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Mo G, Wei P, Hu B, Nie Q, Zhang X. Advances on genetic and genomic studies of ALV resistance. J Anim Sci Biotechnol 2022; 13:123. [PMID: 36217167 PMCID: PMC9550310 DOI: 10.1186/s40104-022-00769-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 08/14/2022] [Indexed: 12/01/2022] Open
Abstract
Avian leukosis (AL) is a general term for a variety of neoplastic diseases in avian caused by avian leukosis virus (ALV). No vaccine or drug is currently available for the disease. Therefore, the disease can result in severe economic losses in poultry flocks. Increasing the resistance of poultry to ALV may be one effective strategy. In this review, we provide an overview of the roles of genes associated with ALV infection in the poultry genome, including endogenous retroviruses, virus receptors, interferon-stimulated genes, and other immune-related genes. Furthermore, some methods and techniques that can improve ALV resistance in poultry are discussed. The objectives are willing to provide some valuable references for disease resistance breeding in poultry.
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Affiliation(s)
- Guodong Mo
- Guangdong Provincial Key Laboratory of Agro-Animal Genomics and Molecular Breeding, College of Animal Science, South China Agricultural University, Guangzhou, 510642, Guangdong, China.,Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou, 510642, Guangdong, China.,State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, 510642, Guangdong, China
| | - Ping Wei
- Institute for Poultry Science and Health, Guangxi University, Nanning, 530001, Guangxi, China
| | - Bowen Hu
- Guangdong Provincial Key Laboratory of Agro-Animal Genomics and Molecular Breeding, College of Animal Science, South China Agricultural University, Guangzhou, 510642, Guangdong, China.,Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou, 510642, Guangdong, China.,State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, 510642, Guangdong, China
| | - Qinghua Nie
- Guangdong Provincial Key Laboratory of Agro-Animal Genomics and Molecular Breeding, College of Animal Science, South China Agricultural University, Guangzhou, 510642, Guangdong, China.,Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou, 510642, Guangdong, China.,State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, 510642, Guangdong, China
| | - Xiquan Zhang
- Guangdong Provincial Key Laboratory of Agro-Animal Genomics and Molecular Breeding, College of Animal Science, South China Agricultural University, Guangzhou, 510642, Guangdong, China. .,Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou, 510642, Guangdong, China. .,State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, 510642, Guangdong, China.
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Li X, Chen W, Zhang H, Li A, Shu D, Li H, Dai Z, Yan Y, Zhang X, Lin W, Ma J, Xie Q. Naturally Occurring Frameshift Mutations in the tvb Receptor Gene Are Responsible for Decreased Susceptibility of Chicken to Infection with Avian Leukosis Virus Subgroups B, D, and E. J Virol 2018; 92:e01770-17. [PMID: 29263268 PMCID: PMC5874434 DOI: 10.1128/jvi.01770-17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 12/13/2017] [Indexed: 12/29/2022] Open
Abstract
The group of highly related avian leukosis viruses (ALVs) in chickens are thought to have evolved from a common retroviral ancestor into six subgroups, A to E and J. These ALV subgroups use diverse cellular proteins encoded by four genetic loci in chickens as receptors to gain entry into host cells. Hosts exposed to ALVs might be under selective pressure to develop resistance to ALV infection. Indeed, resistance alleles have previously been identified in all four receptor loci in chickens. The tvb gene encodes a receptor, which determines the susceptibility of host cells to ALV subgroup B (ALV-B), ALV-D, and ALV-E. Here we describe the identification of two novel alleles of the tvb receptor gene, which possess independent insertions each within exon 4. The insertions resulted in frameshift mutations that reveal a premature stop codon that causes nonsense-mediated decay of the mutant mRNA and the production of truncated Tvb protein. As a result, we observed that the frameshift mutations in the tvb gene significantly lower the binding affinity of the truncated Tvb receptors for the ALV-B, ALV-D, and ALV-E envelope glycoproteins and significantly reduce susceptibility to infection by ALV-B, ALV-D and ALV-E in vitro and in vivo Taken together, these findings suggest that frameshift mutation can be a molecular mechanism of reducing susceptibility to ALV and enhance our understanding of virus-host coevolution.IMPORTANCE Avian leukosis virus (ALV) once caused devastating economic loss to the U.S. poultry industry prior the current eradication schemes in place, and it continues to cause severe calamity to the poultry industry in China and Southeast Asia, where deployment of a complete eradication scheme remains a challenge. The tvb gene encodes the cellular receptor necessary for subgroup B, D, and E ALV infection. Two tvb allelic variants that resulted from frameshift mutations have been identified in this study, which have been shown to have significantly reduced functionality in mediating subgroup B, D, and E ALV infection. Unlike the control of herpesvirus-induced diseases by vaccination, the control of avian leukosis in chickens has relied totally on virus eradication measures and host genetic resistance. This finding enriches the allelic pool of the tvb gene and expands the potential for genetic improvement of ALV resistance in varied chicken populations by selection.
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Affiliation(s)
- Xinjian Li
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
| | - Weiguo Chen
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
- South China Collaborative Innovation Center for Poultry Disease Control and Product Safety, Guangzhou, People's Republic of China
| | - Huanmin Zhang
- USDA, Agriculture Research Service, Avian Disease and Oncology Laboratory, East Lansing, Michigan, USA
| | - Aijun Li
- College of Science and Engineering, Jinan University, Guangzhou, People's Republic of China
| | - Dingming Shu
- Institute of Animal Science, Guangdong Academy of Agriculture Sciences, Guangzhou, People's Republic of China
| | - Hongxing Li
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
| | - Zhenkai Dai
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
| | - Yiming Yan
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
| | - Xinheng Zhang
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
| | - Wencheng Lin
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
- South China Collaborative Innovation Center for Poultry Disease Control and Product Safety, Guangzhou, People's Republic of China
| | - Jingyun Ma
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
- South China Collaborative Innovation Center for Poultry Disease Control and Product Safety, Guangzhou, People's Republic of China
| | - Qingmei Xie
- College of Animal Science, South China Agricultural University and Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou, People's Republic of China
- Key Laboratory of Animal Health Aquaculture and Environmental Control, Guangdong, Guangzhou, People's Republic of China
- South China Collaborative Innovation Center for Poultry Disease Control and Product Safety, Guangzhou, People's Republic of China
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Lee HJ, Lee KY, Jung KM, Park KJ, Lee KO, Suh JY, Yao Y, Nair V, Han JY. Precise gene editing of chicken Na+/H+ exchange type 1 (chNHE1) confers resistance to avian leukosis virus subgroup J (ALV-J). DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2017; 77:340-349. [PMID: 28899753 DOI: 10.1016/j.dci.2017.09.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Revised: 09/08/2017] [Accepted: 09/08/2017] [Indexed: 06/07/2023]
Abstract
Avian leukosis virus subgroup J (ALV-J), first isolated in the late 1980s, has caused economic losses to the poultry industry in many countries. As all chicken lines studied to date are susceptible to ALV infection, there is enormous interest in developing resistant chicken lines. The ALV-J receptor, chicken Na+/H+ exchange 1 (chNHE1) and the critical amino acid sequences involved in viral attachment and entry have already been characterized. However, there are no reported attempts to induce resistance to the virus by targeted genome modification of the receptor sequences. In an attempt to induce resistance to ALV-J infection, we used clustered regularly interspaced short palindromic repeats (CRISPR)-associated (CRISPR/Cas9)-based genome editing approaches to modify critical residues of the chNHE1 receptor in chicken cells. The susceptibility of the modified cell lines to ALV-J infection was examined using enhanced green fluorescent protein (EGFP)-expressing marker viruses. We showed that modifying the chNHE1 receptor by artificially generating a premature stop codon induced absolute resistance to viral infection, with mutations of the tryptophan residue at position 38 (Trp38) being very critical. Single-stranded oligodeoxynucleotide (ssODN)-mediated targeted recombination of the Trp38 region revealed that deletions involving the Trp38 residue were most effective in conferring resistance to ALV-J. Moreover, protein structure analysis of the chNHE1 receptor sequence suggested that its intrinsically disordered region undergoes local conformational changes through genetic alteration. Collectively, these results demonstrate that targeted mutations on chNHE1 alter the susceptibility to ALV-J and the technique is expected to contribute to develop disease-resistant chicken lines.
