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Pramono D, Takeuchi D, Katsuki M, AbuEed L, Abdillah D, Kimura T, Kawasaki J, Miyake A, Nishigaki K. FeLIX is a restriction factor for mammalian retrovirus infection. J Virol 2024; 98:e0177123. [PMID: 38440982 PMCID: PMC11019853 DOI: 10.1128/jvi.01771-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2023] [Accepted: 02/11/2024] [Indexed: 03/06/2024] Open
Abstract
Endogenous retroviruses (ERVs) are remnants of ancestral viral infections. Feline leukemia virus (FeLV) is an exogenous and endogenous retrovirus in domestic cats. It is classified into several subgroups (A, B, C, D, E, and T) based on viral receptor interference properties or receptor usage. ERV-derived molecules benefit animals, conferring resistance to infectious diseases. However, the soluble protein encoded by the defective envelope (env) gene of endogenous FeLV (enFeLV) functions as a co-factor in FeLV subgroup T infections. Therefore, whether the gene emerged to facilitate viral infection is unclear. Based on the properties of ERV-derived molecules, we hypothesized that the defective env genes possess antiviral activity that would be advantageous to the host because FeLV subgroup B (FeLV-B), a recombinant virus derived from enFeLV env, is restricted to viral transmission among domestic cats. When soluble truncated Env proteins from enFeLV were tested for their inhibitory effects against enFeLV and FeLV-B, they inhibited viral infection. Notably, this antiviral machinery was extended to infection with the Gibbon ape leukemia virus, Koala retrovirus A, and Hervey pteropid gammaretrovirus. Although these viruses used feline phosphate transporter 1 (fePit1) and phosphate transporter 2 as receptors, the inhibitory mechanism involved competitive receptor binding in a fePit1-dependent manner. The shift in receptor usage might have occurred to avoid the inhibitory effect. Overall, these findings highlight the possible emergence of soluble truncated Env proteins from enFeLV as a restriction factor against retroviral infection and will help in developing host immunity and antiviral defense by controlling retroviral spread.IMPORTANCERetroviruses are unique in using reverse transcriptase to convert RNA genomes into DNA, infecting germ cells, and transmitting to offspring. Numerous ancient retroviral sequences are known as endogenous retroviruses (ERVs). The soluble Env protein derived from ERVs functions as a co-factor that assists in FeLV-T infection. However, herein, we show that the soluble Env protein exhibits antiviral activity and provides resistance to mammalian retrovirus infection through competitive receptor binding. In particular, this finding may explain why FeLV-B transmission is not observed among domestic cats. ERV-derived molecules can benefit animals in an evolutionary arms race, highlighting the double-edged-sword nature of ERVs.
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MESH Headings
- Animals
- Cats
- Endogenous Retroviruses/genetics
- Endogenous Retroviruses/metabolism
- Gene Products, env/genetics
- Gene Products, env/metabolism
- Leukemia Virus, Feline/classification
- Leukemia Virus, Feline/genetics
- Leukemia Virus, Feline/metabolism
- Leukemia Virus, Gibbon Ape/genetics
- Leukemia Virus, Gibbon Ape/metabolism
- Leukemia, Feline/genetics
- Leukemia, Feline/metabolism
- Leukemia, Feline/virology
- Phosphate Transport Proteins/genetics
- Phosphate Transport Proteins/metabolism
- Receptors, Virus/metabolism
- Retroviridae Infections/metabolism
- Retroviridae Infections/virology
- Solubility
- Female
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Affiliation(s)
- Didik Pramono
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
- Research Institute for Cell Design Medical Science, Yamaguchi University, Yamaguchi, Japan
| | - Dai Takeuchi
