Stathmin 1, a marker of PI3K pathway activation and regulator of
microtubule dynamics, is expressed in early pelvic serous carcinomas
Alison M. Karsta, Keren Levanona,1, Sekhar Duraisamya, Joyce F. Liua, Michelle S. Hirschb,
Jonathan L. Hechtc, Ronny Drapkina,b,⁎
aDepartment of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA
bDepartment of Pathology, Division of Women's and Perinatal Pathology, Brigham and Women's Hospital, Boston, MA, USA
cDepartment of Pathology, Beth Israel Deaconess Medical Center, Boston, MA, USA
a b s t r a c t a r t i c l ei n f o
Received 25 February 2011
Accepted 18 May 2011
Available online 17 June 2011
Pelvic serous carcinoma
Background. Most high-grade pelvic serous carcinomas (HGPSCs) arise from fallopian tube epithelium
(FTE). To date, few markers have been shown to characterize FTE transformation. Stathmin 1 (STMN1) is a
candidate oncogene whose activity is influenced by p53, p27Kip1 (p27), and PI3K/Akt pathway activation. As
a microtubule destabilizing protein, STMN1 regulates cytoskeletal dynamics, cell cycle progression, mitosis,
and cell migration. This study examines the expression of STMN1 and its negative regulator p27 along the
morphologic continuum from normal FTE to invasive carcinoma.
Methods. STMN1 and p27 expression were examined by immunohistochemistry (IHC) in benign (n=12)
and malignant (n=13) fallopian tubes containing normal epithelium, morphologically benign putative
precursor lesions (“p53 signatures”), potential transitional precursor lesions (“proliferative p53 signatures”),
tubal intraepithelial carcinoma (TIC), and/or invasive serous carcinoma. STMN1 expression was further
assessed in 131 late-stage HGPSCs diagnosed as primary ovarian and in 6 ovarian cancer cell lines by IHC and
Western blot, respectively.
Results. STMN1 expression was absent in benign FTE and infrequently detected in p53 signatures.
However, it was weakly expressed in proliferative p53 signatures and robustly induced upon progression to
TIC and invasive carcinoma, typically accompanied by decreased p27 levels. STMN1 was expressed in N80% of
high-grade serous ovarian carcinomas and cell lines.
Conclusions. STMN1 is a novel marker of early serous carcinoma that may play a role in FTE tumor
initiation. Our data are consistent with a model by which STMN1 overexpression, resulting from loss of p27-
mediated regulation, may potentiate aberrant cell proliferation, migration, and/or loss of polarity during early
© 2011 Elsevier Inc. All rights reserved.
High-grade pelvic serous carcinoma (HGPSC) is a lethal malig-
nancy for which there is no curative therapy. The vast majority of
patients are diagnosed with metastatic disease, at which point
cytoreductive surgery and chemotherapy remain the only treatment
options . Despite initial high response rates, most patients recur
and ultimately succumb to chemoresistant disease . Our ability to
detect and effectively treat HGPSC is hampered by a poor under-
standing of the molecular events underlying its pathogenesis. Recent
studies suggest that most HGPSCs, including a significant proportion
diagnosed as “primary ovarian”, arise from fallopian tube epithelium
and a model for HGPSC development has been described based on
pathological studies of women genetically predisposed to ovarian
cancer due to germline BRCA mutations . These studies identified a
benign appearing lesion in the tubal mucosa that appears to precede
development of tubal intraepithelial carcinoma (TIC). The putative
precursor, called a “p53 signature”, occurs in the fimbrial region of the
fallopian tube and is characterized by secretory cell composition,
somatic TP53 mutation, and accumulation of DNA damage [4,5]. The
hypothesis that p53 signatures and TICs are precursors of HGPSC is
supported by the finding that these lesions often share identical p53
mutations with co-existing HGPSC, indicative of clonality, and that
TICs have shorter telomeres than co-existing HGPSC, suggesting that
they represent an earlier disease stage rather than mucosal spread or
metastasis from an advanced tumor [6,7]. However, the genetic
alterations driving tumor initiation in this setting remain uncertain.
Answers may soon be forthcoming with the emergence of large scale
Gynecologic Oncology 123 (2011) 5–12
⁎ Corresponding author at: Department of Medical Oncology, Dana-Farber Cancer
Institute, JFB-215D, 450 Brookline Avenue, MA 02215, USA. Fax: +1 617 582 8761.
