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N-p73
Accumulates in Human Neuroblastic Tumors
From the Centre National de Recherche Scientifique-Unité Mixte deRecherche 1598 et Département de Biologie Clinique,*
the Département de Pathologie,
and theDépartement de Pédiatrie,
InstitutGustave Roussy, Villejuif, France; SanofiRecherche,
Labège, France; and theDepartment of Pathology,¶
State University of NewYork at Stony Brook, New York
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Abstract |
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 Top Abstract Materials and MethodsResultsDiscussionReferences |
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N-p73) were present in all NTs. In
addition, only N-p73, but not
full-length proteins, were detected by immunoblotting,
suggesting a greater stability of N-truncated isoforms.
Importantly, as in the adrenal medulla, most NTs showed
p73-positive immunohistological staining with a cellular distribution
and intensity varying according to the neuronal differentiation.
Surprisingly, we observed redistribution of p73 from the
nucleus to the cytoplasm during neuroblastic differentiation. Our data
suggest that, in undifferentiated NTs, a link may exist
between the accumulation of N-p73
variants and the
"nuclear exclusion" of p53.
Although, in contrast to many cancers,2 p53 is not mutated in human neuroblastoma,3 p53 is sequestered in the cytoplasm of only undifferentiated tumors, strongly suggesting that functional inactivation of the p53 protein is associated with aborted differentiation of malignant neuroblasts.4
Several p53 homologous genes, including p73 5 and p63 (also called KET, p51, and p40),6-9 have very recently been identified. Structurally similar to p53, they conserve the three domains—transcriptional activation domain (TAD), DNA-binding domain (DBD), and oligomerization domain (OD)—that typify this broad spectrum sequence-specific transcription factor which plays a major role in regulating cell growth and apoptosis. DBD, the main domain usually examined for mutations of the p53 gene in human cancers, was found to be unaltered in the p73 gene.5,10,11 Unlike p53, which encodes a unique protein, the p63 gene expresses an array of different N- and C-terminal isotypes (with or without TAD) in normal tissues resulting from alternate splicing. In vitro, these isotypes show remarkable divergent capabilities to transactivate p53 reporter genes and to elicit growth-suppression and apoptosis-inducing activities.9 So far, C-terminal variants have been clearly shown to alter p73 transcriptional activity in vivo.12 In contrast, the role of N-terminal isotypes on this activity remains to be elucidated. Concerning their possible role in oncogenesis, p53 homologues radically differ from their tumor suppressor gene (TSG) archetype which is mutated in most cancers,2 and with germline mutations being associated with an increased risk of cancer in both man13 and rodents.14 Indeed, p73 is totally devoid of mutations in many cancers,15-17 and homozygous p63-/-18,19 as well as p73-/- mouse mutants have no cancer phenotype.20 It is however noteworthy that p73-/- mice show marked neurosensorial defects.
Among the p53 homologues, p73 appeared to be the most relevant candidate gene for neuroectodermal dysembryogenesis and/or NB carcinogenesis because its locus (1p36–33) frequently exhibits loss of heterozygosity (LOH) in undifferentiated NB. No p73 mutations have been reported, either in NB cell lines5 or in NB tumors.10,11 However, monoallelic expression has been observed in the SK-N-SH NB cell line,5 suggesting that the activity of the p73 gene may be regulated by epigenetic mechanisms such as imprinting. Another possibility may be the stoichiometry of the various putative p73 transcript variants (with and without TAD) and the functional activity of the corresponding encoded proteins.
We therefore investigated a possible association between p73
and the differentiation process by assessing the expression of this
gene in various types of NTs. We found 1) an array of transcripts
including full-length and N-truncated species, 2) despite multiple
transcripts, a single -N terminally truncated protein in
undifferentiated NB, and 3) immunostaining present in the
cytoplasm and/or nucleus according to histological differentiation.
Altogether, our data establish a relationship between p73
gene expression and NT differentiation, and point out a role for the
p73 gene in sympathetic neuronal differentiation.
