Obscurin-kinase 1/N-cadherin: a new signaling axis in cardiac structure/function

OBSCN编码一个家族的巨大的，细胞骨架蛋白，obscurin，发挥关键的结构和调节作用， 横纹肌的作用与此相一致，OBSCN中的突变与不同形式的 心肌病暗蛋白-B（~870 kDa），已知最大的暗蛋白同种型，是一种模块蛋白， 免疫球蛋白（IG）和纤连蛋白-III（Fn-III）结构域，随后是一系列串联信号传导基序和 两个COOH末端Ser/Thr激酶结构域，Kin 1和Kin 2与肌球蛋白轻链具有约45%的同源性 激酶。虽然Kin 1和Kin 2的存在是在近二十年前发现的，但它们的酶促反应是在细胞内进行的。 活性、催化底物和（病理）生理作用仍然很难确定。最近，我们集团 证明了Kin 1和Kin 2都具有酶活性。特别是，Kin 1经历自磷酸化， 使N-钙粘蛋白的胞质结构域R化和磷酸化。N-钙粘蛋白是一个重要的组成部分， 存在于闰盘（ICD）中的粘附连接（AJ），这是肌膜的独特微域， 介导相邻心肌细胞的机械和电耦合。鉴于这些调查结果和 考虑到含有Kin 1和N-cadherin的obscurin-B在ICD的一致分布，我们假设， obscurin-Kin 1在心肌细胞粘附和/或通讯中起关键作用（至少部分），通过调节 N-钙粘蛋白的活性通过其胞质结构域的磷酸化。我们将通过以下方式解决这一假设： 阐明调节Kin 1激活的分子机制（Aim 1），确定Kin 1介导的 心脏结构/功能中N-钙粘蛋白的磷酸化（目的2），并评估错义 Kin 1突变与人类扩张型心肌病（DCM）的发展有关（Aim 3）。在过去 十年来，积累了越来越多的证据，强调了obscurin在心脏病中的密切参与。 结构/功能的健康和心脏病的发病机制时，突变或截断。而且 N-钙粘蛋白在相邻心肌细胞的机械和电耦合中的关键作用已经被 广泛记录，虽然调节其功能特性的分子机制只有 很少被检查。我们的建议是出于这一观点，并将提供有关的重要信息， ICD中新的隐匿蛋白-Kin 1/N-cadherin信号轴在健康中的作用及其如何在 疾病因此，它将解决一个具有翻译相关性的基本生物学问题。

OBSCN encodes a family of giant, cytoskeletal proteins, obscurins, that play key structural and regulatory roles in striated muscles. Consistent with this, mutations in OBSCN have been associated with different forms of cardiomyopathies. Obscurin-B (~870 kDa), the largest known obscurin isoform is a modular protein consisting of immunoglobulin (Ig) and fibronectin-III (Fn-III) domains followed by an array of tandem signaling motifs and two COOH-terminal Ser/Thr kinase domains, Kin1 and Kin2 that share ~45% homology with Myosin Light Chain kinases. Although the presence of Kin1 and Kin2 was discovered almost two decades ago, their enzymatic activity, catalytic substrates and (patho)physiological roles have remained largely elusive. Recently, our group demonstrated that both Kin1 and Kin2 are enzymatically active. In particular, Kin1 undergoes autophospho- rylation and phosphorylates the cytoplasmic domain of N-cadherin. N-cadherin is an essential component of the adherens junctions (AJ) present in the intercalated disc (ICD), the unique microdomain of the sarcolemma that mediates the mechanical and electrical coupling of neighboring cardiomyocytes. In view of these findings and given the coincident distribution of obscurin-B containing Kin1 and N-cadherin at the ICD, we hypothesize that obscurin-Kin1 plays key roles in cardiomyocyte adhesion and/or communication (at least in part) by modulating the activities of N-cadherin via phosphorylation of its cytoplasmic domain. We will address this hypothesis by elucidating the molecular mechanisms that regulate Kin1 activation (Aim 1), determine the role of Kin1-mediated phosphorylation of N-cadherin in cardiac structure/function (Aim 2), and assessing the impact of a missense mutation in Kin1 linked to the development of dilated cardiomyopathy (DCM) in humans (Aim 3). During the last decade, mounting evidence has accumulated, highlighting the intimate involvement of obscurins in cardiac structure/function in health and the pathogenesis of heart disease when mutated or truncated. Moreover, the pivotal role of N-cadherin in the mechanical and electrical coupling of adjacent cardiomyocytes has been extensively documented, although the molecular mechanisms that regulate its functional properties have only been scantily examined. Our proposal is motivated by this view and will provide important information about the role of the novel obscurin-Kin1/N-cadherin signaling axis at the ICD in health and how it is compromised in disease. It will therefore address a fundamental biological question that has translational relevance.