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Altered Expression of Two-Pore Domain Potassium (K
2P
)
Channels in Cancer
Sarah Williams
1
, Andrew Bateman
2
, Ita O’Kelly
1
*
1Human Development and Health, Centre for Human Development, Stem Cells and Regeneration, Faculty of Medicine, University of Southampton, Southampton, United
Kingdom, 2Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom
Abstract
Potassium channels have become a focus in cancer biology as they play roles in cell behaviours associated with cancer
progression, including proliferation, migration and apoptosis. Two-pore domain (K
2P
) potassium channels are background
channels which enable the leak of potassium ions from cells. As these channels are open at rest they have a profound effect
on cellular membrane potential and subsequently the electrical activity and behaviour of cells in which they are expressed.
The K
2P
family of channels has 15 mammalian members and already 4 members of this family (K
2P
2.1, K
2P
3.1, K
2P
9.1, K
2P
5.1)
have been implicated in cancer. Here we examine the expression of all 15 members of the K
2P
family of channels in a range
of cancer types. This was achieved using the online cancer microarray database, Oncomine (www.oncomine.org). Each gene
was examined across 20 cancer types, comparing mRNA expression in cancer to normal tissue. This analysis revealed all but
3K
2P
family members (K
2P
4.1, K
2P
16.1, K
2P
18.1) show altered expression in cancer. Overexpression of K
2P
channels was
observed in a range of cancers including breast, leukaemia and lung while more cancers (brain, colorectal, gastrointestinal,
kidney, lung, melanoma, oesophageal) showed underexpression of one or more channels. K
2P
1.1, K
2P
3.1, K
2P
12.1, were
overexpressed in a range of cancers. While K
2P
1.1, K
2P
3.1, K
2P
5.1, K
2P
6.1, K
2P
7.1 and K
2P
10.1 showed significant
underexpression across the cancer types examined. This analysis supports the view that specific K
2P
channels may play a
role in cancer biology. Their altered expression together with their ability to impact the function of other ion channels and
their sensitivity to environmental stimuli (pO2, pH, glucose, stretch) makes understanding the role these channels play in
cancer of key importance.
Citation: Williams S, Bateman A, O’Kelly I (2013) Altered Expression of Two-Pore Domain Potassium (K
2P
) Channels in Cancer. PLoS ONE 8(10): e74589.
doi:10.1371/journal.pone.0074589
Editor: Sven G. Meuth, University of Muenster, Germany
Received June 3, 2013; Accepted August 3, 2013; Published October , 2013
Copyright: ß2013 Williams et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Work funded by the Gerald Kerkut Charitable Trust (http://www.southampton.ac.uk/,gktrust/). The funders had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: I.M.O’Kelly@southampton.ac.uk
Introduction
Traditionally, the study of ion channels has focused on their
roles in excitatory cells (neuronal, cardiac and secretory), however
more recently, ion channels have been recognised for their roles in
the behaviours of cancer cells and the development and
progression of cancer. In the last 15 years increasing evidence
supports the role of ion channels in mitogenesis, the control of
cellular proliferation and apoptosis as well as cell migration and
metastasis [1–8]. Overexpression of some ion channels has been
linked to poor prognosis [9] while other channels are now
recognised as potential biomarkers for particular cancer types
[10,11]. These reports, together with the potential of targeting ion
channel function through pharmacological modulation, make
understanding the role of ion channels in cancer biology of key
importance.
K
+
channels play fundamental roles in cell behaviours linked to
cancer progression, including regulation of cell proliferation,
migration, apoptosis and angiogenesis [2,12–14]. Cell membrane
potential (driven by K
+
channel activity) plays an important
regulatory role in cell cycle progression and proliferation, with
highly proliferating cells displaying a more positive membrane
potential than quiescent cells, while a transient membrane
hyperpolarisation enables G1 progression [15–18]. The precise
regulatory mechanisms are unclear but evidence supports two
hypotheses. The first proposes that changes in membrane potential
due to K
+
channel activity modulates voltage-gated Ca
2+
channels,
thus impacting Ca
2+
influx and downstream signalling [17,19].
The alternative hypothesis proposes that the changes in cell
volume seen during proliferation (cell swelling) and apoptosis (cell
shrinkage) may be regulated by K
+
channel activity [18,20,21]. In
a similar manner, K
+
channel control of membrane potential has
been shown to impact cell migration through regulation of cell
volume, pH and intracellular Ca
2+
concentration. A direct impact
of alteration in membrane potential on cytoskeletal polymerisation
has also been demonstrated [14,22,23].
Altered K
+
channel expression and/or function occurs in a
range of cancer types, with ion channels from each of the K
+
channel families (voltage sensitive (K
V
); calcium sensitive (K
Ca
);
inwardly rectifying (K
ir
); and two-pore domain (K
2P
) channels)
implicated in cancer development and progression. Within the K
V
family, K
V
11.1 (hERG) shows altered expression in an array of
cancer types and has been shown to impact cellular proliferation
(melanoma, colorectal cancer and Barrett’s esophagus), migration
(melanoma, thyroid and breast cancer), malignant transformation
(head & neck carcinoma) and apoptosis (gastric cancer). While
K
V
11.1 is most frequently reported for its role in cancer, an array
of other K
+
channels have also been proposed as molecular
PLOS ONE | www.plosone.org 1 October 2013 | Volume 8 | Issue 10 | e74589
7
components promoting cancer development and progression
[9,10,24–80] (summarised in Table 1).
The potential role of K
2P
channels in cancer is of particular
interest. These channels conduct outward K
+
background currents
and are active at resting membrane potentials, thus they have a
direct influence on baseline cellular activity of cells at rest
including membrane potential, calcium homeostasis and cell
volume regulation. K
2P
channels also show sensitivity to physio-
logical stimuli including pH, oxygen tension, glucose concentra-
tion and stretch; key physiological parameters which are disrupted
within the cancer cells and their environment [81–83].
Of the 15 mammalian K
2P
family members, four K
2P
channels
(K
2P
2.1 (TREK-1), K
2P
3.1 (TASK-1), K
2P
9.1 (TASK-3) and
K
2P
5.1 (TASK-2)) have already been implicated in cancer. In
2003, Mu et al. [77] described KCNK9, the gene encoding K
2P
9.1,
as a potential proto-oncogene where genomic overexpression of
the gene was detected in 10% of breast carcinomas and the protein
was detected in 44% of breast tumours by immunohistochemistry
but not in normal tissue controls. The oncogenic ability (measured
by proliferative advantage) was demonstrated to depend upon a
functional channel [84]. K
2P
9.1 immunopositivity has subsequent-
ly been reported in colorectal carcinomas [78] and melanoma
tissue samples [85].
Increased K
2P
2.1 expression was detected in prostate adeno-
carcinoma samples compared to normal prostate epithelium and
reduced proliferation of prostate cancer cell lines was observed
when K
2P
2.1 was experimentally knocked down [74].
A study by Nogueira et al. (2010) [75] linked K
2P
3.1 expression
to aldosterone production in both aldosterone-producing adeno-
mas and normal adrenals, and proposed K
2P
3.1 may play a role in
Ca
2+
signalling regulation. Equally, K
2P
3.1 and K
2P
9.1 have
previously been reported to play a role in K
+
-dependent apoptosis
in granule cell neurons in culture [86].
Transcriptome analysis in human ductal breast epithelial
tumour cell line, T47D, following either stimulation with either
estrogen receptor (ER) awhich induces proliferation or ERb
which has antiproliferative effects showed that K
2P
5.1 mRNA was
upregulated by ERasignalling [87]. mRNA, protein and
functional expression (acid-sensitive outward currents) of K
2P
5.1
was reported to increase in response to 17b-estradiol stimulation of
ERasignalling in T47D and human breast adenocarcinoma cell
line, MCF-7. While experimental knockdown of K
2P
5.1 moder-
ately reduced basal proliferation of T47D cells, a significantly
greater reduction in estrogen-induced proliferation was observed
[76].
Evidence from these studies supports the hypothesis that
alterations to the expression or function of K
2P
channels in cancer
cells may play a role in cancer development and progression.
Targeting these channels may lead to novel cancer therapies; we
therefore sought to determine the transcript expression of each of
the K
2P
channels in a range of cancers using an online cancer
microarray database, Oncomine (www.oncomine.org, Compendia
biosciences, Ann Arbor, MI, USA). This information documents
changes in the expression of the K
2P
family members in a range of
cancer types and provides a valuable resource to enable further
Table 1. Summary of potassium channel expression in cancer.
