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Journal of Virology, June 2000, p. 5040-5052, Vol. 74, No. 11
Department of Biochemistry and Molecular
Biology1 and Department of Pathology and
Pediatrics,2 University of Medicine and
Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey
07103; Department of Hepatitis and Retroviruses, Pasteur
Institute, Tehran, Iran3; and Department
of Microbiology, Fukushima Medical College, Fukushima,
Japan4
Received 27 August 1999/Accepted 28 February 2000
Productive high-titer infection by human immunodeficiency virus
type 1 (HIV-1) requires the activation of target cells. Infection of
quiescent peripheral CD4 lymphocytes by HIV-1 results in incomplete, labile reverse transcripts and lack of viral progeny formation. An
interplay between Tat and p53 has previously been reported, where Tat
inhibited the transcription of the p53 gene, which may aid in the
development of AIDS-related malignancies, and p53 expression inhibited
HIV-1 long terminal repeat transcription. Here, by using a well-defined
and -characterized stress signal, gamma irradiation, we find that upon
gamma irradiation, HIV-1-infected cells lose their G1/S
checkpoints, enter the S phase inappropriately, and eventually
apoptose. The loss of the G1/S checkpoint is associated with a loss of p21/Waf1 protein and increased activity of a major G1/S kinase, namely, cyclin E/cdk2. The p21/Waf1 protein, a
known cyclin-dependent kinase inhibitor, interacts with the cdk2/cyclin E complex and inhibits progression of cells into S phase. We find that
loss of the G1/S checkpoint in HIV-1-infected cells may in part be due to Tat's ability to bind p53 (a known activator of the
p21/Waf1 promoter) and sequester its transactivation activity, as seen
in both in vivo and in vitro transcription assays. The loss of p21/Waf1
in HIV-1-infected cells was specific to p21/Waf1 and did not occur with
other KIP family members, such as p27 (KIP1) and p57 (KIP2). Finally,
the advantage of a loss of the G1/S checkpoint for HIV-1
per se may be that it pushes the host cell into the S phase, which may
then allow subsequent virus-associated processes, such as RNA splicing,
transport, translation, and packaging of virion-specific genes, to occur.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Loss of G1/S Checkpoint in Human
Immunodeficiency Virus Type 1-Infected Cells Is Associated with a Lack
of Cyclin-Dependent Kinase Inhibitor p21/Waf1
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, UMDNJ-New Jersey Medical School, MSB-E635, Newark, NJ 07103. Phone: (973) 972-1089. Fax: (973) 972-1172. E-mail: kashanfa{at}umdnj.edu.
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