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Affiliation(s)
- Hong Jo Lee
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea.
| | - Kyung Youn Lee
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea.
| | - Kyung Min Jung
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea.
| | - Kyung Je Park
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea.
| | - Ko On Lee
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea.
| | - Jeong-Yong Suh
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea; Institute for Biomedical Sciences, Shinshu University, Nagano, Japan.
| | - Yongxiu Yao
- The Pirbright Institute, Woking, Surrey GU24 0NF, United Kingdom.
| | - Venugopal Nair
- The Pirbright Institute, Woking, Surrey GU24 0NF, United Kingdom.
| | - Jae Yong Han
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, South Korea; Institute for Biomedical Sciences, Shinshu University, Nagano, Japan.
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Kucerová D, Plachy J, Reinisová M, Senigl F, Trejbalová K, Geryk J, Hejnar J. Nonconserved tryptophan 38 of the cell surface receptor for subgroup J avian leukosis virus discriminates sensitive from resistant avian species. J Virol 2013; 87:8399-407. [PMID: 23698309 PMCID: PMC3719790 DOI: 10.1128/jvi.03180-12] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 05/14/2013] [Indexed: 11/20/2022] Open
Abstract
Subgroup J avian leukosis virus (ALV-J) is unique among the avian sarcoma and leukosis viruses in using the multimembrane-spanning cell surface protein Na(+)/H(+) exchanger type 1 (NHE1) as a receptor. The precise localization of amino acids critical for NHE1 receptor activity is key in understanding the virus-receptor interaction and potential interference with virus entry. Because no resistant chicken lines have been described until now, we compared the NHE1 amino acid sequences from permissive and resistant galliform species. In all resistant species, the deletion or substitution of W38 within the first extracellular loop was observed either alone or in the presence of other incidental amino acid changes. Using the ectopic expression of wild-type or mutated chicken NHE1 in resistant cells and infection with a reporter recombinant retrovirus of subgroup J specificity, we studied the effect of individual mutations on the NHE1 receptor capacity. We suggest that the absence of W38 abrogates binding of the subgroup J envelope glycoprotein to ALV-J-resistant cells. Altogether, we describe the functional importance of W38 for virus entry and conclude that natural polymorphisms in NHE1 can be a source of host resistance to ALV-J.
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Affiliation(s)
- Dana Kucerová
- Department of Cellular and Viral Genetics, Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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5
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Farrell KB, Tusnady GE, Eiden MV. New structural arrangement of the extracellular regions of the phosphate transporter SLC20A1, the receptor for gibbon ape leukemia virus. J Biol Chem 2009; 284:29979-87. [PMID: 19717569 DOI: 10.1074/jbc.m109.022566] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Infection of a host cell by a retrovirus requires an initial interaction with a cellular receptor. For numerous gammaretroviruses, such as the gibbon ape leukemia virus, woolly monkey virus, feline leukemia virus subgroup B, feline leukemia virus subgroup T, and 10A1 murine leukemia virus, this receptor is the human type III sodium-dependent inorganic phosphate transporter, SLC20A1, formerly known as PiT1. Understanding the critical receptor functionalities and interactions with the virus that lead to successful infection requires that we first know the surface structure of the cellular receptor. Previous molecular modeling from the protein sequence, and limited empirical data, predicted a protein with 10 transmembrane helices. Here we undertake the biochemical approach of substituted cysteine accessibility mutagenesis to resolve the topology of this receptor in live cells. We discover that there are segments of the protein that are unexpectedly exposed to the outside milieu. By using information determined by substituted cysteine accessibility mutagenesis to set constraints in HMMTOP, a hidden Markov model-based transmembrane topology prediction method, we now propose a comprehensive topological model for SLC20A1, a transmembrane protein with 12 transmembrane helices and 7 extracellular regions, that varies from previous models and should permit approaches that define both virus interaction and transport function.
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Affiliation(s)
- Karen B Farrell
- Section on Molecular Virology, Laboratory of Cellular and Molecular Regulation, National Institute of Mental Health, Bethesda, Maryland 20892, USA
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Efficient subgroup C avian sarcoma and leukosis virus receptor activity requires the IgV domain of the Tvc receptor and proper display on the cell membrane. J Virol 2008; 82:11419-28. [PMID: 18768966 DOI: 10.1128/jvi.01408-08] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
We recently identified and cloned the receptor for subgroup C avian sarcoma and leukosis viruses [ASLV(C)], i.e., Tvc, a protein most closely related to mammalian butyrophilins, which are members of the immunoglobulin protein family. The extracellular domain of Tvc contains two immunoglobulin-like domains, IgV and IgC, which presumably each contain a disulfide bond important for native function of the protein. In this study, we have begun to identify the functional determinants of Tvc responsible for ASLV(C) receptor activity. We found that the IgV domain of the Tvc receptor is responsible for interacting with the glycoprotein of ASLV(C). Additional experiments demonstrated that a domain was necessary as a spacer between the IgV domain and the membrane-spanning domain for efficient Tvc receptor activity, most likely to orient the IgV domain a proper distance from the cell membrane. The effects on ASLV(C) glycoprotein binding and infection efficiency were also studied by site-directed mutagenesis of the cysteine residues of Tvc as well as conserved amino acid residues of the IgV Tvc domain compared to other IgV domains. In this initial analysis of Tvc determinants important for interacting with ASLV(C) glycoproteins, at least two aromatic amino acid residues in the IgV domain of Tvc, Trp-48 and Tyr-105, were identified as critical for efficient ASLV(C) infection. Interestingly, one or more aromatic amino acid residues have been identified as critical determinants in the other ASLV(A-E) receptors for a proper interaction with ASLV glycoproteins. This suggests that the ASLV glycoproteins may share a common mechanism of receptor interaction with an aromatic residue(s) on the receptor critical for triggering conformational changes in SU that initiate the fusion process required for efficient virus infection.
