Previous Article | Next Article 
Molecular and Cellular Biology, December 1998, p. 7288-7293, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Nuclear Export Is Required for Degradation of
Endogenous p53 by MDM2 and Human Papillomavirus E6
Deborah A.
Freedman and
Arnold J.
Levine*
Department of Molecular Biology, Princeton
University, Princeton, New Jersey 08544
Received 22 June 1998/Returned for modification 29 July
1998/Accepted 14 September 1998
 |
ABSTRACT |
The MDM2 oncoprotein targets the p53 tumor suppressor protein for
degradation when the two proteins are expressed in cells. The
regulation of p53 levels by MDM2 requires the ability of MDM2 to be
exported from the nucleus by utilizing its nuclear export signal (NES).
The drug leptomycin B (LMB) blocks the formation of nuclear export
complexes consisting of CRM1, RanGTP, and NES-containing proteins. It
is predicted that LMB should inhibit nuclear-cytoplasmic shuttling by
MDM2 and subsequently stabilize p53. This communication demonstrates
that LMB treatment of various cell lines led to an increase in the
steady-state levels of the p53 protein as a result of an increase in
its stability. The stabilized p53 protein localized to the nucleus and
was an active transcription factor. These results indicate that the low
steady-state levels of p53 in the absence of DNA damage result from
p53's nuclear export for cytoplasmic degradation. LMB also led to p53
stabilization in cell lines that contain human papillomavirus (HPV) DNA
and express HPV E6, a protein that targets p53 for degradation. MDM2 is
not necessary for E6-dependent degradation of p53, as evidenced by the
observation that E6 promoted p53 degradation in cells lacking
endogenous MDM2. In addition, LMB reduced E6's ability to degrade p53
in the absence of MDM2, demonstrating that complete degradation of p53
by E6 requires nuclear export and therefore likely occurs in
cytoplasmic proteasomes. These data suggest that the nuclear export of
p53 to the cytoplasm for degradation is a general mechanism for
regulating p53 levels.
| |
INTRODUCTION |
The p53 tumor suppressor protein is
present at low levels in the cell. In response to physiological stress
such as DNA damage, p53 protein levels rise as a result of a
posttranslational mechanism that leads to its stabilization
(25). As a consequence, p53 becomes active as a
transcription factor, inducing the transcription of genes such as
bax, p21, and GADD45 that help p53
mediate its functions of growth arrest and apoptosis (8, 16, 26,
29). These activities contribute to p53's role as a tumor
suppressor by preventing the establishment of mutations in future
generations of cells. The activated p53 protein also induces the
transcription of the Mdm2 oncogene (1, 2), whose
protein product binds to p53 and inhibits its functions as a
transcription factor and tumor suppressor (4-6, 31). This
inhibition of p53 by MDM2 can occur by at least two mechanisms. The
first is an inhibition of p53's ability to activate transcription of
its downstream target genes; MDM2 binds directly to the transactivation
domain of p53 and blocks its interaction with the TBP-associated
factors TAFII70 and TAFII31 (22, 23,
41). Consistent with this observation, MDM2 can block p53
activity in an in vitro transcription assay (42). In
addition, recent experiments demonstrate that the MDM2 oncoprotein can
target p53 for degradation (15, 17). MDM2 is thus
hypothesized to form an autoregulatory feedback loop with p53, in which
p53 can control both its own levels and its own activity by inducing
the expression of its negative regulator, MDM2 (20, 45).
The Mdm2 oncogene is amplified or overexpressed in a variety
of human tumors (3, 7, 18, 19, 30, 35) and can function as
an oncogene in tissue culture systems (9, 10). Its ability
to inhibit p53 may well contribute to its activity as an oncogene. MDM2
can bind directly to p53 via its amino-terminal domain of approximately
115 amino acids, and this domain is sufficient to block p53's
transcriptional activation (4). MDM2's ability to target
p53 for degradation, however, requires an additional domain of the MDM2
protein: its nuclear export signal (NES) sequence, which is also
required for its ability to shuttle between the nucleus and the
cytoplasm (37). Because nuclear export by MDM2 is required
for its ability to target p53 for degradation, MDM2's nuclear-cytoplasmic shuttling presumably mediates the degradation of
p53 by cytoplasmic proteasomes.
Whether this model truly relates to the regulation of endogenous p53
levels in cells is the subject of this paper. Previous experiments have
relied upon transfection of MDM2 and p53 expression plasmids and do not
therefore determine whether nuclear export regulates the normally low
steady-state levels of endogenous p53 in cells in the absence of DNA
damage (37). This paper demonstrates that the low
steady-state level of p53 in a variety of cell lines is in fact
dependent on nuclear export through the use of a nuclear export
inhibitor, leptomycin B (LMB) (11, 13, 33). The addition of
LMB to various cell lines led to an increase in the levels of the p53
protein, which was localized in the cell nucleus and transcriptionally
active. The effect of LMB on p53 levels results from an increase in the
half-life of the p53 protein, suggesting that nuclear export is
required for the efficient degradation of p53. LMB also elevated the
p53 levels in cell lines that contain human papillomavirus (HPV) E6
protein, and it is shown here that HPV E6 can target p53 for
degradation by a mechanism that at least partially depends on nuclear
export and not on the presence of the MDM2 protein. This result
suggests that the HPV E6 protein, its cellular partner E6-AP, or
another cellular protein mediates the shuttling of p53 to the cytoplasm
for degradation. Thus, the use of nuclear export for the degradation of
p53 may be a general mechanism that regulates the levels and therefore
the activity of the p53 tumor suppressor protein.
| |
MATERIALS AND METHODS |
Cell lines and LMB.
The SiHa and CaSki cell lines were a
gift from Peter Howley (Harvard University). The 1KO and 2KO cell lines
were derived from primary embryo fibroblasts (27) provided
by Guillermina Lozano (M. D. Anderson Cancer Center); the lack of
endogenous MDM2 in the 2KO cell line was confirmed by Northern analysis
as well as by immunoprecipitation followed by Western blotting. LMB, a
gift from Patrick Chene and Michael Becker (Novartis), was stored at
20°C as a 1-mg/ml stock solution in ethanol, and fresh working dilutions in ethanol were made weekly.
Immunoprecipitation and Western analysis.
Cell lysates were
prepared by resuspension of cell pellets and vortexing in lysis buffer
(50 mM Tris-HCl [pH 7.5], 150 mM NaCl, 0.5% Nonidet P-40, and 1 mM
EDTA, with the fresh addition of 1 mM dithiothreitol, 100 µM
phenylmethylsulfonyl fluoride, 1 µM pepstatin A, and 1 µM E-64)
followed by centrifugation to remove insoluble debris. The
concentration of protein in the lysates was determined by Bradford
analysis (Bio-Rad), and equal amounts of protein were either
immunoprecipitated or separated by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred
to nitrocellulose (Hybond ECL [enhanced chemiluminescence] system;
Amersham Life Science). Immunoprecipitations were performed by
incubating lysates with protein A-Sepharose (Sigma) and a polyclonal antibody against MDM2. The beads were then pelleted and washed twice in
SNNTE (50 mM Tris [pH 7.4], 5 mM EDTA, 5% sucrose, 1% Nonidet P-40,
0.5 M NaCl) before products were separated by SDS-PAGE and transferred
to nitrocellulose. MDM2 was then detected on the blots by incubation
with a combination of the monoclonal antibodies (MAbs) 2A10 and 4B11.
For straight Western analysis without immunoprecipitation, p53 was
detected with a combination of MAb 421 and MAb 1801, p21 with
polyclonal serum specific for the human p21 protein, and 
-catenin
and Ran with MAbs from Transduction Laboratories. Blots were then
incubated with antimouse immunoglobulin G (IgG) conjugated to
horseradish peroxidase (Transduction Laboratories) or goat anti-rabbit
IgG peroxidase (Cappel Organon Teknika Corp.), followed by detection by
chemiluminescence (Amersham Life Science).
Indirect immunofluorescence.
Cells were treated with 5 ng of
LMB per ml 20 h prior to fixation in 100% methanol at 20°C
for 5 min. The p53 protein was detected by indirect immunofluorescence
as described previously (12) with 15 µg of protein
A-purified MAb 421 per ml, followed by incubation with goat anti-mouse
IgG-Alexa568 (Molecular Probes, Inc.). Cell staining was observed by
confocal microscopy.
Pulse-chase analysis.
Half of the cell cultures were treated
with 5 ng of LMB per ml for 2.5 h. All of the cells were then
prestarved for 30 min in Dulbecco's modified Eagle's medium (DMEM)
minus methionine with 2% dialyzed fetal bovine serum, maintaining the
same LMB concentration. 35S-Express Easy Tag (NEN Life
Science Products) at 75 µCi/ml was then added to each plate. After
the 3-h labeling pulse, the cells were rinsed three times with
phosphate-buffered saline and chased in DMEM with 10% fetal bovine
serum and 2 mM cold methionine, either with or without the addition of
5 ng of LMB per ml. Cells were harvested at various times after the
chase, lysates were made, and equal numbers of counts were precipitated
with MAb 421. Immunoprecipitates were washed three times, each for 5 min in 1 ml of SNNTE and were then separated by SDS-PAGE and visualized by autoradiography. Quantification was performed on a phosphoimager.
Statistical analysis.
