Na ⁺ /H ⁺ exchanger type 1 is a receptor for pathogenic subgroup J avian leukosis virus

Abstract

Subgroup J avian leukosis virus (ALV-J) is a recently identified avian oncogenic retrovirus responsible for severe economic losses worldwide. In contrast with the other ALV subgroups, ALV-J predominantly induces myeloid leukosis in meat-type chickens. Despite significant homology with the other ALV subgroups across most of the genome, the envelope protein of ALV-J (EnvJ) shares low homology with the others. Pathogenicity and myeloid leukosis induction map to the env gene of ALV-J. A chimeric protein composed of the surface domain of EnvJ fused to the constant region of a rabbit IgG and mass spectrometry were used to identify the chicken Na ؉ ͞H ؉ exchanger type 1 (chNHE1) as a binding protein for ALV-J. Flow cytometry analysis and coprecipitation experiments demonstrated a specific interaction between EnvJ and chNHE1. When introduced into nonpermissive human 293T cells and quail QT6 cells, chNHE1 conferred susceptibility to EnvJ-mediated infection. Furthermore, 293T cells expressing chNHE1 fused with 293T cells expressing EnvJ in a low-pH-dependent manner. Together, these data identify chNHE1 as a cellular receptor for the highly pathogenic ALV-J.retrovirus ͉ viral receptor ͉ viral envelope A vian leukosis viruses (ALV) are a group of avian retroviruses that induce tumors in host birds. The viruses that infect chickens are classified into six subgroups (A-E and J) on the basis of the envelope glycoprotein responsible for specific viral interference patterns, virus neutralization, and host range (1). The most recently identified subgroup, ALV-J, predominantly infects meattype chickens and turkeys (1). ALV-J was identified in 1988 and became widespread in commercial meat-type poultry during the 1990s. The transmission of ALV-J is much higher than other ALV subgroups (2), thus making control and eradication significantly more difficult. The virus also evolves rapidly with sequence variations clustered in hypervariable regions of the envelope protein (Env) (3). In contrast to other subgroups, which primarily cause lymphoma, ALV-J mainly induces myeloid leukosis (4). ALV-J infection causes disease and death in both broiler breeders and egg layers and represents a significant problem for the commercial poultry industry worldwide, with estimated losses of 1.5% per week in excess mortality (5).Retroviruses infect host cells through specific interactions between viral Env and cell surface receptors. The Env surface subunit (SU) directly binds to the receptor, and subsequent conformational changes in the Env transmembrane (TM) subunit drive fusion of the viral and cellular membranes (6). The receptors for all of the other major ALV subgroups (A-E) have been identified (7-10). Receptor distribution is a major determinant of ALV subgroup tropism. Env is also a major determinant for the induction of lymphoid and myeloid tumors by ALV-A and ALV-J, respectively (4), presumably because the specific receptors for ALV-A and ALV-J are differentially expressed on different cell lineages. This hypothesis is supported by the observat...

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

“…cDNA was reverse transcribed from 1 g total RNA with Moloney murine leukemia virus (M-MLV) reverse transcriptase (RT) and oligo(dT) 15 primers (both from Promega). We amplified the left part of the NHE1 coding sequence, which contains all predicted transmembrane domains and extra-and intracellular loops (19), using the forward primer chTVJ1L (5=-CTTCCCTGGGCTCTGCTG-3=, nucleotides 25 to 42 downstream of the ATG initiation codon) and reverse primer chTVJR6 (5=-CAGGAACT GCGTGTGGATCTC-3=, complementary to nucleotides 1,537 to 1,557 of chNHE1). PCR conditions were the following: 98°C for 180 s, 35 cycles of 98°C for 10 s, 67.6°C for 30 s, and 72°C for 100 s, and terminal extension at 72°C for 7 min with Taq polymerase (TaKaRa).…”

“…Infection of cells with ALV-J has been studied in vitro mostly using the prototype HPRS-103 strain or its pseudotypes (16,19). In order to simplify the procedure and improve the quantitative assessment of ALV-J infection, we constructed a GFP-transducing reporter virus of subgroup J specificity based on the RCAS retrovirus vector (25,26).…”

“…In order to identify the amino acid residues critical for the NHE1-EnvJ interaction, we compared the sequence of NHE1 from various galliform species and looked for polymorphisms constantly present in the resistant species. There are two large extracellular loops, ECL1 and ECL5, within NHE1, and ECL1 is highly divergent, with only 39% identity between chNHE1 and human NHE1 (19). We concentrated on the left part of ECL1, which is almost completely divergent between chicken and human.…”

“…The receptor for ALV-J was identified as chicken Na ϩ /H ϩ exchanger type 1 (chNHE1), encoded by the tvj locus on chromosome 23 (19). Although ALV-J is highly diversified, chNHE1 binds all strains.…”

“…chNHE1 contains 12 predicted transmembrane segments, six extracellular loops, and a long C-terminal intracellular tail. The virus-binding site was predicted to reside in the N-terminal part of prominent extracellular loop 1 (ECL1), on the basis of the divergence of otherwise conserved amino acid sequences of sensitive chNHE1 and refractory human NHE1 (19).…”