Cancer Res-2015-Bonastre-1287-97

Molecular and Cellular Pathobiology
PARD3 Inactivation in Lung Squamous Cell
Carcinomas Impairs STAT3 and Promotes
Malignant Invasion
Ester Bonastre1
, Sara Verdura1
, Ilse Zondervan2
, Federica Facchinetti3
,
Sylvie Lantuejoul4
, Maria Dolores Chiara5
, Juan Pablo Rodrigo5
, Julian Carretero6
,
Enric Condom7
, Agustin Vidal7
, David Sidransky8
, Alberto Villanueva9
, Luca Roz3
,
Elisabeth Brambilla4
, Suvi Savola2
, and Montse Sanchez-Cespedes1
Abstract
Correct apicobasal polarization and intercellular adhesions
are essential for the appropriate development of normal epi-
thelia. Here, we investigated the contribution of the cell polar-
ity regulator PARD3 to the development of lung squamous cell
carcinomas (LSCC). Tumor-specific PARD3 alterations were
found in 8% of LSCCs examined, placing PARD3 among the
most common tumor suppressor genes in this malignancy.
Most PAR3-mutant proteins exhibited a relative reduction in
the ability to mediate formation of tight junctions and actin-
based protrusions, bind atypical protein kinase C, activate
RAC1, and activate STAT3 at cell confluence. Thus, PARD3
alterations prevented the formation of contacts between
neighboring cells and the subsequent downstream signaling.
Notably, reconstituting PAR3 activity in vivo reduced tumor-
invasive and metastatic properties. Our findings define PARD3
as a recurrently inactivated cell polarity regulator in LSCC
that affects tumor aggressiveness and metastasis. Cancer Res;
75(7); 1287–97. Ó2015 AACR.
Introduction
Lung cancer is among the most frequent and deadly types of
cancer in western countries. Lung tumors carry alterations at
known genes, some of them highly specific to the tumor histo-
pathology (1, 2). Lung adenocarcinomas (LAC) are the best
characterized, whereas the gene alteration profile of lung squa-
mous cell carcinomas (LSCC) is less well understood (1–3).
Inactivation of TP53 and CDKN2A and amplification of MYC are
among the most common alterations found in LSCCs, whereas
alterations at other genes are only occasionally observed (2–4).
The paucity of information about LSCC genetics has promoted
efforts to find novel genes that are altered in this type of lung
cancer. This has enabled the identification of focal amplification
at FGFR1, SOX2, TFDP1, and CTNND1 and activating mutations
at DDR2 (5–8). More recently, genome-wide sequencing has
revealed mutations at other genes in LSCCs, including loss-of-
function mutations in the HLA-A, NFE2L2, and KEAP1 (9).
However, most of these alterations affect a small percentage of
lung LSCCs.
Homozygous deletion is a common mechanism for inactivat-
ing tumor suppressor genes (10, 11). Using genome-wide strat-
egies, Rothenberg and colleagues (12) found intragenic deletions
at PARD3 in cancer cell lines and primary tumors from head and
neck squamous cell carcinomas (HNSCC), esophageal carcino-
mas, and glioblastomas. The PARD3 (from "partitioning defec-
tive") gene encodes PAR3, first identified in C. elegans (13), and
now found in almost every organism, including mammals (14).
In D. melanogaster, Par3 functions as a scaffolding protein
involved in cell polarity and is the earliest known landmark for
establishing epithelial polarity in the embryo (15). The best
known role of PAR3 in mammals is the formation in the epithelia
of the tight junctions, a specialized type of intercellular adhesion
complex that defines the apical–lateral border of the cell mem-
brane compartments (14–16). The PAR3 protein acts in a com-
plex, the PAR polarity complex, comprising PAR3, PAR6, atypical
protein kinase C (aPKC), and cell division control protein 42
(CDC42; ref. 14).
As further evidence of the role of PAR3 in cancer develop-
ment, it has recently been shown that mice with Pard3
conditionally deleted in the skin epidermis have a strong pre-
disposition to form keratoacanthomas, a common cutaneous
1
Genes and Cancer Group, Cancer Epigenetics and Biology Program
(PEBC), Bellvitge Biomedical Research Institute (IDIBELL), Hospitalet
de Llobregat, Barcelona, Spain. 2
MRC-Holland, Willem Schouten-
straat, the Netherlands. 3
Tumor Genomics Unit, Department of
Experimental Oncology and Molecular Medicine, Fondazione IRCCS
Istituto Nazionale Tumori, Milan, Italy. 4
Department of Pathology,
Institut Albert Bonniot, INSERM U823, University Joseph Fourier,CHU,
Grenoble Hôpital Michallon, Grenoble, France. 5
Department of Oto-
laryngology of the Hospital Universitario Central de Asturias, Oviedo,
Spain. 6
Department of Physiology, Faculty of Medicine and Odontol-
ogy, University of Valencia, Spain. 7
Pathology Department, Bellvitge
Hospital, Hospitalet de Llobregat, Barcelona, Spain. 8
Departments of
Otolaryngology-Head and Neck Surgery, Johns Hopkins University
School of Medicine, Baltimore, Maryland. 9
Translational Research
Laboratory, Catalan Institute of Oncology (ICO)-IDIBELL, Barcelona,
Spain.
Note: Supplementary data for this article are available at Cancer Research
Online (http://cancerres.aacrjournals.org/).
Corresponding Author: Montse Sanchez-Cespedes, Bellvitge Biomedical
Research Institute (IDIBELL), Hospitalet de Llobregat, Barcelona 08908, Spain.
