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Journal of Virology, November 1999, p. 9377-9385, Vol. 73, No. 11
Department of Pathology and Laboratory
Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
19104,1 and Department of Microbiology & Immunology, University of Tennessee
Received 1 March 1999/Accepted 30 July 1999
Infection by the neuropathogenic murine leukemia virus (MLV) TR1.3
results in hemorrhagic disease that correlates directly to in vivo
syncytium formation of brain capillary endothelial cells (BCEC). This
phenotype maps to amino acid 102 in the envelope (Env) protein of
TR1.3. Substitution of glycine (G) for tryptophan (W) at this position
(W102G Env) in the nonpathogenic MLV FB29 induces both syncytium
formation and neurologic disease in vivo. Using an in vitro gene
reporter cell fusion assay, we showed that fusion either with murine
NIH 3T3 cells or with nonmurine target cells that expressed receptors
at or below endogenous murine levels mirrored that seen in BCEC in
vivo. In these instances only TR1.3 and W102G Env induced cell fusion.
In contrast, when receptor levels on nonmurine cells were raised above
endogenous murine levels, FB29 Env was as fusogenic as the
neuropathogenic TR1.3 and W102G Env. These results indicate that TR1.3
Env and W102G Env are intrinsically more fusogenic than FB29 Env, that
the induction of fusion requires a threshold number of receptors that
is greater for FB29 Env than for TR1.3 or W102G Env, and that receptor
density on murine NIH 3T3 cells and BCEC is below the threshold for
FB29-dependent fusion. Surprisingly, receptor density on NIH 3T3 cells
could not be increased by stable expression of exogenous receptors, and
FB29-dependent fusion was not observed in NIH 3T3 cells that transiently expressed elevated receptor numbers. These results suggest
that an additional undefined host cell factor(s) may limit both
receptor expression and fusion potential in murine cells.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Induction of Syncytia by Neuropathogenic Murine Leukemia Viruses
Depends on Receptor Density, Host Cell Determinants, and the Intrinsic
Fusion Potential of Envelope Protein
Memphis, Memphis, Tennessee
381632
*
Corresponding author. Mailing address: Department of
Pathology and Laboratory Medicine, University of Pennsylvania, 354 Clinical Research Building, 421 Curie Blvd., Philadelphia, PA
19104-6142. Phone: (215) 898-2875. Fax: (215) 573-7945. E-mail:
gaulton{at}mail.med.upenn.edu.
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