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
| | - Masato Katsuki
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
| | - Loai AbuEed
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
- Research Institute for Cell Design Medical Science, Yamaguchi University, Yamaguchi, Japan
| | - Dimas Abdillah
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
- Research Institute for Cell Design Medical Science, Yamaguchi University, Yamaguchi, Japan
| | - Tohru Kimura
- The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
| | - Junna Kawasaki
- Faculty of Science and Engineering, Waseda University, Tokyo, Japan
| | - Ariko Miyake
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
- Research Institute for Cell Design Medical Science, Yamaguchi University, Yamaguchi, Japan
| | - Kazuo Nishigaki
- Laboratory of Molecular Immunology and Infectious Disease, The Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan
- Research Institute for Cell Design Medical Science, Yamaguchi University, Yamaguchi, Japan
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Ngo MH, AbuEed L, Kawasaki J, Oishi N, Pramono D, Kimura T, Sakurai M, Watanabe K, Mizukami Y, Ochi H, Anai Y, Odahara Y, Umehara D, Kawamura M, Watanabe S, Miyake A, Nishigaki K. Multiple recombination events between endogenous retroviral elements and feline leukemia virus. J Virol 2024; 98:e0140023. [PMID: 38240589 PMCID: PMC10878261 DOI: 10.1128/jvi.01400-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Accepted: 12/19/2023] [Indexed: 02/21/2024] Open
Abstract
Feline leukemia virus (FeLV) is an exogenous retrovirus that causes malignant hematopoietic disorders in domestic cats, and its virulence may be closely associated with viral sequences. FeLV is classified into several subgroups, including A, B, C, D, E, and T, based on viral receptor interference properties or receptor usage. However, the transmission manner and disease specificity of the recombinant viruses FeLV-D and FeLV-B remain unclear. The aim of this study was to understand recombination events between exogenous and endogenous retroviruses within a host and elucidate the emergence and transmission of recombinant viruses. We observed multiple recombination events involving endogenous retroviruses (ERVs) in FeLV from a family of domestic cats kept in one house; two of these cats (ON-T and ON-C) presented with lymphoma and leukemia, respectively. Clonal integration of FeLV-D was observed in the ON-T case, suggesting an association with FeLV-D pathogenesis. Notably, the receptor usage of FeLV-B observed in ON-T was mediated by feline Pit1 and feline Pit2, whereas only feline Pit1 was used in ON-C. Furthermore, XR-FeLV, a recombinant FeLV containing an unrelated sequence referred to the X-region, which is homologous to a portion of the 5'-leader sequence of Felis catus endogenous gammaretrovirus 4 (FcERV-gamma4), was isolated. Genetic analysis suggested that most recombinant viruses occurred de novo; however, the possibility of FeLV-B transmission was also recognized in the family. This study demonstrated the occurrence of multiple recombination events between exogenous and endogenous retroviruses in domestic cats, highlighting the contribution of ERVs to pathogenic recombinant viruses.IMPORTANCEFeline leukemia virus subgroup A (FeLV-A) is primarily transmitted among cats. During viral transmission, genetic changes in the viral genome lead to the emergence of novel FeLV subgroups or variants with altered virulence. We isolated three FeLV subgroups (A, B, and D) and XR-FeLV from two cats and identified multiple recombination events in feline endogenous retroviruses (ERVs), such as enFeLV, ERV-DC, and FcERV-gamma4, which are present in the cat genome. This study highlights the pathogenic contribution of ERVs in the emergence of FeLV-B, FeLV-D, and XR-FeLV in a feline population.