Channel Expression detected Behavioural impact Ref
K
V
1.3 Breast, lung, lymphoma, pancreatic, prostate Apoptosis, poor prognosis, proliferation [24–28]
K
V
1.4 Gastrointestinal Gene silencing [29]
K
V
1.5 Brain Increased survival [30]
K
V
3.4 Head and neck Proliferation [31]
K
V
4.1 Breast, gastrointestinal Proliferation [32,33]
K
V
10.1 Bone, breast, cervical, colorectal, esophageal, head and neck,
kidney, leukemia (acute myeloid), ovarian
Biomarker, migration, proliferation, poor prognosis [10,34–42]
K
V
10.2 Brain, kidney Proliferation [42,43]
K
V
11.1 Breast, colorectal, esophageal, gastrointestinal, head and neck,
kidney, leukemia (acute myeloid), lung, melanoma, ovarian,
retinoblastoma, thyroid
Migration, proliferation, poor prognosis, [22,34,36,42,44–
49]
K
Ca
1.1 Bone, brain, breast, ovarian, prostate Apoptosis, metastases, microenvironment regulation,
migration, proliferation
[9,50–55]
K
Ca
2.3 Breast, colon, melanoma Migration [56–58]
K
Ca
3.1 Brain, breast, colorectal, melanoma, prostate Migration, proliferation [59–63]
K
ir
2.2 Breast, gastrointestinal, prostate Cell cycle [64]
K
ir
3.1 Breast, lung, pancreatic Metastases, proliferation [27,65,66]
K
ir
3.4 Aldosterone-producing adenomas Mutations detected [67]
Kir4.1 Brain Migration, poor prognosis [68,69]
K
ir
6.1/K
ir
6.2 Brain, breast, melanoma, uterine Apoptosis, cell cycle, proliferation [70–73]
K
2P
2.1 Prostate Proliferation [74]
K
2P
3.1 Aldosterone-producing adenomas Aldosterone production [75]
K
2P
5.1 Breast Proliferation [76]
K
2P
9.1 Breast, colorectal, lung, melanoma Apoptosis, migration, mitochondrial function, proliferation [77–80]
Potassium channels identified in specific cancer types together with the predominant behavioural characteristics. Channels are divided into family groups, voltage-
gated (K
V
), calcium-gated (K
Ca
), inward rectifying (K
ir
) and two-pore domain (K
2P
).
doi:10.1371/journal.pone.0074589.t001
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 2 October 2013 | Volume 8 | Issue 10 | e74589
investigation into the protein expression and potential roles of
these important channels in cancer progression.
Methods
Analysis of KCNK mRNA expression in cancer tissue samples
(meta-analysis of KCNK genes and related statistical analyses)
were performed using the online cancer microarray database,
Oncomine (www.oncomine.org, Compendia biosciences, Ann
Arbor, MI, USA). Oncomine collects publicly available cancer
microarray data and processes all data imposing the same criteria
[88]. The mRNA expression data is organised into cancer types
defined within the original publications. mRNA expression data
was extracted from Oncomine between August 2012 and January
2013. Citations for all primary studies used together with
information on cancer type and staging (where available) is
provided in Table S1 in File S1.
Only datasets examining KCNK gene mRNA expression in
cancer tissue which was matched with normal tissue controls
(cancer vs. normal) were included in this study. Threshold criteria
had to be achieved by each study for inclusion in the analysis. The
threshold search criteria used for this study were a p-value,0.05, a
fold change .2 and a gene rank percentile ,10%. P-values
presented in this study for differential expression analysis of
KCNK genes were calculate by Oncomine using a two-sided
Student’s t-test and multiple testing correction [86,87]. Multiple
testing correction was performed using the false discovery rate
method, where corrected p-values (Q-values) were calculated as
Q = NP/R (where P = p-value, N = total number of genes and R is
the sorted rank of p-value) [88,89]. In this study a p-value less than
0.05 was considered significant. Fold change is defined as the
linear change in mRNA for the gene of interest in cancer tissue
when compared to the normal expression level for that tissue, in
this case a fold change of 2 and greater was included for analysis.
For each dataset the genes studied are ranked by their p-value.
The gene rank percentile is the percentage ranking of the gene of
interest compared to all other genes analysed in that dataset based
on p-values. The average number of genes examined in the
microarray data presented in this study was approximately 14,000
genes. Datasets in which the gene of interest was in the top 10% of
genes changed were included. These threshold values are
connected by the Boolean AND, therefore an analysis was only
classed as above threshold when it met all three criteria.
Initially KCNK genes (KCNK1–18) were examined across a
range of 20 cancer types, which have been grouped by their tissue
of origin (Table S2 in File S1), comparing mRNA expression in
that cancer type to normal tissue controls. Gene summary view in
Oncomine was utilised during this analysis and presented here
with expression ranking indicated by colour shading. Expression
colouring for a gene in a particular cancer relates to the gene rank
percentile for the highest ranking above threshold analysis.
Further analysis was performed on each KCNK gene, for
expression in the most prevalent cancer types based on
GLOBACON 2008 WHO rankings (http://globocan.iarc.fr/)
[90]. Lymphoma, myeloma, sarcoma, liver and ovarian cancers
were removed from further analysis due to low KCNK expression.
The subtype ‘other cancers’ which is defined as cancers which do
not fall into the prescribed subtypes (e.g. uterine and adrenal
cancers) was also removed from further analysis as the large
diversity of cancer subtypes within this group would make detailed
analysis uninformative. Using the threshold criteria described
previously all above threshold analyses for each KCNK gene was
extracted from Oncomine and complied.
Once all above threshold data for each KCNK gene had been
complied, comparative meta-analysis was performed on cancer
subtype with more than five datasets (n$5) available, this analysis
provided a median gene rank and median p-value for that cancer
subtype.
Results and Discussion
KCNK genes show altered expression across different
cancers
KCNK genes 1–18 (with the omission of KCNK8, KCNK14
and KCNK11 which were ascribed proteins but subsequently
withdrawn due to nomenclature duplication) encode the mam-
malian family of K
2P
channels [91]. Initially to obtain a global
view of changes in K
2P
channel expression in cancer, we used the
Oncomine cancer microarray database to analyse the alterations
observed in KCNK gene mRNA expression in the 20 most
commonly diagnosed cancers, grouped by their tissue of origin,
compared to normal tissue controls. For inclusion in the analysis,
changes in gene expression compared to normal controls had to
fulfil threshold criteria of achieving a p-value,0.05, a fold change
.2 and a gene rank percentile ,10%. The gene rank percentile
values for each of the 15 KCNK genes in cancers compared to
normal tissue controls were examined and the percentile of the
highest ranking analyses are shown for each KCNK gene and each
cancer tissue type in Figure 1. Performing analysis in this way
enabled comparison of alterations in gene expression to be
performed between different microarray experiments and revealed
that all KCNK genes with the exception of KCNK4 (K
2P
4.1 or
TRAAK), KCNK16 (K
2P
16.1 or TALK1) and KCNK18
(K
2P
18.1 or TRESK) show altered expression in the 20 cancer
types examined when compared to normal tissue controls
(Figure 1A & B). Cancers from fourteen tissue types showed
over-expression of more than one KCNK gene (Figure 1A) with
five cancer tissue types (breast, kidney, leukaemia, lung, lympho-
ma) showing over-expression of three or more KCNK genes
(Figure 1A). While broad cancer tissue types are considered in this
initial analysis and include a range of different cancer diseases,
they provide valuable preliminary information on the expression
of KCNK genes in cancer and further analysis taking into account
specific cancer subtypes (e.g. acute versus chronic leukaemia) was
performed for specific channels in subsequent analyses.
