Human immunodeficiency virus type 1 Vif causes dysfunction of Cdk1 and CyclinB1: implications for cell cycle arrest.
ABSTRACT The two major cytopathic factors in human immunodeficiency virus type 1 (HIV-1), the accessory proteins viral infectivity factor (Vif) and viral protein R (Vpr), inhibit cell-cycle progression at the G2 phase of the cell cycle. Although Vpr-induced blockade and the associated T-cell death have been well studied, the molecular mechanism of G2 arrest by Vif remains undefined. To elucidate how Vif induces arrest, we infected synchronized Jurkat T-cells and examined the effect of Vif on the activation of Cdk1 and CyclinB1, the chief cell-cycle factors for the G2 to M phase transition. We found that the characteristic dephosphorylation of an inhibitory phosphate on Cdk1 did not occur in infected cells expressing Vif. In addition, the nuclear translocation of Cdk1 and CyclinB1 was disregulated. Finally, Vif-induced cell cycle arrest was correlated with proviral expression of Vif. Taken together, our results suggest that Vif impairs mitotic entry by interfering with Cdk1-CyclinB1 activation.
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ABSTRACT: AIM: To investigate the association of p42.3 expression with clinicopathological characteristics and the biological function of p42.3 in human hepatocellular carcinoma (HCC). METHODS: We used reverse transcription-polymerase chain reaction (RT-PCR), quantitative real-time RT-PCR and western blotting to detect p42.3 mRNA and protein expression in hepatic cell lines. We examined primary HCC samples and matched adjacent normal tissue by immunohistochemistry to investigate the correlation between p42.3 expression and clinicopathological features. HepG2 cells were transfected with a pIRES2-EGFP-p42.3 expression vector to examine the function of the p42.3 gene. Transfected cells were analyzed for their viability and malignant transformation abilities by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, colony formation assay, and tumorigenicity assay in nude mice. RESULTS: p42.3 is differentially expressed in primary HCC tumors and cell lines. Approximately 69.6% (96/138) of cells were p42.3-positive in hepatic tumor tissues, while 30.7% (35/114) were p42.3-positive in tumor-adjacent normal tissues. Clinicopathological characteristics of the HCC specimens revealed a significant correlation between p42.3 expression and tumor differentiation (P = 0.031). However, p42.3 positivity was not related to tumor tumor-node-metastasis classification, hepatitis B virus status, or hepatoma type. Regarding p42.3 overexpression in stably transfected HepG2 cells, we discovered significant enhancement of cancer cell growth and colony formation in vitro, and significantly enhanced tumorigenicity in nude mice. Western blot analysis of cell cycle proteins revealed that enhanced p42.3 levels promote upregulation of proliferating cell nuclear antigen, cyclin B1 and mitotic arrest deficient 2. CONCLUSION: p42.3 promotes tumorigenicity and tumor growth in HCC and may be a potential target for future clinical cancer therapeutics.World Journal of Gastroenterology 05/2013; 19(19):2913-2920. · 2.55 Impact Factor
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ABSTRACT: Baculoviruses are insect viruses extensively exploited as eukaryotic protein expression vectors. Molecular biology studies have provided exciting discoveries on virus-host interactions, but the application of omic high-throughput techniques on the baculovirus-insect cell system has been hampered by the lack of host genome sequencing. While a broader, systems-level analysis of biological responses to infection is urgently needed, recent advances on proteomic studies have yielded new insights on the impact of infection on the host cell. These works are reviewed and critically assessed in the light of current biological knowledge of the molecular biology of baculoviruses and insect cells.Frontiers in Microbiology 01/2012; 3:391.
SHORT REPORT Open Access
Human Immunodeficiency Virus Type 1 Vif causes
dysfunction of Cdk1 and CyclinB1: implications
for cell cycle arrest
Keiko Sakai1,2†, R Anthony Barnitz1,3†, Benjamin Chaigne-Delalande1, Nicolas Bidère1,4and Michael J Lenardo1*
The two major cytopathic factors in human immunodeficiency virus type 1 (HIV-1), the accessory proteins viral
infectivity factor (Vif) and viral protein R (Vpr), inhibit cell-cycle progression at the G2 phase of the cell cycle.