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Affiliation(s)
- Minh Ha Ngo
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Loai AbuEed
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Junna Kawasaki
- Faculty of Science and Engineering, Waseda University, Okubo, Shinjuku-ku, Tokyo, Japan
| | | | - Didik Pramono
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Tohru Kimura
- Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Masashi Sakurai
- Laboratory of Veterinary Pathology, Joint Faculty of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Kenji Watanabe
- Institute of Gene Research, Science Research Center, Yamaguchi University, Minami-kogushi, Ube, Japan
| | - Yoichi Mizukami
- Institute of Gene Research, Science Research Center, Yamaguchi University, Minami-kogushi, Ube, Japan
| | - Haruyo Ochi
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Yukari Anai
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Yuka Odahara
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Daigo Umehara
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Maki Kawamura
- Life Science Division, Advanced Technology Institute, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Shinya Watanabe
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Ariko Miyake
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
| | - Kazuo Nishigaki
- Laboratory of Molecular Immunology and Infectious Disease, Joint Graduate School of Veterinary Medicine, Yamaguchi University, Yoshida, Yamaguchi, Japan
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Could Phylogenetic Analysis Be Used for Feline Leukemia Virus (FeLV) Classification? Viruses 2022; 14:v14020249. [PMID: 35215842 PMCID: PMC8876432 DOI: 10.3390/v14020249] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2021] [Revised: 01/22/2022] [Accepted: 01/23/2022] [Indexed: 12/21/2022] Open
Abstract
The surface envelope (SU) protein determines the cell tropism and consequently the pathogenesis of the feline leukemia virus (FeLV) in felids. Recombination of exogenous FeLV (exFeLV) with endogenous retroviruses (enFeLV) allows the emergence of more pathogenic variants. Currently, phenotypic testing through interference assays is the only method to distinguish among subgroups-namely, FeLV-A, -B, -C, -E, and -T. This study proposes a new method for FeLV classification based on molecular analysis of the SU gene. A total of 404 publicly available SU sequences were used to reconstruct a maximum likelihood tree. However, only 63 of these sequences had available information about phenotypic tests or subgroup assignments. Two major clusters were observed: (a) clade FeLV-A, which includes FeLV-A, FeLV-C, FeLV-E, and FeLV-T sequences, and (b) clade enFeLV, which includes FeLV-B and enFeLV strains. We found that FeLV-B, FeLV-C, FeLV-E, and FeLV-T SU sequences share similarities to FeLV-A viruses and most likely arose independently through mutation or recombination from this strain. FeLV-B and FeLV-C arose from recombination between FeLV-A and enFeLV viruses, whereas FeLV-T is a monophyletic subgroup that has probably originated from FeLV-A through combined events of deletions and insertions. Unfortunately, this study could not identify polymorphisms that are specifically linked to the FeLV-E subgroup. We propose that phylogenetic and recombination analysis together can explain the current phenotypic classification of FeLV viruses.
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The FGF23 and Klotho system beyond mineral metabolism. Clin Exp Nephrol 2016; 21:64-69. [PMID: 27838783 DOI: 10.1007/s10157-016-1357-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 10/25/2016] [Indexed: 12/22/2022]
Abstract
FGF23 is a bone-derived hormone that acts primarily on the kidney to induce phosphaturia and suppress synthesis of 1,25-dihydroxyvitamin D3. The unique feature of FGF23 is that it requires Klotho as an obligate co-receptor. The FGF23-Klotho system has emerged as an endocrine axis indispensable for maintaining phosphate homeostasis. Mineral and bone disorders associated with chronic kidney disease (CKD-MBD) can be viewed as a series of events triggered by a compensatory response of the FGF23-Klotho system to excess phosphate intake relative to the residual nephron number. Furthermore, the fact that disruption of the FGF23-Klotho system causes phosphate retention and a syndrome resembling aging in mammals has led to the notion that phosphate accelerates aging. The aging-like pathology caused by phosphate, or phosphatopathy, may be unique to the higher organisms having the Klotho gene and provides new insights into the molecular mechanism of aging in humans.
