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

OBSCN编码一个巨大的细胞骨架蛋白家族，它发挥着关键的结构和调控作用 在横纹肌中的作用。与此一致的是，OBSCN的突变与不同的形式有关 心肌病的风险。Obscurin-B(~870 kDa)是已知的最大的Obscurin亚型，是一种模块化蛋白，包括 由免疫球蛋白(Ig)和纤维连接蛋白-III(FN-III)结构域组成，后面跟着一系列串联信号基序和 与肌球蛋白轻链有约45%同源性的两个COOH末端的Ser/Thr激酶结构域，Kin1和Kin2 激活剂。虽然Kin1和Kin2的存在是在近20年前发现的，但它们的酶 活性、催化底物和(致病)生理作用在很大程度上仍然难以捉摸。最近，我们的团队 证明了Kin1和Kin2都具有酶活性。尤其是，Kin1经历了自磷酸化- 酰化和磷酸化N-钙粘蛋白的细胞质结构域。N-钙粘附素是 粘着连接(AJ)存在于间盘(ICD)中，是肌膜上独特的微域， 介导相邻心肌细胞的机械和电气耦合。鉴于这些调查结果和 考虑到含有Kin1和N-钙粘蛋白的暗黑蛋白-B在ICD中的一致分布，我们假设 Oblcurin-Kin1在心肌细胞黏附和/或通讯中发挥关键作用(至少部分是通过调节 N-钙粘蛋白通过其胞浆结构域的磷酸化而发挥活性。我们将通过以下方式解决这一假设 阐明调节Kin1激活的分子机制(Aim 1)，确定Kin1介导的作用 N-钙粘附素在心脏结构/功能中的磷酸化(目标2)，并评估错义的影响 Kin1基因突变与人类扩张型心肌病(DCM)的发展有关(目标3)。在过去的几年里 十年来，越来越多的证据积累起来，突显了暗蛋白在心脏疾病中的密切参与 健康中的结构/功能以及心脏病突变或截断时的发病机制。此外， N-钙粘附素在相邻心肌细胞机械和电偶联中的关键作用 广泛记载，尽管调节其功能特性的分子机制只有 被仔细检查过了。我们的建议是基于这一观点，并将提供有关 新的Oblcurin-Kin1/N-cadherin信号轴在ICD中的作用及其在健康中的影响 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.