Phone: 34-93-260-71-32; Fax: 34-93-260-72-19; E-mail: mscespedes@idibell.cat
doi: 10.1158/0008-5472.CAN-14-2444
Ó2015 American Association for Cancer Research.
Cancer
Research
www.aacrjournals.org 1287
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tumor in humans that is thought to arise from a different
cellular origin than squamous cell carcinomas (17). Further-
more, depletion of Par3 in mammary gland cells is evidence of
increased cell growth and the formation of metastasis (18).
Here, we aimed to determine whether PARD3 has a role in
LSCC development.
Materials and Methods
Cell lines and tumor samples
Fifty-one lung cancer cell lines were studied (Supplementary
Table S1). The cell lines were authenticated by testing for TP53 and
other mutations (e.g., SMARCA4, STK11, etc.). The mutations
were genotyped before starting the experiments and were in
agreement with those provided in public databases. Tumors were
obtained from the Johns Hopkins University School of Medicine
(Baltimore, MD), the CNIO Tumour Bank Network (Madrid,
Spain), the Fondazione IRCCS Istituto Nazionale Tumori (Milan,
Italy), and the Hospital Universitario Central de Asturias (Oviedo,
Spain).
Direct sequencing and MS-MLPA of PARD3
For mutation screening of the PARD3, exons 1 to 26
(H. sapiens chromosome 10 reference assembly NC_019619)
were amplified. The sequence of primers used is provided in
Supplementary Table S2.
Methylation-specific multiplex ligation-dependent probe
amplification (MS-MLPA) was used to determine the presence
of intragenic homozygous deletion and promoter hypermethy-
lation of the PARD3 gene. The MLPA analysis was carried out
using SALSA P448-A1-lot0811 PARD3 probe mix and MLPA
reagents (MRC-Holland) following the MS-MLPA protocol (see
Supplementary Methods).
Microarray analysis
RNA (100 ng) was used for the gene expression microarray
employing RNA Integrity. Values ranged from 9.0 to 10.0
(Lab-chip technology with an Agilent 2100 Bioanalyzer). For
labeling, we used the commercial One-Color Microarray-Based
Gene Expression Analysis (version 5.5) Kit, following the
manufacturer's instructions (Agilent manual G4140-90050,
February 2007). Hybridization was performed on the Human
Gene Expression v2 microarray 8 Â 60 K (Agilent microarray
design ID 014850, P/N G4112F).
Results
PARD3 is somatically and biallelically inactivated in LSCCs
We searched in databases for homozygous deletions and
concomitant decreases in gene expression in cancer cell lines
and observed that several members of the PAR family of
proteins are deleted in different types of cancer (Wellcome
Trust Sanger Institute's Cancer Cell Line Project website; ref.
12). Here, we have focused on one of these genes: PARD3. After
confirming the homozygous deletions at PARD3 in the NCI-
H157 (hereafter H157) cell line (Supplementary Fig. S1A and
S1B), we sequenced its coding region in 51 lung cancer cell
lines. We found another cell line, PC10, with two PARD3
alterations: a c.2581A>T change, which causes an amino acid
substitution, and the intronic variant c.223-4C>G, whose effect
is unknown. Despite being in heterozygosis, the missense
change was predominant at the mRNA level (Fig. 1A). This
suggests that the c.223-4C>G variant affects splicing and trig-
gers nonsense-mediated decay of this mRNA, thus implying
that the PC10 cells carry biallelic inactivation of PARD3.
The H157 and PC10 are of the LSCC type. This is consistent
with a previous observation about the presence of PARD3 muta-
tions in primary HNSCCs (12), which are etiologically and
molecularly very similar to LSCCs (19). Given this background,
we decided to screen for PARD3 alterations in LSCCs. In addition
to Sanger sequencing, we used the MLPA assay to search for
intragenic homozygous deletions. The deletion at H157 was
clearly observed by MLPA (Supplementary Fig. S1C).
Overall, we found tumor-specific PARD3 alterations in 8%
of the LSCCs. Interestingly, some of the alterations resulted in
in-frame rearrangements that predict shorter proteins (Table 1).
Noticeably, all the alterations at PARD3 rendering in-frame
deletions only affected common exons. In addition to muta-
tions predicting shorter forms or the complete absence of
PAR3 protein expression, we identified missense alterations at
PARD3. Some of these amino acid substitutions are predicted
to be deleterious by the polymorphism phenotyping tool
(20). We also tested for LOH and confirmed the "two hit"
hypothesis for tumor suppressors (Fig. 1; and Supplementary
Fig. S2; ref. 21).The location of the different mutations within
the domains of the PAR3 protein is detailed in Fig. 1D. All
known SNPs and germ-line variants found are listed in Sup-
plementary Table S3. Information on the mutation status of
PARD3 and the different tumor and patient characteristics is
provided in Supplementary Table S4.
Because CpG promoter hypermethylation is a mechanism for
gene inactivation, we designed MLPA probes to assess this alter-
ation at the promoter of PARD3. One of the probes indicated
the presence of CpG methylation, which was confirmed by
bisulfite sequencing, in a subset of lung cancer cell lines (Sup-
plementary Fig. S3). However, the presence of methylation at
these sites was not correlated with the loss of protein expression,
so we discounted the possibility that this mechanism accounts for
PARD3 loss of expression in lung cancer.