Although Vpr-induced blockade and the associated T-cell death have been well studied, the molecular mechanism
of G2 arrest by Vif remains undefined. To elucidate how Vif induces arrest, we infected synchronized Jurkat T-cells
and examined the effect of Vif on the activation of Cdk1 and CyclinB1, the chief cell-cycle factors for the G2 to M
phase transition. We found that the characteristic dephosphorylation of an inhibitory phosphate on Cdk1 did not
occur in infected cells expressing Vif. In addition, the nuclear translocation of Cdk1 and CyclinB1 was disregulated.
Finally, Vif-induced cell cycle arrest was correlated with proviral expression of Vif. Taken together, our results
suggest that Vif impairs mitotic entry by interfering with Cdk1-CyclinB1 activation.
HIV-1 infection results in cell cycle arrest at the G2
phase accompanied by massive CD4+T-cell death.
Amongst the HIV-1 proteins, Vpr has been a major focus
of studies for cytopathicity and G2 cell cycle arrest [1,2].
We recently showed that Vif also causes CD4+T-cell
death and G2 arrest during HIV-1 infection, unveiling a
connection between virus-induced cell cycle arrest and
cytopathicity . Whereas Vpr-induced G2 blockade has
been extensively studied [4-14], how Vif causes cell cycle
arrest remains poorly defined [3,15-17]. Here, we studied
the effect of Vif expression during HIV-1 infection
in vitro on important mitotic regulatory proteins.
The activation and nuclear accumulation of the Cdk1-
CyclinB1 kinase complex, also known as mitosis promot-
ing factor (MPF), are key molecular events during G2/M-
phase transition [18-21]. Cascades of phosphorylation
and dephosphorylation govern these events at the late G2
phase. Once cells commit to mitotic entry, the Cdc25C
phosphatase activates Cdk1 by removing two inhibitory
phosphates from Thr14 and Tyr15 [22-28]. The
subsequent assembly of an activated Cdk1-CyclinB1
complex initiates a positive feedback loop by phosphory-
lating Cdc25C, which increases its enzymatic activity
. Nuclear accumulation of MPF requires phosphory-
lation of CyclinB1 in the cytoplasmic retention sequence
(CRS) [30-34], possibly by polo-like kinase 1 (PLK1) .
As a result of these events, active MPF accumulates in
the nucleus and phosphorylates nuclear lamins, thereby
ensuring nuclear envelope disassembly and the initiation
of mitosis [36-38].
To investigate Vif-induced cell cycle arrest, we syn-
chronized a Jurkat T cell line with the G1/S phase inhibi-
tor, aphidicolin, and examined the DNA content of
mock- and HIV-1-infected cells by flow cytometry .
Provirus expression was measured by the insertion of
murine CD24 (heat stable antigen, HSA) or the enhanced
green fluorescent protein (EGFP) into the Nef coding
region (Figure 1A) [3,4,7]. Synchronized cells were
released from aphidicolin after 16 hours of infection, and
DNA content was monitored every 3 hours for 24 hours
(Figure 1B and 1C). Cells infected with HIV-1HSAe-f+r+
(Env-negative, Vif-positive, Vpr-positive), expressing
both Vif and Vpr proteins, progressed to the G2/M phase
around 6 hours after release, similar to mock-infected
cells (Figure 1B and 1C). Although mock-infected cells
underwent mitosis and returned to G1 phase at 9 hours
* Correspondence: firstname.lastname@example.org
† Contributed equally
1Laboratory of Immunology, National Institutes of Allergy and Infectious
Diseases, National Institutes of Health, Bethesda, Maryland, USA
Full list of author information is available at the end of the article
Sakai et al. Virology Journal 2011, 8:219
© 2011 Sakai et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
post-release, the majority of Vif+Vpr+ cells remained in
G2/M phase for the duration of the experiment (24
hours) (Figure 1B and 1C). By comparison, the G2 arrest
triggered by a e-f+r- virus was less dramatic than the e-f
+r+ virus. Nevertheless, the infected cells showed striking
G2 peaks that were sustained throughout the course of
infection. Of note, the e-f-r- virus moderately delayed the
cell cycle progression of infected cells, but failed to
prevent cells from traversing back to G1 phase around
15-18 hours after the release (Figure 1B). These data
demonstrate that Vif on its own was able to arrest cells at
the G2 phase, but was less potent than cell cycle blockade
by Vif and Vpr together.