When examining underexpression of KCNK genes, cancer
from 19 of the 20 tissue types analysed showed decreased
expression of one or more KCNK genes when compared to
normal tissue expression (Figure 1B). Six K
2P
family members
(KCNK1, KCNK2, KCNK3, KCNK5, KCNK7 and KCNK10)
show underexpression in over 5 different cancer tissue types of
(Figure 1B). While 10 different cancer tissue types (brain, breast,
colorectal, gastrointestinal, head and neck, kidney, lung, melano-
ma, prostate and sarcoma) show underexpression of at least three
KCNK genes (Figure 1B). Strikingly, specific K
2P
channels show
increased mRNA expression in some cancer tissues while
decreased expression in others. This is particularly apparent for
KCNK1, KCNK3, KCNK5 and KCNK6, which displayed
mRNA expression changes (either up or down in distinct cancers)
which rank them in the top 1% of genes showing altered
expression for those cancers. KCNK1, for example, is in the top
1% of genes showing overexpression in bladder, cervical, lung and
pancreatic cancers, while in cancers of the central nervous system
KCNK1 shows one of the highest reductions in expression when
compared to normal tissue controls (Table 2). These analyses
suggest that the impact of down-regulation of K
2P
channels on cell
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 3 October 2013 | Volume 8 | Issue 10 | e74589
function may be an equally important alteration as increased
expression in cancer biology.
KCNK expression in specific cancer types
The 15 members of the K
2P
channel family are divided into 6
separate groupings on the basis of their sequence homology and
defining biophysical characteristics. The expression of each gene
in each of the 14 cancer tissue types (6 tissues were excluded from
this analysis due to low dataset numbers or high cancer subtype
diversity) was studied in detail using the analysis threshold values
as before (p-value,0.05, fold change .2 and gene rank percentile
,10%) and the results are presented for each channel group
(Tables 2, 3, 4, 5, 6 & Table S3 in File S1). Data from comparative
meta-analysis performed for specific KCNK genes in cancer sub-
types in which a sufficient number of microarray studies (n$5)
examining these genes were available are presented in Tables 2, 3,
4, 5, 6 and was performed using all datasets in which the gene of
interest was examined and not just those which ranked above
threshold values. Meta-analysis provided the median gene rank
and median p-value, thus enabling comparison across different
microarray studies. If the median ranked analysis had a significant
p-value it indicated that the expression trend for that gene was
likely to be altered in that cancer subtype. If less than 5
independent studies for any of the genes in a particular cancer
subtype were not available on Oncomine, meta-analysis of data
which reached threshold was not performed but instead was
collated and presented in Table S3 in File S1.
Figure 1. Expression of KCNK genes across different cancers. Expression of KCNK genes (KCNK1–18) in 20 cancers compared to normal tissue
controls. Shown is the gene and protein names for each channel. A) overexpression of KCNK genes. B) underexpression of KCNK genes. Cancer types
are organised by their tissue of origin, the degree of colour correlates to the gene rank percentile of the highest ranking analyses. Search criteria were
for mRNA datasets and cancer vs. normal analysis only, with threshold values of p-value,0.05, fold change .2 and gene rank percentile ,10%.
doi:10.1371/journal.pone.0074589.g001
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 4 October 2013 | Volume 8 | Issue 10 | e74589
Two-pore domain weak inward rectifying K
+
(TWIK)
channel family
TWIK channels include KCNK1 (K
2P
1.1, TWIK1), KCNK6
(K
2P
6.1, TWIK2) and KCNK7 (K
2P
7.1). None of these channels
have previously been implicated in playing a role in cancer, but
analysis presented here reveals a significant overexpression of
KCNK1 in the majority of cancers analysed (12 out of 20 cancer
tissue types show overexpression with KCNK1 ranked in the top
10% of most altered genes) while 6 cancer tissue types showed
KCNK1 underexpression when compared to normal tissue
(Figure 1). KCNK6 was found to be among the top 1% of genes
overexpressed in breast cancer and top 1% of genes under-
expressed in colorectal cancer. While KCNK7 failed to show
overexpression in any of the cancer types examined it showed
significant underexpression in a range of cancers and was in the
top 1% of underexpressed genes in both melanoma and cervical
cancers (Figure 1).
Cancer subtypes in which KCNK1 showed above threshold
changes in expression are presented in Table 2 (if sufficient studies
were available for meta-analysis (n$5)) or Table S3 in File S1 (if
insufficient number of studies were available for meta-analysis
(n#4)). All cancer sub-types with KCNK1 overexpression eligible
for meta-analysis were found to show significant levels of
overexpression (median p-value#0.05; Table 2). Lung adenocar-
cinomas had the most significant increase in expression compared
Table 2. TWIK family members expression in cancer.
Gene Cancer Subtype Above threshold analyses Median values
p-value Fold change % Ref p-value Gene rank n
KCNK1 Brain Glioblastoma Q1.72E-24 29.574 2 [9] 5.14E-06 560.5 8
Q1.80E-14 220.541 3 [10]
Q1.07E-08 28.483 3 [3]
Q1.03E-05 213.309 4 [6]
q5.89E-04 3.178 6 [5]
Breast Ductal q5.23E-04 2.515 5 [16] 0.002 2547 12
q7.18E-04 3.965 5 [12]
q1.00E-03 2.405 5 [15]
q4.00E-03 2.661 9 [12]
q1.10E-02 2.4 9 [13]
Lobular q2.20E-02 2.177 4 [13] 0.031 3848 5
Cervical Squamous Cell q9.70E-13 2.949 1 [20] 0.043 3326 5
Leukaemia Acute Lymphocytic q4.00E-03 2.173 5 [42] 9.04E-07 4799 7
Lung Adenocarcinoma q3.59E-07 3.984 2 [52] 8.51E-13 511 7
q5.38E-07 2.141 3 [46]
q2.35E-05 4.641 1 [47]
q6.21E-05 2.137 8 [51]
Squamous cell q5.98E-08 2.138 9 [49] 0.002 852 6
q2.61E-06 7.79 2 [47]
Pancreas Adenocarcinoma q9.83E-10 3.526 5 [71] 0.008 787.5 8
q2.61E-04 6.584 3 [72]
q1.41E-04 6.62 5 [73]
q1.21E-08 4.613 1 [74]
q2.00E-03 2.685 9 [75]
KCNK6 Breast Ductal q2.77E-19 2.161 9 [17] 0.076 5236 10
q1.00E-03 2.765 1 [14]
Colorectal Adenocarcinoma Q1.77E-18 22.071 4 [26] 0.028 4860 11
Q2.38E-15 22.11 7 [26]
Q9.37E-15 22.136 1 [26]
KCNK7 Cervical Squamous cell Q5.62E-10 26.76 1 [21] 7.99E-04 519 5
Q1.86E-08 23.055 1 [22]
Q7.99E-04 23.315 5 [22]
Gastrointestinal Adenocarcinoma Q1.60E-02 22.336 10 [29] 0.446 9583 5
The above threshold data for TWIK family members; KCNK1, KCNK6 and KCNK7 is shown. Data is divided into each cancer type and subtypes within that cancer. The p-
value, fold change and gene rank percentile (%) for data which scored above threshold values (p-value,0.05, fold change .2 and gene rank percentile ,10%) are
shown. Comparative meta-analysis was performed using all available analyses for a given cancer subtype which provides median gene rank and median p-value.
Overexpression qand underexpression Qare indicated.
doi:10.1371/journal.pone.0074589.t002
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 5 October 2013 | Volume 8 | Issue 10 | e74589
to normal tissue, with a 3.2260.64 mean fold increase from the 4
studies which reached threshold for inclusion and a median p-
value of 8.51E-13 (n = 7; Table 2). While, pancreatic adenocar-
cinomas showed the highest mean (6SEM) fold increase
(4.8060.79) in KCNK1 transcript compared to the normal
controls in the 5 studies above threshold criteria.
Brain cancers of glial cell origin (astrocytoma, glioblastoma,
oligodendrioglioma), medulloblastoma and melanomas all showed
significant down regulation of KCNK1 with respect to normal
control tissues (Table S3 in File S1). All but glioblastoma had
insufficiently high number of independent analyses to enable
inclusion in comparative meta-analysis (Table S3 in File S1), while
in glioblastoma 4 above threshold analyses showed underexpres-
sion ranging from 8 to 20 fold decreases in KCNK1 transcript
expression whereas one study showed a 3 fold increase of KCNK1
mRNA (Table 2). Comparative meta-analysis of all 8 studies in
which KCNK1 transcript expression was examined revealed an
overall significant (p = 5.14E-6) decreased expression of KCNK1
in glioblastoma (Table 2). KCNK1 is not the only gene to show
apparently conflicting expression profiles but this may be due to
the broad groupings in each of the cancer types. Significantly this
is also observed for KCNK10 in brain glioblastoma (Table 3).