E-mail address: firstname.lastname@example.org (R. Drapkin).
1Present affiliation: Sheba Cancer Research Center, Chaim Sheba Medical Center,
Ramat Gan, Israel.
0090-8258/$ – see front matter © 2011 Elsevier Inc. All rights reserved.
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genomic profiling data of serous ovarian carcinomas, such as The
Cancer Genome Atlas . With insight from such genomic analyses,
we may identify relevant genetic alterations and query their roles at
each stage of the HGPSC progression model in order to identify drivers
of tumor initiation and progression.
The current model of fallopian tube carcinogenesis has been well
described histologically , but few molecular markers other than
p53 and Ki-67 have been shown to characterize the transformation of
fallopian tube secretory epithelial cells (FTSECs). Norquist et al.
recently reported that p53 mutation, clonal proliferation, and loss of
p27 expression occur in preneoplastic lesions of the fallopian tube
epithelium . However, the consequences of p27 loss in this setting
have not been explored. To determine how p27 loss may contribute to
tumorigenesis, we sought to examine the expression of its direct
downstream targets. Among several candidates, Stathmin1 (STMN1)
was of particular interest because it has been shown to regulate
cell division, motility,andmigration; all of which are criticalprocesses
in tumorigenesis. In this report we identify STMN1 as a novel marker
of FTSEC transformation and serous tumor initiation. STMN1 is a
ubiquitous cytoplasmic phosphoprotein that regulates microtubule
dynamics. Microtubules are protein polymers, comprised of α/β
tubulin heterodimers, that constitute a major portion of the
cytoskeleton. They exist in a constant state of polymerization and
depolymerization referred to as “dynamic instability”. STMN1 de-
polymerizes microtubules and is required for all cellular processes
involving microtubule rearrangement, most notably mitosis. At the
onset of mitosis, STMN1 rapidly destabilizes interphase microtubules,
allowing them to be reorganized into a mitotic spindle . During
spindle assembly, STMN1 activity is repressed through phosphoryla-
tion, thus enabling repolymerization . Following chromosomal
segregation, STMN1 is once again activated in order to disassemble
the spindle and begin cytoskeleton reconstruction. STMN1 activity is
therefore critically important for both successful M-phase entry and
timely M-phase exit.
Independent from its role in cell division, STMN1 has also been
shown to regulate cell motility, enhance cell migration, and promote
metastasis [13,14]. The goal of this study was to determine whether
STMN1, and its negative regulator p27, are relevant markers of early
neoplasia in the fallopian tube.
This study was approved by the Institutional Review Boards at the
Brigham and Women's Hospital (BWH), Dana-Farber Cancer Institute
(DFCI), and Beth Israel Deaconess Medical Center (BIDMC).
The following cases were retrieved from the 2004–2010 Depart-
ment of Pathology archives of BWH and BIDMC: (1) 13 cases of HGPSC
clinically diagnosed as stage III–IV fallopian tube carcinoma (n=2, 1
unilateral, 1 bilateral) or ovarian papillary serous adenocarcinoma
(n=11, all bilateral), each with involvement of both the ovary and
fallopian tube; and (2) 76 histologically benign appearing fallopian
tubes collected from prophylactic bilateral salpingo-oophorectomies
or total abdominal or vaginal hysterectomies performed mainly on
patients with germline BRCA1/2 mutations or a personal or family
history of breast cancer. Patient ages ranged from 50 to 73 years for
the HGSPC group and 29 to 69 years for the histologically benign
group. Patients were unselected for BRCA mutational status.
Immunohistochemical staining was performed using Envision
Plus/Horseradish Peroxidase system (DAKO, Carpinteria, CA, USA).
Formalin-fixed paraffin-embedded tissue sections were de-waxed,
rehydrated, and incubated in hydrogen peroxide solution for 30 min
to blockendogenousperoxidase activity.Antigenretrievalwas carried
out by pressure cooker treatment in citrate buffer (pH 6.0) for 40 min.
Sections were incubated with primary antibody using the conditions
specified in Supplemental Table 1. Secondaryantibody wasappliedfor
30 min, followed by DAB for 5 min.
