategy quite unique to the spumaretroviruses. This includes secretion of non-infectious subviral particles and a strict dependence on capsid-glycoprotein interaction for release of infectious virions from the cells. Virus-like particle release is not possible since FV capsid proteins lack a membrane-targeting signal. It is noteworthy that in experimental systems, the important capsid-glycoprotein interaction could be bypassed by fusing heterologous membrane-targeting signals to the capsid protein, thus enabling glycoprotein-independent egress. Aside from that, other systems have been developed to enable envelopment of FV capsids by heterologous Env proteins. In this review article, we will summarize the current knowledge on FV budding, the viral components and their domains involved as well as alternative and artificial ways to promote budding of FV particle structures, a feature important for alteration of target tissue tropism of FV-based gene transfer systems.

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Type of Paper: Review
Title: Feline Foamy Virus-Based Vectors: Advantages of an Authentic Animal Model
Authors: Weibin Liu ^1,2,#, Janet Lei ^1,#, Yang Liu ¹, Dragana Slavkovic Lukic ¹, Ann-Mareen Räthe ¹, Qiuying Bao ¹, Timo Kehl ¹, Anne Bleiholder ¹, Torsten Hechler ^1,3 and Martin Löchelt ^1,*
Affiliations: ¹ Department of Genome Modifications, Research Program Infection and Cancer, German Cancer Research Center, Im Neuenheimer Feld 242, 69120 Heidelberg, Germany; E-Mails: y.liu@dkfz.de (Y.L.); janet.lei@dkfz.de (J.L.); d.slavkovic@dkfz.de (D.S.L.); a.raethe@dkfz.de (A-M.R.); q.bao@dkfz.de (Q.B.); a.bleiholder@dkfz.de (A.B.); t.kehl@dkfz.de (T.K.); m.loechelt@dkfz.de (M.L.); ² Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA; E-Mail: liu.weibin@mayo.edu; ³ Department of Biochemistry, Heidelberg Pharma GmbH, Schriesheimer Str. 101, 68526 Ladenburg, Germany; E-Mail: t.hechler@hdpharma.com; #     Both authors contributed equally; * Author to whom correspondence should be addressed; E-Mail: m.loechelt@dkfz.de; Tel.: +49-6221-424933; Fax: +49-6221-424932.
Abstract: The potential of replication-competent (RC) feline foamy virus (FFV) vectors for vaccination and replication-deficient (RD) FFV-based vectors for gene delivery purposes has been studied over the past years. In this review, the different key achievements as well as the functional evaluation of the corresponding vectors under experimental conditions ranging from in vitro cell culture systems to out-bred cats will be described. The data presented here demonstrate the broad application spectrum of FFV-based vectors from pathogen-specific prophylactic and therapeutic vaccination to classical gene delivery. With regard to the authentic feline animal system, FFV-based vectors provide an advantageous platform for foamy virus (FV) vector studies.
Keywords: Retrovirus vector; foamy virus; vaccine vector; gene therapy vector; animal model; spumaretrovirus; replication-deficient vector; replication-competent vector