While KCNK6 shows overexpression in both ductal (average
fold change 2.46; n = 2) and invasive (fold change 3.57 (n = 1))
breast cancer, overall, KCNK6 and KCNK7 show more
transcript underexpression (Table 2). Though, meta-analysis of
KCNK6 expression in ductal breast cancer found the increased
expression not to reach significance (p = 0.076; n = 10). Both
KCNK6 and KCNK7 show underexpression in melanoma and
oesophageal adenocarcinomas. KCNK6 showed significant de-
creased expression in colorectal adenocarcinoma (median p-
value = 0.028; n = 11) with a mean (6SEM) fold decreased
expression of 2.1160.02 in the 3 above threshold analyses for
underexpression. KCNK7 underexpressed in Barrett’s oesophagus
when compared to normal tissue controls but insufficient numbers
of studies were available to enable further analysis (Table S3 in
File S1). KCNK7 showed significant down-regulation in cervical
squamous cell carcinoma (median p-value of 7.99E-04; n = 5) with
a mean (6SEM) fold decreased expression of 4.3761.19. A
decreased expression of KCNK7 observed in gastrointestinal
adenocarcinomas failed to show significance following meta-
analysis (median p-value 0.446, n = 5) and achieved a median gene
rank of 9583 out of circa 14000 genes suggesting that alterations in
KCNK7 expression are less important in gastrointestinal adeno-
carcinomas.
TWIK-related K
+
(TREK) channel family
The TREK family has 3 family members KCNK2 (K
2P
2.1,
TREK1), KCNK4 (K
2P
4.1, TRAAK) and KCNK10 (K
2P
10.1,
TREK2). KCNK4 failed to show altered expression above the set
thresholds in the 20 cancers examined and therefore was not
further analysed.
KCNK2 was among the top 5% of genes over expressed in lung
cancers and under expressed in breast, gastrointestinal and head
and neck cancers (Figure 1). KCNK10 was among the top 1% of
genes underexpressed (compared to normal tissue controls) in
colorectal and kidney cancers while in breast and brain cancers
KCNK10 was among the top 5% of genes underexpressed
(Figure 1A & B). As seen with KCNK1 in glioblastoma, two of the
above threshold analyses show decreased KCNK10 expression
(compared to normal tissue controls) ranging from 2.9 to 4.8 fold
decreases, while a third analysis shows a 2.5 fold increase in
KCNK10 expression. Meta-analysis including all studies in which
KCNK10 expression was examined in glioblastoma cancer
revealed a significant decreased expression (median p-va-
lue = 5.03E-05; n = 5) but while clear changes in KCNK10
expression levels are observed in glioblastoma further studies
and analysis are required to determine the nature of these
alterations. KCNK10 was also ranked in the top 10% of over-
expressed genes in acute myeloid leukemia (Figure 1A & Table S3
in File S1; n = 4) but insufficient studies were available to enable
robust meta-analysis to be performed to determine the significance
Table 3. TREK family members expression in cancer.
Gene Cancer Subtype Above threshold analyses Median value
p-value Fold change % Ref p-value Gene rank n
KCNK2 Breast Invasive Q5.70E-05 22.23 4 [19] 0.349 8095 11
Lung Squamous cell q2.98E-04 2.111 5 [48] 0.696 6505 5
KCNK10 Brain Glioblastoma Q1.81E-17 24.843 5 [9] 5.03E-05 908 5
Q1.56E-10 22.974 6 [10]
q8.63E-04 2.547 7 [5]
Breast Ductal Q1.00E-03 22.294 2 [18] 0.15 6686.5 10
Q3.85E-04 23.523 2 [14]
Colorectal Adenocarcinoma Q1.74E-25 27.227 1 [26] 8.12E-07 372.5 14
Q3.19E-22 27.914 2 [26]
Q2.85E-18 26.275 1 [26]
Q2.07E-14 24.83 2 [26]
Q1.11E-07 26.275 2 [26]
Q3.42E-07 22.503 3 [26]
The above threshold data for TREK family members; KCNK2 and KCNK10 is shown. Data is divided into each cancer type and subtypes within that cancer. The p-value,
fold change and gene rank percentile (%) for data which scored above threshold values (p-value,0.05, fold change .2 and gene rank percentile ,10%) are shown.
Comparative meta-analysis was performed using all available analyses for a given cancer subtype which provides median gene rank and median p-value.
Overexpression qand underexpression Qare indicated.
doi:10.1371/journal.pone.0074589.t003
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 6 October 2013 | Volume 8 | Issue 10 | e74589
of this change. KCNK10 shows decreased expression in breast
ductal and lobular carcinomas and colorectal adenoma, adeno-
carcinoma and carcinoma as well as kidney clear cell carcinoma
(Table 3 & Table S3 in File S1). Only breast ductal carcinoma and
colorectal adenocarcinoma had sufficient number of studies to
enable meta-analysis (Table 3). This analysis revealed the changes
in breast ductal carcinoma not to be significant (median p-
value = 0.15; n = 5) while colorectal adenocarcinoma showed
significant decreased expression of KCNK10 (median p-va-
lue = 8.12E-07; n = 14)
KCNK2 showed decreased expression in invasive breast cancer,
gastrointestinal adenocarcinoma and head and neck squamous cell
carcinoma but these studies either failed to be included in meta-
analysis due to low study numbers or failed to show significance
following meta-analysis (Table 3 & Table S3 in File S1).
These data while limited by the sample size provide sufficient
evidence to warrant further investigation into the role of KCNK10
in both glioblastoma and colorectal adenocarcinoma.
TWIK-related acid sensitive K
+
(TASK) channel family
The TASK family has three members KCNK3 (K
2P
3.1,
TASK1), KCNK9 (K
2P
9.1, TASK3) and KCNK15 (K
2P
15.1,
TASK5).
Table 4. TASK family members expression in cancer.
Gene Cancer Subtype Above threshold analyses Median value
p-value Fold change % Ref p-value Gene rank n
KCNK3 Brain Glioblastoma Q6.20E-08 25.468 10 [10] 0.007 1486 7
Q2.61E-05 24.471 3 [10]
Breast Invasive q4.41E-17 2.782 4 [11] 0.005 8863 13
q1.50E-02 2.958 6 [14]
Q1.00E-03 22.375 7 [17]
Colorectal Adenoma Q2.37E-04 22.493 10 [24] 2.37E-04 1814 5
Q2.00E-03 24.175 5 [24]
Gastrointestinal Adenocarcinoma q2.85E-04 3.567 6 [28] 1 10604 6
Kidney Clear cell q1.53E-14 8.407 1 [36] 1.14E-04 990 6
q2.57E-07 6.014 5 [36]
q4.01E-05 4.541 7 [38]
q1.89E-04 6.344 6 [41]
Leukemia Acute lymphocytic q1.30E-02 2.177 9 [42] 0.994 8503 7
Lung Adenocarcinoma Q6.55E-34 24.136 1 [50] 4.33E-11 146.5 6
Q8.44E-20 26.89 1 [49]
Q8.67E-11 27.375 2 [52]
Q4.11E-10 22.367 1 [51]
Q2.54E-06 27.399 3 [47]
Q1.08E-04 23.803 4 [48]
Squamous cell Q5.90E-20 212.756 2 [49] 5.90E-20 343 5
Q3.86E-06 28.471 3 [47]
Q1.58E-05 24.28 3 [48]
Q2.00E-03 22.422 7 [53]
Pancreas Adenocarcinoma Q7.34E-06 26.459 1 [74] 2.46E-07 2997 7
Q4.72E-05 25.03 1 [72]
Q1.19E-04 22.191 3 [75]
Prostate Carcinoma Q2.72E-08 22.034 3 [77] 0.029 1515 13
Q1.02E-04 22.638 2 [79]
Q8.94E-04 23.106 4 [76]
KCNK9 Breast Invasive q1.16E-12 3.95 9 [11] 0.459 10188.5 14
KCNK15 Breast Ductal q1.00E-03 5.046 6 [12] 0.008 1578 6
q8.00E-03 2.283 9 [12]
q4.10E-02 8.774 8 [14]
Gastrointestinal Adenocarcinoma Q3.00E-03 22.189 5 [29] 0.043 2990 5
The above threshold data for TASK family members; KCNK3, KCNK9 and KCNK15 is shown. Data is divided into each cancer type and subtypes within that cancer. The p-
value, fold change and gene rank percentile (%) for data which scored above threshold values (p-value,0.05, fold change .2 and gene rank percentile ,10%) are
shown. Comparative meta-analysis was performed using all available analyses for a given cancer subtype which provides median gene rank and median p-value.