Evaluation of p53 Signatures, proliferative p53 Signatures, and TICs
p53 signatures, proliferative p53 signatures, and TIC. A p53 signature
was defined as ≥12 consecutive FTSECs having strong nuclear p53
positive nuclei) . “Proliferative p53 signatures” are putative
transitional precursor lesions bearing features intermediate between a
p53 signature and TIC . A proliferative p53 signature was defined as
≥12 consecutive FTSECs having strong nuclear p53 staining, mild
cytological atypia, and a moderately elevated proliferation index (10–
50% positive nuclei). TIC was defined as a region of FTSECs exhibiting
significant nuclear atypia, loss of cell polarity, and a high Ki-67 index
(N50% positive nuclei). All cases were reviewed by two pathologists
(MSH and RD).
STMN1 and p27 immunostaining
For all cases containing a p53 signature, proliferative p53 signature,
p27 (Supplemental Table 1). In each of these cases, the normal
epithelium was also evaluated for STMN1 and p27 immunoreactivity.
STMN1 staining was scored as 0 (all cells negative), 1+ (scattered rare
cells=b10% positive cells), 2+ (focal or multifocal staining=10–75%
positive cells), or 3+ (diffuse staining=N75% positive cells). In
subsequent data analyses, 0 and 1+ were considered to be “STMN1-
negative”, while 2+ and 3+ were categorized as “STMN1-positive”.
only) controls were stained in parallel with each round of immunohis-
tochemistry (Supplemental Table 1).
Tissue microarray (TMA)
A TMA was constructed from 131 cases of high-grade late-stage
(FIGO III–IV) serous ovarian adenocarcinoma from patients who
underwent cytoreductive surgery at BWH during 1999–2005, as
previously described [16,17]. Each case was represented by quadru-
plicate cores, 0.8 mm in diameter. The TMA was immunostained for
STMN1 and each core was scored as described in the previous section.
Six ovarian cancer cell lines (OVCAR-5, OVCAR-8, OV-90, HEYA8,
IGROV1, and SKOV3) were used in this study and maintained as
previously described . Immortal FTSEC lines were generated from
freshly resected fallopian tubes obtained from the BWH Department of
as recently described [18,19]. Briefly, FTSECs were dissociated by
incubating fimbria in Eagle's Minimum Essential Medium (Cellgro,
Manassas, VA, USA), supplemented with 1.4 mg/ml Pronase (Roche
Diagnostics, Indianapolis, IN, USA) and 0.1 mg/ml DNAse (Sigma-
Aldrich, St Louis, MO, USA), for 48–72 h at 4 °C. Cells were seeded
onto plates coated with human placental collagen (Sigma-Aldrich) and
cultured in Dulbecco's Modified Eagle's Medium (DMEM)/Ham's F-12
1:1 (Cellgro) supplemented with 2% Ultroser G serum substitute (Pall
Life Sciences, Ann Arbor, MI, USA) and 1% penicillin/streptomycin.
FTSECs were immortalized via transduction with retroviral vectors
expressing human Telomerase Reverse Transcriptase (hTERT) ,
A.M. Karst et al. / Gynecologic Oncology 123 (2011) 5–12
mutant Cyclin-Dependent Kinase 4 (CDK4R24C) , and either
plasmids #1774, 11254, 9058, and 10671; Addgene, Cambridge, MA,
Whole cell lysates were prepared using NETN-150 lysis buffer
(20 mM Tris–HCl [pH 8.0], 1 mM EDTA, 0.5% NP-40, 150 mM NaCl).
Proteins were separated by SDS-PAGE on 4–12% Tris–Glycine gels
(Invitrogen, Carlsbad, CA, USA), electroblotted onto nitrocellulose
membranes (Invitrogen), and blocked with 5% BSA-Tween-20
(Boston Bioproducts, Worcester, MA, USA) for 1 h. Membranes were
incubated in STMN1 primary antibody (1:1000, Cell Signaling
Technology, Danvers, MA, USA) overnight at 4 °C, followed by HRP-
conjugated secondary antibody for 1 h. Bound antibody was detected
by HyGLO Chemiluminescent HRP Antibody Detection Reagent
(Denville Scientific, South Plainfield, NJ, USA). Membranes were re-
probed for GAPDH as a loading control.