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Materials and Methods |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Tumor tissues were collected from primary tumors of children with clinically documented NBs,21 most of whom had been treated with induction chemotherapy. Tumors were snap frozen and stored in liquid N2 until needed. Patient lymphocytes obtained at surgery were separated from peripheral blood by the Ficoll Hypaque gradient method. Before nucleic acid extraction, frozen NB tissue samples were systematically embedded in OCT (Miles Laboratories, USA) and cut into 70-µm-thick slices with a cryostat to be used as a quantitative and qualitative histological control; 5 µm of hematoxylin-eosin-stained tissue flanking both sides of the thick tumor slices used for nucleic acid extraction were examined histologically to determine cellularity, percentages of tumor cells, immature neuroblasts, maturating neuroblasts, and differentiated cells as well as the percentage of fibrosis and necrosis. This procedure allowed us to sort out neuroblastic tumors according to a scale of ganglionic sympathetic differentiation1 as immature neuroblastoma (NB), maturating neuroblastoma (NB/GNB), mature ganglioneuroblastoma (GNB), and fully mature ganglioneuroma (GN), and to select only tumor tissues presenting more than 50% of tumor cells for molecular biology studies. gDNA heterozygosity analysis was performed from 61 patients (35, localized stage; 6, IV-S stage; and 20, IV stage) for whom matched lymphocytes/tumors were available. Due to the rarity of tumor material used for gDNA and cDNA studies, material including homozygous p73 patients of this series was also used for p73 protein studies (immunoblotting and immunohistochemistry).
Neuronal Differentiation of Neuroblastoma SH-SY5Y Cells
The parental human neuroblastoma SH-SY5Y cell line was provided by the European Collection of Cell Cultures (Salisbury, UK). Cells were maintained in Dulbecco’s modified Eagle’s medium (DMEM, Gibco BRL) supplemented with L-glutamine and 10% fetal calf serum (Eurobio, Paris). Neuronal differentiation was obtained by either exogenous or endogenous growth factors. FGF1-transfected clones were obtained as previously described.22 Exogenous induction of SH-SY5Y cells differentiation started 24 hours after plating by exposing the cells to 100 ng/ml NGF (nerve growth factor, Peprotech Inc, Rocky Hill, NJ, USA) and 0.3 µmol/L aphidicolin (Sigma, St. Louis, MO, USA) for 8 days.23 Culture medium was changed every 2 days for the duration of the culture. Both models displayed a marked neuronal differentiation phenotype.
DNA and RNA Preparations
DNAs and total RNAs were prepared from 70-µm thick slices of tumor tissue (about 100 mg) by the guanidinium isothiocyanate-CsCl gradient method. DNA was collected from the supernatant, dialyzed, and proteinase K-treated. After phenol-chloroform deproteinization, DNA was precipitated by ethanol and stored in 10 mmol/L Tris-HCl/1 mmol/L EDTA buffer. RNA was collected at the bottom of the centrifuge tube, washed in 70% ethanol, and precipitated with absolute ethanol. After RNase-free DNase (Gibco BRL) treatment, RNA was purified using RNAzol (Bioprobe).
Determination of Allelic Polymorphism in gDNA and LOH Assessment
gDNA (500 ng) was amplified by polymerase chain reaction (PCR)
using the sense 5' CAC CTG CTC CAG GGA TGC 3' and antisense 5' AAA ATA
GAA GCG TCA GTC 3' primers, as described for the p73
gene.5
Amplified DNA fragments were radiolabeled
using -[32P]dATP (3000 Ci/mmol Amersham,
UK); The PCR products were submitted to StyI (Boehringer,
Mannheim, Germany) restriction polymorphism. D1S76 and D1S80 VNTR
sequences were also analyzed for size polymorphism using primers under
the conditions previously described.24
Imbalance and LOH
were defined as a variation in polymorphic signals between the two
alleles of more than 25% and 50%, respectively.
Semiquantitative Determination of Global Levels of p73 Transcript Species in Tissues
The p73 gene can be transcribed into multiple forms
using alternative promoters and/or alternate splicing. cDNA was
obtained by reverse transcription (RT) of 2 µg of total RNA using
Moloney murine leukemia virus reverse transcriptase (Superscript IITM
RNase H-, Gibco BRL kit) and random hexamers or oligodT to prime the
synthesis under the conditions specified by the manufacturer. After
treatment by RNase H, cDNA was submitted to PCR within the coding
region (from exon 1 to exon 14) using various primer sets to obtain
amplicons at different domains (Figure 1)
. The reaction was conducted for 40
cycles (except for core domain which was 35 cycles) of 1 minute at
95°C, 1 minute for annealing temperature (see below the annealing
temperature for each amplicon) and 2 minutes 30 seconds at 72°C using
a Perkin-Elmer Cetus thermocycler (PE Applied Biosystem). An aliquot
(1/10) of the PCR products was analyzed on 2% agarose gel or
polyacrylamide gel electrophoresis (PAGE) gel and visualized by
ultraviolet illuminator.