Effect of PAR3-mutant proteins on cell growth suppression
The PARD3 structure is complex because it has alternative
splice sites and two different stops, resulting in multiple PAR3
protein isoforms, some of which are detectable by Western blot
(Supplementary Fig. S1B). We determined that the transcript
NM_001184785.1 was the most abundant in normal lung (Sup-
plementary Fig. S4).
To assess the effect of the PARD3 mutations in LSCC, we cloned
the most abundant wild-type and five mutant transcripts and
expressed them in H157 cells (Fig. 2A). Of notice, the antiPAR3
antibody did not recognize the p.D41_E689del mutant protein
(Supplementary Fig. S5A). First of all, we evaluated the ability of
the wtPAR3 and the PAR3-mutant proteins to suppress cell growth
in the H157 cell line. Compared with the wtPAR3, the PAR3
mutants, especially p.D41_R74del and p.D41_E689del, were
significantly less able to suppress cell growth (Fig. 2B).
Effect of PAR3-mutant proteins on intercellular contacting and
downstream target activation
We determined the intracellular location of the ectopically
expressed PAR3 proteins. We observed that, although the wtPAR3
and the amino acid change mutants were located in the cell
Bonastre et al.
Cancer Res; 75(7) April 1, 2015 Cancer Research1288

membrane, at cell–cell contacts, and in the cytoplasm, the
p.D41_R74del and p.D41_E689del PAR3 proteins were pre-
dominantly located in the cytoplasm (Fig. 2C).
In addition to PAR3, the PAR complex comprises PAR6,
aPKC, and CDC42. aPKC binds PAR6 that tethers the kinase
to the tight junction where it interacts with PAR3. Once there,
Figure 1.
PARD3-inactivating mutations in LSCCs. A, mutations of the PC10 cells at the genomic DNA (gDNA) and mRNA (cDNA) level. B, mutation in a lung tumor
but not in the matched normal DNA. D10S1780 designates one microsatellite marker showing LOH. The agarose gel depicts the deletion of exon 2 in this tumor
at the mRNA level. C, top, representation of the structure of PARD3, highlighting the location of the exons deleted (red). Bottom, ratio charts of the MLPA
depicting the deletion of exons 2 to 13 (top) and of the normal matched DNA (bottom). Right plots, shorter transcript arising from the deletion. The
D10S1780 depicts the presence of LOH. D, representation of the PAR3 protein structure and the location of those PARD3 mutations that do not predict
truncated proteins. aPKCb, atypical protein kinase C binding site; CC, coiled coil domains; CR1, control region 1; PDZ, PDZ domains.
Table 1. PARD3 gene alterations found in lung cancer cell lines and in lung primary squamous cell carcinomas
Identiﬁcation Nucleotide change Predicted effect Exon/intron Status Somatic Predicted impacta
LSCC cancer cell lines (n ¼ 18)
NCI-H157 c.715-?_2614þ?del No protein E6–E18 LOH NA NA
PC10 c.223-4C>G No protein I2 NO LOH NA NA
PC10 c.2581A>T p.T861S E18 NO LOH NA Damaging
LSCC primaries (N ¼ 108)
1681 (T1) c.223-?_3549þ?del No protein E3–23 LOH Yes NA
141 (T2)b
c.121-2A>G p.D41_R74del I1 LOH Yes NA
181 (T3)b
c.404-?_582þ?del No protein E4 NA NA NA
269 (T4) c.1034G>A p.R345H E9 LOH Yes Damaging
200 (T6) c.1492insG p.A498GfsÃ
9 E10 LOH Yes NA
273 (T7) c.3129A>G p.I1043M E21 LOH Yes Benign
114 (T8)b
c.121-?_2067þ?del p.D41_E689del E2–E13 LOH Yes NA
1529 (T9) c.404-?_3549þ?del No protein E4–E23 LOH Yes NA
NOTE: Ref Seq, mRNA sequence NM. 019619.
Abbreviation: NA, not analyzable.
a
PolyPhen impact.
b
Conﬁrmed at mRNA level.
The PARD3 Tumor Suppressor in Lung Squamous Cell Carcinomas
www.aacrjournals.org Cancer Res; 75(7) April 1, 2015 1289

PAR3 is phosphorylated by aPKC, which stabilizes PAR3 at the
tight junctions (22). We tested whether the PAR3 mutations affect
its interaction with aPKC. Similar levels of endogenous aPKC were
recovered from all the hemagglutinin immunoprecipitates, except
in the case of the p.D41_E689del mutant, for which no aPKC was
detected (Fig. 2D). Therefore, the large deletion was the only
mutation that impaired the binding of PAR3 with aPKC.
To evaluate the effects of the PARD3 inactivation in detail,
we constructed H157-derived isogenic cell lines that express
stable and doxycycline-inducible wtPAR3 (H157tr-wtPAR3
hereafter) and the mutants p.D41_R74del, p.R345H, p.T861S,
and p.I1043M (hereafter, H157tr-D41_R74del, H157tr-R345H,
H157tr-T861S, and H157tr-I1043M, respectively; Fig. 3A). Immu-
nofluorescence confirmed the ectopic expression of PAR3 in
about 40% to 80% of the cell population (Supplementary
Fig. S5B). The induction of PAR3 expression in the H157tr-
wtPAR3 cells resulted in a decreased number of colonies, support-
ing the observations above (Fig. 2B), and discarded a bias
due to differences in transfection efficiency (Supplementary
Fig. S5C). Further, we tested the involvement of PAR3 in cell
proliferation and migration, using the MTT and the xCELLigence
system assays, respectively. Our results show a significant reduc-
tion of cell migration capability but not of cell proliferation, in the
H157tr-wtPAR3 as compared with the control cells (Fig. 3B and
Supplementary Fig. S5D). These observations support a role of
PARD3 inactivation in tumor invasiveness.