Fallopian tube morphology
The morphologic continuum from histologically benign (“normal”)
fallopian tube epithelium through TIC to invasive serous carcinoma is
characterized by several features: increased nuclear/cytoplasmic ratio,
enlarged nuclei with prominent nucleoli, lack of ciliated cells, epithelial
stratification, and loss of polarity (Fig. 1A–D) . Morphologically
benign putative precursors referred to as “p53 signatures” (Fig. 1B) are
thought to precede transformation to intraepithelial carcinoma. These
lesions are histologically unremarkable but can be distinguished from
normal epithelium by intense nuclear p53 immunostaining, which
persists throughout the carcinogenic sequence (Fig. 1E–H). A marked
Fig. 1. STMN1 expression across the morphologic continuum from benign fallopian tube epithelium to invasive serous carcinoma. (A–D) Histological transition from normal
epithelium to benign p53 signature, TIC, and invasive HGPSC. (E–H) Intense nuclear p53 staining characterizes the p53 signature, TIC, and invasive tumor; (I–L) Ki-67 staining
identifies proliferating cells in the TIC and invasive tumor; (M–P) STMN1 expression is absent from benign epithelium but is strongly induced upon progression to TIC; (Q–T) p27
expression is frequently lost in STMN1-positive lesions. All images are from one representative case.
A.M. Karst et al. / Gynecologic Oncology 123 (2011) 5–12
increase in proliferative activity, identified by Ki-67 staining, marks the
transition from benign p53 signature to TIC and remains present in
invasive serous carcinoma (Fig. 1I–L).
Frequency of p53 signatures, proliferative p53 signatures, and TICs
In order to study protein expression patterns across the morpho-
logic continuum from normal to malignant fallopian tube epithelium,
we first examined 13 cases of HGPSC. All 13 cases were found to
contain regions of both normal fallopian tube epithelium and TIC in
addition to the invasive tumor. Immunostaining for p53 and Ki-67
revealed that 7 (54%) of the HGPSC cases also contained a p53
signature and 6 cases (46%) contained a proliferative p53 signature
(Table 1). In 5 cases, both p53 signatures and proliferative p53
signatures were observed in the same patient.
We next looked for p53 signatures by evaluating 76 fallopian tubes
diagnosed as benign with absence of ovarian or peritoneal malignan-
cy. By immunostaining for p53 and Ki-67, we identified 11 cases (15%)
containing a p53 signature and 1 case (1%) containing a proliferative
p53 signature (Table 1). The number of p53 signatures observed in
malignant cases (54%) was consistent with previous reports
[6,10,24,25]. The number observed in benign fallopian tubes (15%)
was lower than that reported by other groups [6,10,24] but was
consistent with the number reported by Shaw et al. . This may be
attributed to the fact that, like Shaw et al., we did not stain multiple
sections when evaluating samples for p53 signatures.
STMN1 is expressed in intraepithelial lesions and HGPSC
In an effort to further characterize the protein expression changes
associated with serous carcinoma pathogenesis, we immunostained
benign and malignant fallopian tubes for STMN1 and p27, two proteins
intimately involved in cell cycle progression. STMN1 is a modulator of
microtubules dynamics that is critically important for mitosis and
whose activation is strongly linked to growth factor receptor signaling
. p27 is a cyclin-dependent kinase inhibitor, governing G0- to
S-phase transition, that negatively regulates STMN1 .
STMN1 immunostaining of morphologically normal tubal mucosa
was largely negative (Fig. 1M) with rare immunoreactive cells (not
shown). Staining, where present, was diffusely cytoplasmic and
restricted to the secretory cell compartment. STMN1 expression
remained negative in most (13 of 18) p53 signatures but was strongly
immunoreactive in all TICs and invasive serous carcinomas (Fig. 1N–P,
Table 1). STMN1 staining in TICs and tumors varied from focal (10–75%
positive cells) to diffuse (N75% positive cells), but was consistently
present in all cases (Fig. 2). Interestingly, varying levels of STMN1
expression were also observed in proliferative p53 signatures (Figs. 2
and 3, Table 1).
