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Journal of Virology, April 1999, p. 2916-2920, Vol. 73, No. 4
Laboratory of Cellular and Molecular
Regulation, National Institute of Mental Health, National Institutes of
Health, Bethesda, Maryland 20892,1 and
Genentech, Inc., South San Francisco, California
940802
Received 24 September 1998/Accepted 19 December 1998
The Chinese hamster cell lines E36 and CHOK1 dramatically differ in
susceptibility to amphotropic murine leukemia virus (A-MuLV) and gibbon
ape leukemia virus (GALV); E36 cells are highly susceptible to both
viruses, CHOK1 cells are not. We have previously shown that GALV can
infect E36 cells by using both its own receptor, HaPit1, and the A-MuLV
receptor, HaPit2. Given that the two cell lines are from the same
species, the loss of function of both of these receptors in CHOK1 cells
is surprising. Other studies have shown that CHOK1 cells secrete
proteins that block A-MuLV entry into CHOK1 as well as E36, suggesting
the two A-MuLV receptors are functionally identical. However, CHOK1
conditioned medium does not block GALV entry into E36, indicating the
secreted inhibitors do not block HaPit1. HaPit1 and ChoPit1 therefore
differ as receptors for GALV; ChoPit1 is either inactivated by secreted
factors or intrinsically nonfunctional. To determine why GALV cannot
infect CHOK1, we cloned and sequenced ChoPit1 and ChoPit2. ChoPit2 is almost identical to HaPit2, which explains why CHOK1 conditioned medium
blocks A-MuLV entry via both receptors. Although ChoPit1 and HaPit1 are
91% identical, a notable difference is at position 550 in the fourth
extracellular region, shown by several studies to be crucial for GALV
infection. Pit1 and HaPit1 have aspartate at 550, whereas ChoPit1 has
threonine at this position. We assessed the significance of this
difference for GALV infection by replacing the aspartate 550 in Pit1
with threonine. This single substitution rendered Pit1 nonfunctional
for GALV and suggests that threonine at 550 inactivates ChoPit1 as a
GALV receptor. Whether native ChoPit1 functions for GALV was determined
by interference assays using Lec8, a glycosylation-deficient derivative
of CHOK1 that is susceptible to both viruses and that has the same
receptors as CHOK1. Unlike with E36, GALV and A-MuLV exhibited
reciprocal interference when infecting Lec8, suggesting that they use
the same receptor. We conclude both viruses can use ChoPit2 in the absence of the inhibitors secreted by CHOK1 and ChoPit1 is nonfunctional.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Gibbon Ape Leukemia Virus Receptor Functions of
Type III Phosphate Transporters from CHOK1 Cells Are Disrupted by
Two Distinct Mechanisms


and
*
Corresponding author. Laboratory of Cellular and
Molecular Regulation, National Institute of Mental Health, Building 36, Room 2A11, 36 Convent Dr., MSC 4068, Bethesda, MD 20892-4068. Phone: (301) 496-9924. Fax: (301) 402-6808. E-mail:
m_eiden{at}codon.nih.gov.
Present address: Cancer Research Unit, Department of Biology,
University of York, Heslington YO1 5DD, United Kingdom.
Present address: ViroLogic, Inc., South San Francisco, CA 94080.
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