Given the involvement of PAR3 in the formation of tight
junctions (14), we explored the capability of the various PAR3-
mutant proteins to colocalize with the tight junction protein,
Zona occludens protein 1 (ZO-1). The analysis confirmed that
wtPAR3 colocalized with ZO-1 and restored the capability of
ZO-1 to accumulate at high density in the cell membrane at
cell–cell contact regions. Similarly, the PAR3 proteins carrying
amino acid substitutions exhibited strong coimmunolocaliza-
tion of PAR3 and ZO-1 at the cell–cell contacts and an accu-
mulation of ZO-1 in the cell membrane, as opposed to the
H157tr and H157tr-D41_R74del cells (Fig. 3C).
For the appropriate control of cell and cytoskeletal polarity, the
PAR complex is connected to various signaling pathways, includ-
ing that of RhoGTPases (22, 23). It is known that PAR3 interacts
Figure 2.
Effects of the PAR3-mutant proteins on cell growth inhibition, protein localization, and binding to aPKC. A, Western blot shows ectopic expression of
the various PAR3 proteins. b-ACTIN, protein-loading control. B, restitution of wtPAR3 significantly reduces colony formation in H157 cells. Right, quantification
of the assay. C, immunofluorescence to determine localization of PAR3. Right, quantification of the assay. Error bars, SD. D, coimmunoprecipitation of
aPKC with anti-HA from extracts of the H157 cells expressing the indicated proteins. One twentieth of the input lysate and of the immunoprecipitated (IP)
fraction were immunoblotted (WB) with hemagglutinin or aPKC antibodies. TUBULIN, protein-loading control. Ã
, P < 0.05; ÃÃ
, P < 0.01.
Bonastre et al.

with the RacGEF, TIAM1, and that this interaction is important
for regulating actin protrusions, e.g., lamellipodia and filopodia,
in various types of migratory mammalian cells (23–25). Consis-
tent with this, we observed that, when sparsely seeded, cells
expressing ectopic wtPAR3 formed actin-rich protrusions oriented
toward other cells, with which cell–cell contacts were established
(Fig. 3D). All protrusions were formed of filamentous actin and
colocalized with the F-actin marker, phalloidin (Supplementary
Fig. S5E). There were significantly fewer protrusions in those cells
lacking PAR3 or in the H157tr-D41_R74del and H157tr-R345H
cells. To rule out cell-specific bias, we determined whether the
behavior was reproduced in the glioma-derived and PARD3-
deficient T98G cells (12). We generated T98G-derived isogenic
cell lines that expressed stable and doxycycline-inducible wt and
mutants of PARD3 (Supplementary Fig. S6A and S6B). In agree-
ment with observations made in the H157-derived cells, the
T98Gtr-wtPAR3 and the amino acid substitution mutants showed
strong immunostaining at the cell–cell contacts, whereas the
T98Gtr-D41_R74del accumulated at the cytoplasm (Supplemen-
taryFig.S6C).Theabilitytoformprotrusionsalsodiffered between
wt- and mutant PAR3–expressing cells (Supplementary Fig. S6D).
The interaction of the PAR3 complex with TIAM1 also leads to
the activation of the small GTPase, RAC1, whereas the inhibition
of the formation of the complex results in RAC1 inactivation
(22, 24). In contrast with this, others reported a constitutively
active Rac1 in cells lacking Par3 (25). Here, we found that
restitution of PAR3 in the H157tr-wtPAR3 cells increases
the levels of the GTP-RAC1 fraction. This also occurred in the
H157tr-R345H and H157tr-T861S mutant cells, but not in the
H157-derived cells expressing other PAR3-mutant proteins
(Fig. 3E). Therefore, our results indicate that PAR3 is required to
promote the activation of RAC1. Intriguingly, the activation of
RAC1 following restitution of wtPAR3 was not observed in the
T98G-derived cells.
We noted that the levels of the p.D41_R74del protein, but
not the mRNA, were low as compared with the wild type
(Fig. 3A and Supplementary Fig. S6B). To determine whether
these observations were a consequence of active degradation,
Figure 3.
Effects of the wtPAR3 and PAR3-mutant proteins on various polarity related parameters. A, Western blot of PAR3, stably expressed under a tet-repressor–controlled
vector. Presence (þ) or absence (À) of doxycycline (dox, 1 ng/mL; 24 h). TUBULIN, protein-loading control. B, xCELLigence system assay, using collagen I or
fibronectin. Error bars, SD. Ã
, P < 0.05; ÃÃ
, P < 0.01. C, immunofluorescence of PAR3 and ZO-1. Nuclei were stained with DAPI. D, right, phase-contrast images of
the indicated cells 24 hours after seeding. Arrows, protrusions. Left, quantification of the percentage of protrusions relative to the total number of cells.
E, amounts of GTP-RAC1 and total RAC1 determined by immunoblotting with anti-RAC1 antibody. Positive (GTP) and negative (GDP) controls are included. Bottom,
relative ratio of RAC1-GTP to total RAC1, normalized with respect to the wt value. F, Western blots of PAR3, following treatment with either MG132 or ALLN,
for the indicated times (hours) after induction with doxycycline. NT, untreated cells.