Type of Paper: Review
Title: Non-simian Foamy Viruses: Molecular Virology, Tropism and Prevalence and Zoonotic/interspecies Transmission
Authors: Timo Kehl ^1,*, Juan Tan ² and Madgalena Materniak ³
Affiliations: ¹ German Cancer Research Center, INF242, 69120 Heidelberg, Germany; E-Mail: t.kehl@dkfz; ² College of Life Sciences, Nankai University, 94 Weijin Road, Tianjin 300071, China; E-Mail: juantan@nankai.edu.cn; ³ Department of Biochemistry, National Veterinary Research Institute, Partyzantow Ave. 57, Pulawy, 24-100, Poland; E-Mail: magdalena.materniak@piwet.pulawy.pl; *   Author to whom correspondence should be addressed; E-Mail: t.kehl@dkfz.de; Tel.: +496221-42-4935; Fax: +496221-42-4932.
Abstract: The understanding about foamy viruses (FVs) still appears to be the most neglected among retroviruses. Their unique replication strategy, the still poorly understood pathogen-host interactions and the mechanism of viral persistency make them very interesting scientific target, especially in the light of recent findings suggesting their ancient origin and further co-evolution with their hosts. Unquestionably the most studied member is the so called primate/prototype foamy virus (PFV), but phylogenetic analysis clearly places it among other old world monkeys and indicates that it is not prototypic even for simian foamy viruses (SFV). Therefore more efforts should be made to get a deeper understanding for the nature of non-simian animal FVs, which are highly attractive candidates for virus-host pathological studies. The review aims at highlighting areas of special interest regarding the structure, biology, host-pathogen interactions and interspecies transmission potential of primate as well as non-primate foamy viruses resulting in new insights into FV biology.
Keywords: Foamy Virus, interspecies transmission, FV tropism, zoonotic potential, animal FVs

Type of Paper: Review
Title: Early Events in Foamy Virus – Host Interaction and Intracellular Trafficking
Authors: Ursula Berka ^1,2,† , Martin Hamann ^1,2,† and Dirk Lindemann ^1,2,*
Affiliations: ¹ Institut für Virologie, Medizinische Fakultät ―Carl Gustav Carus, Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany; ² DFG-Center for Regenerative Therapies Dresden (CRTD)—Cluster of Excellence, Biotechnology Center, Technische Universität Dresden, Fetscherstr. 105, 01307 Dresden, Germany; Ursula.Berka@tu-dresden.de (U.B.); Martin.Hamann@tu-dresden.de (M.H.); dirk.lindemann@tu-dresden.de (D.L.); †     These authors contributed equally to this work and should be considered co-first authors; * Author to whom correspondence should be addressed; E-Mail: dirk.lindemann@tu-dresden.de (D.L.); Tel.: +49-351458-6210; Fax: +49-351-458-6310.
Abstract: Here we review viral and cellular requirements for entry and intracellular trafficking of foamy viruses (FVs) resulting in integration of viral sequences into the host cell genome. The virus encoded glycoprotein harbors all essential viral determinants, which are involved in absorption to the host membrane and triggering the uptake of virus particles. However, only recently light was shed on some details of FV’s interaction with its host cell receptor(s). Latest studies indicate glycosaminoglycans of cellular proteoglycans, particularly heparan sulfate, to be of utmost importance. In a species-specific manner FVs encounter endogenous machineries of the target cell, which are in some cases exploited for fusion and further egress into the cytosol. Mostly triggered by pH-dependent endocytosis, viral and cellular membranes fuse and release naked FV capsids into the cytoplasm. Intact FV capsids are then shuttled along microtubules and are found to accumulate nearby the centrosome where they can remain in a latent state for extended time periods. Depending on the host cell cycle status, FV capsids finally disassemble and, by still poorly characterized mechanisms, the preintegration complex gets access to the host cell chromatin. Host cell mitosis finally allows for viral genome integration, ultimately starting a new round of viral replication.
Keywords: Foamy virus; entry; trafficking