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Lucas ML, Seidel NE, Porada CD, Quigley JG, Anderson SM, Malech HL, Abkowitz JL, Zanjani ED, Bodine DM. Improved transduction of human sheep repopulating cells by retrovirus vectors pseudotyped with feline leukemia virus type C or RD114 envelopes. Blood 2005; 106:51-8. [PMID: 15774617 PMCID: PMC1895126 DOI: 10.1182/blood-2004-11-4491] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Gene therapy for hematopoietic diseases has been hampered by the low frequency of transduction of human hematopoietic stem cells (HSCs) with retroviral vectors pseudotyped with amphotropic envelopes. We hypothesized that transduction could be increased by the use of retroviral vectors pseudotyped with envelopes that recognize more abundant cellular receptors. The levels of mRNA encoding the receptors of the feline retroviruses, RD114 and feline leukemia virus type C (FeLV-C), were significantly higher than the level of gibbon ape leukemia virus (GaLV) receptor mRNA in cells enriched for human HSCs (Lin- CD34+ CD38-). We cotransduced human peripheral blood CD34+ cells with equivalent numbers of FeLV-C and GALV or RD114 and GALV-pseudotyped retroviruses for injection into fetal sheep. Analysis of DNA from peripheral blood and bone marrow from recipient sheep demonstrated that FeLV-C- or RD114-pseudotyped vectors were present at significantly higher levels than GALV-pseudotyped vectors. Analysis of individual myeloid colonies demonstrated that retrovirus vectors with FeLV-C and RD114 pseudotypes were present at 1.5 to 1.6 copies per cell and were preferentially integrated near known genes We conclude that the more efficient transduction of human HSCs with either FeLV-C- or RD114-pseudotyped retroviral particles may improve gene transfer in human clinical trials.
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Affiliation(s)
- M Lee Lucas
- Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
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An W, Telesnitsky A. Human immunodeficiency virus type 1 transductive recombination can occur frequently and in proportion to polyadenylation signal readthrough. J Virol 2004; 78:3419-28. [PMID: 15016864 PMCID: PMC371070 DOI: 10.1128/jvi.78.7.3419-3428.2004] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
One model for retroviral transduction suggests that template switching between viral RNAs and polyadenylation readthrough sequences is responsible for the generation of acute transforming retroviruses. For this study, we examined reverse transcription products of human immunodeficiency virus (HIV)-based vectors designed to mimic postulated transduction intermediates. For maximization of the discontinuous mode of DNA synthesis proposed to generate transductants, sequences located between the vectors' two long terminal repeats (vector "body" sequences) and polyadenylation readthrough "tail" sequences were made highly homologous. Ten genetic markers were introduced to indicate which products had acquired tail sequences by a process we term transductive recombination. Marker segregation patterns for over 100 individual products were determined, and they revealed that more than half of the progeny proviruses were transductive recombinants. Although most crossovers occurred in regions of homology, about 5% were nonhomologous and some included insertions. Ratios of encapsidated readthrough and polyadenylated transcripts for vectors with wild-type and inactivated polyadenylation signals were compared, and transductive recombination frequencies were found to correlate with the readthrough transcript prevalence. In assays in which either vector body or tail could serve as a recombination donor, recombination between tail and body sequences was at least as frequent as body-body exchange. We propose that transductive recombination may contribute to natural HIV variation by providing a mechanism for the acquisition of nongenomic sequences.
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Affiliation(s)
- Wenfeng An
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA
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Klucking S, Young JAT. Amino acid residues Tyr-67, Asn-72, and Asp-73 of the TVB receptor are important for subgroup E avian sarcoma and leukosis virus interaction. Virology 2004; 318:371-80. [PMID: 14972562 DOI: 10.1016/j.virol.2003.09.024] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2003] [Accepted: 09/17/2003] [Indexed: 11/17/2022]
Abstract
The chicken TVB(S1) protein serves as the cellular receptor for the cytopathic subgroups B and D avian sarcoma and leukosis viruses (ASLVs) as well as for the non-cytopathic subgroup E ASLV. Previous studies had mapped the subgroup B viral interaction determinants to a region that was located between residues 32 and 46 of TVB(S1) [J. Virol. 76 (2002) 5404]. To gain a greater insight into ASLV Env-receptor interactions and the possible role of these interactions in viral cytopathic effects, we employed a homolog-scanning mutagenesis approach to identify amino acid residues important for subgroup E viral receptor function by exchanging amino acid residues between TVB(S1) and its human homolog, DR5. These studies identified residues Tyr-67, Asn-72, and Asp-73 of TVB(S1) as important subgroup E viral interaction determinants. Intriguingly, these three residues are conserved between TVB(S1) and DR5, demonstrating that the human protein contains critical subgroup E viral interaction determinants, but in this context, they cannot support viral entry. These data confirm that the molecular determinants of the TVB receptor required for subgroup E viral entry are completely distinct from those used by subgroup B viruses.
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Affiliation(s)
- Sara Klucking
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA
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Zavorotinskaya T, Qian Z, Franks J, Albritton LM. A point mutation in the binding subunit of a retroviral envelope protein arrests virus entry at hemifusion. J Virol 2004; 78:473-81. [PMID: 14671127 PMCID: PMC303374 DOI: 10.1128/jvi.78.1.473-481.2004] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The transmembrane subunits of viral envelope proteins are thought to perform all of the functions required for membrane fusion during entry of enveloped viruses. However, changes in a conserved SPHQ motif near the N terminus of the receptor binding subunit of a murine leukemia virus (MLV) envelope protein block infection and induction of cell-cell fusion but not receptor binding. Here we report evidence that a histidine-to-arginine change at position 8 (H8R) in the SPHQ motif of Moloney MLV blocks infection by arresting virus-cell fusion at the hemifusion state. In cell-cell fusion assays, H8R envelope protein induced mixing of membrane outer leaflet lipids but did not lead to content mixing, a finding indicative of fusion pore formation. Kinetic studies of virus-cell fusion showed that lipid mixing of H8R virus membranes begins much later than for wild-type virus. The length of the delay in lipid mixing decreased upon addition of two second-site changes that increase H8R virus infection to 100-fold less than the wild-type virus. Finally, chlorpromazine, dibucaine, and trifluoperazine, agents that induce pores in an arrested hemifusion state, rescued infection by H8R virus to within 2.5-fold of the level of wild-type virus infection and cell-cell fusion to half that mediated by wild-type envelope protein. We interpret these results to indicate that fusion progressed to the hemifusion intermediate but fusion pore formation was inhibited. These results establish that membrane fusion of Moloney MLV occurs via a hemifusion intermediate. We also interpret these findings as evidence that histidine 8 is a key switch-point residue between the receptor-induced conformation changes that expose fusion peptide and those that lead to six-helix bundle formation.
