Identification of novel subgroup A variants with enhanced receptor binding and replicative capacity in primary isolates of anaemogenic strains of feline leukaemia virus.
BACKGROUND
The development of anaemia in feline leukaemia virus (FeLV)-infected cats is associated with the emergence of a novel viral subgroup, FeLV-C. FeLV-C arises from the subgroup that is transmitted, FeLV-A, through alterations in the amino acid sequence of the receptor binding domain (RBD) of the envelope glycoprotein that result in a shift in the receptor usage and the cell tropism of the virus. The factors that influence the transition from subgroup A to subgroup C remain unclear, one possibility is that a selective pressure in the host drives the acquisition of mutations in the RBD, creating A/C intermediates with enhanced abilities to interact with the FeLV-C receptor, FLVCR. In order to understand further the emergence of FeLV-C in the infected cat, we examined primary isolates of FeLV-C for evidence of FeLV-A variants that bore mutations consistent with a gradual evolution from FeLV-A to FeLV-C.


RESULTS
Within each isolate of FeLV-C, we identified variants that were ostensibly subgroup A by nucleic acid sequence comparisons, but which bore mutations in the RBD. One such mutation, N91D, was present in multiple isolates and when engineered into a molecular clone of the prototypic FeLV-A (Glasgow-1), enhanced replication was noted in feline cells. Expression of the N91D Env on murine leukaemia virus (MLV) pseudotypes enhanced viral entry mediated by the FeLV-A receptor THTR1 while soluble FeLV-A Env bearing the N91D mutation bound more efficiently to mouse or guinea pig cells bearing the FeLV-A and -C receptors. Long-term in vitro culture of variants bearing the N91D substitution in the presence of anti-FeLV gp70 antibodies did not result in the emergence of FeLV-C variants, suggesting that additional selective pressures in the infected cat may drive the subsequent evolution from subgroup A to subgroup C.


CONCLUSIONS
Our data support a model in which variants of FeLV-A, bearing subtle differences in the RBD of Env, may be predisposed towards enhanced replication in vivo and subsequent conversion to FeLV-C. The selection pressures in vivo that drive the emergence of FeLV-C in a proportion of infected cats remain to be established.
Medical Research Council-University of Glasgow Centre for Virus Research, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow, UK. h.stewart.1@research.gla.ac.uk
Hazel
H
Stewart
Karen W
KW
Adema
Elizabeth L
EL
McMonagle
Margaret J
MJ
Hosie
Brian J
BJ
Willett
D000595:Amino Acid Sequence; D000818:Animals; D057134:Antibodies, Neutralizing / Q000276:immunology; D000914:Antibodies, Viral / Q000276:immunology; D002415:Cats; D002460:Cell Line; D003001:Cloning, Molecular; D005347:Fibroblasts / Q000821:virology; D006023:Glycoproteins / Q000235:genetics; D006168:Guinea Pigs; D057809:HEK293 Cells; D006801:Humans; D005256:Leukemia Virus, Feline / Q000145:classification* / Q000472:pathogenicity / Q000502:physiology*; D009052:Leukemia Virus, Murine / Q000235:genetics; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009500:Neutralization Tests; D011485:Protein Binding; D012367:RNA, Viral / Q000235:genetics*; D011991:Receptors, Virus / Q000378:metabolism*; D012641:Selection, Genetic; D014759:Viral Envelope Proteins / Q000235:genetics; D053585:Virus Attachment; D053586:Virus Internalization; D014779:Virus Replication
D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; D006023:Glycoproteins; D026901:Membrane Transport Proteins; D012367:RNA, Viral; D011991:Receptors, Virus; C120043:SLC19A2 protein, human; D014759:Viral Envelope Proteins; C445079:envelope protein, Feline immunodeficiency virus