In contrast, normal fallopian tube epithelium and p53 signatures
were largely positive for p27 with N50% of cells exhibiting nuclear
staining in nearly all cases (Fig. 1Q–R, Table 1). However, TICs and
invasive carcinomas showed reduced p27 levels when compared to
morphologically benign epithelium (P=0.000, Student's T-test)
(Fig. 1S–T, Table 1). p27 was also reduced in some, but not all,
proliferative p53 signatures (Pb0.05, Student's T-test) (Fig. 3, Table 1).
Of note, stromal cell nuclei stained strongly for p27, providing an
internal positive control. In several cases the transition from benign to
malignant epithelium was clearly delineated by a dramatic induction of
STMN1and a markeddecrease in p27expression, asillustratedin Fig. 4.
Additionally, robust STMN1 staining was observed in several stretches
of epithelium that were morphologically consistent with TIC but
exhibited a lower Ki-67 index than expected, suggesting that these
lesions were indeed proliferative (Fig. 4). To determine whether the
apparent inverse relationship between STMN1 and p27 expression was
all putative precursors and malignant lesions (p53 signatures, prolifer-
ative p53 signatures, TICs and invasive tumors) were considered,
STMN1expressionclearlycorrelatedwithlowp27levels (Fisher's exact
test, P=0.000). However, when only putative precursor lesions (p53
STMN1 and p27 immunostaining in benign and malignant fallopian tubes.
Negative (%)* Positive (%)*Low (b50% positive nuclei) (%) High (N50% positive nuclei) (%)
Findings associated with malignancy (N=13)
Normal FTE (n=13)
p53 signature (n=7)
Proliferative p53 signature (n=6)
Invasive tumor (n=13)
Benign/incidental findings (N=12)
Normal FTE (n=12)
p53 signature (n=11)
Proliferative p53 signature (n=1)
*STMN1 scoring system.
Negative=score 0 (all cells negative) or 1+ (b10% positive cells).
Positive=score 2+ (10–75% positive cells) or 3+ (N75% positive cells).
FTE, fallopian tube epithelium; TIC, tubal intraepithelial carcinoma.
Fig. 2. Distribution of STMN1-positive cells in benign and malignant fallopian tube
epithelium. STMN1 staining was negative (b10% positive cells) in both normal FTE and
most p53 signatures, but positive (10–100%) in proliferative p53 signatures, TIC, and
A.M. Karst et al. / Gynecologic Oncology 123 (2011) 5–12
signatures and proliferative p53 signatures) were considered, the trend
sample size. Among the 18 p53 signatures examined, only 4 were
the 7 proliferative p53 signatures examined, 6 were STMN1-positive
and, of these, 2 had reduced p27 expression. Notably, low p27 levels
were not observed in any STMN1-negative putative precursors or
Fig. 3. STMN1 is expressed inputative precursors to HGPSC. A p53 signature (A–E) and proliferative p53 signature (F–J) from the same patient. The p53 signature is non-proliferative,
STMN1-negative, and p27 positive. Proliferative p53 signatures are transitional lesions exhibiting features intermediate between a p53 signature and TIC. Here, mildly increased
proliferative activity is accompanied by expression of STMN1 and reduced p27.
A.M. Karst et al. / Gynecologic Oncology 123 (2011) 5–12
STMN1 is strongly expressed in invasive high-grade serous ovarian
TMA analysis was used to assess STMN1 expression in a large panel
of primary and metastatic high-grade late-stage serous ovarian
(score 0 or 1+) and 84% (110/131) was positive (score 2+ or 3+)
(Fig. 5A). The percentage of STMN1 positive cells did not correlate with
overall survival or response to chemotherapy. Nor did it differ
site (data not shown).
STMN1 protein levels were also examined in 6 ovarian carcinoma
cell lines and 2 immortalized, non-transformed FTSEC lines by Western
blot (Fig. 5B). The Müllerian origin of these lines was confirmed by
immunoblotting for PAX8, a lineage marker expressed by FTSECs and
serous ovarian carcinomas [18,19,27–29]. Five out of 6 ovarian cancer
cell lines expressed STMN1 whereas the protein was undetectable in
immortal FTSEC lines, consistent with their low proliferation rates.
