Molecular Physiology of KCNE Potassium Channel Subunits

描述（由申请人提供）：电压门控钾（Kv）通道由至少三种不同类型的辅助蛋白调节，包括KCNE家族的单跨膜蛋白。在人类基因组中，KCNE蛋白由KCNE1到KCNE5五个基因编码。三个KCNE基因的生理重要性已通过与心脏和骨骼肌兴奋性遗传性疾病的关联得到证实。KCNE1的突变损害了缓慢激活的心脏延迟整流电流（IKS）的产生，这是一种有助于心肌复极化的关键钾电流，可以通过与KCNE1异种共表达重组KCNQ1钾通道在体外重建。其他kcnne蛋白对异种表达的KCNQ1也有不同的功能作用。KCNQ1与KCNE3、KCNE4或KCNE5的共表达特别有趣，其功能影响范围从组成激活（KCNE3）到抑制（KCNE4、KCNE5）。我们最近已经证明，所有的KCNE基因在人类心肌细胞中不同程度地表达。我们进一步证明，KCNE4和KCNE5对异源表达的IKappaS具有强大的抑制作用，在这种情况下，KCNE4似乎比KCNE1占优势。除了与KCNQ1的潜在相互作用外，kcnne蛋白还影响其他克隆钾通道的功能特性。这些体外观察的生理相关性仍然不确定。

DESCRIPTION (provided by applicant): Voltage-gated potassium (Kv) channels are modulated by at least three distinct classes of accessory proteins including the KCNE family of single transmembrane proteins. In the human genome, KCNE proteins are encoded by five genes designated KCNE1 through KCNE5. The physiological importance of three KCNE genes has been demonstrated by associations with inherited disorders of cardiac and skeletal muscle excitability. Mutation of KCNE 1 impairs generation of the slowly activating cardiac delayed rectifier current (IKS), a critical potassium current contributing to myocardial repolarization that can be reconstituted in vitro by heterologous co-expression of recombinant KCNQ1 potassium channels with KCNE1. Other KCNE proteins also exert diverse functional effects on heterologously expressed KCNQ1. Co-expression of KCNQ1 with KCNE3, KCNE4 or KCNE5 is particularly interesting with functional effects ranging from constitutive activation (KCNE3) to suppression (KCNE4, KCNE5). We have recently demonstrated that all KCNE genes are expressed in human cardiac myocytes to varying degrees. We have further demonstrated that KCNE4 and KCNE5 exert potent inhibitory influences on heterologously expressed IKappaS and KCNE4 appears dominant over KCNE1 in this context. In addition to potential interactions with KCNQ1, KCNE proteins affect the functional properties of other cloned potassium channels. The physiological relevance of these in vitro observations remains uncertain. The observations that multiple KCNE proteins can modulate KCNQ1 channels to produce diverse biophysical phenotypes raises several intriguing questions with important implications for understanding the regulation of IKS as well as other potassium currents in normal and diseased heart. Can different KCNE subtypes compete functionally with KCNE1 for modulation of KCNQ1? Can KCNQ1 associate with more than one KCNE subtype in the same cell and at the same time? Do KCNE4 and KCNE5 participate in the pathophysiology of heart failure and other arrhythmia-prone conditions? In this proposal, we outline several experimental approaches for defining the physiological importance of KCNE subunits with a particular focus on KCNE4 and KCNE5. In Specific Aim 1, we will use a heterologous expression system to assess the range of functional and biochemical interactions possible between KCNQ1 and different KCNE subunits with a focus on KCNE4 and KCNE5. In Specific Aim 2, we will test the hypothesis that KCNE4 and KCNE5 are physiologically significant regulators of potassium currents in native cardiac myocytes by using two independent gene silencing approaches. Finally in Specific Aim 3, we will examine expression patterns of KCNQ1 and KCNE genes in diseased human heart and in an experimental canine model of ventricular arrhythmia susceptibility. Results from these studies will have implications for advancing our knowledge of the complex interplay between pore-forming and accessory subunits that comprise human potassium channels expressed in the heart and in other tissues.