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Affiliation(s)
- Tatiana Zavorotinskaya
- Department of Molecular Sciences, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - Zhaohui Qian
- Department of Molecular Sciences, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - John Franks
- Department of Molecular Sciences, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - Lorraine M. Albritton
- Department of Molecular Sciences, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
- Corresponding author. Mailing address: Department of Molecular Sciences, University of Tennessee Health Sciences Center, 858 Madison Ave., Memphis, TN 38163. Phone: (901) 448-5521. Fax: (901) 448-7360. E-mail:
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Abstract
Infection by all enveloped viruses occurs via the fusion of viral and cellular membranes and delivery of the viral nucleocapsid into the cell cytoplasm, after association of the virus with cognate receptors at the cell surface. This process is mediated by viral fusion proteins anchored in the viral envelope and can be defined based on the requirement for low pH to trigger membrane fusion. In viruses that utilize a pH-dependent entry mechanism, such as influenza virus, viral fusion is triggered by the acidic environment of intracellular organelles after uptake of the virus from the cell surface and trafficking to a low-pH compartment. In contrast, in viruses that utilize a pH-independent entry mechanism, such as most retroviruses, membrane fusion is triggered solely by the interaction of the envelope glycoprotein with cognate receptors, often at the cell surface. However, recent work has indicated that the alpharetrovirus, avian sarcoma and leukosis virus (ASLV), utilizes a novel entry mechanism that combines aspects of both pH-independent and pH-dependent entry. In ASLV infection, the interaction of the envelope glycoprotein (Env) with cognate receptors at the cell surface causes an initial conformational change that primes (activates) Env and renders it sensitive to subsequent low-pH triggering from an intracellular compartment. Thus unlike other pH-dependent viruses, ASLV Env is only sensitive to low-pH triggering following interaction with its cognate receptor. In this manuscript we review current research on ASLV Env-receptor interactions and focus on the specific molecular requirements of both the viral fusion protein and cognate receptors for ASLV entry. In addition, we review data pertaining to the novel two-step entry mechanism of ASLV entry and propose a model by which ASLV Env elicits membrane fusion.
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Affiliation(s)
- R J O Barnard
- McArdle Laboratories for Cancer Research, Department of Oncology, University of Wisconsin Madison, 1400 University Ave, Madison, WI 53706, USA
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12
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Qian Z, Donald R, Wang H, Chen Q, Albritton LM. Identification of a critical basic residue on the ecotropic murine leukemia virus receptor. J Virol 2003; 77:8596-601. [PMID: 12857932 PMCID: PMC165247 DOI: 10.1128/jvi.77.15.8596-8601.2003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Susceptibility to ecotropic murine leukemia viruses (MLV) is restricted to mice and rats at the level of virus binding to the host cell receptor. Asparagine 232, valine 233, tyrosine 235, and glutamic acid 237 in the third extracellular domain (EL3) of the receptor are critical determinants of the host range difference between mice and humans. However, placing these residues in the human homolog confers only partial binding, indicating that other divergent sequences are involved. We sought to determine if the other sequences lie within or outside EL3. Here we report the identification of lysine 234 as another critical residue that influences virus binding and infection, as well as evidence that the unidentified sequences lie outside EL3. Each of the four basic residues in the third extracellular domain were changed to an acidic residue and initially examined in combination with a change at position 235 or position 237. Substitution of lysine 211, 215, or 222 combined with substitution of the critical tyrosine 235 or glutamic acid 237 did not affect virus infection. However, combined substitution of lysine 234, a conserved residue between mice and humans, and tyrosine 235 resulted in a marked decrease in virus infection and binding. A lysine 234 change alone reduced virus binding, contrary to previous observations that at least two of the other four residues must be changed before binding is reduced. Interestingly, there was no decrease in infection when lysine 234 was replaced in combination with glutamic acid 237. This result suggests that residue 234 may act by influencing the local structure of residues 233 to 235, whereas the presence of a glycine at position 236 may prevent this influence from extending to residue 237. With this report, the involvement of all the residues divergent between mice and humans in the third extracellular domain has been ruled out, suggesting that as yet unidentified determinants lie in other extracellular domains.
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Affiliation(s)
- Zhaohui Qian
- Department of Molecular Sciences, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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13
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Onafuwa A, An W, Robson ND, Telesnitsky A. Human immunodeficiency virus type 1 genetic recombination is more frequent than that of Moloney murine leukemia virus despite similar template switching rates. J Virol 2003; 77:4577-87. [PMID: 12663764 PMCID: PMC152108 DOI: 10.1128/jvi.77.8.4577-4587.2003] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Retroviral recombinants result from template switching between copackaged viral genomes. Here, marker reassortment between coexpressed vectors was measured during single replication cycles, and human immunodeficiency virus type 1 (HIV-1) recombination was observed six- to sevenfold more frequently than murine leukemia virus (MLV) recombination. Template switching was also assayed by using transduction-type vectors in which donor and acceptor template regions were joined covalently. In this situation, where RNA copackaging could not vary, MLV and HIV-1 template switching rates were indistinguishable. These findings argue that MLV's lower intermolecular recombination frequency does not reflect enzymological differences. Instead, these data suggest that recombination rates differ because coexpressed MLV RNAs are less accessible to the recombination machinery than are coexpressed HIV RNAs. This hypothesis provides a plausible explanation for why most gammaretrovirus recombinants, although relatively rare, display evidence of multiple nonselected crossovers. By implying that recombinogenic template switching occurs roughly four times on average during the synthesis of every MLV or HIV-1 DNA, these results suggest that virtually all products of retroviral replication are biochemical recombinants.
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Affiliation(s)
- Adewunmi Onafuwa
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA
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14
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Kizhatil K, Albritton LM. System y+ localizes to different membrane subdomains in the basolateral plasma membrane of epithelial cells. Am J Physiol Cell Physiol 2002; 283:C1784-94. [PMID: 12388095 DOI: 10.1152/ajpcell.00061.2002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We report here that the system y+ cationic amino acid transporter ATRC1 localized to clusters within the basolateral membrane of polarized Madin-Darby canine kidney and human embryonic kidney (HEK) cells, suggesting that the transporters are restricted to discrete membrane microdomains in epithelial cells. Based on solubility in nonionic detergents, two populations of ATRC1 molecules existed: approximately half of the total ATRC1 in HEK cells associated with the actin membrane cytoskeleton, whereas another one-fourth resided in detergent-resistant membranes (DRM). In agreement with these findings, cytochalasin D reduced the amount of ATRC1 associated with the actin membrane cytoskeleton. Although some ATRC1 clusters in HEK cells colocalized with caveolin, the majority of ATRC1 did not colocalize with this marker protein for a type of DRM called caveolae. This distribution of ATRC1 is somewhat different from that reported for pulmonary artery endothelial cells in which transporters cluster predominantly in caveolae, suggesting that differences in the proportion of ATRC1 in specific membrane microdomains correlate with differences in the physiological role of the transporter in polarized kidney epithelial vs. vascular endothelial cells.