To elucidate the molecular defects causing cell cycle
arrest in Vif-expressing cells, we examined the translo-
cation of MPF, which occurs at the G2/M phase
Figure 1 Vif causes prominent G2 arrest in the absence of Vpr. (A) Schematic of the NL4-3 HIV-1 molecular clones used. The NL4-3e-n-HSA
(e-f+r+) lacks a functional env gene, due to a frameshift mutation, and the nef gene was replaced with HSA . The NL4-3e-n-GFPhas the same
env frameshift, but the nef gene was replaced with EGFP [4,6]. The e-f+r- and e-f-r- mutants of NL4-3e-n-HASand NL4-3e-n-GFPhave been
previously described [3,4]. (B) Jurkat cells were synchronized with a G1/S-phase blocker, aphidicolin, for 16 hours and then released for 10 hours
prior to infection. The cells were blocked again at the time of infection with the following HIV-1 NL4-3e-n-HSAstrains at an MOI of 5: e-f+r+, e-f+r-
, or e-f-r-. DNA content was examined by flow cytometry using the cell permeable dye DRAQ5 (Biostatus) every 3 hours after release from the
second aphidicolin blockade as previously described . Infected cells highly expressing HSA and mock-infected cells are shown. These data are
representative of three experiments using either the HSA- or GFP-expressing viruses. (C) The percentage of cells in the G2 phase of the cell cycle
was graphed over the course of the experiment represented in panel B. Data are represented as the mean ± the standard deviation (SD) of
quadruplicates and are representative of three experiments.
Sakai et al. Virology Journal 2011, 8:219
Page 2 of 8
transition. Synchronized Jurkat cells were examined at
3-hour intervals post-release for the subcellular localiza-
tion of Cdk1 by confocal immunofluorescence micro-
scopy as previously described (Figure 2A and 2B). In
mock-infected cells, Cdk1 was mostly cytoplasmic at 6
hours post-release. It then translocated into the nucleus
at 9 hours, prior to disappearing presumably due to pro-
teasomal degradation (Figure 2A and 2B). By contrast,
Cdk1 remained essentially cytoplasmic in cells infected
with either the e-f+r+ or the e-f+r- virus (Figure 2Aa-c
and 2B). The cells infected with the e-f-r- virus, lacking
both Vif and Vpr, exhibited similar nuclear translocation
of Cdk1 as the mock-infected cells, but with delayed
kinetics (Figure 2Aa-c and 2B). Thus, our data suggest
that Vif inhibits Cdk1 nuclear translocation whether or
not Vpr is present.
Activation of Cdk1 is regulated by phosphorylation
[18,21]. Inactive Cdk1 remains cytoplasmic with inhibi-
tory phosphates attached to Thr14 and Tyr15 until cells
clear the G2 checkpoint [27,40-42]. Because of the per-
sistent cytoplasmic localization in HIV-infected cells, we
examined the phosphorylation status at Tyr15 of Cdk1
by western blot analysis as previously described . In
mock-infected cells, Tyr15 phosphorylation increased at
3 hours post-release, coinciding with the S to G2 phase
transition (Figure 1B and 2B). Then, after 6 hours, the
phosphorylated form, as well as the total amount of
Cdk1, started to decline (Figure 2C and 2D). However,
the ratio of phosphorylated to total Cdk1 continued to
increase until 12 hours post-release (Figure 2D). This
ratio then decreased until 18 hours post-release when
both the phosphorylated form and the total amount of
Cdk1 were barely detectable (Figure 2C and 2D). These
data suggest that Cdk1 had become active, carried out
its mitosis promoting function, and undergone degrada-
tion. Cells infected with the e-f+r+ virus maintained
constant Cdk1 protein levels but showed inconsistent
Tyr15 phosphorylation (Figure 2C and 2D). However,
Cdk1 was strongly phosphorylated and remained unde-
graded throughout the course of the experiment in cells
infected with the e-f+r- virus (Figure 2C and 2D). Inter-
estingly, Tyr15 phosphorylation was more pronounced
in Vif-induced G2 blockade (in the absence of Vpr).
While previous studies have shown that cells expressing
Vpr have more phosphorylated Cdk1 than normal cells
[43-45], Vpr can also increase phosphorylation of Cdk1
at Thr14 as well as Tyr15 . This may explain the
discrepancy in the Tyr15 status between cells infected
with the e-f+r+ virus versus the e-f+r- virus in our
experiments. Perhaps the Cdk1 in the cells infected with
the e-f+r+ virus, expressing both Vpr and Vif, is still
inactive due to Thr14 phosphorylation. The phosphory-
lation of Cdk1 Tyr15 in cells infected with the e-f-r-
virus was similar to the mock-infected cells, with
increased and decreased phosphorylation following the
stages of the cell cycle (Figures 1B and 2C and 2D).