Type of Paper: Review
Title: Foamy Virus Budding and Release
Authors: Sylvia Hütter ^1,2,†, Irena Zurnic ^1,2,† and Dirk Lindemann ^1,2,*
Affiliations: ¹ Institut für Virologie, Medizinische Fakultät “Carl Gustav Carus”, Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany; ² DFG-Center for Regenerative Therapies Dresden (CRTD)—Cluster of Excellence, Technische Universität Dresden, Fetscherstr. 105, 01307 Dresden, Germany; Sylvia.huetter@mailbox.tu-dresden.de (S.H); irena.zurnic@tu-dresden.de (I.Z.); dirk.lindemann@tu-dresden.de (D.L.); † These authors contributed equally to this work and should be considered co-first authors; * Author to whom correspondence should be addressed; E-Mail: E-Mail: dirk.lindemann@tu-dresden.de (D.L.); Tel.: +49-351458-6210; Fax: +49-351-458-6310.
Abstract: As for all other viruses, a successful egress of functional particles from infected cells is a prerequisite for foamy virus (FV) spread within the host. The budding process of FVs involves steps, which are shared by other retroviruses, such as interaction of the capsid protein with components of cellular vacuolar protein sorting (Vps) machinery via late domains identified in some FV capsid proteins. Additionally, there are features of the FV budding strategy quite unique to the spumaretroviruses. This includes secretion of non-infectious subviral particles and a strict dependence on capsid-glycoprotein interaction for release of infectious virions from the cells. Virus-like particle release is not possible since FV capsid proteins lack a membrane-targeting signal. It is noteworthy, that in experimental systems the important capsid-glycoprotein interaction could be bypassed by fusing heterologous membrane-targeting signals to the capsid protein, thus enabling glycoprotein-independent egress. Aside from that, other systems have been developed to enable envelopment of FV capsids by heterologous Env proteins. In this review article, we will summarize the current knowledge on FV budding, the viral components and their domains involved as well as alternative and artificial ways to promote budding of FV particle structures, a feature important for alteration of target tissue tropism of FV-based gene transfer systems.
Keywords: foamy virus, budding, virus egress, capsid-glycoprotein interaction, pseudotyping, subviral particles

Type of Paper: Review
Title: Foamy Virus Assembly with Emphasis on Pol Encapsidation
Authors: Eun-Gyung Lee 1, Carolyn R. Stenbak 2 and Maxine L. Linial 1,*
Affiliations: ¹ Fred Hutchinson Cancer Research Center, Basic Sciences Division; 1100 Fairview Avenue North, Seattle, WA 98109, USA; elee@fhcrc.org (EGL); mlinial@fhcrc.org (MLL); ² Seattle University, Biology Department; 901 12th Avenue, Seattle, WA 98122, USA; stenbakc@seattleu.edu; * Authors to whom correspondence should be addressed; E-Mail: mlinial@fhcrc.org; Tel.: +1-206-667-4442; Fax: +1-206-667-5939
Abstract: Foamy viruses (FVs) differ from all other genera of retroviruses (orthoretroviruses) in many aspects of viral replication. In some respects they are more similar to the hepadnaviruses, another group of reverse transcriptase-encoding viruses. In this review we discuss FV assembly with special emphasis on Pol incorporation. FV assembly takes place intracellularly near the pericentriolar region, at a site similar to that used by betaretroviruses. The regions of Gag, Pol, and genomic RNA required for viral assembly are described. In contrast to orthoretroviral Pol which is synthesized as a Gag-Pol fusion protein and packaged through Gag-Gag interactions, FV Pol is synthesized from a spliced mRNA lacking all Gag sequences. Thus, encapsidation of FV Pol requires a different mechanism. We detail how WT Pol lacking Gag sequences is incorporated into virus particles. In addition a mutant in which Pol is expressed as an orthoretroviral-like Gag-Pol fusion protein is discussed. We also discuss temporal regulation of the protease, reverse transcriptase, and integrase activities of WT FV Pol.
Keywords: Foamy virus assembly; Pol expression; Pol encapsidation; Pol enzymatic activities