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Affiliation(s)
- Krishnakumar Kizhatil
- Department of Molecular Sciences, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163, USA
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15
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An W, Telesnitsky A. Effects of varying sequence similarity on the frequency of repeat deletion during reverse transcription of a human immunodeficiency virus type 1 vector. J Virol 2002; 76:7897-902. [PMID: 12097604 PMCID: PMC136404 DOI: 10.1128/jvi.76.15.7897-7902.2002] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Genetic recombination contributes to human immunodeficiency virus type 1 (HIV-1) diversity, with homologous recombination being more frequent than nonhomologous recombination. In this study, HIV-1-based vectors were used to assay the effects of various extents of sequence divergence on the frequency of the recombination-related property of repeat deletion. Sequence variation, similar in degree to that which differentiates natural HIV-1 isolates, was introduced by synonymous substitutions into a gene segment. Repeated copies of this segment were then introduced into assay vectors. With the use of a phenotypic screen, the deletion frequency of identical repeats was compared to the frequencies of repeats that differed in sequence by various extents. During HIV-1 reverse transcription, the deletion frequency observed with repeats that differed by 5% was 65% of that observed with identical repeats. The deletion frequency decreased to 26% for repeats that differed by 9%, and when repeats differed by 18%, the deletion frequency was about 5% of the identical repeat value. Deletion frequencies fell to less than 0.3% of identical repeat values when genetic distances of 27% or more were examined. These data argue that genetic variation is not as inhibitory to HIV-1 repeat deletion as it is to the corresponding cellular process and suggest that, for sequences that differ by about 25% or more, HIV-1 recombination directed by sequence homology may be no more frequent than that which is homology independent.
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Affiliation(s)
- Wenfeng An
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA
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16
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Knauss DJ, Young JAT. A fifteen-amino-acid TVB peptide serves as a minimal soluble receptor for subgroup B avian leukosis and sarcoma viruses. J Virol 2002; 76:5404-10. [PMID: 11991969 PMCID: PMC137033 DOI: 10.1128/jvi.76.11.5404-5410.2002] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2001] [Accepted: 02/20/2002] [Indexed: 11/20/2022] Open
Abstract
The TVB receptor for subgroup B, D, and E avian sarcoma and leukosis viruses (ASLVs) is a tumor necrosis factor receptor-related protein that is most closely related to the TRAIL receptors. Here we show that the major subgroup B viral interaction determinants of TVB are contained within a linear 15-amino-acid peptide derived from the N-terminal region of the receptor. Moreover, this peptide was sufficient not only for binding to ASLV-B but also for activating viral entry into mammalian cells that lacked the cognate viral receptor. Peptide-dependent viral entry was blocked in the presence of bafilomycin A1, indicating that virions can be trafficked to an acidic endosomal fusion compartment without the need for physical attachment of the viral receptor to a cellular membrane.
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Affiliation(s)
- Daniel J Knauss
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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17
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Kizhatil K, Gromley A, Albritton LM. Two point mutations produce infectious retrovirus bearing a green fluorescent protein-SU fusion protein. J Virol 2001; 75:11881-5. [PMID: 11689670 PMCID: PMC114775 DOI: 10.1128/jvi.75.23.11881-11885.2001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Two second-site mutations in Moloney murine leukemia virus envelope surface protein (SU) were previously shown to rescue infection of two different SU mutants, a fusion-defective point mutant and a fusion-defective modified SU that exhibits weak subunit association. We report here that they also rescue infection of a third defective SU, one modified by insertion of the green fluorescent protein (GFP) between serine 6 and proline 7. GFP-SU assembled into virions and showed a strong association with the transmembrane protein (TM). However, these virions were noninfectious. GFP-SU expression was not maintained within cells, suggesting that the protein was toxic. Addition of the second-site mutations rendered the GFP-SU virus infectious and resulted in prolonged expression of the modified envelope protein. This virus showed a slight reduction in receptor binding but not in envelope protein processing, suggesting that addition of the GFP sequences results in subtle structural changes. Extrapolating these data, we see that the fundamental problem with the GFP-SU envelope protein appears to be a folding problem, suggesting that the second-site mutations rescue GFP-SU primarily by a mechanism that involves stabilizing the envelope protein structure.
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Affiliation(s)
- K Kizhatil
- Department of Molecular Sciences, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163, USA
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18
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An W, Telesnitsky A. Frequency of direct repeat deletion in a human immunodeficiency virus type 1 vector during reverse transcription in human cells. Virology 2001; 286:475-82. [PMID: 11485415 DOI: 10.1006/viro.2001.1025] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Retroviral genetic rearrangements can result from reverse transcriptase template switching. Most published data suggest that errors such as base misincorporation occur at similar frequencies for HIV-1 and for simple retroviruses such as spleen necrosis virus (SNV) and murine leukemia virus (MuLV). However, previous reports have suggested that template switch-mediated recombination is much more frequent for HIV-1 than for simple retroviruses. In this report, direct repeat deletion vectors similar to those previously used for measuring template switching events for SNV and MuLV were developed for HIV-1. Forward mutation rates and the frequency of template switching during a single cycle of HIV-1 replication were determined. The frequency of HIV-1-mediated repeat deletion was measured for three separate internal repeats in lacZ and was compared to rates observed with identical repeats for MuLV. The results indicated that the error rate and the frequency of repeat deletion of HIV-1 were similar to those of MuLV.
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Affiliation(s)
- W An
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA
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19
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Zavorotinskaya T, Albritton LM. Two point mutations increase targeted transduction and stabilize vector association of a modified retroviral envelope protein. Mol Ther 2001; 3:323-8. [PMID: 11273774 DOI: 10.1006/mthe.2001.0262] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The current strategy of targeting retroviral vector transduction by inserting a peptide ligand into the envelope protein has met with several obstacles. These modified proteins redirected vector binding to a new cognate receptor on a specific cell type but gave little or no gene transfer because they did not fuse the vector and target cell membranes. They dissociated readily from vectors and often required coassembly of wild-type envelope protein. Here we report a novel strategy to overcome the fusion and stability defects of modified retroviral envelope proteins. We inserted a prototypic ligand, the receptor binding domain of amphotropic murine leukemia virus, into an ecotropic murine leukemia virus envelope protein mutant containing glutamine 227-to-arginine plus aspartate 243-to-tyrosine substitutions. This modified protein increased transduction redirected to human cells expressing the amphotropic receptor to a level within 10-fold that of wild-type amphotropic virus, an increase of as great as 2000-fold over transduction by modified protein lacking the mutations. In addition to suppressing the fusion defect, these mutations unexpectedly stabilized the association of the modified protein with vector particles. Insertion of clinically relevant ligands into this envelope mutant should improve the efficiency and reliability of retroviral transduction of specific cell types for gene therapy applications.