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Role of Cysteines in Stabilizing the Randomized Receptor Binding Domains within Feline Leukemia Virus Envelope Proteins. J Virol 2015; 90:2971-80. [PMID: 26719270 DOI: 10.1128/jvi.02544-15] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 12/22/2015] [Indexed: 01/20/2023] Open
Abstract
UNLABELLED Retargeting of gammaretroviral envelope proteins has shown promising results in the isolation of novel isolates with therapeutic potential. However, the optimal conditions required to obtain high-affinity retargeted envelope proteins with narrow tropism are not understood. This study highlights the advantage of constrained peptides within receptor binding domains and validates the random library screening technique of obtaining novel retargeted Env proteins. Using a modified vector backbone to screen the envelope libraries on 143B osteosarcoma cells, three novel and unique retargeted envelopes were isolated. The use of complex disulfide bonds within variable regions required for receptor binding is found within natural gammaretroviral envelope isolates. Interestingly, two of the isolates, named AII and BV2, have a pair of cysteines located within the randomized region of 11 amino acids similar to that identified within the CP Env, an isolate identified in a previous Env library screen on the human renal carcinoma Caki-1 cell line. The amino acids within the randomized region of AII and BV2 envelopes that are essential for viral infection have been identified in this study and include these cysteine residues. Through mutagenesis studies, the putative disulfide bond pairs including and beyond the randomized region were examined. In parallel, the disulfide bonds of CP Env were identified using mass spectrometry. The results indicate that this pair of cysteines creates the structural context to position key hydrophobic (F and W) and basic (K and H) residues critical for viral titer and suggest that AII, BV2, and CP internal cysteines bond together in distinct ways. IMPORTANCE Retargeted gammaretroviral particles have broad applications for therapeutic use. Although great advances have been achieved in identifying new Env-host cell receptor pairs, the rules for designing optimal Env libraries are still unclear. We have found that isolates with an additional pair of cysteines within the randomized region have the highest transduction efficiencies. This emphasizes the importance of considering cysteine pairs in the design of new libraries. Furthermore, our data clearly indicate that these cysteines are essential for viral infectivity by presenting essential residues to the host cell receptor. These studies facilitate the screening of Env libraries for functional entry into target cells, allowing the identification of novel gammaretroviral Envs targeting alternative host cell receptors for gene and protein delivery.
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Disruption of thiamine uptake and growth of cells by feline leukemia virus subgroup A. J Virol 2012; 87:2412-9. [PMID: 23269813 DOI: 10.1128/jvi.03203-12] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Feline leukemia virus (FeLV) is still a major cause of morbidity and mortality in domestic cats and some wild cats despite the availability of relatively effective vaccines against the virus. FeLV subgroup A (FeLV-A) is transmitted in natural infections, and FeLV subgroups B, C, and T can evolve directly from FeLV-A by mutation and/or recombination with endogenous retroviruses in domestic cats, resulting in a variety of pathogenic outcomes. The cell surface entry receptor for FeLV-A is a putative thiamine transporter (THTR1). Here, we have addressed whether FeLV-A infection might disrupt thiamine uptake into cells and, because thiamine is an essential nutrient, whether this disruption might have pathological consequences. First, we cloned the cat ortholog of the other of the two known thiamine transporters in mammals, THTR2, and we show that feline THTR1 (feTHTR1) and feTHTR2 both mediate thiamine uptake, but feTHTR2 does not function as a receptor for FeLV-A. We found that feTHTR1 is widely expressed in cat tissues and in cell lines, while expression of feTHTR2 is restricted. Thiamine uptake mediated by feTHTR1 was indeed blocked by FeLV-A infection, and in feline fibroblasts that naturally express feTHTR1 and not feTHTR2, this blockade resulted in a growth arrest at physiological concentrations of extracellular thiamine. The growth arrest was reversed at high extracellular concentrations of thiamine. Our results show that FeLV-A infection can indeed disrupt thiamine uptake with pathological consequences. A prediction of these experiments is that raising the plasma levels of thiamine in FeLV-infected cats may ameliorate the pathogenic effects of infection.
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Stewart H, Jarrett O, Hosie M, Willett B. Are endogenous feline leukemia viruses really endogenous? Vet Immunol Immunopathol 2011; 143:325-31. [DOI: 10.1016/j.vetimm.2011.06.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Bupp K, Sarangi A, Roth MJ. Probing sequence variation in the receptor-targeting domain of feline leukemia virus envelope proteins with peptide display libraries. J Virol 2005; 79:1463-9. [PMID: 15650172 PMCID: PMC544108 DOI: 10.1128/jvi.79.3.1463-1469.2005] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Determinants of cellular tropism and receptor targeting lie within a short peptide in the Vr1 region of the envelope (Env) proteins of feline leukemia virus (FeLV) subgroups A and C. Libraries of FeLV Env proteins with random amino acid substitutions in the peptide were screened for their ability to deliver a marker gene to D17 and AH927 cells. Screening on D17 canine cells yielded D17-specific Env proteins that used the FeLV-C receptor. Screening on AH927 cells yielded Env proteins with a broader host range, with maximal titers on AH927 cells and similar or lower titers on other cells. These Env proteins used an unidentified non-FeLV receptor for entry. The A5 isolate obtained from the AH927 screen was readily concentrated to yield titers of 10(5) on human PC-3 prostate tumor cells. The sequence divergence observed among targeting peptides of library-selected Env proteins was greater than that found in parental FeLV isolates. Substitution analyses of a conserved R in the middle of the targeting peptide held constant during screening indicated that maximal titers were obtained only when R was present in both a D17 selected isolate and an AH927 selected isolate. The ability to isolate Env proteins with unique tropisms dependent on the cells on which the library is screened has direct implications for targeting gene delivery vectors.