Overexpression qand underexpression Qare indicated.
doi:10.1371/journal.pone.0074589.t004
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 7 October 2013 | Volume 8 | Issue 10 | e74589
KCNK3 showed altered expression in the majority of cancers
examined (13 out of 20) and was in the top 1% of up-regulated
genes in kidney cancer and top 5% of up-regulated genes in breast,
leukaemia and lymphoma (Figure 1A). KCNK3 was in the top 1%
of under-expressed genes in sarcoma, breast, lung and pancreatic
cancers. KCNK3 was also in the top 5% of under-expressed genes
in cancers of the CNS, bladder, colorectal and prostate (Figure 1B).
Detailed meta-analysis of cancer subtypes with decreased KCNK3
expression revealed underexpression to be significant in pancreatic
adenocarcinoma (median p-value = 2.46E-07; n = 7), lung adeno-
carcinoma (median p-value = 4.33E-11; n = 6), colorectal adeno-
ma (median p-value = 2.37E-04; n = 5) and glioblastoma (median
p-value = 0.007; n = 7; Table 4). Lung squamous cell carcinoma
showed both the highest level of significance following meta-
analysis of 5 studies in which KCNK3 gene expression was
examined (median p-value = 5.90E-20) and highest mean fold
decrease in KCNK3 expression from the 4 studies which reached
threshold (6.9862.30; Table 4).
Analysis of KCNK3 transcript expression in specific cancers
within the broad cancer types shows significant increase in
KCNK3 expression in invasive breast (median p-value = 0.005)
and clear cell kidney (median p-value = 1.14E-04) cancers with a
4.5 to 8.4 fold increase in expression in clear cell kidney
carcinomas when compared to normal tissue controls (Table 4).
While K
2P
9.1 has previously been identified in breast, colon and
melanoma cancers [78,82,83], KCNK9 only showed an above
threshold analysis for invasive breast carcinomas (p-value = 1.16E-
12; Table 4). When comparative meta-analysis was performed
with 14 analyses examining KCNK9 in invasive breast carcino-
mas, the changes were found not to be significant (median p-
value = 0.459).
KCNK15 shows significant overexpression, by comparative
analysis, in ductal breast carcinomas (median p-value = 0.008;
5.3761.88 mean fold increase in 3 above threshold analyses) and
underexpression in gastrointestinal adenocarcinomas (median p-
value = 0.043; Table 4).
TWIK-related alkaline pH activated K
+
(TALK) channel
family
The TALK family has three family members KCNK5 (K
2P
5.1,
TASK2), KCNK16 (K
2P
16.1, TALK1) and KCNK17 (K
2P
17.1,
TALK2). KCNK16 failed to show altered expression above the set
thresholds in the 20 carcinomas examined initially and therefore
was not further analysed.
KCNK5 showed altered expression in 50% of cancers
examined. It was in the top 1% of up-regulated genes in
esophageal cancers and top 5% of up-regulated genes in breast
and lung cancers (Figure 1A). Decreased expression of KCNK5
was observed in a wider range of cancer subtypes with KCNK5 in
the top 1% of under-expressed genes in melanoma and top 5% of
under-expressed genes in breast, colorectal, kidney, leukaemia,
liver cancers and sarcoma (Figure 1B). Although not all cancer
subtypes which demonstrated changes in expression of KCNK5
had sufficient number of studies for comparative analysis (Table
S3 in File S1), meta-analysis of colorectal adenocarcinoma studies
showed a significant decrease in KCNK5 expression (median p-
Table 5. TALK family members expression in cancer.
Gene Cancer Subtype Above threshold analyses Median value
p-value Fold change % Ref p-value Gene rankn
KCNK5 Breast Ductal q2.14E-04 2.977 3 [12] 0.233 4729 9
Q7.70E-04 23.629 4 [12]
Q2.00E-03 22.498 2 [18]
Q1.00E-03 23.856 6 [12]
Colorectal Adenocarcinoma Q2.42E-12 23.18 3 [26] 2.35E-07 1052 11
Q1.95E-11 22.498 5 [26]
Q7.86E-08 23.199 2 [26]
KCNK17 Breast Invasive q2.20E-02 3.265 8 [14] 0.752 14529 12
The above threshold data for TALK family members; KCNK5 and KCNK17 is shown. Data is divided into each cancer type and subtypes within that cancer. The p-value,
fold change and gene rank percentile (%) for data which scored above threshold values (p-value,0.05, fold change .2 and gene rank percentile ,10%) are shown.
Comparative meta-analysis was performed using all available analyses for a given cancer subtype which provides median gene rank and median p-value.
Overexpression qand underexpression Qare indicated.
doi:10.1371/journal.pone.0074589.t005
Table 6. THIK family member, KCNK13 expression in cancer.
Gene Cancer Subtype Above threshold analyses Median value
p-value Fold change % Ref p-value Gene rank n
KCNK13 Breast Invasive q3.35E-12 3.193 10 [11] 0.399 10349 11
q4.99E-08 2.05 10 [17]
The above threshold data for THIK family member; KCNK13 is shown. Data is divided into each cancer type and subtypes within that cancer. The p-value, fold change
and gene rank percentile (%) for data which scored above threshold values (p-value,0.05, fold change .2 and gene rank percentile ,10%) are shown. Comparative
meta-analysis was performed using all available analyses for a given cancer subtype which provides median gene rank and median p-value. Overexpression qand
underexpression Qare indicated.
doi:10.1371/journal.pone.0074589.t006
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 8 October 2013 | Volume 8 | Issue 10 | e74589
value = 2.35E-07; n = 11; Table 5) with a mean fold decrease of
2.9660.23 (n = 4). Further studies are required to determine if the
down-regulation of KCNK5 observed in other cancer subtypes are
also significant.
A single study reached the threshold criteria and showed a 3.26
fold increase in KCNK17 expression in invasive breast carcinomas
(Table 5). However when comparative meta-analysis was per-
formed with all analyses examining KCNK17 in invasive breast
carcinomas (n = 12) it was found not to be significant (median p-
value = 0.752) suggesting the study which reached threshold may
not be representative of KCNK17 expression in breast cancer.
Two pore domain halothane inhibited K
+
(THIK) channel
family
The THIK family has two family members KCNK12 (K
2P
12.1,
THIK1) and KCNK13 (K
2P
13.1, THIK2).
KCNK12 showed altered expression compared to normal tissue
controls in 7 of the 20 cancer types examined with both
overexpression and underexpression observed (Figure 1 & Table
S3 in File S1). Above threshold reductions in KCNK12 expression
were observed in astrocytoma and glioblastoma, while increased
expression was seen in acute lymphocytic leukaemia and lung
adenocarcinoma but insufficient sample sizes for any of these
cancer subtypes prevented any comparative meta-analysis of
KCNK12 to be performed. KCNK13 showed two above
threshold analysis for invasive breast carcinomas with 2.6260.57
mean (6SEM) fold increase in KCNK13 expression. However
when comparative analysis was performed with 11 analyses
examining KCNK13 in invasive breast carcinomas, altered
expression of KCNK13 failed to reach significance (median p-
value = 0.399; Table 6).
Potential role for K
2P
channels in cancer therapy
This study provides a comprehensive overview of the current
data available on KCNK gene family expression in cancer and
clearly demonstrates altered expression of these genes is observed
in the majority of cancer types examined. In all of the 20 cancers
examined with the exception of ovarian cancer KCNK genes were
found in the top 10% of altered genes and were in the top 1% in
13 of these cancers. In several instances, specific cancer subtypes
show changes in a number of KCNK genes. Specifically brain
glioblastoma showed significant down regulation of KCNK1,
KCNK3 and KCNK10; while KCNK12 also showed decreased
expression but insufficient studies were available to enable
comparative analysis. Likewise, breast ductal cancer showed
significant increased expression of KCNK1, KCNK6 and
KCNK15. Noteworthy is the observation that in some cancer
subtypes overexpression of one KCNK gene occurs alongside
underexpression of another, this is observed in lung adenocarci-
noma, lung squamous and pancreatic adenocarcinomas, where in
all three of these cancer subtypes KCNK1 shows significant over-
expression while KCNK3 is significantly under-expressed. As
specific K
2P
family members show altered sensitivities to different
modulators such as intracellular and extracellular pH (TWIK,
TREK, TASK, TALK), hypoxia and reactive oxygen species
(TASK, TALK, THIK) and glucose concentration (TASK),
changing the relative expression of different K
2P
channels may
impact the response of cells to environmental cues [81–83,91–96].