The fraction of p53 remaining at each
time point of each pulse-chase experiment, compared to that in the
relevant treated or untreated unchased sample, was calculated. The
natural log of the average of four experiments was plotted versus time,
and linear regression was performed to derive the half-life of p53 in
each case. The statistical significance of the difference between the
fractions of p53 remaining with and without LMB at each time point was
determined by multivariate analysis of covariance with Quick STATISTICA
4.0 (StatSoft). The Scheffé test was employed for post hoc
analysis. A P level of less than 0.01 was considered significant.
HPV E6-mediated degradation of p53.
Cells were transfected
with combinations of 2 µg of pRC/CMV-hp53; 4 µg of pCMV-HDM2 or its
empty vector, CMV-neo-bam3; 2 µg of p1436 (E6) and 2 µg
of its empty vector, p1318; or 4 µg of p1318 (28) and 2 µg of pGL2-Control (Promega) by lipofection with Lipofectamine
reagent (Life Technologies) following the procedure supplied by the
manufacturer. When indicated, LMB was added 8 h after the start of
the transfection, following washing of the cells with PBS. Cells were
lysed 24 h posttransfection, and luciferase activity in each
sample was determined by using the Enhanced Luciferase Assay kit
(Analytical Luminescence Laboratory) as described in the procedures
provided by the manufacturer. Equal relative light units were run on
each lane of SDS-PAGE for detection of p53 by Western analysis.
Quantification was performed with the NIH Image program.
| |
RESULTS |
Inhibition of nuclear export increases the steady-state levels of
p53.
The drug LMB blocks the formation of ternary complexes in the
nucleus, consisting of CRM1, RanGTP, and proteins that contain NES
sequences (11, 13, 33). The formation of these complexes is
required for the nuclear export of NES-containing proteins; LMB
therefore blocks their export from the nucleus (11, 13, 33).
MDM2 contains an NES sequence that mediates its nuclear export and is
required for its ability to target p53 for degradation (37).
The addition of LMB to cells is then expected to prevent the nuclear
export of MDM2, which in turn should result in the stabilization of the
p53 protein in these cells. Consistent with this model, the addition of
LMB to a variety of cell lines that contain wild-type or mutant p53 led
to a marked increase in the steady-state levels of the p53 protein
(Fig. 1). Total cellular protein from
untreated cells or from cells 6 or 20 h after treatment with 5 ng
of LMB per ml was fractionated by SDS-PAGE, and the p53 protein was
quantitatively detected by immunoblotting. As expected, no p53 was
detected in the p53-null human lung carcinoma cell line H1299 (Fig. 1).
LMB addition caused approximate increases in the levels of wild-type
p53 20 h post-LMB treatment of 16-fold in the human osteosarcoma
cell line SJSA, 5-fold in the human breast carcinoma cell line MCF-7,
and 4-fold in the immortalized murine cell line 12(1). The levels of
mutant p53 in the human melanoma cell line SK-mel-2 increased
approximately fivefold (Fig. 1). The addition of LMB to each of these
cell lines, however, did not lead to an increase in the steady-state
levels of the -catenin and Ran proteins in the same lysates (Fig.
1), indicating that the effect is specific for p53. This increase in
p53 levels, seen as early as 3 h after the addition of the drug
and at a concentration as low as 1 ng/ml (data not shown), suggests
that LMB may in fact stabilize the p53 protein by blocking its export
to the cytoplasm for degradation.
View larger version (29K):
[in this window]
[in a new window]
|
FIG. 1.
LMB increases p53 protein levels in several cell lines.
LMB (5 ng/ml) was added 6 or 20 h prior to the harvest of the
cells. The steady-state levels of p53, -catenin, and Ran in each
lysate were observed by separation of total protein by SDS-PAGE and
immunoblotting with antibodies specific for each of the proteins. The
name of each cell line is indicated at the top; less protein was used
for the determination of p53 levels in SK-mel-2, due to the high levels
of the mutant p53 protein in these cells. The addition of LMB led to an
increase in the levels of the p53 protein in each cell line, except in
the p53-null H1299 cell line. Such an effect of LMB is not seen in the
levels of the -catenin and Ran proteins, demonstrating the
specificity of the observation for p53.
|
|
The induction of p53 by LMB was also observed in these cells by
immunofluorescence. In the SJSA cell line, the p53 protein
is present
at low levels, localized in a diffuse manner throughout
the cell (Fig.
2A). As expected, the addition of 5 ng of
LMB per
ml resulted in increased levels of p53 protein that was
predominantly
localized to the nucleus at 20 h after the addition
of the drug
(Fig.
2B). In the case of MCF-7 cells, which contain
cytoplasmic
p53 (Fig.
2C), the increased levels of p53 protein found
20 h
after the addition of 5 ng of LMB per ml were observed mainly
in the nucleus (Fig.
2D). One interpretation of this result is
that the
p53 protein in MCF-7 cells constantly shuttles between
the nucleus and
the cytoplasm, likely in an MDM2-dependent fashion,
and the pool of p53
is partially degraded in the cytoplasm. Upon
the addition of LMB, the
p53 protein that enters the nucleus is
retained in this compartment,
where it cannot be degraded by cytoplasmic
proteasomes.
View larger version (156K):
[in this window]
[in a new window]
|
FIG. 2.
The p53 protein induced by LMB is localized to the
nucleus. SJSA cells (A and B) and MCF-7 cells (C and D) were left
untreated (A and C) or were treated with 5 ng of LMB per ml (B and D)
20 h prior to fixation. The p53 protein was detected with MAb 421, followed by goat anti-mouse IgG-Alexa568. In both cases, the induced
p53 protein is localized to the nucleus of the cells following LMB
treatment.
|
|
To determine if the p53 protein that is induced by the addition of LMB
is in fact active as a transcription factor, the levels
of
p53-responsive MDM2 and p21 proteins were determined before
and after
the addition of LMB. Using the same lysates as in Fig.
1,
immunoprecipitation followed by Western analysis was performed
for MDM2
and Western analysis was performed for p21. The addition
of 5 ng of LMB
per ml to SJSA and MCF-7 cells, which contain wild-type
p53, led to an
increase in the levels of MDM2 and p21 protein
(Fig.
3). The levels of these two proteins did
not, however, increase
in response to LMB addition in the SK-mel-2 cell
line, which contains
mutant p53, and in the p53-null H1299 cell line
(Fig.
3). These
results indicate that the increases in MDM2 and p21
proteins are
dependent on the presence of functional p53 protein, and
thus
the p53 protein induced by LMB treatment of cells is active for
transcription.
View larger version (36K):
[in this window]
[in a new window]
|
FIG. 3.
The p53 protein induced by LMB is transcriptionally
active. Cells were treated with 5 ng of LMB per ml 6 and 20 h
prior to harvesting. The steady-state levels of p53 and p21 in each
lysate were observed by separation of total protein by SDS-PAGE
followed by immunoblotting. MDM2 protein was immunoprecipitated prior
to immunoblotting. The levels of MDM2 and p21 increased in response to
LMB in wild-type p53-containing SJSA and MCF-7 cells, but not in
SK-mel-2 and H1299 cells that lack functional p53 protein. A longer
exposure is shown for the left half of the MDM2 blot because of the
lower levels of MDM2 in these cells, and a shorter exposure is shown
for the p21 blot of MCF-7 cells due to the higher levels of p21 in this
cell line.
|
|
The addition of LMB to cells led to an inhibition of the cell cycle
which was not solely due to the increased levels of p53,
since cells
that lack the p53 protein were arrested upon the addition
of LMB. These
p53-negative cells include the H1299 cell line and
an immortalized
mouse cell line, 10(3) (data not
shown).
Inhibition of nuclear export by LMB stabilizes the p53
protein.
To determine whether the change in the steady-state
levels of p53 after the addition of LMB was a result of a block of the p53 protein's degradation in the cytoplasm via its retention in the
nucleus, the half-life of the p53 protein was determined in the
presence and absence of LMB by using the 12(1) immortalized mouse 3T3
cell line. Half of the cell cultures were treated with 5 ng of LMB per
ml in growth media for 2.5 h, in media lacking methionine for 30 min, and then in media containing [35S]methionine for
3 h. These cells were also chased in media containing an excess of
unlabeled methionine in the presence of the same concentration of LMB.
The remaining cell cultures were incubated in media lacking
methionine, labeled, and then chased, all without the addition of
LMB. Lysates were immunoprecipitated with MAb 421 against p53 or
with MAb 419 against simian virus 40 large T antigen to serve as a
negative control. After washing, the immunoprecipitates were separated
by SDS-PAGE and visualized by autoradiography (Fig. 4A). After quantification of four
separate experiments, the half-life of p53 was found to increase
approximately fourfold after LMB addition from an average of 57 min to
236 min (P < 0.005; Fig. 4B). This difference
indicates that the increase in the steady-state levels of p53 seen
after blocking nuclear export is in fact due to an inhibition of the
degradation of p53. As seen in Fig. 4, the p53 protein, although
increased in stability, is still being degraded in the presence of LMB.
This degradation could be a result of the p53 protein being degraded by
an MDM2-independent mechanism using nuclear proteasomes or could result
from an incomplete block of nuclear export by LMB. The cellular
proteasome inhibitor MG-132 inhibits both nuclear and cytoplasmic
proteasomes and leads to a virtually complete block in p53 degradation
(24).
View larger version (43K):
[in this window]
[in a new window]
|
FIG. 4.