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Affiliation(s)
- T Zavorotinskaya
- Department of Microbiology & Immunology, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163, USA
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20
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Zavorotinskaya T, Albritton LM. A hydrophobic patch in ecotropic murine leukemia virus envelope protein is the putative binding site for a critical tyrosine residue on the cellular receptor. J Virol 1999; 73:10164-72. [PMID: 10559332 PMCID: PMC113069 DOI: 10.1128/jvi.73.12.10164-10172.1999] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the receptor for ecotropic murine leukemia viruses, tyrosine 235 contributes a critical hydrophobic side chain to the virus-receptor interaction (14). Here we report that tryptophan 142 in ecotropic Moloney murine leukemia virus envelope protein is essential to virus binding and infection. Replacement of tryptophan 142 by alanine or serine resulted in misfolding. However, replacement by methionine (W142M) allowed correct folding of the majority of glycoprotein molecules. W142M virus showed a marked reduction in virus binding and was almost noninfectious, suggesting that tryptophan 142 is involved in receptor binding. In contrast, W142Y virus containing a replacement of tryptophan 142 with an aromatic residue (tyrosine) was as efficient as wild-type virus in infection and binding of cells expressing the wild-type receptor. However, W142Y virus was 100-fold less efficient than wild-type virus in infection of cells expressing a mutant receptor containing tryptophan instead of the critical tyrosine. These results strongly support tryptophan 142 being an essential residue on the virus envelope protein that interacts directly with the critical hydrophobic residue at position 235 of the ecotropic receptor. Tryptophan 142 forms one side of a shallow hydrophobic pocket on the surface of the envelope protein, suggesting that it might comprise the complete putative binding site for tyrosine 235. We discuss the implications of our findings with respect to two models of the envelope protein trimer. Interestingly, both models place tryptophan 142 at the interface between adjacent subunits of the trimer.
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MESH Headings
- 3T3 Cells
- Alanine/genetics
- Alanine/physiology
- Amino Acid Sequence
- Animals
- Binding Sites
- Cell Line, Transformed
- Friend murine leukemia virus/genetics
- Friend murine leukemia virus/metabolism
- Glycoproteins/biosynthesis
- Glycoproteins/genetics
- Glycoproteins/metabolism
- Glycoproteins/physiology
- Humans
- Membrane Glycoproteins/genetics
- Membrane Glycoproteins/metabolism
- Methionine/genetics
- Mice
- Models, Molecular
- Molecular Sequence Data
- Moloney murine leukemia virus/genetics
- Moloney murine leukemia virus/metabolism
- Mutagenesis, Site-Directed
- Phenylalanine/genetics
- Protein Conformation
- Protein Processing, Post-Translational
- Receptors, Virus/genetics
- Receptors, Virus/metabolism
- Retroviridae Proteins, Oncogenic/biosynthesis
- Retroviridae Proteins, Oncogenic/genetics
- Retroviridae Proteins, Oncogenic/metabolism
- Retroviridae Proteins, Oncogenic/physiology
- Sequence Homology, Amino Acid
- Tryptophan/genetics
- Tryptophan/metabolism
- Tryptophan/physiology
- Tyrosine/genetics
- Tyrosine/metabolism
- Viral Envelope Proteins/biosynthesis
- Viral Envelope Proteins/genetics
- Viral Envelope Proteins/metabolism
- Viral Envelope Proteins/physiology
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Affiliation(s)
- T Zavorotinskaya
- Department of Microbiology, University of Tennessee-Memphis, Memphis, Tennessee 38163, USA
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21
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Chung M, Kizhatil K, Albritton LM, Gaulton GN. Induction of syncytia by neuropathogenic murine leukemia viruses depends on receptor density, host cell determinants, and the intrinsic fusion potential of envelope protein. J Virol 1999; 73:9377-85. [PMID: 10516046 PMCID: PMC112972 DOI: 10.1128/jvi.73.11.9377-9385.1999] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Infection by the neuropathogenic murine leukemia virus (MLV) TR1.3 results in hemorrhagic disease that correlates directly to in vivo syncytium formation of brain capillary endothelial cells (BCEC). This phenotype maps to amino acid 102 in the envelope (Env) protein of TR1.3. Substitution of glycine (G) for tryptophan (W) at this position (W102G Env) in the nonpathogenic MLV FB29 induces both syncytium formation and neurologic disease in vivo. Using an in vitro gene reporter cell fusion assay, we showed that fusion either with murine NIH 3T3 cells or with nonmurine target cells that expressed receptors at or below endogenous murine levels mirrored that seen in BCEC in vivo. In these instances only TR1.3 and W102G Env induced cell fusion. In contrast, when receptor levels on nonmurine cells were raised above endogenous murine levels, FB29 Env was as fusogenic as the neuropathogenic TR1.3 and W102G Env. These results indicate that TR1.3 Env and W102G Env are intrinsically more fusogenic than FB29 Env, that the induction of fusion requires a threshold number of receptors that is greater for FB29 Env than for TR1.3 or W102G Env, and that receptor density on murine NIH 3T3 cells and BCEC is below the threshold for FB29-dependent fusion. Surprisingly, receptor density on NIH 3T3 cells could not be increased by stable expression of exogenous receptors, and FB29-dependent fusion was not observed in NIH 3T3 cells that transiently expressed elevated receptor numbers. These results suggest that an additional undefined host cell factor(s) may limit both receptor expression and fusion potential in murine cells.
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Affiliation(s)
- M Chung
- Department of Pathology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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22
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Masuda M, Kakushima N, Wilt SG, Ruscetti SK, Hoffman PM, Iwamoto A. Analysis of receptor usage by ecotropic murine retroviruses, using green fluorescent protein-tagged cationic amino acid transporters. J Virol 1999; 73:8623-9. [PMID: 10482615 PMCID: PMC112882 DOI: 10.1128/jvi.73.10.8623-8629.1999] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Entry of ecotropic murine leukemia virus (MuLV) into host cells is initiated by interaction between the receptor-binding domain of the viral SU protein and the third extracellular domain (TED) of the receptor, cationic amino acid transporter 1 (CAT1). To study the molecular basis for the retrovirus-receptor interaction, mouse CAT1 (mCAT1) was expressed in human 293 cells as a fusion protein with jellyfish green fluorescent protein (GFP). Easily detected by fluorescence microscopy and immunoblot analysis with anti-GFP antibodies, the mCAT1-GFP fusion protein was expressed in an N-glycosylated form on the cell surface and in the Golgi apparatus, retaining the ecotropic receptor function. The system was applied to compare Friend MuLV (F-MuLV) and its neuropathogenic variant, PVC-211 MuLV, which exhibits a unique cellular tropism and host range, for the ability to use various CAT family members as a receptor. The results indicated that F-MuLV and PVC-211 MuLV could infect the cells expressing wild-type mCAT1 at comparable efficiencies and that rat CAT3, but not mCAT2, conferred a low but detectable level of susceptibility to F-MuLV and PVC-211 MuLV. The data also suggested that CAT proteins might be expressed in an oligomeric form. Further application of the system developed in this study may provide useful insights into the entry mechanism of ecotropic MuLV.
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Affiliation(s)
- M Masuda
- Department of Microbiology, Graduate School of Medicine, University of Tokyo, Tokyo 113-0033, Japan.