Moreover, either increased or decreased expression of these
channels has the potential to induce membrane hyperpolarisation
or depolarisation respectively. As noted previously, alterations to
membrane potential is recognised to drive changes in cell
proliferation, apoptosis and migration [14–18,21]. As K
2P
channels are active over physiological membrane potential ranges,
this means these channels are ideally positioned to directly impact
cellular membrane potential at rest. This, together with their acute
sensitivity to the internal and external environment of the cell
which is known to change in the cancer microenvironment means
that altered expression of these channels may provide cancer cells
with a survival advantage.
Understanding the molecular and pharmacological regulation
of these channels together with a detailed knowledge of the
expression of these channels in cancer will enable these important
membrane proteins to be considered as potential therapeutic
targets in cancer treatment.
Supporting Information
File S1 Contains Tables S1, S2, and S3. Oncomine
datasets for all above threshold analyses used in this
study. Datasets are referenced in text from 1–80 and indicated is
the Oncomine nomenclature for a study, the original publication
reference and sample descriptions. (Information from www.
oncomine.org , Compendia Bioscience, Ann Arbor, MI).
(DOCX)
Acknowledgments
We are grateful to the contributors of data to Oncomine and those who
have made their data publicly available.
Author Contributions
Conceived and designed the experiments: IO SW AB. Performed the
experiments: SW. Analyzed the data: SW IO. Contributed reagents/
materials/analysis tools: AB. Wrote the paper: IO SW.
References
1. DeCoursey TE, Chandy KG, Gupta S, Cahalan MD (1984) Voltage-gated K+
channels in human T lymphocytes: a role in mitogenesis? Nature 307: 465–468.
2. Lang F, Foller M, Lang KS, Lang PA, Ritter M, et al. (2005) Ion channels in cell
proliferation and apoptotic cell death. J Membr Biol 205: 147–157.
3. Fiske J, Fomin V, Brown M, Duncan R, Sikes R (2006) Voltage-sensitive ion
channels and cancer. Cancer and Metastasis Reviews 25: 493–500.
4. Cuddapah VA, Sontheimer H (2011) Ion channels and tranporters in cancer. 2.
Ion channels and the control of cancer cell migration. American Journal of
Physiology - Cell Physiology 301: 541–549.
5. Kunzelmann K (2005) Ion channels and cancer. Journal of Membrane Biology
205: 159–173.
6. Fraser SP, Pardo LA (2008) Ion channels: functional expression and therapeutic
potential in cancer. EMBO Rep 9: 512–515.
7. Scho¨nherr R (2005) Clinical Relevance of Ion Channels for Diagnosis and
Therapy of Cancer. J Membr Biol 205: 175–184.
8. Pardo LA, del Camino D, Sanchez A, Alves F, Bruggemann A, et al. (1999)
Oncogenic potential of EAG K+channels. EMBO J 18: 5540–5547.
9. Ousingsawat J, Spitzner M, Puntheeranurak S, Terracciano L, Tornillo L, et al.
(2007) Expression of Voltage-Gated Potassium Channels in Human and Mouse
Colonic Carcinoma. Clinical Cancer Research 13: 824–831.
10. Rodriguez-Rasgado JA, Acuna-Macias I, Camacho J (2012) Eag1 channels as
potential cancer biomarkers. Sensors (Basel) 12: 5986–5995.
11. D’Amico M, Gasparoli L, Arcangeli A (2013) Potassium channels novel
emerging biomarkers and targets for therapy in cancer. Recent Pat Anticancer
Drug Discov 8: 53–65.
12. Hanahan D, Weinberg RA (2000) The Hallmarks of Cancer. Cell 100: 57–70.
13. Hanahan D, Weinberg RA (2011) Hallmarks of cancer: the next generation. Cell
144: 646–674.
14. Schwab A, Fabian A, Hanley PJ, Stock C (2012) Role of Ion Channels and
Transporters in Cell Migration. Physiological Reviews 92: 1865–1913.
15. Arcangeli A, Bianchi L, Becchetti A, Faravelli L, Coronnello M, et al. (1995) A
novel inward-rectifying K+current with a cell-cycle dependence governs the
resting potential of mammalian neuroblastoma cells. J Physiol 489: 455–471.
16. Wonderlin WF, Strobl JS (1996) Potassium Channels, Proliferation and G1
Progression. Journal of Membrane Biology 154: 91–107.
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 9 October 2013 | Volume 8 | Issue 10 | e74589
17. Pardo LA (2004) Voltage-gated potassium channe ls in cell proliferation.
Physiology (Bethesda) 19: 285–292.
18. Wang Z (2004) Roles of K+channels in regulating tumour cell proliferation and
apoptosis. Pflugers Arch 448: 274–286.
19. Felipe A, Vicente R, Villalonga N, Roura-Ferrer M, Martinez-Marmol R, et al.
(2006) Potassium channels: new targets in cancer therapy. Cancer Detect Prev
30: 375–385.
20. Lang F, Busch GL, Ritter M, Vo¨lkl H, Waldegger S, et al. (1998) Functional
Significance of Cell Volume Regulatory Mechanisms. Physiological Reviews 78:
247–306.
21. Bortner CD, Cidlowski JA (2007) Cell shrinkage and monovalent cation fluxes:
Role in apoptosis. Archives of Biochemistry and Biophysics 462: 176–188.
22. Afrasiabi E, Hietama¨ki M, Viitanen T, Sukumaran P, Bergelin N, et al. (2010)
Expression and significance of HERG (KCNH2) potassium channels in the
regulation of MDA-MB-435S melanoma cell proliferation and migration.
Cellular Signalling 22: 57–64.
23. Callies C, Fels J, Liashkovich I, Kliche K, Jeggle P, et al. (2011) Membrane
potential depolarization decreases the stiffness of vascular endothelial cells.
Journal of Cell Science 124: 1936–1942.
24. Wang LH, Wang N, Lu XY, Liu BC, Yanda MK, et al. (2012) Rituximab
inhibits Kv1.3 channels in human B ly mphoma cells via ac tivation of
FcgammaRIIB receptors. Biochim Biophys Acta 1823: 505–513.
25. Jang S, Kang K, Ryu P, Lee S (2009) Kv1.3 voltage-gated K(+) channel subunit
as a potential diagnostic marker and therapeutic target for breast cancer. BMB
Rep 42: 535–539.
26. Abdul M, Hoosein N (2006) Reduced Kv1.3 Potassium Channel Expression in
Human Prostate Cancer. J Membr Biol 214: 99–102.
27. Brevet M, Fucks D, Chatelain D, Regimbeau J-M, Delcenserie R, et al. (2009)
Deregulation of 2 Potassium Channels in Pancreas Adenocarcinomas:
Implication of KV1.3 Gene Promoter Methylation. Pancreas 38: 649–654.
28. Brevet M, Haren N, Sevestre H, Merviel P, Ouadid-Ahidouch H (2009) DNA
Methylation of Kv1.3 Potassium Channel Gene Promoter is Associated with
Poorly Differentiated Breast Adenocarcinoma. Cellular Physiology and Bio-
chemistry 24: 25–32.
29. Zheng Y, Chen L, Li J, Yu B, Su L, et al. (2011) Hypermethylated DNA as
potential biomarkers for gastric cancer diagnosis. Clin Biochem 44: 1405–1411.
30. Arvind S, Arivazhagan A, Santosh V, Chandramouli BA (2012) Differential
expression of a novel voltage gated potassium channel – Kv1.5 in astrocytomas
and its impact on prognosis in glioblastoma. British Journal of Neurosurgery 26:
16–20.
31. Mene´ndez ST, Rodrigo JP, Allonca E, Garcı
´a-Carracedo D, A
´lvarez-Alija G, et
al. (2010) Expression and clinical significance of the Kv3.4 potassium channel
subunit in the development and progression of head and neck squamous cell
carcinomas. The Journal of Pathology 221: 402–410.