LMB leads to an increase in the half-life of p53 in
12(1) cells. (A) Five plates of 12(1) cells were pretreated with 5 ng
of LMB per ml for 2.5 h prior to being prestarved for 30 min in
media lacking methionine and then were labeled with 75 µCi of
35S-Express per ml for 3 h, both in the presence of
the same concentration of LMB. Six plates were prestarved and labeled
similarly, but without the addition of LMB. Cell were washed, chased
with media containing excess cold methionine with or without 5 ng of
LMB per ml, and harvested at different times. Samples were
immunoprecipitated with MAb 419 (419 IP) against simian virus 40 large
T antigen as a negative control or with MAb 421 against p53, washed,
and run on SDS-PAGE. Molecular weights (MW) are shown to the left
(thousands). (B) The levels of p53 remaining at each time were
quantified from four separate experiments on a phosphoimager,
background was subtracted, and values were normalized to the samples
that were not chased in the same experiment. The average fractions of
p53 remaining and their associated standard deviations are shown at the
various chase times on the left-hand plot, in the absence of LMB (solid
line) and in the presence of 5 ng of LMB per ml (dashed line). The
natural log (ln) transform of this plot is also shown on the right;
linear regression of this plot was used to calculate the average
half-life of p53 without (57 min) and with (236 min) the addition of 5 ng of LMB per ml. The difference between the fraction of p53 remaining
at each time point in the presence or absence of LMB was tested by
multivariate analysis of covariance with the Scheffé test for
post hoc analysis. Asterisks (*) denote time points that are
significantly different between the two conditions (P < 0.01).
|
|
HPV E6-mediated degradation of p53 also involves nuclear
export.
In order to explore whether mechanisms for p53 degradation
other than that which are mediated by MDM2 also require nuclear export,
cell lines containing integrated DNA sequences from HPV types 16 and 18 (HPV-16 and -18, respectively) were used. Such cells express both HPV
E6 and E7 proteins; the E6 protein from these viral isotypes binds to
p53 and targets it for degradation (38, 43). The p53 protein
levels in HeLa (HPV-18), SiHa (HPV-16), and CaSki (HPV-16) cells
increased 20 h after the addition of 5 ng of LMB per ml (Fig.
5), suggesting that E6-mediated
degradation of p53 utilizes a nuclear export step. One possible
explanation for this observation is that the export of p53 is mediated
by the low levels of the MDM2 protein in these cells; thus MDM2 and E6
could cooperate to target p53 for cytoplasmic degradation. To test this
possibility, a transfection experiment was performed with the MDM2-null
2KO cell line, which was obtained by passage on a 3T3 schedule of
primary mouse embryo fibroblasts derived from a mouse null for both the
p53 and Mdm2 genes. Cotransfection of HPV-16 E6
and p53 expression plasmids into these cells led to a decrease in the
amount of p53 detected in these cells by immunoblotting as compared to
the p53 levels obtained by transfection of the p53 plasmid alone (Fig.
6, lanes 3 and 4). Similarly,
cotransfection of an MDM2 expression plasmid with p53 led to a
decreased amount of p53 protein (Fig. 6, lanes 3 and 5). The reduction
in the p53 protein levels after transfection of E6 or MDM2 plasmids
(approximately 10- and 3-fold, respectively) was similar to that
observed in the 1KO cell line, which is null only for p53 and contains
functional MDM2 (data not shown). This result indicates that the E6
protein does not require MDM2 for the degradation of p53.
View larger version (19K):
[in this window]
[in a new window]
|
FIG. 5.
LMB induces the p53 protein in HPV E6-expressing cells.
Cells were treated, lysates were prepared, and p53 was detected by
immunoblotting as described in the legend to Fig. 1.
Baculovirus-purified human p53 was loaded in the first lane as a
positive control. HeLa cells contain HPV-18 sequences, while SiHa and
CaSki cells contain HPV-16 sequences. The p53 protein levels in each of
these cell lines increased after 20 h in the presence of 5 ng of
LMB per ml. Molecular weights (MW) are shown to the left (thousands).
|
|
View larger version (24K):
[in this window]
[in a new window]
|
FIG. 6.
HPV E6 degradation of p53 is MDM2-independent and LMB
sensitive. The 2KO cell line, which lacks endogenous MDM2, was
transfected with pGL2-Control which leads to constitutive expression of
luciferase (lanes 2 to 8), empty vectors (lane 2), human p53 (lanes 3 to 8), HPV-16 E6 (lanes 4 and 7), and/or human MDM2 (lanes 5 and 8).
Eight hours after transfection, 5 ng of LMB per ml was added to half of
the samples (lanes 6 to 8). At 24 h posttransfection, lysates were
made and luciferase activity in each sample was determined in order to
normalize for transfection efficiency. Equal relative light units were
run on SDS-PAGE, and p53 was visualized by immunoblotting as described
in the legend to Fig. 1. E6-mediation degradation of p53 does not
require MDM2, but is partially blocked by LMB. Molecular weights (MW)
are shown to the left (thousands).
|
|
To determine if the degradation of p53 by E6 was dependent on nuclear
export even in the absence of MDM2, LMB was added to
the cells 8 h
posttransfection. As expected, the addition of 5
ng of LMB per ml to
cells transfected with MDM2 and p53 almost
completely blocked the
ability of the MDM2 protein to lower the
steady-state levels of p53 in
the transfected cells (Fig.
6, lanes
6 and 8; a less than 20%
reduction in p53 levels). In contrast,
the addition of LMB only
partially blocked the ability of E6 to
lower the steady-state levels of
p53 in transfected cells, such
that a three- to fourfold reduction was
still observed (Fig.
5,
lanes 6 and 7). One reason for the incomplete
block in E6-mediated
p53 degradation may be that E6 can target p53 for
degradation
in both the nucleus and cytoplasm. Alternatively, it may be
that
there is too much E6 protein present in this overexpression assay
for a full block of p53 degradation by LMB. One final explanation
for
the incomplete effect of LMB on E6-mediated degradation in
this assay
could be the speed with which E6 can target p53 for
degradation in the
cytoplasm, such that some degradation occurs
before p53 can enter the
nucleus. The addition of LMB does, however,
consistently decrease the
level of p53 degradation by E6 by at
least twofold in this assay,
indicating that E6-mediated degradation
of p53 utilizes a nuclear
export function that can be observed
in the absence of MDM2. It remains
to be determined if the HPV
E6 protein itself has nuclear export
ability or whether some other
cellular protein performs this
function.
| |
DISCUSSION |
The ability of LMB to stabilize the p53 protein as shown in this
communication clearly demonstrates that the low steady-state levels of
p53 in the absence of DNA damage are maintained by CRM1-dependent nuclear export. Although it is possible that LMB could, in addition to
blocking nuclear export, be causing DNA damage or providing a DNA
damage-like signal to p53, several observations indicate that this is
unlikely. For instance, the induction of p53 by LMB occurs in cell
lines that do not respond to certain types of DNA damage. The HeLa cell
line does not respond after UV irradiation by increasing levels of p53;
however, this cell line responds to LMB addition with an increase in
levels of p53 (Fig. 5 and data not shown). In addition, one effect of
DNA damage, the p53-independent decrease in MDM2 protein levels
(44), does not occur after the addition of LMB to the SJSA
cell line, whereas it does occur after UV irradiation (data not shown).
This result demonstrates that the cellular response to DNA damage can
be differentiated from the response to LMB.
As seen in Fig. 4, the addition of LMB does not completely block the
degradation of p53 in the 12(1) immortalized murine cell line. One
possible explanation for this observation is that the block of nuclear
export by LMB is incomplete, allowing some p53 protein to be exported
to the cytoplasm, where it is rapidly degraded. Alternatively, it is
possible that p53 is degraded, albeit with slower kinetics, in the
nucleus. Such degradation is likely to be MDM2-independent, for reasons
discussed below, and may represent a second pathway for the regulation
of p53 levels.
Three lines of evidence suggest that MDM2's degradation of p53 occurs
exclusively in the cytoplasm. The first is that a mutant form of MDM2
that is unable to be exported from the nucleus is also unable to target
p53 for degradation (37). Second, the NLS-rex protein, which
efficiently competes with MDM2 for shuttling from the nucleus to the
cytoplasm, blocks MDM2's ability to leave the nucleus and its ability
to mediate p53 degradation (37). The third line of evidence
is that the addition of LMB, which blocks nuclear export, blocks
MDM2-mediated degradation of p53 (Fig. 6). Proteasomal complexes are
located in both the cytoplasm and the nucleus, and there is some
indication that the two populations have a unique subunit composition
(34, 36, 40). It is likely that the proteasomal components
recognized by MDM2 after shuttling p53 are exclusively cytoplasmic.
Alternatively, a factor may be present in the nucleus that blocks
MDM2's interaction with nuclear proteasomes.
The E6 protein, on the other hand, may be able to target p53 to both
cytoplasmic and nuclear proteasomes, because the addition of LMB to
cells transfected with p53 and E6 plasmids only partially blocks the
degradation of p53 by E6 (Fig. 6). This result suggests that E6, unlike
MDM2, might recognize both nuclear and cytoplasmic proteasomes.
Alternatively, it is possible that the E6 protein is able to degrade a
fraction of the p53 protein present in the cytoplasm prior to its
initial import into the nucleus. Although these possibilities cannot be
distinguished at this point, the partial effect of LMB on E6
degradation of p53 demonstrates that CRM1-dependent nuclear export is
required for the complete degradation of p53 by E6.