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E1F, E3bisF are the forward primers able to reveal transcripts initiated from P1 and P3. (Primer sequence to detect transcript initiated from P2 can be obtained on request from Dr. Caput). Quantification was performed by Phosphorimager scanning (Storm 840, Molecular Dynamics) of each p73 transcript species using GAPDH expression as a loading control.
Immunohistochemical and Immunocytochemical Studies
Immunohistochemical (IHC) studies were performed on frozen tumor sections according to previously reported protocols.4 For immunocytochemical (ICC), SH-SY5Y cells cultured on coverslips were fixed for 30 minutes in 4% paraformaldehyde. In all cases, IHC and ICC incubations were done overnight at 4°C with primary antibody using the streptavidin-biotin peroxidase technique. To detect p73 localization, the primary antibody (Ab) was a rabbit polyclonal Ab raised against p73 human (provided by Sanofi-Recherche, Labège) at a dilution of 1/300 in phosphate-buffered saline (PBS). This antibody recognizes epitopes at the C-terminal residues of the p73 protein. To detect p53 localization, two specific primary monoclonal antibodies, which recognized epitopes between amino acids 32 to 79 (Pab 1801, Oncogene Science, Boston, MA, USA), and 17 to 26 (DO-1, Oncogene Science) were used at a dilution of 1 µg/ml. A biotinylated anti-rabbit IgG and a biotinylated rabbit anti-mouse IgG (Zymed, CA, USA) were used as secondary antibodies. A human neuroblastoma (NT no. 692) with overexpressed nuclear p53 whose gene sequence harbored a missense mutation in the fifth exon was systematically included in each set of experiments as a positive control. Rabbit IgG or normal mouse IgG was used for p73 or p53 experiments, respectively, as a negative control.
P73 Immunoblotting
Protein lysates (50 µg) were submitted to 7.5% sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred
onto BioRad (Hercules, CA, USA) membranes. Blocking was performed in
10% milk, 0.1% Tween 20 Tris-buffered saline (TBS) for 2 hours at
25°C followed by incubation overnight at 4°C in the presence of a
rabbit p73 human polyclonal IgG (Sanofi-Recherche, Labège) at
1/1000 dilution in TBS. After three washes and a further incubation
with anti-rabbit IgG-peroxidase conjugated at 25°C for 1 hour, the
blot was developed by the Amersham ECL technique. Full-length p73
and N-truncated p73 were obtained from SK-N-AS NB cells transfected
by plasmids containing p73 full-length (1–2-3) or
N-p73 (3bis-4–5) genes under CMV promoter
control (Sanofi Recherche, Labège). The total protein extracts
from the plasmid transfected cells yield the corresponding reference
isoforms.
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Results |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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A panel of 61 NTs comprising 35 localized stages, 20 IV stages, and 6 IV-S stages (classified according to a scale of ganglionic sympathetic differentiation as undifferentiated "NB," differentiating "NB/GNB," differentiated ganglioneuroblastoma "GNB," and fully differentiated ganglioneuroma "GN")1 were screened using PCR-restriction fragment length polymorphism (PCR-RFLP) analysis for the two naturally occurring p73 alleles denoted GC and AT.5 Only 20 out of the 61 NTs were determined to be GC:AT heterozygotes. Interestingly, 7 of these 20 informative tumors (35%), showed an imbalance ratio of GC:AT alleles suggesting a loss of heterozygosity at the p73 locus, further confirmed by fluorescence in situ hibridization (FISH) analysis (data not shown). Finally, DNA sequencing performed on 15 NTs demonstrated an absence of mutations for remaining p73 allele suggesting that Knudson’s "two-hit" model for candidate tumor suppressor genes may not apply to p73.
To investigate whether qualitative and/or quantitative variations of
p73 transcripts correlate with differentiation defects in
NTs, we analyzed transcript species using a semiquantitative PCR
strategy which yields robust and short PCR products spanning the three
domains of the p73 gene, TAD, DBD, and OD (Figure 1)
. PCR
experiments are exemplified in Figure 2
and data obtained for 20 informative NTs are compiled in Table 1
.
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and ß isoforms (Figure 2B)
were found to be co-expressed in 15 of 20 NTs. No other isofoms,
such as 
and 
, previously described12
were detected.
