Inflammatory Proteases, Ubiquitin Proteasome System, and Myocyte Death

描述(由申请人提供)：心脏缺血再灌注(IR)损伤可导致心功能障碍，进而发展为心力衰竭。这一进程中最早的事件之一被认为涉及炎性细胞及其蛋白酶。虽然在心肌损伤后的早期阶段有好处，但过度的炎症反应会导致心肌细胞死亡、疤痕形成和心肌功能障碍。我们已经证明，中性粒细胞衍生的丝氨酸蛋白酶，组织蛋白G(CG)，通过失巢凋亡诱导心肌细胞死亡，这涉及到下调维持肌节完整性和收缩功能的蛋白质，包括焦点黏附(FA)和细胞骨架蛋白。在心肌细胞中，维持FA蛋白完整性并确定其稳定性的具体机制知之甚少。泛素蛋白酶体系统(UPS)是监控和降解蛋白质的主要效应器之一。原癌基因Casitas b-Lineage淋巴瘤(Cbl)是一种具有固有E3泛素连接酶活性的接头蛋白，靶向受体酪氨酸激酶信号转导，导致其泛素化和蛋白酶体降解。我们的初步研究表明，心肌IR损伤后Cbl的激活增加，这与包括FA蛋白在内的几种蛋白质泛素化的增加有关。此外，我们还发现CG在体外诱导新生大鼠心肌细胞Cbl激活，这与其与FAK的相互作用有关。我们还发现，FAK在对CG的反应中失活和降解之前，会被严重的丝氨酸磷酸化，这支持了蛋白质的丝氨酸磷酸化与其靶向蛋白酶体之间的关系。这些数据支持这一假说，即响应CG的FAK的丝氨酸磷酸化启动其与Cbl的联系，从而导致其泛素化和被UPS降解。这些步骤最终导致FA信号的改变和心肌细胞的失巢死亡。目的1确定丝氨酸磷酸化在FAK周转和心肌细胞失巢凋亡中的意义。目的2确定泛素连接酶Cbl在CG诱导的FAK下调和心肌细胞失巢凋亡中是否起作用。AIM 3将确定在CG诱导的心肌细胞失巢失巢过程中，FAK下游导致启动子caspase激活的信号通路。最后，Aim 4将确定CG和Cbl是否参与了FAK泛素化/降解和在体IR损伤时诱导的心肌细胞损失。该提案寻求将FAK丝氨酸在炎症区域的过度磷酸化与其在UPS中的降解联系起来。这项研究产生的基本新知识应该确定可以减少心肌IR损伤后心肌细胞死亡和功能障碍重塑的新靶点。公共卫生相关性：本申请中提出的研究将描绘泛素连接酶在炎性蛋白酶引起的局部黏附信号改变中的作用，并将确定丝氨酸蛋白酶和泛素连接酶Cb1是否可以成为减少心肌IR损伤后心肌细胞死亡和功能障碍重塑的治疗新靶点。

DESCRIPTION (provided by applicant): Cardiac ischemia reperfusion (IR) injury can cause cardiac dysfunction that progresses to heart failure. One of the earliest events in this progression is thought to involve inflammatory cells and their proteases. Although beneficial at early stages after myocardial injury, excessive inflammatory reaction leads to myocyte death, scar formation, and myocardial dysfunction. We have shown that the neutrophil derived serine protease, cathepsin G (CG), induces myocyte death by anoikis that involves downregulation of proteins that maintain sarcomere integrity and contractile function including focal adhesion (FA) and cytoskeletal proteins. Little is known about specific mechanisms that maintain the integrity of FA proteins and determine their stability in cardiac myocytes. One of the primary effectors of monitoring and degrading proteins is the Ubiquitin Proteasome System (UPS). The proto-oncogene Casitas b-lineage lymphoma (Cbl) is an adaptor protein with an intrinsic E3 ubiquitin ligase activity that targets receptor tyrosine kinase signaling, resulting in their ubiquitylation and proteasomal degradation. Our preliminary studies showed increased Cbl activation in response to myocardial IR injury that was associated with an increase in ubiquitylation of several proteins including FA proteins. Furthermore, we found that CG induced Cbl activation in neonatal rat cardiomyocytes in-vitro that was associated with its interaction with FAK. We also found that FAK becomes heavily serine phosphorylated prior to its inactivation and degradation in response to CG, supportive of a relationship between serine phosphorylation of proteins and their targeting to the proteasome. These data support the hypothesis that serine phosphorylation of FAK in response to CG initiates its association with Cbl, thus leading to its ubiquitylation and degradation by the UPS. These steps ultimately lead to FA signaling alteration and myocyte death by anoikis. Aim 1 will identify the implication of serine phosphorylation in FAK turnover and myocyte anoikis. Aim 2 will identify whether the ubiquitin ligase Cbl play a role in CG-induced FAK downregulation and myocyte anoikis. Aim 3 will identify the signaling pathways downstream from FAK that lead to the activation of initiator caspases during CG-induced myocyte anoikis. Finally, aim 4 will determine if CG and Cbl are involved in FAK ubiquitylation/degradation and myocyte loss induced in-vivo during IR injury. This proposal seeks to link FAK serine hyper-phosphorylation in areas of inflammation to its degradation by the UPS. The fundamental new knowledge resulting from this study should identify novel targets that could diminish myocyte death and dysfunctional remodeling after myocardial IR injury. PUBLIC HEALTH RELEVANCE: The research proposed in this application will delineate the role of ubiquitin ligases in focal adhesion signaling alterations caused by inflammatory proteases and will determine if serine proteases and the ubiquitin ligase Cbl could be novel targets for therapies that diminish myocyte death and dysfunctional remodeling after myocardial IR injury.