That E6-mediated degradation of p53 utilizes a nuclear export step and
that this can occur in the absence of MDM2 suggests that some
NES-containing protein other than MDM2 is shuttling p53 to the
cytoplasm in E6-containing cells. Candidates for this function include
both HPV E6, which contains a potential NES sequence, and E6-AP, which
contains several such potential NES sequences. The shuttling abilities
of both proteins remain to be determined, but evidence suggests that
E6-AP is localized to both the nucleus and the cytoplasm
(14), and the E6 protein has been shown to colocalize with
p53 in the cytoplasm of HeLa, SiHa, and CaSki cells (21). In
addition, p53 itself contains a putative NES and may be able to mediate
its own nuclear export under certain circumstances (39a).
The results presented here support the model presented in Fig.
7 but do not prove that MDM2 is required
for the export of p53 from the nucleus. An alternative model in which
MDM2 and p53 are exported separately from the nucleus, meeting in the
cytoplasm, where MDM2 then targets p53 to cytoplasmic proteasomes, is
also consistent with the data presented here. Recent work shows that p53 itself contains a leucine-rich putative NES present in the tetramerization domain (such that only monomers and dimers should be
exported) and that exogenous wild-type p53 can be exported from the
nucleus in cells lacking MDM2 (39a). These observations indicate that some protein other than MDM2, whether p53 itself or some
other cellular protein, might mediate the nuclear export of p53, at
least, in an overexpression assay. This conclusion is consistent with
the observation that complete p53 degradation by HPV E6 requires a
nuclear export function that occurs in the absence of MDM2 (Fig. 6).
View larger version (30K):
[in this window]
[in a new window]
|
FIG. 7.
A model for the degradation of p53 by MDM2. MDM2, p53,
CRM1, and RanGTP are predicted to form a ternary complex in the
nucleus, which is transported to the cytoplasm through the nuclear
pore. p53 is then targeted to cytoplasmic proteasomes, where it is
degraded. CRM1, Ran (now in the GDP-bound form), and possibly MDM2
return to the nucleus to repeat the process. The addition of LMB
prevents the formation of this complex in the nucleus so that p53 is
not shuttled to the cytoplasm for degradation. As predicted by the
model, p53 levels in the nucleus rise after LMB treatment.
|
|
Several lines of evidence support the model presented in Fig. 7, in
which MDM2 shuttles p53 from the nucleus to the cytoplasm, rather than
the model in which they exit the nucleus separately. First, it is clear
that p53 and MDM2 do interact in the nucleus in many cell lines
(4, 32), consistent with the model presented in Fig. 7.
Second, p53 is localized to the cytoplasm in some cell lines that
overexpress MDM2, such as MCF-7 (Fig. 2C). DNA damage, which modifies
p53 such that it can no longer interact with MDM2, leads to p53
accumulation in the nucleus in these cells (39). This
observation is also consistent with the model in which MDM2 is
responsible for the continual shuttling of p53 molecules from the
nucleus to the cytoplasm, localizing most of the p53 protein there
and/or targeting it for degradation by cytoplasmic proteasomes. Third,
a cytoplasm-localized mutant form (
150-230) of MDM2 can efficiently
bind to p53 in vitro, but fails to bind to and inhibit the
transcriptional activity of p53 in vivo (4), suggesting that
p53 is retained in the nucleus in the absence of the shuttling activity
of MDM2. Experiments are currently under way to directly demonstrate
CRM1-dependent shuttling of p53 by MDM2.
| |
ACKNOWLEDGMENTS |
We thank D. Notterman, D. Resnick, A. Casau, and other members of
the laboratory for helpful discussions and critical reading of the
manuscript. We also thank Peter Howley (Harvard University) and Gigi
Lozano (M. D. Anderson Cancer Center) for cell lines, Patrick
Chene and Michael Becker (Novartis) for LMB, and Andrew Marchini and
Thomas Shenk (Princeton University) for plasmids.
This work was supported by a grant from the Novartis Corporation.
| |
FOOTNOTES |
*
Corresponding author. Present address: The Rockefeller
University, 1230 York Ave., New York, NY 10021-6399. Phone: (212)
327-8134. Fax: (212) 327-7444. E-mail:
alevine{at}rockvax.rockefeller.edu.
| |
REFERENCES |
| 1.
|
Barak, Y.,
E. Gottlieb,
T. Juven-Gershon, and M. Oren.
1994.
Regulation of mdm2 expression by p53: alternative promoters produce transcripts with nonidentical translation potential.
Genes Dev.
8:1739-1749[Abstract/Free Full Text].
|
| 2.
|
Barak, Y.,
T. Juven,
R. Haffner, and M. Oren.
1993.
mdm2 expression is induced by wild type p53 activity.
EMBO J.
12:461-468[Medline].
|
| 3.
|
Bueso-Ramos, C. E.,
Y. Yang,
E. deLeon,
P. McCown,
S. A. Stass, and M. Albitar.
1993.
The human MDM-2 oncogene is overexpressed in leukemias.
Blood
82:2617-2623[Abstract/Free Full Text].
|
| 4.
|
Chen, J.,
J. Lin, and A. J. Levine.
1995.
Regulation of transcription functions of the p53 tumor suppressor by the mdm-2 oncogene.
Mol. Med.
1:142-152[Medline].
|
| 5.
|
Chen, J.,
V. Marechal, and A. J. Levine.
1993.
Mapping of the p53 and mdm-2 interaction domains.
Mol. Cell. Biol.
13:4107-4114[Abstract/Free Full Text].
|
| 6.
|
Chen, J.,
X. Wu,
J. Lin, and A. J. Levine.
1996.
mdm-2 inhibits the G1 arrest and apoptosis functions of the p53 tumor suppressor protein.
Mol. Cell. Biol.
16:2445-2452[Abstract].
|
| 7.
|
Cordon-Cardo, C.,
E. Latres,
M. Drobnjak,
M. R. Oliva,
D. Pollack,
J. M. Woodruff,
M. F. Brennan,
V. Marechal,
J. Chen, and A. J. Levine.
1994.
Molecular abnormalities of mdm-2 and p53 genes in adult soft tissue sarcomas.
Cancer Res.
54:794-799[Abstract/Free Full Text].
|
| 8.
|
El-Deiry, W. S.,
T. Tokino,
V. E. Velculescu,
D. B. Levy,
R. Parsons,
J. M. Trent,
D. Lin,
W. E. Mercer,
K. W. Kinzler, and B. Vogelstein.
1993.
WAF1, a potential mediator of p53 tumor suppression.
Cell
75:817-825[Medline].
|
| 9.
|
Fakharzadeh, S. S.,
S. P. Trusko, and D. L. George.
1991.
Tumorigenic potential associated with enhanced expression of a gene that is amplified in a mouse tumor cell line.
EMBO J.
10:1565-1569[Medline].
|
| 10.
|
Finlay, C. A.
1993.
The mdm-2 oncogene can overcome wild-type p53 suppression of transformed cell growth.
Mol. Cell. Biol.
13:301-306[Abstract/Free Full Text].
|
| 11.
|
Fornerod, M.,
M. Ohno,
M. Yoshida, and I. W. Mattaj.
1997.
CRM1 is an export receptor for leucine-rich nuclear export signals.
Cell
90:1051-1060[Medline].
|
| 12.
|
Freedman, D. A.,
C. B. Epstein,
J. C. Roth, and A. J. Levine.
1997.
A genetic approach to mapping the p53 binding site in the MDM2 protein.
Mol. Med.
3:248-259[Medline].
|
| 13.
|
Fukuda, M.,
S. Asano,
T. Nakamura,
M. Adachi,
M. Yoshida,
M. Yanagida, and E. Nishida.
1997.
CRM1 is responsible for intracellular transport mediated by the nuclear export signal.
Nature
390:308-311[Medline].
|
| 14.
|
Hatakeyama, S.,
J. P. Jensen, and A. M. Weissman.
1997.
Subcellular localization and ubiquitin-conjugating enzyme (E2) interactions of mammalian HECT family ubiquitin protein ligases.
J. Biol. Chem.
272:15085-15092[Abstract/Free Full Text].
|
| 15.
|
Haupt, Y.,
R. Maya,
A. Kazaz, and M. Oren.
1997.
Mdm2 promotes the rapid degradation of p53.
Nature
387:296-299[Medline].
|
| 16.
|
Kastan, M. B.,
Q. Zhan,
W. S. El-Deiry,
F. Carrier,
T. Jacks,
W. V. Walsh,
B. S. Plunkett,
B. Vogelstein, and A. J. Fornace, Jr.
1992.
A mammalian cell cycle checkpoint pathway utilizing p53 and GADD45 is defective in ataxia-telangiectasia.
Cell
71:587-597[Medline].
|
| 17.
|
Kubbutat, M. H. G.,
S. N. Jones, and K. H. Vousden.
1997.
Regulation of p53 stability by Mdm2.
Nature
387:299-303[Medline].
|
| 18.
|
Ladanyi, M.,
C. Cha,
R. Lewis,
S. C. Jhanwar,
A. G. Huvos, and J. H. Healey.
1993.
MDM2 gene amplification in metastatic osteosarcoma.
Cancer Res.
53:16-18[Abstract/Free Full Text].
|
| 19.
|
Leach, F. S.,
T. Tokino,
P. Meltzer,
M. Burrell,
J. D. Oliner,
S. Smith,
D. E. Hill,
D. Sidransky,
K. W. Kinzler, and B. Vogelstein.
1993.
p53 mutation and MDM2 amplification in human soft tissue sarcomas.
Cancer Res.
53:2231-2234[Abstract/Free Full Text].
|
| 20.
|
Levine, A. J.
1997.
p53, the cellular gatekeeper for growth and division.
