Novel Feline Leukemia Virus Interference Group Based on the env Gene

Abstract

cFeline leukemia virus (FeLV) subgroups have emerged in infected cats via the mutation or recombination of the env gene of subgroup A FeLV (FeLV-A), the primary virus. We report the isolation and characterization of a novel env gene, TG35-2, and report that the TG35-2 pseudotype can be categorized as a novel FeLV subgroup. The TG35-2 envelope protein displays strong sequence identity to FeLV-A Env, suggesting that selection pressure in cats causes novel FeLV subgroups to emerge. Feline leukemia viruses (FeLVs) are pathogenic retroviruses of domestic cats (1, 2), which are classified into subgroups A (the parent virus), B, C, D, and T based on their interference and in vitro host range properties (3,4,5,6,7,8). Subgroups B and D arose from the recombination of FeLV-A env and the env genes of endogenous FeLV or endogenous retroviruses in the genomes of domestic cats (ERV-DCs) (7, 9, 10). Subgroups C and T possibly arose from mutations in FeLV-A env (11,12). The recombination or mutation of env often alters the interference and host ranges of FeLVs by affecting their receptor usage (5,6,13,14,15,16).FeLV env genes were isolated by PCR from the blood DNA of a 1-year-old castrated male cat, TG35, with a bite injury, stomatitis, loss of appetite, and FeLV infection, although he had been vaccinated with inactivated FeLV (genotype III) (16). Five clones (TG35-1 to -5) were isolated, and we focused on TG35-2, TG35-4, and TG35-5. The env sequences of these clones showed strong similarity ( Fig. 1), and the viruses clustered phylogenetically with those of genotype I/clade I FeLV, found mainly in Japan (16). The encompassing variable region A (VRA) of TG35-2 Env differs at eight amino acids from those of the TG35-4 and TG35-5 Env proteins. The proline-rich regions of TG35-2 and TG35-4, but not TG35-5, contain an inserted sequence of 25 amino acids (Fig. 1) not found in the cat genome database and of unknown origin.To identify the FeLV subgroup to which this viral strain belongs, we used an interference assay (16) and generated ␤-galactosidase (LacZ)-encoding pseudotype viruses expressing TG35-2, TG35-4, or TG35-5 envelope (Env) proteins in GPLac cells (7). Pseudotype viruses TG35-2, -4, and -5 infected uninfected HEK293T cells (Table 1). However, HEK293T cells preinfected with FeLV-A/clone 33 (293T/clone 33 cells) (17) or FeLV-A/Glasgow-1 (293T/Glasgow-1 cells) (9) were infected by pseudotype virus TG35-2, but not by TG35-4 or TG35-5. Neither cell type was infected by FeLV-A/clone 33 or FeLV-A/Glasgow-1. Therefore, only the TG35-4 and TG35-5 viruses interfered with FeLV-A. Neither the TG35-2, TG35-4, nor TG35-5 pseudotype interfered with other subgroups of FeLV, or with retroviruses such as ERV-DC10, a replication-competent feline ERV (7) ( Table 1). Therefore, FeLV TG35-4 and TG35-5 belong to the FeLV-A subgroup. However, TG35-2 could not be categorized.We next constructed a replication-competent virus (33TGE2) containing the TG35-2 env gene and the LTR, gag, and pol genes of When we examined AH927 feline cells, the TG35-2...

Differential and defective expression of Koala Retrovirus indicate complexity of host and virus evolution

“…This situation would be analogous to that seen in FeLV where the FeLV A strain is the only one that spreads from cat to cat, with the B, C, D, T and feline fibrosarcoma strains arising independently in individual animals via env mutations or recombination with endogenous loci or the acquisition of cellular oncogenes. The derived strains of FeLV use different receptors, and display altered pathogenicity, to the FeLV A strain 43,44 again analogous to KoRV where the KoRV B and E variants use a different receptor to KoRV A 23,42 . Should it prove the case that only one strain of KoRV is transmissible, this bears promise for the success of a vaccination effort 34 ; the commercial FeLV vaccines that target only the A variant have been highly successful in reducing the incidence of clinical FeLV disease 45 .…”

Existence of Two Distinct Infectious Endogenous Retroviruses in Domestic Cats and Their Different Strategies for Adaptation to Transcriptional Regulation

“…We initially established indicator cells, termed 293Lac cells (54), by stably transfecting a LacZ-expressing retroviral vector, pMxs-nlLacZ, into HEK293T cells to monitor viral infection and replication. The supernatant from 293Lac cells transfected with a full-length ERV-DC14 plasmid was filtered and then used to treat fresh HEK293T cells for 2 days, after which LacZ staining was performed.…”

Presence of a Shared 5′-Leader Sequence in Ancestral Human and Mammalian Retroviruses and Its Transduction into Feline Leukemia Virus

“…This virus is known to induce various pathologies in domestic cats (Felis silvestris catus), such as lymphoma, myelodysplastic syndrome, anaplastic anemia, acute myelogenous leukemia, and immune deficiency (42,43). The mechanisms by which this virus induces the multifarious symptoms of FeLV-associated diseases are still unclear; however, the genetic structural polymorphisms resulting from substitutions or recombinations have led to changes in FeLV pathogenicity and unexpected symptoms (8,(44)(45)(46)(47)(48).…”