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Journal of Virology, September 2000, p. 8085-8093, Vol. 74, No. 17
Department of Biochemistry and Molecular
Biology, Oregon Health Sciences University, Portland, Oregon
97201-3098
Received 20 March 2000/Accepted 2 June 2000
The baboon endogenous retrovirus (BaEV) belongs to a large, widely
dispersed interference group that includes the RD114 feline endogenous
virus and primate type D retroviruses. Recently, we and another
laboratory independently cloned a human receptor for these viruses and
identified it as the human sodium-dependent neutral amino acid
transporter type 2 (hASCT2). Interestingly, mouse and rat cells are
efficiently infected by BaEV but only become susceptible to RD114 and
type D retroviruses if the cells are pretreated with tunicamycin, an
inhibitor of protein N-linked glycosylation. To investigate this host
range difference, we cloned and analyzed NIH Swiss mouse ASCT2
(mASCT2). Surprisingly, mASCT2 did not mediate BaEV infection, which
implied that mouse cells might have an alternative receptor for this
virus. In addition, elimination of the two N-linked oligosaccharides
from mASCT2 by mutagenesis, as substantiated by protein
N-glycosidase F digestions and Western immunoblotting, did
not enable it to function as a receptor for RD114 or type D
retroviruses. Based on these results, we found that the related ASCT1
transporters of humans and mice are efficient receptors for BaEV but
are relatively inactive for RD114 and type D retroviruses. Furthermore,
elimination of the two N-linked oligosaccharides from extracellular
loop 2 of mASCT1 by mutagenesis enabled it to function as an efficient
receptor for RD114 and type D retroviruses. Thus, we infer that the
tunicamycin-dependent infection of mouse cells by RD114 and type D
retroviruses is caused by deglycosylation of mASCT1, which unmasks
previously buried sites for viral interactions. In contrast, BaEV
efficiently employs the glycosylated forms of mASCT1 that occur
normally in untreated mouse cells.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Sodium-Dependent Neutral Amino Acid Transporter
Type 1 Is an Auxiliary Receptor for Baboon Endogenous
Retrovirus
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Rd., Mail Code L224, Portland, OR
97201-3098. Phone: (503) 494-8442. Fax: (503) 494-8393. E-mail:
kabat{at}ohsu.edu.
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