Cell
88:323-331[Medline].
|
| 21.
|
Liang, X. H.,
M. Volkmann,
R. Klein,
B. Herman, and S. J. Lockett.
1993.
Co-localization of the tumor-suppressor protein p53 and human papillomavirus E6 protein in human cervical carcinoma cell lines.
Oncogene
8:2645-2652[Medline].
|
| 22.
|
Lin, J.,
J. Chen,
B. Elenbaas, and A. J. Levine.
1994.
Several hydrophobic amino acids in the p53 amino-terminal domain are required for transcriptional activation, binding to mdm-2 and the adenovirus 5 E1B 55-kD protein.
Genes Dev.
8:1235-1246[Abstract/Free Full Text].
|
| 23.
|
Lu, H., and A. J. Levine.
1995.
Human TAFII31 protein is a transcriptional coactivator of the p53 protein.
Proc. Natl. Acad. Sci. USA
92:5154-5158[Abstract/Free Full Text].
|
| 24.
|
Maki, C. G.,
J. M. Huibregtse, and P. M. Howley.
1996.
In vivo ubiquitination and proteasome-mediated degradation of p53.
Cancer Res.
56:2649-2654[Abstract/Free Full Text].
|
| 25.
|
Maltzman, W., and L. Czyzyk.
1984.
UV irradiation stimulates levels of p53 cellular tumor antigen in nontransformed mouse cells.
Mol. Cell. Biol.
4:1689-1694[Abstract/Free Full Text].
|
| 26.
|
Miyashita, T., and J. C. Reed.
1995.
Tumor suppressor p53 is a direct transcriptional activator of the human bax gene.
Cell
80:293-299[Medline].
|
| 27.
|
Montes de Oca Luna, R.,
D. S. Wagner, and G. Lozano.
1995.
Rescue of early embryonic lethality in mdm2-deficient mice by deletion of p53.
Nature
378:203-206[Medline].
|
| 28.
|
Munger, K.,
W. C. Phelps,
V. Bubb,
P. M. Howley, and R. Schlegel.
1989.
The E6 and E7 genes of the human papillomavirus type 16 together are necessary and sufficient for transformation of primary human keratinocytes.
J. Virol.
63:4417-4421[Abstract/Free Full Text].
|
| 29.
|
Okamoto, K., and D. Beach.
1994.
Cyclin G is a transcriptional target of the p53 tumor suppressor protein.
EMBO J.
13:4816-4822[Medline].
|
| 30.
|
Oliner, J. D.,
K. W. Kinzler,
P. S. Meltzer,
D. L. George, and B. Vogelstein.
1992.
Amplification of a gene encoding a p53-associated protein in human sarcomas.
Nature
358:80-83[Medline].
|
| 31.
|
Oliner, J. D.,
J. A. Pietenpol,
S. Thiagalingam,
J. Gyuris,
K. W. Kinzler, and B. Vogelstein.
1993.
Oncoprotein MDM2 conceals the activation domain of tumour suppressor p53.
Nature
362:857-860[Medline].
|
| 32.
|
Olson, D. C.,
V. Marechal,
J. Momand,
J. Chen,
C. Romocki, and A. J. Levine.
1993.
Identification and characterization of multiple mdm2 proteins and mdm2-p53 protein complexes.
Oncogene
8:2353-2360[Medline].
|
| 33.
|
Ossareh-Nazari, B.,
F. Bachelerie, and C. Dargemont.
1997.
Evidence for a role of CRM1 in signal-mediated nuclear protein export.
Science
278:141-144[Abstract/Free Full Text].
|
| 34.
|
Palmer, A.,
A. J. Rivett,
S. Thomson,
K. B. Hendil,
G. W. Butcher,
G. Fuertes, and E. Knecht.
1996.
Subpopulations of proteasomes in rat liver nuclei, microsomes and cytosol.
Biochem. J.
316:401-407.
|
| 35.
|
Reifenberger, G.,
L. Liu,
K. Ichimura,
E. E. Schmidt, and V. P. Collins.
1993.
Amplification and overexpression of the MDM2 gene in a subset of human malignant gliomas without p53 mutations.
Cancer Res.
53:2736-2739[Abstract/Free Full Text].
|
| 36.
|
Rivett, A. J.
1998.
Intracellular distribution of proteasomes.
Curr. Opin. Immunol.
10:110-114[Medline].
|
| 37.
|
Roth, J.,
M. Dobbelstein,
D. A. Freedman,
T. Shenk, and A. J. Levine.
1998.
Nucleo-cytoplasmic shuttling of the hdm2 oncoprotein regulates the levels of the p53 protein via a pathway used by the human immunodeficiency virus rev protein.
EMBO J.
17:554-564[Medline].
|
| 38.
|
Scheffner, M.,
B. A. Werness,
J. M. Huibregtse,
A. J. Levine, and P. M. Howley.
1990.
The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53.
Cell
63:1129-1136[Medline].
|
| 39.
|
Shieh, S.-Y.,
M. Ikeda,
Y. Taya, and C. Prives.
1997.
DNA damage-induced phosphorylation of p53 alleviates inhibition by MDM2.
Cell
91:325-334[Medline].
|
| 39a.
| Stommel, J., and G. Wahl. Personal communication.
|
| 40.
|
Strack, P. R.,
E. F. Wajnberg,
L. Waxman, and J. M. Fagan.
1992.
Comparison of the multicatalytic proteinases isolated from the nucleus and cytoplasm of chicken red blood cells.
Int. J. Biochem.
24:887-895[Medline].
|
| 41.
|
Thut, C. J.,
J.-L. Chen,
R. Klemm, and R. Tjian.
1995.
p53 transcriptional activation mediated by coactivators TAFII40 and TAFII60.
Science
267:100-104[Abstract/Free Full Text].
|
| 42.
|
Thut, C. J.,
J. A. Goodrich, and R. Tjian.
1997.
Repression of p53-mediated transcription by MDM2: a dual mechanism.
Genes Dev.
11:1974-1986[Abstract/Free Full Text].
|
| 43.
|
Werness, B. A.,
A. J. Levine, and P. M. Howley.
1990.
Association of human papillomavirus types 16 and 18 E6 proteins with p53.
Science
248:76-79[Abstract/Free Full Text].
|
| 44.
|
Wu, L., and A. J. Levine.
1997.
Differential regulation of the p21/WAF-1 and mdm2 genes after high-dose UV irradiation: p53-dependent and p53-independent regulation of the mdm2 gene.
Mol. Med.
3:441-451[Medline].
|
| 45.
|
Wu, X.,
J. H. Bayle,
D. Olson, and A. J. Levine.
1993.
The p53-mdm-2 autoregulatory feedback loop.
Genes Dev.
7:1126-1132[Abstract/Free Full Text].
|
Molecular and Cellular Biology, December 1998, p. 7288-7293, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Murawala, P., Tripathi, M. M., Vyas, P., Salunke, A., Joseph, J.
(2009). Nup358 interacts with APC and plays a role in cell polarization. J. Cell Sci.
122: 3113-3122
[Abstract]
[Full Text]
-
Mutka, S. C., Yang, W. Q., Dong, S. D., Ward, S. L., Craig, D. A., Timmermans, P. B.M.W.M., Murli, S.
(2009). Identification of Nuclear Export Inhibitors with Potent Anticancer Activity In vivo. Cancer Res.
69: 510-517
[Abstract]
[Full Text]
-
Cai, X., Liu, X.
(2008). Inhibition of Thr-55 phosphorylation restores p53 nuclear localization and sensitizes cancer cells to DNA damage. Proc. Natl. Acad. Sci. USA
105: 16958-16963
[Abstract]
[Full Text]
-
Grespin, M. E., Bonamy, G. M. C., Roggero, V. R., Cameron, N. G., Adam, L. E., Atchison, A. P., Fratto, V. M., Allison, L. A.
(2008). Thyroid Hormone Receptor {alpha}1 Follows a Cooperative CRM1/Calreticulin-mediated Nuclear Export Pathway. J. Biol. Chem.
283: 25576-25588
[Abstract]
[Full Text]
-
Neuber, A., Franke, J., Wittstruck, A., Schlenstedt, G., Sommer, T., Stade, K.
(2008). Nuclear Export Receptor Xpo1/Crm1 Is Physically and Functionally Linked to the Spindle Pole Body in Budding Yeast. Mol. Cell. Biol.
28: 5348-5358
[Abstract]
[Full Text]
-
Shangary, S., Wang, S.
(2008). Targeting the MDM2-p53 Interaction for Cancer Therapy. Clin. Cancer Res.
14: 5318-5324
[Abstract]
[Full Text]
-
Cheong, J. K., Gunaratnam, L., Hsu, S. I-H.
(2008). CRM1-mediated Nuclear Export Is Required for 26 S Proteasome-dependent Degradation of the TRIP-Br2 Proto-oncoprotein. J. Biol. Chem.
283: 11661-11676
[Abstract]
[Full Text]
-
Khacho, M., Mekhail, K., Pilon-Larose, K., Payette, J., Lee, S.
(2008). Cancer-Causing Mutations in a Novel Transcription-Dependent Nuclear Export Motif of VHL Abrogate Oxygen-Dependent Degradation of Hypoxia-Inducible Factor. Mol. Cell. Biol.
28: 302-314
[Abstract]
[Full Text]
-
Chen, Z., Knutson, E., Wang, S., Martinez, L. A., Albrecht, T.
(2007). Stabilization of p53 in Human Cytomegalovirus-initiated Cells Is Associated with Sequestration of HDM2 and Decreased p53 Ubiquitination. J. Biol. Chem.
