title: Are endogenous feline leukemia viruses really endogenous?
abstract: Full length endogenous feline leukemia virus (FeLV) proviruses exist within the genomes of many breeds of domestic cat raising the possibility that they may also exist in a transmissible exogenous form. Such viruses would share receptor usage with the recombinant FeLV-B subgroup, a viral subgroup that arises in vivo by recombination between exogenous subgroup A virus (FeLV-A) and endogenous FeLV. Accordingly, all isolates of FeLV-B made to date have contained a "helper" FeLV-A, consistent with their recombinatorial origin. In order to assess whether endogenous viruses are transmitted between cats, we examined primary isolates of FeLV for which the viral subgroup had been determined for the presence of a subgroup B virus that lacked an FeLV-A. Here we describe the identification of two primary field isolates of FeLV (2518 and 4314) that appeared to contain subgroup B virus only by classical interference assays, raising the possibility of between-host transmission of endogenous FeLV. Sequencing of the env gene and U3 region of the 3' long terminal repeat (LTR) confirmed that both viral genomes contained endogenous viral env genes. However the viral 3' LTRs appeared exogenous in origin with a putative 3' recombination breakpoint residing at the 3' end of the env gene. Further, the FeLV-2518 virions also co-packaged a truncated FeLV-A genome containing a defective env gene, termed FeLV-2518(A) whilst no helper subgroup A viral genome was detected in virions of FeLV-4314. The acquisition of an exogenous LTR by the endogenous FeLV in 4314 may have allowed a recombinant FeLV variant to outgrow an exogenous FeLV-A virus that was presumably present during first infection. Given time, a similar evolution may also occur within the 2518 isolate. The data suggest that endogenous FeLVs may be mobilised by acquisition of exogenous LTRs yielding novel viruses that type biologically as FeLV-B.
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Bearsden Road, Glasgow G61 1QH, United Kingdom. h.stewart.1@research.gla.ac.uk
authors.forename: H
authors.initials: H
authors.lastname: Stewart
authors.forename: O
authors.initials: O
authors.lastname: Jarrett
authors.forename: M J
authors.initials: MJ
authors.lastname: Hosie
authors.forename: B J
authors.initials: BJ
authors.lastname: Willett
mesh_terms: D000818:Animals; D002415:Cats / Q000821:virology; D002460:Cell Line; D003001:Cloning, Molecular; D004279:DNA, Viral / Q000235:genetics; D016679:Genome, Viral / Q000235:genetics; D015151:Immunoblotting / Q000662:veterinary; D005256:Leukemia Virus, Feline / Q000254:growth & development* / Q000502:physiology; D016582:Leukemia, Feline / Q000821:virology*; D016133:Polymerase Chain Reaction / Q000662:veterinary; D011533:Proviruses / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics; D011991:Receptors, Virus / Q000235:genetics; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics
chemical_list: D004279:DNA, Viral; D012367:RNA, Viral; D011991:Receptors, Virus; D014764:Viral Proteins