These data suggest that Vif can directly impede Cdk1
activation and subsequent nuclear translocation.
We also investigated the effect of HIV-1-induced cell
cycle arrest on CyclinB1. Immunofluorescent staining of
mock-infected cells showed that CyclinB1 translocates
from the cytoplasm (6 hours post-release) to the nucleus
(9 hours) (Figure 3Aa-b and 3B). Similar to Cdk1,
CyclinB1 was evidently degraded and almost undetect-
able after 12-15 hours when cells re-entered the G1
phase (Figures 1B and 3Ac-d and 3B). This was expected
since CyclinB1 is known to be degraded upon exit from
mitosis [46-52]. Intriguingly, unlike Cdk1, CyclinB1
retained the ability to translocate into the nucleus by 9
hours in cells infected with either the e-f+r+ or the e-f+r-
virus (Figure 3Ab and 3B). In addition, CyclinB1 levels
persisted in infected cells throughout the course of the
experiment (Figure 3A and 3B). However, after 12 hours,
many HIV-infected cells that expressed Vif showed
CyclinB1 had returned to the cytoplasm (Figure 3Ac-d
and 3B). Cells infected with the e-f-r- virus, which do not
express Vif or Vpr, exhibited similar CyclinB1 transloca-
tion and degradation as mock-infected cells, but with
delayed kinetics (Figure 3A and 3B). Western blot analy-
sis confirmed the findings from microscopy. The levels of
CyclinB1 in mock-infected cells increased when cells
were in G2 phase (6 hours), declined when cells were in
G1 and S phases (12-18 hours), and began to increase
again after 21 hours (Figures 1B and 3C). By contrast,
CyclinB1 levels remained stable throughout the entire
time course in HIV-1-infected cells that expressed Vif
(Figure 3C). Similar to the confocal data, the levels of
CyclinB1 in cells infected with the e-f-r- virus followed a
similar, but delayed pattern compared to mock-infected
cells (Figure 3C).
Because CyclinB1 retained the capacity to enter the
nucleus in arrested cells expressing Vif, in the presence
or absence of Vpr, we also examined PLK1, which phos-
phorylates the CyclinB1 CRS to target it to the nucleus
. In mock-infected cells and cells infected with the
e-f-r- virus, PLK1 expression peaked around 6-9 hours,
occurring before and during the nuclear accumulation
of CyclinB1 as its published role would suggest. PLK1
expression then decreased at 12-18 hours, when cells
progressed through mitosis (Figure 1B and 3C). Cells
infected with either Vif-expressing virus exhibited an
abnormal phenotype. Once PLK1 expression was
induced between 3 and 12 hours, the levels remained
elevated, possibly due to the G2 cell cycle arrest (Figure
3C). This increased expression of PLK1 could possibly
explain the ability of CyclinB1 to still translocate into
the nucleus. However, PLK1 expression remained ele-
vated when CyclinB1 returned to the cytoplasm after
Sakai et al. Virology Journal 2011, 8:219
Page 3 of 8
12 hours (Figure 3). This may be due to a difference in
binding to the 14-3-3θ scaffold protein (increased for
CyclinB1 and decreased for PLK1) as we have previously
A recent study reported that Vif induced a delay in
cell cycle rather than complete arrest . It is difficult
to compare our results and those reported by DeHart
and colleagues because the experimental system used in
their study, especially the cells (SupT1 cells) and level of
infection (multiplicities of infection [MOI] of 1-2), is dif-
ferent from ours [3,15]. We observed that the G2 arrest
due to Vif alone was most pronounced at a high MOI.