This study identifies STMN1 as a novel marker of fallopian tube
epithelial transformation, characterizing the transition from benign
to malignant mucosa. Generally speaking, terminally differentiated
or quiescent (G0) cells express low levels of STMN1 . Accordingly,
we did not observe STMN1 staining in normal fallopian tube
epithelium, nor in most p53 signatures, which are both defined by a
low Ki-67 proliferation index (Figs. 1 and 2). However, STMN1
was expressed in “proliferating p53 signatures” — potential precursor
lesions exhibiting increased Ki-67 positivity compared to p53
signatures, albeit lower than that typically seen in TICs (Figs. 2
and 3). STMN1 induction in these lesions possibly marks the
Fig. 4. Examples of reciprocal STMN1 and p27 expression in TICs. (A–T) Coordinated changes in STMN1 and p27 levels occur at the transitions from benign to malignant epithelium.
Note the continuity of STMN1 staining throughout each lesion, even in regions with variable Ki-67 immunoreactivity.
A.M. Karst et al. / Gynecologic Oncology 123 (2011) 5–12
transition from benign precursor to proliferative lesion. Alternatively,
STMN1 expression in this setting could reflect a loss of TP53 tumor
suppressor function. TP53 mutations are present within an over-
whelming majority of HGPSCs  and about half have already
occurred by the p53 signature stage . Wild-type p53 transcription-
ally represses STMN1, and mutant p53 can impair this negative
regulation, leading to increased STMN1 levels [31–33]. Silencing
STMN1 expression reportedly inhibits proliferation, viability, and
clonogenicity of mutant TP53 breast cancer cells in vitro, recapitulat-
ing a wild-type TP53 phenotype .
We observed strong STMN1 expression in TICs and invasive serous
carcinomas, which is not unexpected given their high mitotic index.
However, we were surprised by how dramatically STMN1 expression
increased at the juncture between benign and malignant epithelium
(Fig. 4). STMN1 expression clearly correlated with increased Ki-67, a
proliferation marker associated with late S-phase . However, there
4), implying that STMN1 is not merely a mitotic cell marker but, rather,
identifies cells with proliferative potential, including cycling interphase
cells that have exited G0but may not be actively dividing. This is
interphase. It is important to note that STMN1 expression in early
lesions (proliferative p53 signatures and TICs) was not uniquely
observed in cases of HGPSC, but also occurred in incidental lesions in
the absence of overt malignancy (data not shown). This suggests that
STMN1 induction does not merely reflect a cellular response to the
tumor microenvironment, but is truly associated with tumor initiation.
Moreover, given the possibility that some TICs may represent mucosal
spread rather than precursor lesions in cases of advanced disease, it is
significant that a similar pattern of STMN1 expression was observed in
incidental TICs (data not shown). Accordingly, STMN1 may be a useful
supplemental marker for determining the cell cycle status of seemingly
benign yet atypical lesions in the fallopian tube.
Whether STMN1 expression directly contributes to fallopian tube
epithelial transformation or is merely an indicator of cellular transfor-
mation events remains to be determined. STMN1 expression has been
closely linked to phosphatidylinositol 3-kinase (PI3K)-mediated signal
transduction. Therefore, STMN1 induction in tubal lesions may indicate
the activation of this pathway. At least two studies have identified
STMN1as a robust biomarker of PI3K activation. The first, conducted by
Saal et al., generated an IHC-based gene expression signature of PI3K
activation using N100 breast cancer biopsies . Of 246 candidate
genes, STMN1 was the most reliable surrogate marker of PI3K pathway
activation and was readily detectable by IHC, thereby compensating for
a lack of suitable antibodies against more obvious markers such as
phosphorylated AKT. A second study, published by Andersen et al.,
employed phosphoprofiling to identify drug-specific biomarkers of
responsiveness to PI3K small molecule inhibitors . Among the most
prominently inhibited phosphoproteins following PI3K inhibitor treat-
ment were the cytoskeletal machinery proteins, including STMN1.