282: 29284-29295
[Abstract]
[Full Text]
-
Nonclercq, D., Journe, F., Laios, I., Chaboteaux, C., Toillon, R.-A., Leclercq, G., Laurent, G.
(2007). Effect of nuclear export inhibition on estrogen receptor regulation in breast cancer cells. J Mol Endocrinol
39: 105-118
[Abstract]
[Full Text]
-
Derheimer, F. A., O'Hagan, H. M., Krueger, H. M., Hanasoge, S., Paulsen, M. T., Ljungman, M.
(2007). RPA and ATR link transcriptional stress to p53. Proc. Natl. Acad. Sci. USA
104: 12778-12783
[Abstract]
[Full Text]
-
Luo, L., Uerlings, Y., Happel, N., Asli, N. S., Knoetgen, H., Kessel, M.
(2007). Regulation of Geminin Functions by Cell Cycle-Dependent Nuclear-Cytoplasmic Shuttling. Mol. Cell. Biol.
27: 4737-4744
[Abstract]
[Full Text]
-
Nayak, M. S., Yang, J.-M., Hait, W. N.
(2007). Effect of a Single Nucleotide Polymorphism in the Murine Double Minute 2 Promoter (SNP309) on the Sensitivity to Topoisomerase II-Targeting Drugs. Cancer Res.
67: 5831-5839
[Abstract]
[Full Text]
-
Yu, D., Carroll, M., Thomas-Tikhonenko, A.
(2007). p53 status dictates responses of B lymphomas to monotherapy with proteasome inhibitors. Blood
109: 4936-4943
[Abstract]
[Full Text]
-
Lindstrom, M. S., Jin, A., Deisenroth, C., White Wolf, G., Zhang, Y.
(2007). Cancer-Associated Mutations in the MDM2 Zinc Finger Domain Disrupt Ribosomal Protein Interaction and Attenuate MDM2-Induced p53 Degradation. Mol. Cell. Biol.
27: 1056-1068
[Abstract]
[Full Text]
-
Koivusalo, R., Mialon, A., Pitkanen, H., Westermarck, J., Hietanen, S.
(2006). Activation of p53 in Cervical Cancer Cells by Human Papillomavirus E6 RNA Interference Is Transient, but Can Be Sustained by Inhibiting Endogenous Nuclear Export-Dependent p53 Antagonists. Cancer Res.
66: 11817-11824
[Abstract]
[Full Text]
-
Kulikov, R., Winter, M., Blattner, C.
(2006). Binding of p53 to the Central Domain of Mdm2 Is Regulated by Phosphorylation. J. Biol. Chem.
281: 28575-28583
[Abstract]
[Full Text]
-
Chen, Y., Dai, X., Haas, A. L., Wen, R., Wang, D.
(2006). Proteasome-dependent down-regulation of activated Stat5A in the nucleus. Blood
108: 566-574
[Abstract]
[Full Text]
-
Oh, W., Lee, E.-W., Sung, Y. H., Yang, M.-R., Ghim, J., Lee, H.-W., Song, J.
(2006). Jab1 Induces the Cytoplasmic Localization and Degradation of p53 in Coordination with Hdm2. J. Biol. Chem.
281: 17457-17465
[Abstract]
[Full Text]
-
Ohkubo, S., Tanaka, T., Taya, Y., Kitazato, K., Prives, C.
(2006). Excess HDM2 Impacts Cell Cycle and Apoptosis and Has a Selective Effect on p53-dependent Transcription. J. Biol. Chem.
281: 16943-16950
[Abstract]
[Full Text]
-
Jackson, M. W., Patt, L. E., LaRusch, G. A., Donner, D. B., Stark, G. R., Mayo, L. D.
(2006). Hdm2 Nuclear Export, Regulated by Insulin-like Growth Factor-I/MAPK/p90Rsk Signaling, Mediates the Transformation of Human Cells. J. Biol. Chem.
281: 16814-16820
[Abstract]
[Full Text]
-
Zheng, X., Ruas, J. L., Cao, R., Salomons, F. A., Cao, Y., Poellinger, L., Pereira, T.
(2006). Cell-Type-Specific Regulation of Degradation of Hypoxia-Inducible Factor 1{alpha}: Role of Subcellular Compartmentalization. Mol. Cell. Biol.
26: 4628-4641
[Abstract]
[Full Text]
-
Utama, B., Shen, Y. H., Mitchell, B. M., Makagiansar, I. T., Gan, Y., Muthuswamy, R., Duraisamy, S., Martin, D., Wang, X., Zhang, M.-X., Wang, J., Wang, J., Vercellotti, G. M., Gu, W., Li Wang, X.
(2006). Mechanisms for human cytomegalovirus-induced cytoplasmic p53 sequestration in endothelial cells. J. Cell Sci.
119: 2457-2467
[Abstract]
[Full Text]
-
Ferrone, M., Perrone, F., Tamborini, E., Paneni, M. S., Fermeglia, M., Suardi, S., Pastore, E., Delia, D., Pierotti, M. A., Pricl, S., Pilotti, S.
(2006). Functional analysis and molecular modeling show a preserved wild-type activity of p53C238Y.. Molecular Cancer Therapeutics
5: 1467-1473
[Abstract]
[Full Text]
-
Ding, B., Liu, C.-j., Huang, Y., Yu, J., Kong, W., Lengyel, P.
(2006). p204 Protein Overcomes the Inhibition of the Differentiation of P19 Murine Embryonal Carcinoma Cells to Beating Cardiac Myocytes by Id Proteins. J. Biol. Chem.
281: 14893-14906
[Abstract]
[Full Text]
-
Briggs, R. C., Shults, K. E., Flye, L. A., McClintock-Treep, S. A., Jagasia, M. H., Goodman, S. A., Boulos, F. I., Jacobberger, J. W., Stelzer, G. T., Head, D. R.
(2006). Dysregulated Human Myeloid Nuclear Differentiation Antigen Expression in Myelodysplastic Syndromes: Evidence for a Role in Apoptosis.. Cancer Res.
66: 4645-4651
[Abstract]
[Full Text]
-
Nishi, M., Kawata, M.
(2006). Brain Corticosteroid Receptor Dynamics and Trafficking: Implications from Live Cell Imaging. Neuroscientist
12: 119-133
[Abstract]
-
Lengner, C. J., Steinman, H. A., Gagnon, J., Smith, T. W., Henderson, J. E., Kream, B. E., Stein, G. S., Lian, J. B., Jones, S. N.
(2006). Osteoblast differentiation and skeletal development are regulated by Mdm2-p53 signaling.. JCB
172: 909-921
[Abstract]
[Full Text]
-
Giri, D. K., Ali-Seyed, M., Li, L.-Y., Lee, D.-F., Ling, P., Bartholomeusz, G., Wang, S.-C., Hung, M.-C.
(2005). Endosomal Transport of ErbB-2: Mechanism for Nuclear Entry of the Cell Surface Receptor. Mol. Cell. Biol.
25: 11005-11018
[Abstract]
[Full Text]
-
Mekhail, K., Khacho, M., Carrigan, A., Hache, R. R.J., Gunaratnam, L., Lee, S.
(2005). Regulation of ubiquitin ligase dynamics by the nucleolus. JCB
170: 733-744
[Abstract]
[Full Text]
-
Stewart, D., Ghosh, A., Matlashewski, G.
(2005). Involvement of Nuclear Export in Human Papillomavirus Type 18 E6-Mediated Ubiquitination and Degradation of p53. J. Virol.
79: 8773-8783
[Abstract]
[Full Text]
-
Acheampong, E. A., Parveen, Z., Muthoga, L. W., Wasmuth-Peroud, V., Kalayeh, M., Bashir, A., Diecidue, R., Mukhtar, M., Pomerantz, R. J.
(2005). Molecular Interactions of Human Immunodeficiency Virus Type 1 with Primary Human Oral Keratinocytes. J. Virol.
79: 8440-8453
[Abstract]
[Full Text]
-
Boulanger, J., Vezina, A., Mongrain, S., Boudreau, F., Perreault, N., Auclair, B. A., Laine, J., Asselin, C., Rivard, N.
(2005). Cdk2-dependent Phosphorylation of Homeobox Transcription Factor CDX2 Regulates Its Nuclear Translocation and Proteasome-mediated Degradation in Human Intestinal Epithelial Cells. J. Biol. Chem.
280: 18095-18107
[Abstract]
[Full Text]
-
Bader, A. G., Vogt, P. K.
(2005). Inhibition of Protein Synthesis by Y Box-Binding Protein 1 Blocks Oncogenic Cell Transformation. Mol. Cell. Biol.
25: 2095-2106
[Abstract]
[Full Text]
-
Xia, J., Kemper, B.
(2005). Structural Determinants of Constitutive Androstane Receptor Required for Its Glucocorticoid Receptor Interacting Protein-1-mediated Nuclear Accumulation. J. Biol. Chem.
280: 7285-7293
[Abstract]
[Full Text]
-
Meertens, L., Chevalier, S., Weil, R., Gessain, A., Mahieux, R.
(2004). A 10-Amino Acid Domain within Human T-cell Leukemia Virus Type 1 and Type 2 Tax Protein Sequences Is Responsible for Their Divergent Subcellular Distribution. J. Biol. Chem.
279: 43307-43320
[Abstract]
[Full Text]
-
Cullinan, S. B., Gordan, J. D., Jin, J., Harper, J. W., Diehl, J. A.