Furthermore, unlike the combination of Vpr and Vif,
Vif-induced cell cycle arrest showed a direct relationship
with increasing MOI (and therefore the increasing
expression level of Vif), whereas the arrest caused by
the e-f+r+ virus appeared to be independent of MOI
(Figure 4A-D). However, similar to the cell cycle
Figure 2 Vif-induced dysfunction of Cdk1. Jurkat cells were synchronized and infected as in Figure 1 with the GFP-expressing viruses. These
data are representative of three experiments with infection efficiencies ranging from 85-95% based on GFP expression. (A) Nuclear translocation
of Cdk1 was barely detectable in Vif-expressing cells. Vif and Cdk1 localization patterns were visualized by immunofluorescent confocal
microscopy using the following antibodies: rabbit anti-Vif (AIDS Research and Reference Reagent Program [ARRRP]) , mouse anti-Cdk1 (anti-
cdc2, Santa Cruz Biotechnology), goat anti-rabbit-Alexa565 (Molecular Probes), and goat anti-mouse-Alexa647 (Molecular Probes). GFP, expressed
by infected cells, was measured by direct fluorescence. Nuclei were counterstained with Hoechst 33342 (Molecular Probes). (B) At least 350 cells
were counted from representative fields, and the percentage of cells showing the indicated phenotypes for Cdk1 were plotted at each time
point. (C) Cdk1 is phosphorylated (inactivated) in Vif-expressing cells. Bulk lysates were prepared at the indicated time points and analyzed for
inhibitory Cdk1 Tyr15 phosphorylation by immunoblotting using a rabbit anti-phospho-Cdk1 Tyr15 antibody (anti-phospho-cdc2 Tyr15, Cell
Signaling Technology). Total Cdk1 expression was examined using a mouse anti-Cdk1 antibody (anti-cdc2, Santa Cruz Biotechnology) on the
same blot after stripping off the phospho-Cdk1 antibody. An immunoblot using a mouse-anti b-actin antibody (anti-b-actin, Sigma-Aldrich) is
provided as a loading control. (D) Densitometry of the bands in panel C was performed using ImageJ (NIH), and the intensity of each band was
normalized to b-actin. The normalized ratio of phospho-Cdk1 to total Cdk1 was plotted for each time point.
Sakai et al. Virology Journal 2011, 8:219
Page 4 of 8
blockade caused by the e-f+r+ virus, cells infected with
the e-f+r- virus showed the highest G2/G1 ratio on day
2 post-infection, when the expression of the provirus
peaks (Figure 4 and data not shown). We observed
strong cell cycle arrest caused by high levels of Vif
expression in both synchronized and non-synchronized
Jurkat cells (Figures 1B and 4B). As previously shown
, the e-f-r- virus caused no significant G2 arrest (Fig-
ure 4E and 4F). Thus, high expression of Vif arrested
cells in the G2 phase, although not to the same degree
as the combined expression of Vpr and Vif.
The HIV-1 accessory proteins Vif and Vpr block cells
at the G2 phase of the cell cycle . We now provide
some molecular insights on how Vif induces cell cycle
Figure 3 Vif-induced abnormalities in CyclinB1 and PLK1. Jurkat cells were synchronized and infected as in Figure 1 with the GFP-expressing
viruses. These data are representative of three experiments with infection efficiencies ranging from 85-95% based on GFP expression. (A)
CyclinB1 localizes to the nucleus in Vif-expressing cells, but is not degraded normally. Subcellular localization of CyclinB1 and Vif was determined
by immunofluorescent confocal microscopy as in Figure 2 panel A using a mouse anti-Vif antibody (ARRRP) [54-56] and a rabbit anti-CyclinB1
antibody (Santa Cruz Biotechnology). (B) At least 350 cells were counted from representative fields, and the percentage of cells showing either a
degraded, nuclear, or cytoplasmic phenotype for CyclinB1 were plotted at each time point. (C) CyclinB1 degradation is not observed in infected
cells, and PLK1 expression is elevated in infected cells. A duplicate blot from Figure 2 panel C was probed with a mouse anti-CyclinB1 antibody
(Cell Signaling Technology). PLK1 expression was examined using a mouse anti-PLK1 antibody (Upstate/Millipore). The expression of b-actin
using a mouse-anti b-actin antibody (anti-b-actin, Sigma-Aldrich) is provided as a loading control.
Sakai et al. Virology Journal 2011, 8:219
Page 5 of 8
arrest. Our study strongly suggests that Cdk1-CyclinB1
dysregulation accounts for Vif-mediated G2 blockade.