we treated the cells with MG132, which is a very efficient
proteasome inhibitor (26), and with N-[N-(N-Acetyl-L-leu-
cyl)-L-leucyl]-L-norleucine (ALLN), which inhibits neutral cys-
teine proteases and the proteasome. The levels of the p.
D41_R74del protein were substantially higher after the addi-
tion of either MG132 or ALLN, whereas the levels of the
wtPAR3 protein remained high in the H157- and T98G-derived
cells (Fig. 3F and Supplementary Fig. S6E). Interestingly, the
accumulation of p.D41_R74del protein was more evident after
treatment with the MG132 than with the ALLN inhibitor.
Altogether, the results demonstrate that the p.D41_R74del
suffers from protein degradation by the proteasome. Despite
this, the levels of p.D41_R74del protein after 24 hours of
doxycycline induction were in the range of the endogenous
levels of PAR3 (Supplementary Fig. S7A). Because of that, it is
unlikely that the relatively lower abundance of this mutant
protein would affect its subcellular localization or other para-
meters and, thus, we considered that the H157tr-D41_R74del
cells are suitable for carrying out a molecular study of the effects
of the CR1 region on PAR3 functionality.
The gene expression signature of PAR3 is enriched in transcripts
involved in cell adhesion and the cell junction
Next, we compared the gene expression profiles of the H157tr
control and the H157tr-D41_R74del with that of the H157tr-
wtPAR3 cells after induction of PAR3 expression. About 150 genes
were differentially expressed (Supplementary Table S5) in the
H157tr-wtPAR3 cells. Gene ontology analysis linked the PAR3
gene expression signature to functions associated with cell adhe-
sion, cell motion, and the cell junction (Fig. 4A and B). We
selected six transcripts representing different gene functions to
test how the different mutants of PAR3 affect the expression levels
of these genes. Interestingly, the H157tr-I1043M cells showed the
same gene expression profile for five of the six transcripts as the
Figure 4.
Gene expression signature of PAR3. A, enriched gene ontology (GO) classifications (P < 0.05) among genes upregulated by PAR3 (Supplementary Table S5). B, left,
heatmap of the transcripts comprising the PAR3 gene expression signature. Right, heatmap of selected genes from each indicated gene ontology category. C, mRNA
levels assessed by real-time quantitative PCR of representative transcripts (relative to ACTB). Error bars, SD. Ã
, P < 0.05; ÃÃ
, P < 0.01; ÃÃÃ
, P < 0.005. D, graph of
the ranked gene lists from the Gene Set Enrichment Analysis (GSEA) comparisons. Probabilities and FDRs are indicated. E, top, Western blot depicting levels
of the indicated proteins after induction of PAR3 expression (doxycycline, 1 ng/mL; 24 h). F, Western blot of the indicated proteins. Left, cells grown to different
degrees of confluence. Right, calcium switch assay; 0, 3, and 6 hours after readdition of calcium; NCM, normal calcium–containing medium. G, Western blot
depicting the downregulation of PAR3 levels, with two independent shRNAs (sh#1/sh#2). sh-cntl, scramble control. TUBULIN, protein-loading control. E–G, bottom
panels, densitometric analysis to quantify the levels of pY-STAT3 relative to total STAT3.
Bonastre et al.

H157tr or the H157tr-D41_R74del cells, which highlights its
inactivating nature (Fig. 4C). In contrast, the expression levels
of the selected genes in the H157tr-p.R345H and H157tr-p.T861S
mutants had a variable pattern, halfway between that of the mock
and wild-type cells.
PAR3 is required to activate STAT3 upon cell–cell contact
Among the transcripts that were upregulated in the H157tr-
wtPAR3 cells were also cytokines and targets of STAT3 (Fig. 4B),
suggesting a PAR3–STAT3 functional relationship. We therefore
decided to explore this further.
First, we compared the gene-expression profile of the H157tr-
wtPAR3 cells with that of two human cancer cell lines after
knockdown of STAT3 (27) and observed an inverse association
(Fig. 4D). Phosphorylation of STAT3 at the tyrosine 705 (pY-
STAT3) induces its activation and thus dimerization, nuclear
translocation, and DNA binding (28). We observed that the
levels of pY-STAT3 were higher in the H157tr-wtPAR3 cells than
in the control cells and in the mutant counterparts (Fig. 4E).
The phosphorylation levels of other PAR3-related proteins,
such as aPKC, remain unchanged. The increase in pY-STAT3
following restitution of PAR3 was particularly evident when
cells were grown at high density (Fig. 4F), which is consistent
with previous reports showing that STAT3 activity dramatically
increases with cell confluence (29, 30). These observations were
confirmed using calcium depletion experiments. Withdrawal of
calcium from the medium causes rapid loss of cell–cell junc-
tions (25), a process that can be reversed by readdition of
calcium (a calcium switch). A strong decrease in pY-STAT3 was
observed after calcium depletion in the H157tr-wtPAR3 cells
(Fig. 4F). The levels of pY-STAT3 were recovered 24 hours after
calcium readdition (Supplementary Fig. S7B). Furthermore, we
depleted PARD3 expression in lung cancer cells with wild-type
endogenous PAR3, such as the H1299 and H2170 cells, and
observed a decrease in the levels of pY-STAT3 in high-density
cell cultures (Fig. 4G). Taken together, these observations
suggest that, upon cell–cell contact, the formation of tight
junction triggers an increase in the activation of STAT3, in a
process that requires the activity of wtPAR3. Similarly to what it
was observed for RAC1, the activation of STAT3 following resti-
tution of PAR3 was not evident in the T98G cells, which could
reflect differences in the cell and tissue of origin. The LSCC cells
derive from the respiratory epithelia,a tissuethat relies stronglyon
tight junctions for maintaining epithelial integrity (31). In this
case, the loss of tight junctions may permit contact-inhibited cells
to separate from neighboring cells and proliferate and invade
other tissues. However, the T98G derive from glia cells of the
nervous tissue, where the regulation of cell–cell contact is different
as it is in the respiratory epithelia.