(2004). The Keap1-BTB Protein Is an Adaptor That Bridges Nrf2 to a Cul3-Based E3 Ligase: Oxidative Stress Sensing by a Cul3-Keap1 Ligase. Mol. Cell. Biol.
24: 8477-8486
[Abstract]
[Full Text]
-
Ghosh, A., Stewart, D., Matlashewski, G.
(2004). Regulation of Human p53 Activity and Cell Localization by Alternative Splicing. Mol. Cell. Biol.
24: 7987-7997
[Abstract]
[Full Text]
-
Trausch-Azar, J. S., Lingbeck, J., Ciechanover, A., Schwartz, A. L.
(2004). Ubiquitin-Proteasome-mediated Degradation of Id1 Is Modulated by MyoD. J. Biol. Chem.
279: 32614-32619
[Abstract]
[Full Text]
-
Suzuki, N., Shibata, Y., Urano, T., Murohara, T., Muramatsu, T., Kadomatsu, K.
(2004). Proteasomal Degradation of the Nuclear Targeting Growth Factor Midkine. J. Biol. Chem.
279: 17785-17791
[Abstract]
[Full Text]
-
Rogoff, H. A., Pickering, M. T., Frame, F. M., Debatis, M. E., Sanchez, Y., Jones, S., Kowalik, T. F.
(2004). Apoptosis Associated with Deregulated E2F Activity Is Dependent on E2F1 and Atm/Nbs1/Chk2. Mol. Cell. Biol.
24: 2968-2977
[Abstract]
[Full Text]
-
Monte, M., Benetti, R., Collavin, L., Marchionni, L., Del Sal, G., Schneider, C.
(2004). hGTSE-1 Expression Stimulates Cytoplasmic Localization of p53. J. Biol. Chem.
279: 11744-11752
[Abstract]
[Full Text]
-
Perry, M. E.
(2004). Mdm2 in the Response to Radiation. Mol Cancer Res
2: 9-19
[Abstract]
[Full Text]
-
Li, M., Brooks, C. L., Wu-Baer, F., Chen, D., Baer, R., Gu, W.
(2003). Mono- Versus Polyubiquitination: Differential Control of p53 Fate by Mdm2. Science
302: 1972-1975
[Abstract]
[Full Text]
-
Iwakuma, T., Lozano, G.
(2003). MDM2, An Introduction. Mol Cancer Res
1: 993-1000
[Abstract]
[Full Text]
-
Moll, U. M., Petrenko, O.
(2003). The MDM2-p53 Interaction. Mol Cancer Res
1: 1001-1008
[Abstract]
[Full Text]
-
Deb, S. P.
(2003). Cell Cycle Regulatory Functions of the Human Oncoprotein MDM2. Mol Cancer Res
1: 1009-1016
[Abstract]
[Full Text]
-
Rasoulpour, R. J., Schoenfeld, H. A., Gray, D. A., Boekelheide, K.
(2003). Expression of a K48R Mutant Ubiquitin Protects Mouse Testis from Cryptorchid Injury and Aging. Am. J. Pathol.
163: 2595-2603
[Abstract]
[Full Text]
-
O'Keefe, K., Li, H., Zhang, Y.
(2003). Nucleocytoplasmic Shuttling of p53 Is Essential for MDM2-Mediated Cytoplasmic Degradation but Not Ubiquitination. Mol. Cell. Biol.
23: 6396-6405
[Abstract]
[Full Text]
-
JOSEPH, T. W., ZAIKA, A., MOLL, U. M.
(2003). Nuclear and cytoplasmic degradation of endogenous p53 and HDM2 occurs during down-regulation of the p53 response after multiple types of DNA damage. FASEB J.
17: 1622-1630
[Abstract]
[Full Text]
-
Amazit, L., Alj, Y., Tyagi, R. K., Chauchereau, A., Loosfelt, H., Pichon, C., Pantel, J., Foulon-Guinchard, E., Leclerc, P., Milgrom, E., Guiochon-Mantel, A.
(2003). Subcellular Localization and Mechanisms of Nucleocytoplasmic Trafficking of Steroid Receptor Coactivator-1. J. Biol. Chem.
278: 32195-32203
[Abstract]
[Full Text]
-
Kinyamu, H. K., Archer, T. K.
(2003). Estrogen Receptor-Dependent Proteasomal Degradation of the Glucocorticoid Receptor Is Coupled to an Increase in Mdm2 Protein Expression. Mol. Cell. Biol.
23: 5867-5881
[Abstract]
[Full Text]
-
Renton, A., Llanos, S., Lu, X.
(2003). Hypoxia induces p53 through a pathway distinct from most DNA-damaging and stress-inducing agents. Carcinogenesis
24: 1177-1182
[Abstract]
[Full Text]
-
Arabi, A., Rustum, C., Hallberg, E., Wright, A. P. H.
(2003). Accumulation of c-Myc and proteasomes at the nucleoli of cells containing elevated c-Myc protein levels. J. Cell Sci.
116: 1707-1717
[Abstract]
[Full Text]
-
McCoy, M. A., Gesell, J. J., Senior, M. M., Wyss, D. F.
(2003). Flexible lid to the p53-binding domain of human Mdm2: Implications for p53 regulation. Proc. Natl. Acad. Sci. USA
100: 1645-1648
[Abstract]
[Full Text]
-
Le Roux, L. G., Moroianu, J.
(2003). Nuclear Entry of High-Risk Human Papillomavirus Type 16 E6 Oncoprotein Occurs via Several Pathways. J. Virol.
77: 2330-2337
[Abstract]
[Full Text]
-
Bartl, S., Ban, J., Weninger, H., Jug, G., Kovar, H.
(2003). A small nuclear RNA, hdm365, is the major processing product of the human mdm2 gene. Nucleic Acids Res
31: 1136-1147
[Abstract]
[Full Text]
-
Mendrysa, S. M., McElwee, M. K., Michalowski, J., O'Leary, K. A., Young, K. M., Perry, M. E.
(2003). mdm2 Is Critical for Inhibition of p53 during Lymphopoiesis and the Response to Ionizing Irradiation. Mol. Cell. Biol.
23: 462-472
[Abstract]
[Full Text]
-
Lingbeck, J. M., Trausch-Azar, J. S., Ciechanover, A., Schwartz, A. L.
(2003). Determinants of Nuclear and Cytoplasmic Ubiquitin-mediated Degradation of MyoD. J. Biol. Chem.
278: 1817-1823
[Abstract]
[Full Text]
-
Itoh, M., Adachi, M., Yasui, H., Takekawa, M., Tanaka, H., Imai, K.
(2002). Nuclear Export of Glucocorticoid Receptor is Enhanced by c-Jun N-Terminal Kinase-Mediated Phosphorylation. Mol. Endocrinol.
16: 2382-2392
[Abstract]
[Full Text]
-
Eichwald, V., Daeffler, L., Klein, M., Rommelaere, J., Salome, N.
(2002). The NS2 Proteins of Parvovirus Minute Virus of Mice Are Required for Efficient Nuclear Egress of Progeny Virions in Mouse Cells. J. Virol.
76: 10307-10319
[Abstract]
[Full Text]
-
Wang, X., Pongrac, J. L., DeFranco, D. B.
(2002). Glucocorticoid Receptors in Hippocampal Neurons that Do Not Engage Proteasomes Escape from Hormone-Dependent Down-Regulation but Maintain Transactivation Activity. Mol. Endocrinol.
16: 1987-1998
[Abstract]
[Full Text]
-
Harada, J. N., Shevchenko, A., Shevchenko, A., Pallas, D. C., Berk, A. J.
(2002). Analysis of the Adenovirus E1B-55K-Anchored Proteome Reveals Its Link to Ubiquitination Machinery. J. Virol.
76: 9194-9206
[Abstract]
[Full Text]
-
Rogoff, H. A., Pickering, M. T., Debatis, M. E., Jones, S., Kowalik, T. F.
(2002). E2F1 Induces Phosphorylation of p53 That Is Coincident with p53 Accumulation and Apoptosis. Mol. Cell. Biol.
22: 5308-5318
[Abstract]
[Full Text]
-
Groulx, I., Lee, S.
(2002). Oxygen-Dependent Ubiquitination and Degradation of Hypoxia-Inducible Factor Requires Nuclear-Cytoplasmic Trafficking of the von Hippel-Lindau Tumor Suppressor Protein. Mol. Cell. Biol.
22: 5319-5336
[Abstract]
[Full Text]
-
DeFranco, D. B.
(2002). Navigating Steroid Hormone Receptors through the Nuclear Compartment. Mol. Endocrinol.
16: 1449-1455
[Abstract]
[Full Text]
-
Alarcon-Vargas, D., Ronai, Z.'e.
(2002). p53-Mdm2--the affair that never ends. Carcinogenesis
23: 541-547
[Abstract]
[Full Text]
-
Glickman, M. H., Ciechanover, A.
(2002). The Ubiquitin-Proteasome Proteolytic Pathway: Destruction for the Sake of Construction. Physiol. Rev.
82: 373-428
[Abstract]
[Full Text]
-
Migliorini, D., Danovi, D., Colombo, E., Carbone, R., Pelicci, P. G., Marine, J.-C.
(2002). Hdmx Recruitment into the Nucleus by Hdm2 Is Essential for Its Ability to Regulate p53 Stability and Transactivation. J. Biol. Chem.
277: 7318-7323
[Abstract]
[Full Text]
-
Garcia, J. F., Villuendas, R., Sanchez-Beato, M., Sanchez-Aguilera, A., Sanchez, L., Prieto, I., Piris, M. A.
