Nonconserved Tryptophan 38 of the Cell Surface Receptor for Subgroup J Avian Leukosis Virus Discriminates Sensitive from Resistant Avian Species

Abstract

Subgroup J avian leukosis virus (ALV-J) is unique among the avian sarcoma and leukosis viruses in using the multimembranespanning 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.T he first step in retrovirus infection is attachment of the virus envelope glycoproteins to the specific cell surface receptor. Consequently, the susceptibility of each cell strictly depends on the expression and display of proper receptor molecules. This attachment, as well as the following phases of virus entry, requires a perfect match of receptors and envelope glycoproteins (1). Structural alterations within variable and hypervariable envelope glycoprotein regions easily abrogate the infectivity or even change the receptor usage and broaden the host range. This is best exemplified by avian sarcoma and leukosis viruses (ASLVs), a closely related group of retroviruses which evolved into five subgroups, A to E, that utilize three different receptors encoded by three genetic loci, tva, tvb, and tvc (1, 2). The tva locus encodes a protein belonging to the family of low-density lipoprotein receptors and determines susceptibility to the subgroup A ASLVs (3, 4). The tumor necrosis factor receptor-related protein encoded by the tvb locus confers susceptibility to subgroup B, D, and E ASLVs (5-7). Finally, subgroup C ASLVs utilize the Tvc protein of the butyrophilin family with two immunoglobulin-like domains (8). The complete resistance or decreased susceptibility of host chicken cells to a particular ASLV subgroup can then be caused by premature termination or a frameshift in the receptor-encoding loci (8-10), decreased receptor expression and display (11), and even single amino acid substitutions in the receptor sequence (9, 12).Subgroup J avian leukosis virus (ALV-J), the prototype virus isolate of which is HPRS-103, is an independent envelope subgroup which does not interfere with subgroups A to E and cannot be neutralized by antisera raised against subgroups A to E (13). ALV-J was originally d...

Identification of New World Quails Susceptible to Infection with Avian Leukosis Virus Subgroup J

“…Our finding that W38 is present in ECL1 of the NHE1 receptor suggested that New World quails are susceptible to ALV-J, and this was directly confirmed by infecting New World quail embryo fibroblasts with a recombinant retroviral vector of subgroup J specificity. Our results not only identified New World quails susceptible to ALV-J but also validated our bioprospective approach based on the detection of W38 in galliform species (20,21). Future surveys of galliform species might reveal new NHE1 alleles with the ability to serve as functional receptors for ALV-J.…”

“…NHE1 nucleotide coding sequences of the following bird species, obtained in previous studies (20,21) or this study, were used: chicken (NCBI Nucleotide database accession number DQ256198.1), turkey (DQ883630.1), mountain quail (KX823320), northern bobwhite (KX823321), California quail (KX823322), Gambel's quail (KX823323), helmeted guineafowl (KX823324), Reeves=s pheasant (KX823325), ring-necked pheasant (KX823326), gray peacockpheasant (KX823327), Malayan peacock-pheasant (KX823328), green peafowl (KX823329), Japanese quail (KX823330), gray partridge (KX823331), chukar partridge (KX823332), and common mallard (KX823333). The sequences were aligned using a codon-based MUSCLE algorithm implemented in MEGA 6 software (46) and were checked manually.…”

“…Molecular evolution of NHE1 in galliform birds. Since the ECL1 region of the NHE1 gene determines the host susceptibility to ALV-J, we further analyzed its evolution in galliform birds examined previously (20,21) and in this study. We looked at the signature of positive selection acting on this region.…”

The Novel Avian Leukosis Virus Subgroup K Shares Its Cellular Receptor with Subgroup A

“…Here, we identified Tva as a K subgroup receptor while comparing the host ranges of JS11C1 virus and A subgroup ALV. This comparison might also be useful for delineation of the binding site or at least definition of the amino acid residues that are critical for receptor function, as it helped to identify W38 of chicken NHE1 as the residue discriminating species susceptible or resistant to ALV-J (17). In our screen, we found only the guinea fowl to be resistant to JS11C1, and we hope to profit from future analyses of Tva polymorphisms.…”

“…The host escapes this selection force via the evolution of receptor variants that exhibit decreased or even abrogated binding to retroviral envelopes. Numerous ALV-resistant receptor alleles have been described (5,(15)(16)(17), and positive selection was demonstrated to act within the extracellular loop 1 of NHE1, the critical region for ALV-J susceptibility (18). We have also identified receptor variants that lead to decreased susceptibility to avian sarcoma and leukosis virus (ASLV) infection (19,20).…”