However, the precise mechanism of this dysfunction
remains to be determined. Intriguingly, cells infected
with the e-f+r+ or the e-f+r- viruses showed differences
in phenotypes, especially the status of Cdk1, likely indi-
cating different mechanisms of action for the two
Why HIV-1 has evolved two molecularly different
mechanisms for G2 inhibition is an important unanswered
Figure 4 Vif-induced cell cycle arrest is partially dependent on MOI. Non-synchronized Jurkat cells were infected with NL4-3e-n-GFPe-f+r+ (A
and B), e-f+r- (C and D), and e-f-r- (E and F) at the indicated MOIs. (A, C, and E) DNA content of GFP+cells was examined by flow cytometry
using DRAQ5 at 24 and 42 hours post-infection as previously described . The percentage of the G2 and G1 populations were modeled using
the Watson Pragmatic cell cycle model and the ratio was plotted . All data were represented as mean ± the SD of triplicates. The ns, single
(*), double (**), and triple (***) asterisks denote p > 0.05, p < 0.05, p < 0.01, and p < 0.001, respectively, using a one-way analysis of variance
(ANOVA) with multiple-comparison tests (Prism, Graph-Pad Software). For each MOI at each time point the G2/G1 ratio for e-f+r+>e-f+r->e-f-r-
with p < 0.00001 as analyzed by a one-way ANOVA with multiple-comparison tests. (B, D, and F) The expression of Vif and Vpr increases with
increasing MOIs. Lysates were prepared from infected cells at 24 hours post-infection and analyzed for the expression of viral proteins by
immunoblotting. The following antibodies were used: mouse anti-p24-capsid (ARRRP) [55,57], rabbit anti-Vpr (a kind gift from B. Sun), mouse
anti-Vif (ARRRP) [54-56], and mouse-anti-b-actin (Sigma-Aldrich). Densitometry of the bands was performed using ImageJ (NIH), and the intensity
of each band was normalized to b-actin. The fold change of Vif expression is shown under the immunoblots. These data are representative of
Sakai et al. Virology Journal 2011, 8:219
Page 6 of 8
question. Both forms of arrest could be byproducts of viral
metabolism. Alternatively, it may be that the G2 phase is
so important for a productive viral infection cycle that the
virus must ensure G2 cell cycle arrest by two distinct
mechanisms. In either case, both Vif and Vpr are major
players in HIV-1 cytopathicity, and virus-induced cell
cycle inhibition may be intrinsically related to viral patho-
genesis. Consistent with this possibility, our previous work
showed that both Vif and Vpr can independently contri-
bute to HIV-1 cytopathicity . It will be important to
determine how the specific molecular pathways converge
in necrotic death of arrested, infected T-cells.
List of Abbreviations
HIV-1: human immunodeficiency virus type 1; HSA: heat-stable antigen; MOI:
multiplicity of infection; PLK1: polo-like kinase 1; Thr: threonine; Tyr: tyrosine;
Vif: viral infectivity factor; Vpr: viral protein R.
The following reagents were obtained through the AIDS Research and
Reference Reagent Program, Division of AIDS, NIAID, NIH: HIV-1 Vif
Monoclonal Antibody (#319) from Dr. Michael H. Malim and HIV-1HXB2Vif
Antiserum from Dr. Dana Gabuzda. We thank Owen Schwartz for microscopy
assistance; Anthony Fauci for generous availability of his BL-3 facility; Diane
Bolton and the members of the Lenardo laboratory for helpful discussions.
This research was supported by the Intramural Research Program of the
National Institutes of Allergy and Infectious Diseases, National Institutes of
Health, USA. KS was partially supported as a Research Fellow by Japan
Society for the Promotion of Science (JSPS).
1Laboratory of Immunology, National Institutes of Allergy and Infectious
Diseases, National Institutes of Health, Bethesda, Maryland, USA.2Division of
Viral Immunology, Center for AIDS Research, Kumamoto University,
Kumamoto, Japan.3Department of Pediatric Oncology, Dana-Farber Cancer
Institute, Harvard Medical School, Boston, Massachusetts, USA.4Institut
National de la Santé et de la Recherche Médicale, Unité 542, Université Paris-
Sud, Hôpital Paul Brousse, Villejuif, France.
KS, RAB, and MJL designed the study. KS, RAB, BCD, and NB carried out the
experiments. KS, RAB, BCD, NB, and MJL interpreted data. KS, RAB, and MJL
wrote the manuscript. MJL provided financial support. All authors read and
approved the final manuscript.
The authors declare that they have no competing interests.
Received: 18 August 2010 Accepted: 11 May 2011
Published: 11 May 2011
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Cite this article as: Sakai et al.: Human Immunodeficiency Virus Type 1
Vif causes dysfunction of Cdk1 and CyclinB1: implications for cell cycle
arrest. Virology Journal 2011 8:219.
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