(2002). Nucleolar p14ARF Overexpression in Reed-Sternberg Cells in Hodgkin's Lymphoma : Absence of p14ARF/Hdm2 Complexes Is Associated with Expression of Alternatively Spliced Hdm2 Transcripts. Am. J. Pathol.
160: 569-578
[Abstract]
[Full Text]
-
Korgaonkar, C., Zhao, L., Modestou, M., Quelle, D. E.
(2002). ARF Function Does Not Require p53 Stabilization or Mdm2 Relocalization. Mol. Cell. Biol.
22: 196-206
[Abstract]
[Full Text]
-
Lohrum, M. A. E., Woods, D. B., Ludwig, R. L., Balint, E., Vousden, K. H.
(2001). C-Terminal Ubiquitination of p53 Contributes to Nuclear Export. Mol. Cell. Biol.
21: 8521-8532
[Abstract]
[Full Text]
-
Gu, J., Nie, L., Wiederschain, D., Yuan, Z.-M.
(2001). Identification of p53 Sequence Elements That Are Required for MDM2-Mediated Nuclear Export. Mol. Cell. Biol.
21: 8533-8546
[Abstract]
[Full Text]
-
Kawai, H., Nie, L., Wiederschain, D., Yuan, Z.-M.
(2001). Dual Role of p300 in the Regulation of p53 Stability. J. Biol. Chem.
276: 45928-45932
[Abstract]
[Full Text]
-
Vogt Sionov, R., Coen, S., Goldberg, Z., Berger, M., Bercovich, B., Ben-Neriah, Y., Ciechanover, A., Haupt, Y.
(2001). c-Abl Regulates p53 Levels under Normal and Stress Conditions by Preventing Its Nuclear Export and Ubiquitination. Mol. Cell. Biol.
21: 5869-5878
[Abstract]
[Full Text]
-
Gu, J., Nie, L., Kawai, H., Yuan, Z.-M.
(2001). Subcellular Distribution of p53 and p73 Are Differentially Regulated by MDM2. Cancer Res.
61: 6703-6707
[Abstract]
[Full Text]
-
Zilfou, J. T., Hoffman, W. H., Sank, M., George, D. L., Murphy, M.
(2001). The Corepressor mSin3a Interacts with the Proline-Rich Domain of p53 and Protects p53 from Proteasome-Mediated Degradation. Mol. Cell. Biol.
21: 3974-3985
[Abstract]
[Full Text]
-
Zhang, Y., Xiong, Y.
(2001). A p53 Amino-Terminal Nuclear Export Signal Inhibited by DNA Damage-Induced Phosphorylation. Science
292: 1910-1915
[Abstract]
[Full Text]
-
Wang, G., McCaffery, J. M., Wendland, B., Dupré, S., Haguenauer-Tsapis, R., Huibregtse, J. M.
(2001). Localization of the Rsp5p Ubiquitin-Protein Ligase at Multiple Sites within the Endocytic Pathway. Mol. Cell. Biol.
21: 3564-3575
[Abstract]
[Full Text]
-
Wang, S., Shi, X.
(2001). Mechanisms of Cr(VI)-induced p53 activation: the role of phosphorylation, mdm2 and ERK. Carcinogenesis
22: 757-762
[Abstract]
[Full Text]
-
Zhang, Y., Xiong, Y.
(2001). Control of p53 Ubiquitination and Nuclear Export by MDM2 and ARF. Cell Growth Differ.
12: 175-186
[Abstract]
[Full Text]
-
Modestou, M., Puig-Antich, V., Korgaonkar, C., Eapen, A., Quelle, D. E.
(2001). The Alternative Reading Frame Tumor Suppressor Inhibits Growth through p21-dependent and p21-independent Pathways. Cancer Res.
61: 3145-3150
[Abstract]
[Full Text]
-
Liang, X. H., Yu, J., Brown, K., Levine, B.
(2001). Beclin 1 Contains a Leucine-rich Nuclear Export Signal That Is Required for Its Autophagy and Tumor Suppressor Function. Cancer Res.
61: 3443-3449
[Abstract]
[Full Text]
-
Hofmann, W., Reichart, B., Ewald, A., Muller, E., Schmitt, I., Stauber, R. H., Lottspeich, F., Jockusch, B. M., Scheer, U., Hauber, J., Dabauvalle, M.-C.
(2001). Cofactor Requirements for Nuclear Export of Rev Response Element (Rre)-And Constitutive Transport Element (Cte)-Containing Retroviral Rnas: An Unexpected Role for Actin. JCB
152: 895-910
[Abstract]
[Full Text]
-
Seluanov, A., Gorbunova, V., Falcovitz, A., Sigal, A., Milyavsky, M., Zurer, I., Shohat, G., Goldfinger, N., Rotter, V.
(2001). Change of the Death Pathway in Senescent Human Fibroblasts in Response to DNA Damage Is Caused by an Inability To Stabilize p53. Mol. Cell. Biol.
21: 1552-1564
[Abstract]
[Full Text]
-
Wang, X. Q., Ongkeko, W. M., Lau, A. W. S., Leung, K. M., Poon, R. Y. C.
(2001). A Possible Role of p73 on the Modulation of p53 Level through MDM2. Cancer Res.
61: 1598-1603
[Abstract]
[Full Text]
-
Nakamura, S., Roth, J. A., Mukhopadhyay, T.
(2000). Multiple Lysine Mutations in the C-Terminal Domain of p53 Interfere with MDM2-Dependent Protein Degradation and Ubiquitination. Mol. Cell. Biol.
20: 9391-9398
[Abstract]
[Full Text]
-
Rodriguez, M. S., Desterro, J. M. P., Lain, S., Lane, D. P., Hay, R. T.
(2000). Multiple C-Terminal Lysine Residues Target p53 for Ubiquitin-Proteasome-Mediated Degradation. Mol. Cell. Biol.
20: 8458-8467
[Abstract]
[Full Text]
-
Lin, J., Jin, X., Page, C., Sondak, V. K., Jiang, G., Reynolds, R. K.
(2000). A Modified p53 Overcomes mdm2-mediated Oncogenic Transformation: A Potential Cancer Therapeutic Agent. Cancer Res.
60: 5895-5901
[Abstract]
[Full Text]
-
Petersen, B. O., Wagener, C., Marinoni, F., Kramer, E. R., Melixetian, M., Denchi, E. L., Gieffers, C., Matteucci, C., Peters, J.-M., Helin, K.
(2000). Cell cycle- and cell growth-regulated proteolysis of mammalian CDC6 is dependent on APC-CDH1. Genes Dev.
14: 2330-2343
[Abstract]
[Full Text]
-
Pollenz, R. S., Barbour, E. R.
(2000). Analysis of the Complex Relationship between Nuclear Export and Aryl Hydrocarbon Receptor-Mediated Gene Regulation. Mol. Cell. Biol.
20: 6095-6104
[Abstract]
[Full Text]
-
Hietanen, S., Lain, S., Krausz, E., Blattner, C., Lane, D. P.
(2000). Activation of p53 in cervical carcinoma cells by small molecules. Proc. Natl. Acad. Sci. USA
97: 8501-8506
[Abstract]
[Full Text]
-
Goodman, R. H., Smolik, S.
(2000). CBP/p300 in cell growth, transformation, and development. Genes Dev.
14: 1553-1577
[Full Text]
-
Nevels, M., Rubenwolf, S., Spruss, T., Wolf, H., Dobner, T.
(2000). Two Distinct Activities Contribute to the Oncogenic Potential of the Adenovirus Type 5 E4orf6 Protein. J. Virol.
74: 5168-5181
[Abstract]
[Full Text]
-
Marchenko, N. D., Zaika, A., Moll, U. M.
(2000). Death Signal-induced Localization of p53 Protein to Mitochondria. A POTENTIAL ROLE IN APOPTOTIC SIGNALING. J. Biol. Chem.
275: 16202-16212
[Abstract]
[Full Text]
-
Ashcroft, M., Taya, Y., Vousden, K. H.
(2000). Stress Signals Utilize Multiple Pathways To Stabilize p53. Mol. Cell. Biol.
20: 3224-3233
[Abstract]
[Full Text]
-
Chen, F., Chang, D., Goh, M., Klibanov, S. A., Ljungman, M.
(2000). Role of p53 in Cell Cycle Regulation and Apoptosis following Exposure to Proteasome Inhibitors. Cell Growth Differ.
11: 239-246
[Abstract]
[Full Text]
-
Molinari, A. M., Bontempo, P., Schiavone, E. M., Tortora, V., Verdicchio, M. A., Napolitano, M., Nola, E., Moncharmont, B., Medici, N., Nigro, V., Armetta, I., Abbondanza, C., Puca, G. A.
(2000). Estradiol Induces Functional Inactivation of p53 by Intracellular Redistribution. Cancer Res.
60: 2594-2597
[Abstract]
[Full Text]
-
Burchardt, M., Burchardt, T., Shabsigh, A., De La Taille, A., Benson, M. C., Sawczuk, I.
(2000). Current Concepts in Biomarker Technology for Bladder Cancers. Clin. Chem.
46: 595-605
[Abstract]
[Full Text]
-
Rosorius, O., Fries, B., Stauber, R. H., Hirschmann, N., Bevec, D., Hauber, J.
(2000). Human Ribosomal Protein L5 Contains Defined Nuclear Localization and Export Signals. J. Biol. Chem.
275: 12061-12068
[Abstract]
[Full Text]
Top
Abstract
Introduction