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23
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Zavorotinskaya T, Albritton LM. Failure To cleave murine leukemia virus envelope protein does not preclude its incorporation in virions and productive virus-receptor interaction. J Virol 1999; 73:5621-9. [PMID: 10364311 PMCID: PMC112620 DOI: 10.1128/jvi.73.7.5621-5629.1999] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
It is thought that complete cleavage of retroviral envelope protein into mature surface protein (SU) and transmembrane protein (TM) is critical for its assembly into virions and the formation of infectious virus particles. Here we report the identification of highly infectious, cleavage-deficient envelope mutant proteins. Substitution of aspartate for lysine 104, arginines 124 and 126, or arginines 223 and 225 strongly suppressed cleavage of the envelope precursor and yet allowed efficient incorporation of precursor molecules as the predominant species in virions that were almost as infectious as the wild-type virus. These results indicate that cleavage of the envelope precursor into mature SU and TM is not necessary for assembly into virions. Moreover, they call into question how many mature envelope protein subunits are required to complete virus entry, suggesting that a very few molecules suffice. The failure of host cell proteases to cleave these mutant proteins, whose substitutions are distal to the actual site of cleavage, suggests that the envelope precursor is misfolded, sequestering the cleavage site. In agreement with this, all cleavage mutant proteins exhibited significant losses of receptor binding, suggesting that these residues play roles in proper envelope protein folding. We also identified a charged residue, arginine 102, whose substitution suppressed envelope cleavage and allowed precursor incorporation but resulted in virions that were virtually noninfectious and that exhibited the greatest reduction in receptor binding. Placement of these cleavage mutations into envelope proteins of targeted retroviral vectors for human gene therapy may prevent loss of the modified surface proteins from virions, improving their infectivity and storage hardiness.
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Affiliation(s)
- T Zavorotinskaya
- Department of Microbiology and Immunology, University of Tennessee, Memphis, Tennessee, USA
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24
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Zavorotinskaya T, Albritton LM. Suppression of a fusion defect by second site mutations in the ecotropic murine leukemia virus surface protein. J Virol 1999; 73:5034-42. [PMID: 10233966 PMCID: PMC112548 DOI: 10.1128/jvi.73.6.5034-5042.1999] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Entry of ecotropic murine leukemia virus initiates when the envelope surface protein recognizes and binds to the virus receptor on host cells. The envelope transmembrane protein then mediates fusion of viral and host cell membranes and penetration into the cytoplasm. Using a genetic selection, we isolated an infectious retrovirus variant containing three changes in the surface protein-histidine 8 to arginine, glutamine 227 to arginine, and aspartate 243 to tyrosine. Single replacement of histidine 8 with arginine (H8R) resulted in almost complete loss of infectivity, even though the mutant envelope proteins were stable and efficiently incorporated into virions. Virions carrying H8R envelope were proficient at binding cells expressing receptor but failed to induce cell-cell fusion of XC cells, indicating that the histidine at position 8 plays an essential role in fusion during penetration of the host cell membrane. Thus, there is at least one domain in SU that is involved in fusion; the fusion functions do not reside exclusively in TM. In contrast, envelope with all three changes induced cell-cell fusion of XC cells and produced virions that were 10,000-fold more infectious than those containing only the H8R substitution, indicating that changes at positions 227 and 243 can suppress a fusion defect caused by loss of histidine 8 function. Moreover, the other two changes acted synergistically, indicating that both compensate for the loss of the same essential function of histidine 8. The ability of these changes to suppress this fusion defect might provide a means for overcoming postbinding defects found in targeted retroviral vectors for use in human gene therapy.
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Affiliation(s)
- T Zavorotinskaya
- Department of Microbiology and Immunology, University of Tennessee-Memphis, Memphis, Tennessee 38163, USA
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25
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Davey RA, Zuo Y, Cunningham JM. Identification of a receptor-binding pocket on the envelope protein of friend murine leukemia virus. J Virol 1999; 73:3758-63. [PMID: 10196270 PMCID: PMC104153 DOI: 10.1128/jvi.73.5.3758-3763.1999] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Based on previous structural and functional studies, a potential receptor-binding site composed of residues that form a pocket at one end of the two long antiparallel helices in the receptor-binding domain of Friend 57 murine leukemia virus envelope protein (RBD) has been proposed. To test this hypothesis, directed substitutions for residues in the pocket were introduced and consequences for infection and for receptor binding were measured. Receptor binding was measured initially by a sensitive assay based on coexpression of receptor and RBD in Xenopus oocytes, and the findings were confirmed by using purified proteins. Three residues that are critical for both binding and infection (S84, D86, and W102), with side chains that extend into the pocket, were identified. Moreover, when mCAT-1 was overexpressed, the infectivity of Fr57-MLV carrying pocket substitutions was partially restored. Substitutions for 18 adjacent residues and 11 other previously unexamined surface-exposed residues outside of the RBD pocket had no detectable effect on function. Taken together, these findings support a model in which the RBD pocket interacts directly with mCAT-1 (likely residues, Y235 and E237) and multiple receptor-envelope complexes are required to form the fusion pore.
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Affiliation(s)
- R A Davey
- Howard Hughes Medical Institute and Division of Hematology/Oncology, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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26
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Rong L, Gendron K, Strohl B, Shenoy R, Wool-Lewis RJ, Bates P. Characterization of determinants for envelope binding and infection in tva, the subgroup A avian sarcoma and leukosis virus receptor. J Virol 1998; 72:4552-9. [PMID: 9573218 PMCID: PMC109965 DOI: 10.1128/jvi.72.6.4552-4559.1998] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Tva is the cellular receptor for subgroup A avian leukosis and sarcoma virus (ALSV-A). The viral interaction domain of Tva is determined by a 40-residue, cysteine-rich module closely related to the ligand binding domain of the human low-density lipoprotein receptor (LDLR). In this report, we examined the role of the LDLR-like module of Tva in envelope binding and viral infection by mutational analysis. We found that the entire LDLR module in Tva is essential for efficient binding to the viral envelope protein. However, the 17 N-terminal residues of this module can be deleted without affecting receptor function, suggesting that the major determinants for viral entry are located at the C terminus of the module. The effect on viral infection of many amino acid substitutions and deletions in the LDLR module is context dependent, suggesting that the residues important for viral entry are dispersed throughout the LDLR module. In addition, we found that all 27 mutations at residues D46, E47, and W48 greatly reduced envelope binding. These results are discussed in relation to a recently elucidated structure for an LDLR module.
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Affiliation(s)
- L Rong
- Department of Microbiology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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27
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Abstract
The envelope glycoprotein (Env) of Moloney murine leukemia virus (MoMuLV) is proteolytically processed and transported to the cell surface where it can be incorporated into budding virions. Cell surface Env is frequently detected using an indirect immunofluorescence assay and fluorescence-activated cell sorting (FACS). We found that the detection of Env in this manner requires the expression of the MoMuLV receptor (ATRC-1) on the cell surface, and the level of envelope protein detected correlates with the level of receptors expressed on the cell. In addition, Env detection corresponds to the Env protein's ability to bind to its receptor and can be competed out by the addition of a truncated form of the Env protein. These data suggest that Env detected on the cell surface by the FACS assay is protein that has rebound to its receptor after being secreted or shed, rather than actual surface-expressed protein. In contrast, a combined immunoprecipitation and biotinylation assay detected equal amounts of Env on the surface of both receptor-lacking and receptor-expressing cell lines. The immunoprecipitation-biotinylation assay is therefore a more appropriate method for detecting surface expression of the MoMuLV envelope protein.