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Affiliation(s)
- Keith Bupp
- Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, 675 Hoes Lane, Piscataway, NJ 08854, USA.
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Quigley JG, Yang Z, Worthington MT, Phillips JD, Sabo KM, Sabath DE, Berg CL, Sassa S, Wood BL, Abkowitz JL. Identification of a human heme exporter that is essential for erythropoiesis. Cell 2004; 118:757-66. [PMID: 15369674 DOI: 10.1016/j.cell.2004.08.014] [Citation(s) in RCA: 296] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2004] [Revised: 07/22/2004] [Accepted: 07/27/2004] [Indexed: 01/11/2023]
Abstract
FLVCR, a member of the major facilitator superfamily of transporter proteins, is the cell surface receptor for feline leukemia virus, subgroup C. Retroviral interference with FLVCR display results in a loss of erythroid progenitors (colony-forming units-erythroid, CFU-E) and severe anemia in cats. In this report, we demonstrate that human FLVCR exports cytoplasmic heme and hypothesize that human FLVCR is required on developing erythroid cells to protect them from heme toxicity. Inhibition of FLVCR in K562 cells decreases heme export, impairs their erythroid maturation and leads to apoptosis. FLVCR is upregulated on CFU-E, indicating that heme export is important in primary cells at this stage. Studies of FLVCR expression in cell lines suggest this exporter also impacts heme trafficking in intestine and liver. To our knowledge, this is the first description of a mammalian heme transporter.
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Affiliation(s)
- John G Quigley
- Department of Medicine/Hematology, University of Washington, Seattle 98195, USA
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Lavillette D, Kabat D. Porcine endogenous retroviruses infect cells lacking cognate receptors by an alternative pathway: implications for retrovirus evolution and xenotransplantation. J Virol 2004; 78:8868-77. [PMID: 15280495 PMCID: PMC479092 DOI: 10.1128/jvi.78.16.8868-8877.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A PHQ motif near the amino termini of gammaretroviral envelope glycoprotein surface (SU) subunits is important for infectivity but not for incorporation into virions or binding to cognate receptors. The H residue of this motif is most critical, with all substitutions we tested being inactive. Interestingly, porcine endogenous retroviruses (PERVs) of all three host-range groups, A, B, and C, lack full PHQ motifs, but most members have an H residue at position 10. H10A PERV mutants are noninfectious but were efficiently transactivated by adding to the assays a PHQ-containing SU or receptor-binding subdomain (RBD) derived from a gibbon ape leukemia virus (GALV). A requirement of this transactivation was a functional GALV receptor on the cells. In contrast to this heterologous transactivation, PERV RBDs and SUs were inactive in all tested cells, including porcine ST-IOWA cells. Surprisingly, transactivation by GALV RBD enabled wild-type or H10A mutant PERVs of all three host-range groups to efficiently infect cells from humans and rodents that lack functional PERV receptors and it substantially enhanced infectivities of wild-type PERVs, even for cells with PERV receptors. Thus, PERVs can suboptimally infect cells that contain cognate receptors or they can employ a transactivation pathway to more efficiently infect all cells. This ability to infect cells lacking cognate receptors was previously demonstrated only for nontransmissible variant gammaretroviruses with recombinant and mutant envelope glycoproteins. We conclude that some endogenously inherited mammalian retroviruses also have a receptor-independent means for overcoming host-range and interference barriers, implying a need for caution in xenotransplantation, especially of porcine tissues.