Regarding TAD, strikingly, reverse transcription-polymerase chain
reaction (RT-PCR) analysis revealed transcripts encoding p73 proteins
that lack an amino-terminal transactivation domain, in addition to the
regular full-length and ß p73 species. A study performed on
transcript species in the N terminus according to the Rapid
Amplification of cDNA Ends (RACE) PCR method led to identify two
additional promoters, P2 and P3 (F McKeon, D Caput, data not shown).
Like the transcripts encoding
N-p63,18
N-p73
transcripts (3bis-4–5) are initiated from an alternative promoter P3
located in intron 3; consequently, exons 1, 2, and 3 in these
transcripts are replaced by a unique exon named exon 3bis (Figure 1)
.
Interestingly, transcripts of this exon were consistently detected in
all NTs (Figure 2A
, right panel; Table 1
). Finally, a substantial
amount of p73-encoding transcripts were splice variants
lacking exon 2 (Figure 2A
, left panel) as already reported in the human
NB cell line SK-N-SH.5
It is noteworthy that exons 1 and
3bis, corresponding to two distinct origins of transcription, were
equally transcribed in NT, suggesting a similar and/or coordinated
transcriptional control at the promoter level (Figure 2A)
. The
frequency of the transcripts lacking exon 2 (species 1–3) appeared to
be higher in undifferentiated (7 of 11) than in differentiating and
differentiated tumors (3 of 9). RT-PCR experiments performed on matched
lymphocyte/tumor pairs and representing the histological spectrum NB,
NB/GNB, GNB, GNB/GN showed that the P1-exon2 (1–3) transcript
species of lymphocytes was mostly absent or only faintly expressed when
compared to the corresponding tumors (Figure 2C)
.
Overall, the RT-PCR data indicate that the two promoters P1 and P3 are
consistently used in NTs, regardless of the histological status. By
contrast, the p73 transcripts lacking exon 2 typify
undifferentiated NBs. To ascertain the identity of the transcript
variant species, we performed Northern blot analyses from total RNA
using -[32P] probes corresponding to
amplified exons. Despite a 2 week exposure, the radiolabeled bands
obtained were barely detectable even in the core domain (data not
shown). This implies that p73 transcript levels are very low
and are only detectable by RT-PCR.
p73 Protein Expression in Neuroblastic Tumors
To characterize p73 isoforms in NTs, lysates obtained from large
amounts of frozen tumor specimens from 15 patients were
successively analyzed by immunoblotting and immunohistochemistry.
Surprisingly, immunoblotting using the p73 polyclonal antibody
revealed a single band of similar migration to N-p73
reference isoform (Figure 3)
. In
undifferentiated NB, only the N-truncated isotype band
was detected, often accompanied by a p73 cross-reacting lighter band
(at about 50 kd), very likely to represent a product of specific
proteolysis. A heavier protein species (130 to 150 kd) was also
observed. Importantly, this protein species was present at high levels
in differentiating-differentiated NTs (NB/GNB and GNB/GN,
respectively), but rarely in undifferentiated NTs (Figure 3
, lane 5).
This heavy protein was the only species found in the fully
differentiated GNB/GN of this series (Figure 3
, lane 8). The nature of
this SDS-PAGE resistant protein remains to be determined.
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isoform.5
Formalin-fixed tissues were analyzed including five specimens of normal
human adrenal medulla from which most NTs originate, and 23 NTs
including 6 undifferentiated, 16 poorly differentiated NTs, and one GN.
Histological criteria of sympathetic differentiation in NTs are based
on cell morphology:1
undifferentiated neuroblasts appear
as small round cells with a prominent nucleus, whereas very large
mature ganglionic cells have an abundant and distinct cytoplasm, marked
nucleoli and a prominent nuclear membrane. In normal human adrenal
medulla tissue, conspicuous immunoperoxidase staining appeared to be
restricted to the nuclei of the chromaffin cells, but it was also
intense in the nuclear membrane and associated with faint but
significant staining in the cytoplasm (Figure 4a)
. Nineteen (83%) of the 23 NTs showed
positive p73 staining. p73 immunoperoxidase staining was found in
neuroblasts and ganglionic cells, but was absent in S100-positive
Schwann cells (Figure 4, b and d)
. Nuclear staining was intense in
small cells (undifferentiated neuroblasts lacking visible cytoplasm),
and still present, but less intense in fully differentiated ganglionic
cells (very large cells with a prominent cytoplasm, Figure 4d
). Faint
but significant cytoplasmic staining was also noted in differentiated
and fully differentiated ganglionic cells (Figure 4, c and d)
.