Type of Paper: Review
Title: Simian Foamy Virus in Non-Human Primates and Cross-Species Transmission to Humans in Gabon: An Emerging Zoonotic Disease in Central Africa?
Authors: Mirdad Kazanji ^1,2,* and Augustin Mouinga-Ondémé ²
Affiliations: ¹ Institut Pasteur de Bangui, BP 923, Bangui, Central African Republic; ² Unité de Rétrovirologie, Centre International de Recherches Médicales, Franceville, Gabon; * Author to whom correspondence should be addressed; E-Mail: mirdad.kazanji@pasteur.fr; Tel.: +236-21-61-0866; Fax: +236-21-61-0109.
Abstract: It is now known that all human retroviruses have a non-human primate counterpart. It has been reported that the presence of these retroviruses in humans is the result of interspecies transmission. Several authors have described the passage of a simian retrovirus, simian foamy virus (SFV), from primates to humans. To better understand this retroviral ‘zoonosis’ in natural settings, we evaluated the presence of SFV in both captive and wild non-human primates and in humans at high risk, such as hunters and people injured by a bite from a non-human primate in Gabon, central Africa. A high prevalence of SFV was found in blood samples from non-human primates and in bush meat collected across the country. Mandrills were found to be highly infected with one of two strains of SFV, depending on their geographical location. Furthermore, samples collected from hunters and primate laboratory workers showed clear, extensive interspecies transmission of SFV from primates. People who had been bitten by mandrills, gorillas and chimpanzees had persistent SFV infection with low genetic drift. Thus SFV is presumed to be transmitted from non-human primates mainly through severe bites, involving contact between infected saliva and blood. We evaluated therefore the viral load in peripheral blood mononuclear cells and saliva as well as in CD4+ and CD8+ T cells from naturally infected mandrills. We showed that the mean load was higher in PBMCs than in the saliva and was also with significantly higher in CD8+ than in CD4+ cells. In this review, we summarize and discuss our 5-year observations on the prevalence and dissemination of SFV in humans and non-human primates in Gabon.
Keywords: SFV; mandrills; wild-born non-human primates; interspecies transmission; Gabon; central Africa

Type of Paper: Review
Title: Structural and Functional Insights into Foamy Viral Integrase
Authors: Md. Alamgir Hossain, Md. Khadem Ali, and Cha-Gyun Shin *
Affiliation: Department of Biotechnology, Chung-Ang University, Ansung 456-756, South Korea; alamgir_bge@yahoo.com; khadem_bge05@yahoo.com; * Author to whom correspondence should be addressed; E-Mail: cgshin@cau.ac.kr; Tel.: +82-31-670-3067; Fax: +82-31-675-0409.
Abstract: Successful integration of retroviral DNA into the host chromosome is key for viral replication to occur through virally encoded integrase (IN) and is orchestrated by 3'-end processing and the strand transfer reaction. Several studies have described in vitro reaction conditions, including substrate specificity, cofactor usage, and the cellular binding partners for such reactions by three distinct domains of prototype foamy viral integrase (PFV-IN). Recent studies on the three-dimensional structure of the interaction between PFV-IN and DNA, cofactors, binding partners, or inhibitors have explored the mechanistic details of such interactions, which can be utilized as an ideal system to develop anti-retroviral drugs such as anti-HIV. The presence of a potent, non-transferable nuclear localization signals in the PFV C-terminal domain extends its use as a model for investigating cellular trafficking of large molecular complexes through the nuclear pore complex and also to identify novel cellular targets for such trafficking. This review focuses on recent advancements in the structural analysis and in vitro functional aspects of PFV-IN.
Keywords: Integrase, anti-retroviral drugs, cellular trafficking

Type of Paper: Review
Title: The Foamy Virus Gag Proteins – Same Same but Different
Author: Erik Müllers 1,2,*
Affiliations: ¹ Department of Cell and Molecular Biology, Karolinska Institutet, SE-17177 Stockholm, Sweden; E-Mail: erik.mullers@ki.se (E.M.); ² Institut für Virologie, Medizinische Fakultät “Carl Gustav Carus”, Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany; * Author to whom correspondence should be addressed; E-Mail: erik.mullers@ki.se (E.M.); Tel.: +46-8-52487374.
Abstract: Gag proteins are the central elements of the retroviral replication cycle. They orchestrate viral assembly, interact with numerous host cell proteins, engage in regulation of viral gene expression and provide the main driving force for virus intracellular trafficking and budding. Foamy Viruses (FV), also known as spumaviruses, display a number of unique features among retroviruses. Many of these features can be attributed to their Gag proteins. FV Gag proteins lack characteristic orthoretroviral domains like membrane-binding domains (M domains), the major homology region (MHR), and the hallmark Cys-His motifs. In contrast, they contain several distinct domains such as the essential Gag-Env interaction domain or the glycine and arginine rich boxes (GR boxes). Furthermore, FV Gag only undergoes limited maturation and follows an unusual pathway for nuclear translocation. This review summarizes the known FV Gag domains and motifs and their functions. In particular, it provides an overview of the unique structural and functional properties that distinguish FV Gag proteins from orthoretroviral Gag proteins.
Keywords: Foamy Virus Gag; functional domains; virus assembly; nuclear localization