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Affiliation(s)
- Dimitri Lavillette
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 S.W. Sam Jackson Park Rd., Portland, OR 97239-3098, USA
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Anderson MM, Lauring AS, Robertson S, Dirks C, Overbaugh J. Feline Pit2 functions as a receptor for subgroup B feline leukemia viruses. J Virol 2001; 75:10563-72. [PMID: 11602698 PMCID: PMC114638 DOI: 10.1128/jvi.75.22.10563-10572.2001] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Different subgroups of feline leukemia virus (FeLV) use different host cell receptors for entry. Subgroup A FeLV (FeLV-A) is the virus that is transmitted from cat to cat, suggesting that cells expressing the FeLV-A receptor are important targets at the earliest stages of infection. FeLV-B evolves from FeLV-A in the infected cat through acquisition of cellular sequences that are related to the FeLV envelope gene. FeLV-Bs have been shown to infect cells using the Pit1 receptor, and some variants can infect cells at a lower efficiency using Pit2. Because these observations were made using receptor proteins of human or rodent origin, the role that Pit1 and Pit2 may play in FeLV-B replication in the cat is unclear. In this study, the feline Pit receptors were cloned and tested for their ability to act as receptors for different FeLV-Bs. Some FeLV-Bs infected cells expressing feline Pit2 and feline Pit1 with equal high efficiency. Variable region A (VRA) in the putative receptor-binding domain (RBD) was a critical determinant for both feline Pit1 and feline Pit2 binding, although other domains in the RBD appear to influence how efficiently the FeLV-B surface unit can bind to feline Pit2 and promote entry via this receptor. An arginine residue at position 73 in VRA was found to be important for envelope binding to feline Pit2 but not feline Pit1. Interestingly, this arginine is not found in endogenous FeLV sequences or in recombinant viruses recovered from feline cells infected with FeLV-A. Thus, while FeLV-Bs that are able to use feline Pit2 can evolve by recombination with endogenous sequences, a subsequent point mutation during reverse transcription may be needed to generate a virus that can efficiently enter the cells using the feline Pit2 as its receptor. These studies suggest that cells expressing the feline Pit2 protein are likely to be targets for FeLV-B infection in the cat.
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Affiliation(s)
- M M Anderson
- Division of Human Biology, Fred Hutchinson Cancer Research Center, University of Washington, Seattle, 98109-1024, USA
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Salaün C, Rodrigues P, Heard JM. Transmembrane topology of PiT-2, a phosphate transporter-retrovirus receptor. J Virol 2001; 75:5584-92. [PMID: 11356966 PMCID: PMC114271 DOI: 10.1128/jvi.75.12.5584-5592.2001] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2000] [Accepted: 03/16/2001] [Indexed: 12/19/2022] Open
Abstract
PiT-1 and PiT-2 are related multiple transmembrane proteins which function as sodium-dependent phosphate transporters and as the cell receptors of several oncoretroviruses. Two copies of a homology domain that is found in distantly related species assign these proteins to a large family of phosphate transporters. A current membrane topology model of PiT-1 and PiT-2 predicts 10 transmembrane domains. However, the validity of this model has not been addressed experimentally. We addressed this issue by a comprehensive study of human PiT-2. Evidence was obtained for glycosylation of asparagine 81. Epitope tagging showed that the N- and C-terminal extremities are extracellular. The orientation of C-terminal-truncation mutants expressed in cell-free translation assays and incorporated into microsomal membranes was examined by immunoprecipitation. Data were interpreted with respect to previous knowledge about retrovirus binding sites, to the existence of repeated homology domains, and to predictions made in family members. A model in which PiT-2 has 12 transmembrane domains and extracellular N- and C-terminal extremities is proposed. This model, which differs significantly from previous predictions about PiT-2 topology, may be useful for further investigations of PiT-2 interactions with other proteins and for the understanding of PiT-2 transporter and virus receptor functions.
