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Journal of Virology, January 2000, p. 483-492, Vol. 74, No. 1
Laboratory of
Virology1 and Laboratory of Clinical
Biochemistry,2 Istituto Superiore di
Sanità, Rome, Italy
Received 12 March 1999/Accepted 10 September 1999
F12 human immunodeficiency virus type 1 (HIV-1) nef is
a naturally occurring nef mutant cloned from the provirus
of a nonproductive, nondefective, and interfering HIV-1 variant
(F12-HIV). We have already shown that cells stably transfected with a
vector expressing the F12-HIV nef allele do not
downregulate CD4 receptors and, more peculiarly, become resistant to
the replication of wild type (wt) HIV. In order to investigate the
mechanism of action of such an HIV inhibition, the F12-HIV
nef gene was expressed in the context of the NL4-3 HIV-1
infectious molecular clone by replacing the wt nef gene
(NL4-3/chi). Through this experimental approach we established the
following. First, NL4-3/chi and nef-defective (
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Copyright © 2000, American Society for Microbiology. All rights reserved.
cis Expression of the F12 Human Immunodeficiency Virus
(HIV) Nef Allele Transforms the Highly Productive NL4-3 HIV Type 1 to
a Replication-Defective Strain: Involvement of both Env gp41
and CD4 Intracytoplasmic Tails
nef) NL4-3 viral particles behave very similarly in
terms of viral entry and HIV protein production during the first
replicative cycle. Second, no viral particles were produced from cells
infected with NL4-3/chi virions, whatever the multiplicity of infection used. The viral inhibition apparently occurs at level of viral assembling and/or release. Third, this block could not be relieved by
in-trans expression of wt nef. Finally,
NL4-3/chi reverts to a producer HIV strain when F12-HIV Nef is deprived
of its myristoyl residue. Through a CD4 downregulation competition
assay, we demonstrated that F12-HIV Nef protein potently inhibits the
CD4 downregulation induced by wt Nef. Moreover, we observed a
redistribution of CD4 receptors at the cell margin induced by F12-HIV
Nef. These observations strongly suggest that F12-HIV Nef maintains the
ability to interact with the intracytoplasmic tail of the CD4 receptor
molecule. Remarkably, we distinguished the intracytoplasmic tails of
Env gp41 and CD4 as, respectively, viral and cellular targets of the
F12-HIV Nef-induced viral retention. For the first time, the inhibition
of the viral life cycle by means of in-cis expression
of a Nef mutant is here reported. Delineation of the F12-HIV Nef
mechanism of action may offer additional approaches to interference
with the propagation of HIV infection.
*
Corresponding author. Mailing address: Laboratory of
Virology, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy. Phone: 39-06-49903248. Fax: 39-06-49387184. E-mail: federico{at}virus1.net.iss.it.
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