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Journal of Virology, December 2001, p. 11503-11514, Vol. 75, No. 23
Molecular Oncology Division, Department of
Internal Medicine, Washington University School of Medicine,
St. Louis, Missouri
Received 18 May 2001/Accepted 30 August 2001
Human immunodeficiency virus type 1 (HIV-1) infection in vivo is
dependent upon the interaction of the viral envelope glycoprotein gp120
with CC chemokine receptor 5 (CCR5) or CXC chemokine receptor 4 (CXCR4). To study the determinants of the gp120-coreceptor association, we generated a set of chimeric HIV-1 coreceptors which express all
possible combinations of the four extracellular domains of CCR5 and
CXCR4. Stable U87 astroglioma cell lines expressing CD4 and individual
chimeric coreceptor proteins were tested against a variety of R5, X4,
and R5X4 envelope glycoproteins and virus strains for their ability to
support HIV-1-mediated cell fusion and infection, respectively. Each of
the cell lines promoted fusion with cells expressing an HIV envelope
glycoprotein, except for U87.CD4.5455, which presents the first
extracellular loop (ECL1) and flanking sequences of CXCR4 in the
context of CCR5. However, all of the chimeric coreceptors allowed
productive infection by one or more of the viral strains tested. Viral
phenotype was a predictive factor for the observed activity of the
chimeric molecules; X4 and R5X4 HIV strains utilized a majority of the
chimeras, while R5 strains were limited in their ability to infect
cells expressing these chimeric molecules. The expression of CCR5 ECL2
within the CXCR4 backbone supported infection by an R5 primary isolate,
but no chimeras bearing the N terminus of CCR5 exhibited activity with
R5 strains. Remarkably, the introduction of any CXCR4 domain into the
CCR5 backbone was sufficient to allow utilization by multiple X4
strains. However, critical determinants within ECL2 and/or ECL3 of
CXCR4 were apparent for all X4 viruses upon replacement of these
domains in CXCR4 with CCR5 sequences. Unexpectedly, chimeric coreceptor-facilitated entry was blocked in all cases by the presence of the CXCR4-specific inhibitor AMD3100. Our data provide proof that
CCR5 contains elements that support usage by X4 viral strains and
demonstrate that the gp120 interaction sites of CCR5 and CXCR4 are
structurally related.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.23.11503-11514.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Evidence for Common Structural Determinants of
Human Immunodeficiency Virus Type 1 Coreceptor Activity Provided
through Functional Analysis of CCR5/CXCR4 Chimeric
Coreceptors
*
Corresponding author. Mailing address: Department of
Internal Medicine, Washington University School of Medicine, 660 S. Euclid, Campus Box 8069, St. Louis, MO 63110. Phone: (314) 362-8836. Fax: (314) 747-2797. E-mail: lratner{at}imgate.wustl.edu.
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