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Affiliation(s)
- C Salaün
- Laboratoire Rétrovirus et Transfert Génétique, CNRS URA 1930, Institut Pasteur, 75724 Paris, France
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Phipps AJ, Hayes KA, Al-dubaib M, Roy-Burman P, Mathes LE. Inhibition of feline leukemia virus subgroup A infection by coinoculation with subgroup B. Virology 2000; 277:40-7. [PMID: 11062034 DOI: 10.1006/viro.2000.0606] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Feline leukemia virus (FeLV) subgroup B arises de novo through recombination between the env genes of exogenous FeLV subgroup A and endogenous FeLV-like sequences. FeLV-B, which by itself is poorly infectious, will increase to high titer in the presence of FeLV-A, and is associated with FeLV-related neoplastic disease. Although the participation of FeLV-B in disease progression has not been definitively proven, circumstantial evidence supports the hypothesis that the generation of FeLV-B is linked to disease progression. The present study was designed to evaluate whether increasing the levels of FeLV-B early in FeLV-A infection could result in reduction of the incubation period for development of neoplastic disease. For this study, an isolate of FeLV-B, designated FeLV-1B3, was biologically cloned, partially sequenced, and subgroup typed. In in vivo studies, none of the neonatal cats inoculated with FeLV-1B3 alone converted to viremia positive, and all remained healthy throughout the observation period. All of the kittens inoculated with FeLV-A alone became chronically viremic, and those held for long-term observation all developed either neoplastic disease or anemia. However, kittens inoculated with the combination of FeLV-1B3 and FeLV-A showed attenuated infections whereby the majority of cats failed to develop chronic viremia. The apparent interference of FeLV-A infection by FeLV-B was time and titer dependent. This unexpected result suggests that FeLV-B may act as an attenuated virus, causing inhibition of FeLV-A possibly through an immune-mediated mechanism. Partial support for this view was provided by postmortem examination of cats inoculated with FeLV-1B3 alone. Even though none of these cats became viremic, FeLV antigen was detected as focal infections in select tissues, especially salivary gland epithelium, where enough antigen may be expressed to provide an immunizing dose against gag and pol cross-reacting antigens. This work may also provide another approach to vaccine development based on endogenous retrovirus vector systems.
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MESH Headings
- Amino Acid Sequence
- Animals
- Animals, Newborn
- Antibody Formation
- Antigens, Viral/analysis
- Cats
- Cloning, Molecular
- Disease Progression
- Genes, env
- Leukemia Virus, Feline/classification
- Leukemia Virus, Feline/genetics
- Leukemia Virus, Feline/pathogenicity
- Leukemia, Feline/immunology
- Leukemia, Feline/pathology
- Leukemia, Feline/physiopathology
- Leukemia, Feline/virology
- Molecular Sequence Data
- Polymerase Chain Reaction
- Recombination, Genetic
- Sequence Alignment
- Sequence Homology, Amino Acid
- Terminal Repeat Sequences
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Affiliation(s)
- A J Phipps
- Department of Veterinary Biosciences, The Center for Retrovirus Research, Comprehensive Cancer Center, The Ohio State University, 1925 Coffey Road, Columbus, Ohio, 43210, USA
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Dreyer K, Pedersen FS, Pedersen L. A 13-amino-acid Pit1-specific loop 4 sequence confers feline leukemia virus subgroup B receptor function upon Pit2. J Virol 2000; 74:2926-9. [PMID: 10684313 PMCID: PMC111787 DOI: 10.1128/jvi.74.6.2926-2929.2000] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Feline leukemia virus subgroup B (FeLV-B) and gibbon ape leukemia virus (GALV) utilize the human protein Pit1 but not the related protein, Pit2, as receptor. A stretch of 9 amino acids, named region A, was identified in the putative fourth extracellular loop of Pit1 (residues 550 through 558) as critical for FeLV-B and GALV receptor function. However, the presence of Pit1 region A did not confer receptor function for FeLV-B upon Pit2, while it did so for GALV. We have here shown that the presence of two Pit1-specific loop 4 residues (tyrosine 546 and valine 548) in addition to Pit1 region A is sufficient to make Pit2 an efficient FeLV-B receptor; that is, a stretch of 13 amino acids encompassing all loop 4 amino acid differences between Pit1 and Pit2 comprises a C-terminal determinant for FeLV-B receptor function. Thus, the same limited receptor region is sufficient to confer receptor function for both viruses upon Pit2.
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Affiliation(s)
- K Dreyer
- Department of Molecular and Structural Biology, University of Aarhus, DK-8000 Aarhus C, Denmark
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