Type of Paper: Review
Title: Molecular Biology of Foamy Virus Assembly and Pol Encapsidation
Authors: Eun-Gyung Lee¹, Carolyn R. Stenbak² and Maxine L. Linial^1,*
Affiliations: ¹ Fred Hutchinson Cancer Research Center, Basic Sciences Division; 1100 Fairview Avenue North, Seattle, WA 98109; elee@fhcrc.org (EGL); mlinial@fhcrc.org (MLL); ²Seattle University; 901 12th Avenue, Seattle, WA 98122; stenbakc@seattleu.edu * Authors to whom correspondence should be addressed; E-Mail: mlinial@fhcrc.org; Tel.: +1-206-667-4442; Fax: +1-206-667-5939
Abstract: Foamy viruses (FV) differ from orthoretroviruses in many aspects of viral replication cycle. In some respects they are similar to the only other family of vertebrate reverse transcriptase-encoding viruses, the Hepadnavirinae. In this review we discuss FV replication with a special emphasis on viral assembly. FV genomic RNA, Gag, and Pol must co-localize intracellularly at the site of capsid formation near the pericentriolar region. The portions of Gag, Pol, and RNA as well as some cellular proteins required for viral assembly are described. Unlike orthoretroviruses, FV Pol is synthesized independently of Gag from a spliced mRNA. This unique mode of Pol expression requires distinct mechanisms to ensure proper levels of Pol expression and encapsidation into virions. The incorporation of WT Pol lacking Gag sequences into viral particles is detailed. In addition a mutant in which Pol is expressed as an orthoretroviral-like Gag-Pol fusion protein has been created and its packaging is also discussed. Pol as in orthoretroviruses, FV Pol contains protease (PR), reverse transcriptase (RT), and integrase (IN). We also discuss temporal regulation of enzymatic activities of the individual Pol proteins when expressed as a precursor Pol, PR-RT-IN. Overall this review highlights the differences between FV assembly and orthoretroviral assembly.
Keywords: Foamy virus assembly; Pol expression; Pol encapsidation; Pol enzymatic activities

Type of Paper: Brief Report
Tiltle: Transcriptome microarray analysis of BoMac cells after infection with bovine foamy virus
Authors: Rola-Łuszczak Marzena, Materniak Magdalena, Pluta Aneta, Hulst Marcel, Kuzmak Jacek
Affiliation: National Veterinary Research Institute, Pulawy, Poland; Animal sciences Group of Wageningen UR, Lelystad, The Netherlands
Abstract: Bovine Foamy Virus (BFV) infections are highly prevalent among cattle worldwide and ranges from 28 to 70%. However relatively little is known about impact of this virus on host immune system. In our study we have focused on bovine macrophage cell line (BoMac) and examined changes in BoMac transcriptome after in vitro infection with BFV. To analyse expression profile of genes total RNA was isolated from non infected and infected BoMac cells. RNA samples were reverse transcribed, labeled with fluor dyes and hybridized independently against controls to bovine BLOPlus oligo microarrays. Differentially expressed genes were defined as those that had absolute fold change ratios greater than 1.5 ( p≤0.1). 124  genes have shown significant changes in expression level. The PANTHER software was used for the  gene ontology analysis of the differentially expressed genes. The biological process categories found to be enriched include metabolic processes, cell communication, transport, immune system processes and response to stimulus. qRT-PCR was applied to validate results obtained for respective genes.