Restoration of wtPAR3 reduces tumor invasiveness and
prevents formation of metastasis in vivo
To investigate the tumorigenicity of the H157tr-wtPAR3 and
H157tr cells in vivo, we examined their capacity to grow ortho-
topically and to form tumors in the lung parenchyma of athymic
nude mice. Animals were randomly assigned to two groups, each
containing 11 mice, and were implanted with the H157tr-wtPAR3
and H157tr cells. We counted the number of cancer lesions in the
lung and in the liver, an organ that is a common target for
metastasis in lung cancer patients. Both groups of mice developed
orthotopic tumors and the H157tr-wtPAR3 tumors efficiently
expressed wtPAR3 and higher levels of pY-STAT3 (Fig. 5A). Liver
metastases and cancer lesions in the lung were detected in both
groups of mice. The generation of liver metastasis indicates that
this model closely follows the natural pathology of metastasis
development from lung primary tumor growth. Overall, we
observed that the wtPAR3-expressing tumors had significantly
fewer lesions in the lungs and metastases to the liver than mice
whose tumors did not express PAR3 (Fig. 5B).
These observations prompted us to generate another mouse
model to test, specifically, the differences in the metastatic capa-
bility of the cells. Mice were divided into two groups: those
carrying H157tr-wtPAR3 (n ¼ 7) or H157tr (n ¼ 6) cells,
implanted into the spleen of the animals. We then measured the
number and size of the metastases generated in the lungs and
livers. We also confirmed the effective induction of ectopic
wtPAR3 and increased pY-STAT3 levels (Fig. 5C). Significantly
fewer metastatic lesions were found in the lungs of mice carrying
H157tr-wtPAR3 (Fig. 5D). In addition, we observed that cancer
lesions that arose in the liver of the mice implanted with the
H157tr-wtPAR3 were smaller and round in shape, suggesting a
reduced invasive capability, than the liver lesions found in the
H157tr group of mice (Fig. 5E).
Patterns of PAR3 immunostaining in lung primary tumors and
in HNSCCs
Next, we performed immunohistochemistry of PAR3 in lung
tumors and HNSCCs. We included HNSCCs because these
tumors are histologically similar to that of LSCC (19). A
collection of about 190 lung primary tumors of different
histopathologies, i.e., LACs and LSCCs and a panel of 262
HNSCCs, were tested. As expected, those lung tumors carrying
PARD3 mutations predicting no protein expression were neg-
ative for PAR3 immunostaining. On the other hand, the tumors
carrying the p.D41_R74del and p.D41_E689del showed mod-
erate and negative immunostaining of PAR3, respectively (Sup-
plementary Fig. S8A). This is consistent with the observations
made in Western blots and in immunofluorescences.
Very strong levels of PAR3 were detected in some of the
tumors that were wild type for PARD3. PAR3 immunostaining
was evident in the cell membrane and the cytoplasm of these
tumors (Fig. 6A and B). We observed that more LACs exhibit-
ed strong immunostaining than did LSCCs and HNSCCs
(Fig. 6C). Intriguingly, in some lung tumors, predominantly
LACs, the strong PAR3 immunostaining appeared as punctuate
clusters (Fig. 6A). Although we do not know the biologic
significance, it is interesting to note that similar punctuate
clusters containing PAR3 have previously been observed in
Caco-2 cells derived from colorectal adenocarcinomas (32, 33).
Likewise, in some of the HNSCCs, there was a notable hetero-
geneous pattern of PAR3 immunostaining, whereby staining
was stronger in those regions where the tumor became invasive
(Supplementary Fig. S8B).
In the HNSCCs, we examined the pattern of the PAR3 immu-
nostaining in normal epithelia and in preneoplastic lesions,
adjacent to tumor regions. In the normal epithelia, the PAR3
protein was detected predominantly in the apical region of the
cells from the basal layer. The hyperplasic and dysplastic lesions
exhibited a similar pattern. The distribution of the PAR3 immu-
nostaining was similar among the two different types of preneo-
plastic lesions, although the number of samples is too small to
draw definitive conclusions (Supplementary Fig. S8B).

Lung tumors of patients with high and moderate levels of
PAR3 were larger than those showing negative or low levels of
PAR3. No associations were observed between the different
levels of PAR3 and the development of distant or lymph node
metastasis (Supplementary Fig. S8C). Finally, we performed
immunohistochemistry of pY-STAT3 in a panel of 88 lung
cancers specimens, which included most tumors tested for
PAR3 immunostaining and for PARD3 mutations. As expected,
PARD3-mutant tumors were negative for pY-STAT3 immunos-
taining. Similarly to PAR3, we observed that more LACs exhib-
ited strong immunostaining of pY-STAT3 than did LSCCs
(Fig. 6D and Supplementary Table S4).