Ganglionic maturation is often observed after induction chemotherapy in
NT patients. In a particular patient, comparison of the GNB tumor
specimen taken before (Figure 4c)
and after (Figure 4d)
chemotherapy
indicated more intense cytoplasmic staining in fully differentiated
ganglionic cells. This subcellular localization may suggest that a
nuclear-cytoplasm shuttling of active p73 forms could mark the neuronal
differentiation process. Strikingly, p73 subcellular localization in
NTs differed from that of p53. Indeed undifferentiated NTs readily
showed detectable p53 cytoplasmic retention (Figure 5,A and B)
, as previously
reported,4
while differentiating and differentiated NTs
show only minimal and no staining, respectively (Figure 5, C and D)
.
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for stable FGF-transfected cells and
Figure 6G
for NGF-exogenous induction) and N-myc
down-regulation associated with gap43 up-regulation at the
molecular level were used as standard differentiation
markers.22
In differentiated SH-SY5Y cells, ICC studies
revealed a nuclear staining as well as a p73 punctuated cytoplasmic
staining (Figure 6, F and I
, black arrows); by contrast, in control
cells, the p73 staining was exclusively nuclear (Figure 6C)
.
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Discussion |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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and ß
variants5
and other minor species.12,17
In
this study, we showed that the N-terminal domain of the gene is also
subject to regulation. Based on NT transcript and protein analyses, we
propose a role in sympathetic differentiation for the p73
gene with regards to N. terminal domain. Transcript Profiles and Stoichiometry Discriminate NTs
RT-PCR screening of the first three exons yielded the expected
products from the two main promoters (P1 and P3), but also revealed a
new variant in which exon 2 had been spliced out (Table 1)
. Transcripts
initiated from P1 and P3 promoters were equally frequent, irrespective
of the tumor differentiation status. By contrast, the spliced-out exon
2 variant initiated from P1 (ie, the 1–3 species) was far more
expressed in undifferentiated than in differentiating and
differentiated NTs. These data strongly suggest that the amount of the
compiled transcript isotypes 1–3 and 3bis-4–5 with putative
dominant-negative activity, is probably higher in undifferentiated NTs
than in NTs in the process of differentiation. As DBD was not subjected
to splicing, it appeared to be consistently transcribed in all NTs. The
and ß COOH-terminal splice variants were found to be frequently
co-expressed in NTs; however 4 of 11 undifferentiated NBs lack ß
isotype while 9 of 9 differentiating and differentiated NTs express
this variant (Table 1)
. This evidence provides an additional link
between the C-terminus integrity of the p73 gene and
sympathetic differentiation.
An Array of Multiple Transcripts, but a Single Protein Profile
In undifferentiated NBs, a single -N truncated p73 isotype was
identified which contrasts sharply with the multiple transcripts
putatively encoding an array of isoforms. These data strongly imply a
marked difference in the p73 protein turnover or highly stable
N-truncated isotypes compared to full-length isotypes. With regards to
N-p63, known to yield a dominant negative activity on p63
itself and/or p53 transactivation,18
a stable truncated
protein would exert a similar activity while a labile full-length
protein would elicit transient transcriptional activity. In full
agreement with this hypothesis, it has been recently shown that in the
development of sympathetic neurons, N-truncated p73 is an essential
anti-apoptotic protein which, by directly binding to p53, counteracts
the pro-apoptotic function of p53.25
We are unable to
specify the identity of the single N-p73 protein band
since mRNA species (either 3bis-4–5 initiated from P3 or
exon21-3
initiated from P1) encode proteins of similar
theoretical Mr (64 kd). However, the products of
3bis-4–5 transcript should be favored given its consistent occurrence
in all NTs except one. Whether the N-p73 isoform and the
one encoded by the spliced-out exon 2 variant mostly found in
undifferentiated NBs exert similar biological role remains to be
elucidated, as it has been recently described in other
models.26,27
The fact that N-p73 protein was detected but not
p73 full-length can be explained by its higher stability. Another
possibility is the association of this isoform with another protein to
be identified. Therefore, this sheds light on an interesting parallel
with the wild type p53 stability, in view of data demonstrating that i)
full-length p73 interacts via its N-terminus, thereby
involving the TAD with p53, MDM2, and p300/CBP, and that, ii) in
contrast to p53, MDM2-p73 complex inactivates p73 without degrading
it.28-31
Moreover, recent studies have identified a
larger molecular weight product proposed to be the sumolated
version of N-p73.32
p73 Is an Attractive Candidate for a Differentiation Function
Immunohistochemistry revealed specific p73 expression localized
within the nucleus, in particular at the nuclear membrane as well as in
the cytoplasm of chromaffin cells of normal adrenal medulla. Moreover,
most NTs, including malignant neuroblasts and ganglionic cells, but not
Schwann cells, also exhibited significant p73 expression. p73 is mainly
localized in the nucleus of undifferentiating NBs, with a low intensity
in the perinuclear and cytoplasmic area of differentiated GNB/GN.