32. Jang SH, Choi C, Hong S-G, Yarishkin OV, Bae YM, et al. (2009) Silencing of
Kv4.1 potassium channels inhibits cell proliferation of tumorigenic human
mammary epithelial cells. Biochem Biophys Res Commun 384: 180–186.
33. Kim H-J, Jang SH, Jeong YA, Ryu PD, Kim D-Y, et al. (2010) Involvement of
Kv4.1 K+Channels in Gastric Cancer Cell Proliferation. Biological and
Pharmaceutical Bulletin 33: 1754–1757.
34. Menendez ST, Villaronga MA, Rodrigo JP, Alvarez-Teijeiro S, Garcia-
Carracedo D, et al. (2012) Frequent aberrant expression of the human ether a
go-go (hEAG1) potassium channel in head and neck cancer: pathobiological
mechanisms and clinical implications. J Mol Med (Berl) 90: 1173–1184.
35. Wu J, Wu X, Lian K, Lin B, Guo L, et al. (2012) Overexpression of potassium
channel ether a` go-go in human osteosarcoma. Neoplasma 59: 207–215.
36. Asher V, Warren A, Shaw R, Sowter H, Bali A, et al. (2011) The role of Eag and
HERG channels in cell proliferation and apoptotic cell death in SK-OV-3
ovarian cancer cell line. Cancer Cell Int 11.
37. Agarwal J, Griesinger F, Stuhmer W, Pardo L (2010) The potassium channel
Ether a go-go is a novel prognostic factor with functional relevance in acute
myeloid leukemia. Mol Cancer 9.
38. Spitzner M, Martins JR, Soria RB, Ousingsawat J, Scheidt K, et al. (2008) Eag1
and Bestrophin 1 Are Up-regulated in Fast-growing Colonic Cancer Cells.
Journal of Biological Chemistry 283: 7421–7428.
39. Ding X-W, Wang X-G, Luo H-S, Tan S-Y, Gao S, et al. (2008) Expression and
Prognostic Roles of Eag1 in Resected Esophageal Squamous Cell Carcinomas.
Digestive Diseases and Sciences 53: 2039–2044.
40. Ding X-W, Yan J-J, An P, Lu¨ P, Luo H-S (2007) Aberrant expression of ether a`
go-go potassium channel in colorectal cancer patients and cell lines. World
Journal of Gastroenterology 13: 1257–1261.
41. Hammadi M, Chopin V, Matifat F, Dhennin-Duthille I, Chasseraud M, et al.
(2012) Human ether a-gogo K(+) channel 1 (hEag1) regulates MDA-MB-231
breast cancer cell migration through Orai1-dependent calcium entry. J Cell
Physiol 227: 3837–3846.
42. Wadhwa S, Wadhwa P, Dinda A, Gupta N (2009) Differential expression of
potassium ion channels in human renal cell carcinoma. International Urology
and Nephrology 41: 251–257.
43. Huang X, Dubuc AM, Hashizume R, Berg J, He Y, et al. (2012) Voltage-gated
potassium channel EAG2 controls mitotic entry and tumor growth in
medulloblastoma via regulating cell volume dynamics. Genes Dev 26: 1780–
1796.
44. Lastraioli E (2004) herg1 Gene and HERG1 Protein Are Overexpressed in
Colorectal Cancers and Regulate Cell Invasion of Tumor Cells. Cancer
Research 64: 606–611.
45. Glassmeier G, Hempel K, Wulfsen I, Bauer CK, Schumacher U, et al. (2012)
Inhibition of HERG1 K+channel protein expression decreases cell proliferation
of human small cell lung cancer cells. Pflugers Arch 463: 365–376.
46. Ding X-W, Luo H-S, Luo B, Xu D-Q, Gao S (2008) Overexpression of hERG1
in resected esophageal squamous cell carcinomas: A marker for poor prognosis.
Journal of Surgical Oncology 97: 57–62.
47. Fortunato P, Pillozzi S, Tamburini A, Pollazzi L, Franchi A, et al. (2010)
Irresponsiveness of two retinoblastoma cases to conservative therapy correlates
with up- regulation of hERG1 channels and of the VEGF-A pathway. BMC
Cancer 10.
48. Banderali U, Belke D, Singh A, Jayanthan A, Giles WR, et al. (2011) Curcumin
Blocks Kv11.1 (erg) Potassium Current and Slows Proliferation in the Infant
Acute Monocytic Leukemia Cell line THP-1. Cellular Physiology and
Biochemistry 28: 1169–1180.
49. Shao X-D, Wu K-C, Guo X-Z, Xie M-J, Zhang J, et al. (2008) Expression and
significance of HERG protein in gastric cancer. Cancer Biology & Therapy 7:
45–50.
50. Ma YG, Liu WC, Dong S, Du C, Wang XJ, et al. (2012) Activation of BK(Ca)
channels in zoledronic acid-induced apoptosis of MDA-MB-231 breast cancer
cells. PLoS One 7: e37451.
51. Han X, Xi L, Wang H, Huang X, Ma X, et al. (2008) The potassium ion
channel opener NS1619 inhibits proliferation and induces apoptosis in A2780
ovarian cancer cells. Biochem Biophys Res Commun 375: 205–209.
52. Steinle M, Palme D, Misovic M, Rudner J, Dittmann K, et al. (2011) Ionizing
radiation induces migration of glioblastoma cells by activating BK K+channels.
Radiotherapy and Oncology 101: 122–126.
53. Khaitan D, Sankpal U, Weksler B, Meister E, Romero I, et al. (2009) Role of
KCNMA1 gene in breast cancer invasion and metastasis to brain. BMC Cancer
9.
54. Coiret G, Borowiec A-S, Mariot P, Ouadid-Ahidouch H, Matifat F (2007) The
Antiestrogen Tamoxifen Activates BK Channels and Stimulates Proliferation of
MCF-7 Breast Cancer Cells. Mol Pharmacol 71: 843–851.
55. Cambien B, Rezzonico R, Vitale S, Rouzaire-Dubois B, Dubois J, et al. (2008)
Silencing of hSlo potassium channels in human osteosarcoma cells promotes
tumorigenesis. Int J Cancer 123: 365–371.
56. Chantome A, Girault A, Potier M, Collin C, Vaudin P, et al. (2009) KCa2.3
channel-dependent hyperpolarization increases melanoma cell motility. Exper-
imental Cell Research 315: 3620–3630.
57. Potier M, Joulin V, Roger S, Besson P, Jourdan M-L, et al. (2006) Identification
of SK3 channel as a new mediator of breast cancer cell migration. Molecular
Cancer Therapeutics 5: 2946–2953.
58. Potier M, Tran TA, Chantome A, Girault A, Joulin V, et al. (2010) Altered
SK3/KCa2.3-mediated migration in adenomatous polyposis coli (Apc) mutated
mouse colon epithelial cells. Biochem Biophys Res Commun 397: 42–47.
59. Catacuzzeno L, Aiello F, Fioretti B, Sforna L, Castigli E, et al. (2011) Serum-
activated K and Cl currents underlay U87-MG glioblastoma cell migration.
Journal of Cellular Physiology 226: 1926–1933.
60. Schmidt J, Friebel K, Schonherr R, Coppolino MG, Bosserhoff A-K (2010)
Migration-associated secretion of melanoma inhibitory activity at the cell rear is
supported by KCa3.1 potassium channels. Cell Res 20: 1224–1238.
61. Lai W, Chen S, Wu H, Guan Y, Liu L, et al. (2011) PRL-3 promotes the
proliferation of LoVo cells via the upregulation of KCNN4 channels. Oncol Rep
26: 909–917.
62. Lallet-Daher H, Roudbaraki M, Bavencoffe A, Mariot P, Gackiere F, et al.
(2009) Intermediate-conductance Ca2+-activated K+channels (IKCa1) regulate
human prostate cancer cell proliferation through a close control of calcium
entry. Oncogene 28: 1792–1806.
63. Faouzi M, Chopin V, Ahidouch A, Ouadid-Ahidouch H (2010) Intermediate
Ca2+-Sensitive K+Channels are Necessary for Prolactin-Induced Proliferation
in Breast Cancer Cells. Journal of Membrane Biology 234: 47–56.