may be clinically useful for predicting susceptibility to anti-PI3K
In several cases we examined, STMN1 induction at the transition
from benign to malignant fallopian tube epithelium coordinated with
reduced p27 expression (Fig. 4), suggesting that p27 down-regulation
may be required for the initiation of FTSEC proliferative activity. This
observation is consistent with a recent study by Norquist et al., which
reported decreased p27 expression in the “p53 foci” of BRCA1/2
mutation carriers but not in those of normal controls. p53 foci are
essentially variants of the p53 signature, defined by Norquist et al. as
focal p53 staining(N75% positive cells) withoutspecific reference to Ki-
67 index [10,25]. It is difficult to compare our findings to theirs because
expression has also been described in pre-malignant lesions of the oral
mucosa (oral dysplasia) and prostate (prostatic hypertrophy), and in
cyclin-dependent kinase inhibitor, p27 inhibits G0- to S-phase transi-
G1- to S-phase genes . Regulation of p27 activity is complex and
and MAPK pathways. Aberrant p27 depletion in tumor cells is typically
attributed to reduced transcription, increased degradation, or altered
subcellular localization .
Coordinated changes in STMN1 and p27 expression may be
significant for at least two reasons. Firstly, STMN1 expression in
FTSECs could be interpreted as direct evidence of cell cycle entry, and
this event likely follows a release of p27-mediated restrictions on cell
proliferation. Secondly, p27 has been shown to directly bind to and
inhibit STMN1 in the context of cell migration . Microtubule
dynamics are important not only for mitosis but also for cell motility.
p27 appears to interfere with STMN1's depolymerizing ability, thus
impairing the cytoskeletal remodeling required for cell movement
. STMN1 expression in “proliferative p53 signatures” and TICs
could reflect an acquisition of migratory potential by FTSECs. The
ability to migrate is important during early tumorigenesis because it
supports anchorage independence and enables neoplastic cells to
move away from their site of origin. This is particularly relevant in the
setting of pelvic serous carcinoma where rapid spread of malignant
cells over peritoneal membranes often occurs at very early stages of
the disease. Baldassarre et al. demonstrated that p27 overexpression
inhibits sarcoma cell motility and this effect can be reversed by co-
expression of STMN1 . Furthermore, they found that a low
Fig. 5. STMN1 is strongly expressed in serous ovarian carcinomas. (A) In a tissue
microarray analysis of 131 high-grade serous ovarian carcinomas, 16% of samples was
STMN1-negative [score 0 (all cells negative) or 1+ (b10% positive cells)] while 84% was
STMN1-positive [score 2+ (10–75% positive cells) or 3+ (N75% positive cells)]. (B) 5/6
ovarian cancer cell lines express high levels of STMN1 whereas 2 immortalized FTSEC
lines are negative, determined by Western blotting. The Müllerian origin of the cell
lines was confirmed by PAX8 immunoblotting. GAPDH is a loading control.
A.M. Karst et al. / Gynecologic Oncology 123 (2011) 5–12
p27/STMN1 ratio in sarcoma tumors correlated with increased Download full-text
metastasis. However, we cannot eliminate the possibility that other
upstream regulators, aside from p27, are driving STMN1 expression in
the setting of fallopian tube epithelial transformation.
In conclusion, our study has identified STMN1 as a novel marker of
serous tumorigenesis in the fallopian tube. The dynamics of STMN1
expression observed in early tubal lesions suggest that STMN1 plays a
critical role in FTSEC cell cycle progression. Its induction in pre-
neoplastic cells may signal cell cycle entry and identify pre-mitotic
contribute to HGPSC pathogenesis by relaying oncogenic growth
signals to the cytoskeleton or by potentiating early-stage cell
migration and loss of polarity.
Supplementary materials related to this article can be found online
Conflict of interest statement
The authors declare no conflicts of interest.
Special thanks to the faculty and staff of the BWH Department of
Pathology for allocation of tissues. This work was supported by a
Canadian Institutes of Health Research Fellowship (AMK), Marsha
Rivkin Foundation Scientific Scholar Award (KL), AACR–George and
Patricia Sehl Fellowship for Cancer Genetics Research (KL), American
Physicians Fellowship for Medicine in Israel — Claire and Emmanuel
G. Rosenblatt Foundation Grant (KL); ASCO Young Investigator Award
and Prevent Cancer Foundation (JFL), Pallotta Investigator Fund (JFL),
NIH — K12 CA08772307 (JFL) and P50 CA105009 (SPORE), Novartis
Pharmaceuticals (RD), Ovarian Cancer Research Fund (RD); Robert
and Debra First Fund (RD), Randi and Joel Cutler Ovarian Cancer
Research Fund (RD), and The Mary Kay Foundation (RD).
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