Similar data were observed between parental SH-SY5Y cells and
differentiated cells resulting from either FGF1 endogenous activity or
exogenous NGF/aphidicolin induction. By combining these findings with
the expression of an N-truncated -isotype in undifferentiated NBs
and a large protein complex in fully differentiated GN, a plausible
postulate would be that the full-length cytoplasmic form of p73 is
involved in sympathetic differentiation, while the nuclear N-truncated
form of p73 expresses oncogenic properties in the nucleus with a
dominant-negative impact on p53 transactivation of target
genes. In full agreement with in vivo results strongly
favoring p73 involvement in neuronal differentiation is the recent
in vitro finding reported by De Laurenzi et
al33
who showed that transfected full-length p73 cDNA
induced neuronal differentiation in the murine N1E-115 neuroblastoma
model, while these cells do not undergo differentiation when
co-transfected with full-length and N-p73
cDNAs. The mechanisms conferring cytoplasmic localization to p73
protein in differentiated sympathetic cells are currently unknown. We
propose that full-length p73 is instrumental in the differentiation
process. This hypothesis could be tested using in vitro
studies. Importantly, the p73 cellular localization appears to be
opposite to that of p53 which is overexpressed and localized in the
cytoplasm in undifferentiated NBs,4
and down-regulated
(not visible by ICC) in differentiated GNB or GN. Differentiation of
malignant neuroblasts is accompanied by a decrease in the p53 level
in vitro.34
The nucleus-cytoplasm transfer of
p53 and p73 occurs in opposite directions and it could be hypothesized
that a single protein or proteic complex is in charge of the transfer
for both proteins. Transgenic p73-/- mice show lack of
tumors, in contrast to p53-/- mice, but exhibit neurosensorial
defects and hydrocephaly20
and a decrease of urinary
catecholamines (D Caput, personal communication). In nullizygous
p73-/- mice, N-p73, the physiological p53
antagonist25
being absent would explain the lack of NTs
because of early p53-dependent death of sympathetic neurons.
p73 does not possess the properties of a typical tumor suppressor gene, but its versatile regulation of transcription and translation shows some correlation with the pathogenesis of NTs. The equilibrium between the various isotypes with divergent biological activities could determine whether or not the sympathetic differentiation process occurs.
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Acknowledgements |
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Footnotes |
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Supported by Sanofi Recherche, and in part by Association pour la Recherche Sur le Cancer, the Ligue contre le Cancer, Comité du Cher, Fédération nationale des Groupements des Entreprises françaises et monégasques dans la lutte contre le Cancer, and the Institute Gustave Roussy.
Accepted for publication November 6, 2001.
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References |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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(p73exon2) inhibits apoptosis and competes with p53. Oncogene 2001, 20:514-522[Medline]
without targeting degradation Oncogene 1999, 18:3923-3929[Medline]
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P. Puig, P. Capodieci, M. Drobnjak, D. Verbel, C. Prives, C. Cordon-Cardo, and C. J. Di Como p73 Expression in Human Normal and Tumor Tissues: Loss of p73{alpha} Expression Is Associated with Tumor Progression in Bladder Cancer Clin. Cancer Res., November 15, 2003; 9(15): 5642 - 5651. [Abstract] [Full Text] [PDF]
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V. Vella, J. Zhu, F. Frasca, C.-Y. Li, P. Vigneri, R. Vigneri, and J. Y. J. Wang Exclusion of c-Abl from the Nucleus Restrains the p73 Tumor Suppression Function J. Biol. Chem., June 27, 2003; 278(27): 25151 - 25157. [Abstract] [Full Text] [PDF]
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