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Affiliation(s)
- H Yu
- Gene Therapy Laboratories, Norris Cancer Center, School of Medicine, University of Southern California, Los Angeles 90033, USA
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Adkins HB, Brojatsch J, Naughton J, Rolls MM, Pesola JM, Young JA. Identification of a cellular receptor for subgroup E avian leukosis virus. Proc Natl Acad Sci U S A 1997; 94:11617-22. [PMID: 9326659 PMCID: PMC23555 DOI: 10.1073/pnas.94.21.11617] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Genetic studies in chickens and receptor interference experiments have indicated that avian leukosis virus (ALV)-E may utilize a cellular receptor related to the receptor for ALV-B and ALV-D. Recently, we cloned CAR1, a tumor necrosis factor receptor (TNFR)-related protein, that serves as a cellular receptor for ALV-B and ALV-D. To determine whether the cellular receptor for ALV-E is a CAR1-like protein, a cDNA library was made from turkey embryo fibroblasts (TEFs), which are susceptible to ALV-E infection, but not to infection by ALV-B and ALV-D. The cDNA library was screened with a radioactively labeled CAR1 cDNA probe, and clones that hybridized with the probe were isolated. A 2.3-kb cDNA clone was identified that conferred susceptibility to ALV-E infection, but not to ALV-B infection, when expressed in transfected human 293 cells. The functional cDNA clone is predicted to encode a 368 amino acid protein with significant amino acid similarity to CAR1. Like CAR1, the TEF protein is predicted to have two extracellular TNFR-like cysteine-rich domains and a putative death domain similar to those of TNFR I and Fas. Flow cytometric analysis and immunoprecipitation experiments demonstrated specific binding between the TEF CAR1-related protein and an immunoadhesin composed of the surface (SU) envelope protein of subgroup E (RAV-0) virus fused to the constant region of a rabbit immunoglobulin. These two activities of the TEF CAR1-related protein, specific binding to ALV-E SU and permitting entry only of ALV-E, have unambiguously identified this protein as a cellular receptor specific for subgroup E ALV.
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Affiliation(s)
- H B Adkins
- Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
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Bae Y, Kingsman SM, Kingsman AJ. Functional dissection of the Moloney murine leukemia virus envelope protein gp70. J Virol 1997; 71:2092-9. [PMID: 9032341 PMCID: PMC191299 DOI: 10.1128/jvi.71.3.2092-2099.1997] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The envelope protein of Moloney murine leukemia virus (Mo-MLV) is a complex glycoprotein that mediates receptor binding and entry via fusion with cell membranes. By using a series of substitution mutations and truncations in the Mo-MLV external envelope surface protein gp70, we have identified regions important for these processes. Firstly, truncations of gp70 revealed that the minimal continuous receptor-binding region is amino acids 9 to 230, in broad agreement with other studies. Secondly, within this region there are two key basic amino acids, Arg-83 and Arg-95, that are essential for receptor binding and may interact with a negatively charged residue(s) or with the pi electrons of the aromatic ring on a hydrophobic residue(s) in the basic amino acid transporter protein that is the Mo-MLV ecotropic receptor. Finally, we showed that outside the minimal receptor-binding region at amino acids 2 to 8, there is a region that is essential for postbinding fusion events.
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Affiliation(s)
- Y Bae
- Department of Biochemistry, University of Oxford, United Kingdom
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Chu TH, Dornburg R. Toward highly efficient cell-type-specific gene transfer with retroviral vectors displaying single-chain antibodies. J Virol 1997; 71:720-5. [PMID: 8985404 PMCID: PMC191105 DOI: 10.1128/jvi.71.1.720-725.1997] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Recently, we constructed retroviral vector particles derived from spleen necrosis virus (SNV) that display a single-chain antibody (scA) on the viral surface. By transient transfection protocols, we showed that such particles are competent for infection and cell type specific. Efficient infection was dependent on the presence of wild-type envelope, although wild-type SNV was not infectious on target cells (T.-H. T. Chu and R. Dornburg, J. Virol. 69:2659-2663, 1995; T.-H. T. Chu, I. Martinez, W. C. Sheay, and R. Dornburg, Gene Ther. 1:292-299, 1994). In this study, stable packaging lines were constructed and detailed biological and biochemical studies were performed. Chimeric scA-envelope fusion proteins were expressed as efficiently as wild-type envelope and were stable over a period of at least 6 h. Only a fully functional wild-type envelope could act as a helper for efficient virus penetration. The ratio of wild-type envelope protein to chimeric envelope protein appears to determine the efficiency of infection. Virus titers of targeting vectors obtained from stable packaging lines were as high as 10(4) CFU/ml. A 25-fold concentration of vector virus stocks resulted in a 200-fold increase in virus titers (up to 10(6) CFU/ml). These data indicate that an inhibitor of infection was (at least partially) removed by the concentration protocol. Our data show that this technology has several variables for further improvements and, therefore, has the potential to become a powerful tool for cell-type-specific in vivo human gene therapy.
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Affiliation(s)
- T H Chu
- Department of Molecular Genetics and Microbiology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway 08854, USA
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Zingler K, Young JA. Residue Trp-48 of Tva is critical for viral entry but not for high-affinity binding to the SU glycoprotein of subgroup A avian leukosis and sarcoma viruses. J Virol 1996; 70:7510-6. [PMID: 8892869 PMCID: PMC190818 DOI: 10.1128/jvi.70.11.7510-7516.1996] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Previously, mutant Tva receptors were classified as either partially or completely defective in mediating subgroup A avian leukosis and sarcoma virus (ALSV-A) entry (C. Bélanger, K. Zingler, and J. A. T. Young, J. Virol. 69:1019-1024, 1995; K. Zingler, C. Bélanger, R. Peters, D. Agard, and J. A. T. Young, J. Virol. 69:4261-4266, 1995). To specifically test the abilities of these mutant Tva proteins to bind ALSV-A surface (SU) protein, binding studies were performed with a subgroup A SU-immunoadhesin. This fusion protein is composed of the subgroup A Schmidt-Ruppin SU protein fused in frame to a rabbit immunoglobulin constant region. This reagent was conjugated to fluorescein isothiocyanate and used for flow cytometric analysis with transfected human 293 cells expressing different forms of Tva. The SU-immunoadhesin bound the wild-type Tva protein with a KD of approximately 1.5 nM. Amino acid substitutions that reduced viral entry at Asp-46 and at Cys-35 and Cys-50, which are predicted to form an intrachain disulfide bond in Tva, drastically reduced the binding affinity for the SU-immunoadhesin. Thus, the effects on viral entry of some mutations could be explained solely by changes in the binding affinity for ALSV-A SU. However, this was not true for other mutations tested, especially those with amino acid substitutions that replaced Trp-48. Compared with the wild-type receptor, these latter mutations led to approximately 43- to 200-fold reductions in viral infectivity but only to approximately 2.5- to 3.4-fold reductions in the binding affinity for the SU-immunoadhesin. These results support a role for Trp-48 of Tva in mediating steps of viral entry subsequent to binding ALSV-A SU.
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Affiliation(s)
- K Zingler
- Department of Microbiology and Immunology, University of California School of Medicine, San Francisco 94143, USA
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