Cardiovascular Journal of Africa: Vol 27 No 1 (January/February 2016)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 27, No 1, January/February 2016 4 AFRICA
Cardiovascular Topics
Filamin C: a novel component of the KCNE2 interactome
during hypoxia
Annika Neethling, Jomien Mouton, Ben Loos, Valerie Corfield, Carin de Villiers, Craig Kinnear
Abstract
Aim: KCNE2 encodes for the potassium voltage-gated chan-
nel, KCNE2. Mutations in KCNE2 have been associated
with long-QT syndrome (LQTS). While KCNE2 has been
extensively studied, the functions of its C-terminal domain
remain inadequately described. Here, we aimed to elucidate
the functions of this domain by identifying its protein interac-
tors using yeast two-hybrid analysis.
Methods: The C-terminal domain of KCNE2 was used as bait
to screen a human cardiac cDNA library for putative inter-
acting proteins. Co-localisation and co-immunoprecipitation
analyses were used for verification.
Results: Filamin C (FLNC) was identified as a putative inter-
actor with KCNE2. FLNC and KCNE2 co-localised within
the cell, however, a physical interaction was only observed
under hypoxic conditions.
Conclusion: The identification of FLNC as a novel KCNE2
ligand not only enhances current understanding of ion
channel function and regulation, but also provides valuable
information about possible pathways likely to be involved in
LQTS pathogenesis.
Keywords: LQTS, KCNE2, filamin C (FLNC), hypoxia, arrhyth-
mia
Submitted 4/9/14, accepted 17/5/15
Cardiovasc J Afr 2016; 27: 4–11
DOI: 10.5830/CVJA-2015-049
Long-QT syndrome (LQTS) is a cardiac repolarisation disorder
with an estimated global prevalence of 1:2 000 to 1:7 000.1,2
It is characterised by a prolonged QT interval on a surface
electrocardiogram (ECG), with symptoms including syncope,
cardiac arrest and sudden death. 1,3,4 Occasionally, sudden cardiac
death may be the first and only manifestation of LQTS.5,6
To date, different types of LQTS (LQT1–LQT13), classified
according to the primary disease causal gene, have been
identified, with more than 700 mutations leading to disease
pathogenesis. 7,8 Yet a large number of patients with clinically
diagnosed LQTS have no mutations within any of the known
LQTS causal genes,9-11 and numerous patients, despite carrying
the same disease-causing mutation, display variable phenotypic
expression and disease penetrance.12 To complicate matters
further, LQTS can also be acquired through the use of certain
prescribed medications, such as antipsychotics, antidepressants
and antibiotics,13,14 adding to the growing challenge of clinical
management and treatment of affected individuals.
The LQT type 6 (LQT6) causal gene, KCNE2 encoding for
the potassium voltage-gated channel subfamily E member 2
(KCNE2) protein,15 has been implicated in the development
of inherited, acquired and sporadic forms of LQTS. 13,16-18 This
protein consists of an extracellular N-terminal, a transmembrane
and intracellular C-terminal domain. It comprises the beta-
( β) subunits of ion channel complexes and co-assembles with
many different alpha- (α) subunits, including the frequently
studied human Ether-à-go-go-related (HERG) channel protein
encoded for by the potassium voltage-gated channel, subfamily
H (eag-related), member 2 (KCNH2) gene.15,17,19 In combination
with KCNE2, properties of the different ion channel currents
are modulated,20 assisting in cardiac pacemaker activity and
repolarisation to ensure adequate myocardial recharging and the
maintenance of a regular rhythm.15,21-23
A unique quality of many cardiac ion channels, including
those containing KCNE2 and HERG, is their ability to adapt
to hypoxic conditions. Hypoxia, defined as the decrease in
available oxygen, causes changes in the electrical characteristics
of ion channels and has been reported to predispose individuals
to fatal arrhythmias.24-27 Additionally, hypoxic conditions affect
the expression, folding, maturation and trafficking of various
channels.28-30 In a recent study, it was noted that the expression
of genes from the KCNE family (including KCNE2) could be
affected by hypoxia in the heart. 31 It has been observed that
acute ischaemic hearts of rats after myocardial infarction show
increased expression of KCNE proteins, attributable to hypoxia. 31
The intricacy of processes causing and modifying cardiac
arrhythmias highlights the importance of identifying the protein
DST/NRF Centre of Excellence in Biomedical Tuberculosis
Research, SA MRC Centre for Tuberculosis Research,
Division of Molecular Biology and Human Genetics,
Department of Biomedical Sciences, Faculty of Medicine
and Health Sciences, Stellenbosch University, South Africa
Annika Neethling, MSc,
Jomien Mouton, PhD
Valerie Corfield, PhD
Carin de Villiers, PhD
Craig Kinnear, PhD
Department of Physiological Sciences, Faculty of Science,
Stellenbosch University, Stellenbosch, South Africa
Ben Loos, PhD