64. Lee I, Park C, Kang WK (2010) Knockdown of Inwardly Rectifying Potassium
Channel Kir2.2 Suppresses Tumorigenesis by Inducing Reactive Oxygen
Species–Mediated Cellular Senescence. Molecular Cancer Therapeutics 9:
2951–2959.
65. Stringer BK, Cooper AG, Shepard SB (2001) Overexpression of the G-Protein
Inwardly Rectifying Potassium Channel 1 (GIRK1) in Primary Breast
Carcinomas Correlates with Axillary Lymph Node Metastasis. Cancer Research
61: 582–588.
66. Plummer H, Dhar M, Cekanova M, Schuller H (2005) Expression of G-protein
inwardly rectifying potassium channels (GIRKs) in lung cancer cell lines. BMC
Cancer 5.
67. Choi M, Scholl UI, Yue P, Bjo¨rklund P, Zhao B, et al. (2011) K+Channel
Mutations in Adrenal Aldosterone-Pro ducing Adenomas and Hered itary
Hypertension. Science 331: 768–772.
68. Tan G, Sun S-q, Yuan D-l (2008) Expression of Kir 4.1 in human astrocytic
tumors: Correlation with pathologic grade. Biochem Biophys Res Commun 367:
743–747.
69. Veeravalli KK, Ponnala S, Chetty C, Tsung AJ, Gujrati M, et al. (2012) Integrin
a9b1-mediated cell migration in glioblastoma via SSAT and Kir4.2 potassium
channel pathway. Cellular Signalling 24: 272–281.
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 10 October 2013 | Volume 8 | Issue 10 | e74589
70. Park S-H, Ramachandran S, Kwon S-H, Cha S-D, Seo EW, et al. (2008)
Upregulation of ATP-sensitive potassium channels for estrogen-mediated cell
proliferation in human uterine leiomyoma cells. Gynecological Endocrinology
24: 250–256.
71. Huang L, Li B, Li W, Guo H, Zou F (2009) ATP-sensitive potassium channels
control glioma cells proliferation by regulating ERK activity. Carcinogenesis 30:
737–744.
72. Nunez M, Medina V, Cricco G, Croci M, Cocca C, et al. (2013) Glibenclamide
inhibits cell growth by inducing G0/G1 arrest in the human breast cancer cell
line MDA-MB-231. BMC Pharmacology and Toxicology 14.
73. Suzuki Y, Inoue T, Murai M, Suzuki-Karasaki M, Ochiai T, et al. (2012)
Depolarization potentiates TRAIL-induced apoptosis in human melanoma cells:
role for ATP-sensitive K+channels and endoplasmic reticulum stress. Int J Oncol
41: 465–475.
74. Voloshyna I, Besana A, Castillo M, Matos T, Weinstein IB, et al. (2008) TREK-
1 is a novel molecular target in prostate cancer. Cancer Res 68: 1197–1203.
75. Nogueira EF, Gerry D, Mantero F, Mariniello B, Rainey WE (2010) The role of
TASK1 in aldosterone production and its expression in normal adrenal and
aldosterone-producing adenomas. Clin Endocrinol (Oxf) 73: 22–29.
76. Alvarez-Baron CP, Jonsson P, Thomas C, Dryer SE, Williams C (2011) The
Two-Pore Domai n Potassium Chan nel KCNK5: Induc tion by Estrogen
Receptor aand Role in Proliferation of Breast Cancer Cells. Molecular
Endocrinology 25: 1326–1336.
77. Mu D, Chen L, Zhang X, See L-H, Koch CM, et al. (2003) Genomic
amplification and oncogenic properties of the KCNK9 potassium channel gene.
Cancer Cell 3: 297–302.
78. Kim CJ, Cho YG, Jeong SW, Kim YS, Kim SY, et al. (2004) Altered expression
of KCNK9 in colorectal cancers. APMIS 112: 588–594.
79. Kosztka L, Rusznak Z, Nagy D, Nagy Z, Fodor J, et al. (2011) Inhibition of
TASK-3 (KCNK9) channel biosynthesis changes cell morphology and decreases
both DNA content and mitochondrial function of melanoma cells maintained in
cell culture. Melanoma Res 21: 308–322.
80. Lee GW, Park HS, Kim EJ, Cho YW, Kim GT, et al. (2012) Reduction of breast
cancer cell migration via up-regulation of TASK-3 two-pore domain K+
channel. Acta Physiologica 204: 513–524.
81. Enyedi P, Czirja´k G (2010) Molecular Background of Leak K+Currents: Two-
Pore Domain Potassium Channels. Physiological Reviews 90: 559–605.
82. Goldstein SA, Bockenhauer D, O’Kelly I, Zilberberg N. (2001) Potassium leak
channels and the KCNK family of two-P-domain subunits. Nat Rev
Neurosci3:175–84.
83. Bittner S, Budde T, Wiendl H, Meuth SG (2010) From the background to the
spotlight: TASK channels in pathological conditions. Brain Pathol 6:999–1009.
84. Pei L, Wiser O, Slavin A, Mu D, Powers S, et al. (2003) Oncogenic potential of
TASK3 (Kcnk9) depends on K+channel function. Proc Natl Acad Sci U S A
100: 7803–7807.
85. Pocsai K, Kosztka L, Bakondi G, Gonczi M, Fodor J, et al. (2006) Melanoma
cells exhibit strong intracellular TASK-3-specific immunopositivity in both tissue
sections and cell culture. Cell Mol Life Sci 63: 2364–2376.
86. Lauritzen I, Zanzouri M, Honore E, Duprat F, Ehrengruber MU, et al. (2003)
K+-dependent cerebellar granule neuron apoptosis. Role of task leak K+
channels. J Biol Chem 278: 32068–32076.
87. Williams C, Edvardsson K, Lewandowski SA, Strom A, Gustafsson J-A (2007) A
genome-wide study of the repressive effects of estrogen receptor beta on estrogen
receptor alpha signaling in breast cancer cells. Oncogene 27: 1019–1032.
88. Rhodes DR, Kalyana-Sundaram S, Mahavisno V, Varambally R, Yu J, et al.
(2007) Oncomine 3.0: Genes, Pathways, and Networks in a Collection of 18,000
Cancer Gene Expression Profiles. Neoplasia 9: 166–180
89. Rhodes DR, Yu J, Shanker K, Deshpande N, Varambally R, et al. (2004)
ONCOMINE: a cancer microarray database and integrated data-mining
platform. Neoplasia 6: 1–6.
90. Ferlay J, Shin HR, Bray F, For man D, Mathers C and Parkin DM.
GLOBOCAN 2008 v2.0, Cancer Incidence and Mortality Worldwide: IARC
CancerBase No. 10 Lyon, France: International Agency for Research on
Cancer; 2010. Available from: http://globocan.iarc.fr, accessed on 14/07/2013.
91. Goldstein SA, Ba yliss DA, Kim D, Lesage F, Plant LD, et al. (2005)
International Union of Pharmacology. LV. Nomenclature and molecular
relationships of two-P potassium channels. Pharmacol Rev 57: 527–540.
92. O’Kelly I, Stephens RH, Peers C, Kemp PJ (1999) Potential identification of the
O2-sensitive K+current in a human neuroepithelial body-derived cell line.
American Journal of Physiology - Lung Cellular and Molecular Physiology 276:
L96–L104.
93. Duprat F, Girard C, Jarretou G, Lazdunski M (2005) Pancreatic two P domain
K+channels TALK-1 and TALK-2 are activated by nitric oxide and reactive
oxygen species. J Physiol 562: 235–244.
94. Campanucci VA, Brown ST, Hudasek K, O’Kelly IM, Nurse CA, et al. (2005)
O2 sensing by recombinant TWIK-related halothane-inhibitable K+channel-1
background K+channels heterologously expressed in human embryonic kidney
cells. Neuroscience 135: 1087–1094.
95. Duprat F, Lauritzen I, Patel A, Honore´ E (2007) The TASK background K2P
channels: chemo- and nutrient sensors. Trends Neurosci 11: 573–80.
96. Mant A, Williams S, Roncoroni L, Lowry E, Johnson D, et al. (2012) N-
glycosylation-dependent control of functional expression of background
potassium channels K2P3.1 and K2P9.1. Journal of Biological Chemistry.
K
2P
Channel Expression in Cancer
PLOS ONE | www.plosone.org 11 October 2013 | Volume 8 | Issue 10 | e74589