Discussion
We discovered recurrent tumor-specific inactivating alterations
of the polarity-related gene PARD3 in 8% of LSCCs. This frequen-
cy is very similar to that of other well-established tumor suppres-
sor genes, such as PTEN (2). Homozygous deletions in other
components of the PAR3 complex have been found in various
types of cancer cells (12), indicating that abnormalities in the
control of cell polarity are relatively widespread in cancer. It is
worth mentioning that the tumor suppressor gene LKB1, which is
commonly inactivated in lung cancer (34), also controls cell
polarity and has been associated with the PAR complex
(16, 35). However, LKB1 is deleted in the H157 cells (2), which
argues against the hypothesis that inactivation of LKB1 or PARD3
is functionally equivalent in cancer development.
The p.D41_R74del and the p.D41_E689del proteins had an
impaired ability to localize at the edge of the cell membrane,
preventing colocalization with ZO-1. The 33 amino acids missing
from the p.D41_R74del mutants are located within the control
region 1 (CR1) domain, attesting to the involvement of thisregion
in correctly positioning PAR3 at the edge of the cell membrane.
This is consistent with previous observations in the PARD3
homolog in Drosophila (33, 36). The aberrant location of the
Figure 5.
PAR3 expression decreased tumor cell invasiveness and metastasis, in vivo. A, the H157tr and the H157tr-wtPAR3 cells were grown orthotopically in athymic nude
mice (45, 46). Representative Western blots (top) and RT-PCRs (bottom) of the induction of PAR3 in lung orthotopic tumors. The levels of pY-STAT3 are also
shown. TUBULIN, protein-loading control. B, mean frequency of intrapulmonary cancer lesions and liver metastases in each group. Error bars, SDs. Right,
representative hematoxylin and eosin preparations of the metastases (arrow) in the lung and liver (magnification, Â100). C, cells were implanted in the spleen.
Representative Western blot (top) and RT-PCR (bottom) of the induction of PAR3 in tumors derived from the indicated cancer cells. Levels of pY-STAT3 and of
total STAT3 are also shown. D, left, mean frequency of intrapulmonary metastases and the area of the liver affected by metastasis. Error bars, SD. Right,
representative hematoxylin and eosin preparations of the metastases (arrows; magnification, Â100). E, hematoxylin and eosin staining of liver metastasis in the
splenic mouse model. Purple and pink areas, tumor and normal liver cells, respectively. In the left column, the third and fourth images from top to bottom correspond
to a single tumor from the same animal. Arrows, well-defined and round-shaped cancer lesions. B and D, Ã
, P < 0.05; ÃÃ
, P < 0.01; ÃÃÃÃ
, P < 0.001.
Bonastre et al.

p.D41_R74del in the cytosol could explain its degradation by
the proteasome, as our current results show. The p.R345H,
p.D41_R74del mutations showed a significantly reduced ability
to form large filamentous actin protrusions. These filaments,
probably lamellipodia and filopodia, are involved in substrate
adhesion and in directed locomotion toward establishing con-
tacts between epithelial cells. The p.R345H, p.D41_R74del muta-
tions affect the PDZ1 domain of PAR3, which is required to form
a complex with the discoidin domain receptor 1 (DDR1) and
with PAR6 to antagonize ROCK-driven actomyosin contractility
(37–40). DDR1 has also been found to prevent the activation of
STAT3 (41). Thus, the fewer large actin protrusions observed
in these mutants could be a consequence of defective binding
to DDR1. It is worth remembering that oncogenic mutations at
DDR1 and DDR2 have been found in breast cancer and LSCCs,
respectively (7, 40).
The T861S substitution is located near the aPKC binding
domain, close to residues that are phosphorylated by aPKC
(S827/S829) or Rho-kinase (T833; refs. 37, 38). Phosphorylation
at these residues reduces the affinity for aPKC/PAR6, thereby
suppressing the activity of the PAR complex (18, 37–39).
Although in our study only the p.D41_E689del mutant PAR3
failed to bind aPKC, we cannot rule out the possibility that the
T861S mutation affects the affinity of interaction with other
Figure 6.
PAR3 immunostaining in lung and HNSCC primary tumors. A, top, representative immunostainings of PAR3 in lung tumors (magnification, Â200). Bottom
plots are insets from the indicated pictures. Arrows, cells showing PAR3 localization at the cell edge. B, immunostaining of PAR3 in HNSCC (magnification,
Â200). C, bar graphs, distribution of LACs, LSCCs, and HNSCCs by PAR3 immunostaining categories. Inside the bars, number of tumors within each category.
D, top, representative immunostainings of pY-STAT3 in lung tumors (magnification, Â200). Bottom, bar graphs showing the distribution of lung AC and SCC
by pY-STAT3 immunostaining categories. E, top, representation of PAR3, showing the mutations and the functionalities of PAR3 that are affected in each
case. (Ã
), effects on the functionalities of PAR3 are inferred from the observations made for the p.D41_R74del protein. Bottom, representation of cell
processes that require PAR3 and of the downstream targets activated in each case. Left, wtPAR3 promotes the formation of protrusions, allowing the
sensation of chemotropic cues that will result in substrate adhesion and in directed locomotion toward establishing contacts between cells. This would
involve the activation of RAC1 but not of STAT3. Right, the proximity of neighboring cells promotes the formation of a tight junction (TJ) by a PAR3-
dependent process. This triggers the activation of both RAC1 and STAT3. Thus, the absence of wtPAR3 subverts the mechanisms of recognition and
interaction between neighboring cells. This can be deleterious for most epithelial tissues, including the respiratory epithelia, which rely strongly on tight
junctions for maintaining their integrity. C and D, Ã
, P < 0.05; ÃÃ
, P < 0.01; ÃÃÃÃ
, P < 0.001.

partners. The I1043M mutation is located in the coiled-coil
domain, whose function is unknown.
Restitution of PAR3 led to a pattern of gene expression that is
compatible with its role in cell adhesion and polarity and includ-
ed transcriptional targets of STAT3. This was correlated with an
increase in the activation of STAT3, especially when cells were
grown at high density. Our findings are consistent with those
showing the involvement of PAR3 in the activation of RAC1 (37),
which is required to promote STAT3 activation (42). However, the
presence of activating mutations at STAT3 in some leukemias
attests to an oncogenic role for STAT3 (43). The reasons why a
tumor suppressor, PAR3, would promote the activity of an onco-
gene, STAT3, are puzzling. Patterns of STAT3 activation differ,
resulting from the formation of tight intercellular interactions
following a transitory and regulated pattern (30), whereas most
STAT3 mutations render a constitutively active STAT3 (43). More-
over, STAT3 can act as a negative regulator of tumor growth, in the
context of thyroid cancer, indicating that the activation of STAT3 is
not always oncogenic (44). The formation of tight intercellular
contacts may not be as important in nonepithelial tissues. Sup-
porting this view, the glioma-derived cells T98G yielded no
evidence of STAT3 activation upon PAR3 restitution. Figure 6E
summarizes the functions that were altered in the PAR3-mutant
proteins, and provides a schematic model of the pathways and
downstream targets that would be activated during cell–cell
recognition and during the formation of cell–cell contacts.
Consistent with the findings from a previous mouse model in
which the depletion of Par3 promoted the formation of metas-
tasis (18), here we show, in two different in vivo models, that the
restitution of PAR3 reduced the capability to develop metastasis.
This is compatible with the participation of PAR3 in promoting
intercellular recognition and interactions. The immunostaining
analysis in the LSCCs and in HNSCCs revealed no correlation
between the levels of PAR3 and the presence of metastasis. This
does not discount a role of PAR3 in promoting metastasis, because
other components of the PAR3 complex can be altered in the
tumors. In this regard, we believe that the strong and aberrant
PAR3 immunostaining found in some of the lung tumors, wild
type for PARD3, reflects the operation of feedback mechanisms
derived from gene alterations at other key point controllers of the
PAR3 complex or pathway.
In conclusion, we report recurrent and tumor-specific inacti-
vation of PARD3 in LSCC, which leaves little doubt that it acts as a
bona fide tumor suppressor gene. Our findings also highlight how
PARD3 inactivation contributes to LSCC development and metas-
tasis through the abrogation of some important properties of
epithelial cells, such as cell–cell recognition and the formation of
cell contacts.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
Authors' Contributions
Conception and design: E. Bonastre, M. Sanchez-Cespedes
Development of methodology: E. Bonastre, S. Verdura, F. Facchinetti,
A. Villanueva, E. Brambilla, S. Savola
Acquisition of data (provided animals, acquired and managed patients,
provided facilities, etc.): E. Bonastre, S. Verdura, I. Zondervan, S. Lantuejoul,
M.D. Chiara, J.P. Rodrigo, E. Condom, A. Vidal, D. Sidransky, A. Villanueva,
L. Roz, E. Brambilla, M. Sanchez-Cespedes
Analysis and interpretation of data (e.g., statistical analysis, biostatistics,
computational analysis): E. Bonastre, S. Verdura, I. Zondervan, M.D. Chiara,
J.P. Rodrigo, J. Carretero, E. Condom, A. Vidal, A.Villanueva, L. Roz, M. Sanchez-
Cespedes
Writing, review, and/or revision of the manuscript: E. Bonastre, A. Vidal,
L. Roz, E. Brambilla, M. Sanchez-Cespedes
Administrative, technical, or material support (i.e., reporting or organizing
data, constructing databases): S. Verdura, I. Zondervan
Study supervision: M. Sanchez-Cespedes
Acknowledgments
The authors acknowledge the technical assistance of Patricia Cabral (Genes
and Cancer Group) at IDIBELL and of Dolores Moreno at the Human Pathology
Department of the Hospital Universitario de Bellvitge.
Array data have been deposited in the Gene Expression Omnibus under
accession reference GSE51506.
Grant Support
This work was supported by Spanish grants SAF2011-22897, RTICCs [RD12/
0036/0045 (M. Sanchez-Cespedes) and RD12/0036/0015 (M.D. Chiara)], the
Fondo de Investigacion Sanitaria (FIS PI11/929; M.D. Chiara and J.P.
Rodrigo), the European Community's Seventh Framework Programme (FP7/
2007-13), under grant agreement n
HEALTH-F2-2010-258677–CURELUNG,
and grants from the Associazione Italiana per la Ricerca sul Cancro (AIRC
IG9227 and IG13403; L. Roz). E. Bonastre is supported by a fellowship from the
Spanish MINECO.
The costs of publication of this article were defrayed in part by the payment
of page charges. This article must therefore be hereby marked advertisement
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received August 19, 2014; revised December 22, 2014; accepted December
29, 2014; published online April 1, 2015.
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2015;75:1287-1297.Cancer Res
Ester Bonastre, Sara Verdura, Ilse Zondervan, et al.
STAT3 and Promotes Malignant Invasion
Inactivation in Lung Squamous Cell Carcinomas ImpairsPARD3
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