Role of the SR/ER E3 Ubiquitin Ligase Synoviolin 1 in Cardiac Hypertrophy

 说明(申请人提供)：心肌细胞病理性肥大生长可导致心力衰竭；抑制这种生长可避免心力衰竭。虽然我们对心脏中的生长激活过程有很好的了解，但我们对生长抑制过程的理解存在差距。这项建议的目的是通过检测心肌细胞肌浆网(SR/ER)中的蛋白质数量和质量控制(PQQC)系统来弥补这一差距，我们已经证明该系统可以调节心肌细胞的生长。这一目标与我们的长期目标一致，即确定通过减少病理性肥厚来避免心力衰竭的创新战略。我们发现，SR/ER PQQC系统的一个关键成员，转录因子ATF6，可以减少心肌细胞的肥大。ATF6也具有心脏保护作用，是一种感知生长信号的SR/ER跨膜(TM)蛋白。我们发现ATF6可诱导SR/ER TM E3泛素(Ub)连接酶SYVN1；SR/ER TM Ub连接酶在心脏中尚未被研究。令人惊讶的是，SYVN1没有影响全球蛋白质的泛素化或降解，但它减少了心肌细胞对生长刺激的肥大。假设SYVN1通过靶向SR/ER中产生的末端错误折叠的蛋白质进行降解，从而减少有毒蛋白质的错误折叠。此外，SYVN1可以针对特定的信号蛋白进行降解，如胞浆促生长蛋白、血清/糖皮质激素调节的激酶1、SGK1，这些功能有助于SYVN1调节中度心肌肥厚的能力。该方法将使用病毒介导的基因转移到培养的心肌细胞和体内的小鼠心脏，以检查SYVN1功能获得和丧失的影响。本研究旨在探讨SYVN1功能缺失与心肌肥大的关系，以及错折叠SR/ER蛋白在心肌肥大过程中的降解作用，以及SGK1在心肌肥厚过程中的水平、位置、活性及其对心肌细胞肥大的影响。这些研究有望表明，作为PQQC的调节者，SYVN1有助于平衡蛋白质合成和蛋白质折叠能力。这些结果将具有重要意义，因为它们将揭示抑制肥厚的新机制，并将确定HF治疗的新靶点。这项拟议的研究具有创新性，因为SR/ER PQQC，特别是SR/ER TM E3 Ub连接酶在生长调节中的作用尚未在任何组织中进行过研究。

 DESCRIPTION (provided by applicant): Pathological hypertrophic growth of cardiac myocytes can lead to heart failure; inhibiting this growth can avert heart failure. While we have a good understanding of growth-activating processes in the heart, there is a gap in our understanding of growth-inhibiting processes. The objective of this proposal is to address this gap by examining the protein quantity and quality control (PQQC) system in the sarco/endoplasmic reticulum (SR/ER) of cardiac myocytes, which we have shown can moderate cardiac myocyte growth. This objective aligns with our long-term goal of defining innovative strategies for averting heart failure by reducing pathological hypertrophy. We found that a key member of the SR/ER PQQC system, the transcription factor, ATF6, decreases cardiac myocyte hypertrophy. ATF6, which is also cardioprotective, is an SR/ER transmembrane (TM) protein that senses growth signals. We showed that ATF6 induces the SR/ER TM E3 ubiquitin (Ub) ligase, synoviolin (Syvn1); SR/ER TM Ub ligases have not been studied in the heart. Surprisingly, Syvn1 did not affect global protein ubiquitination or degradation, but it decreased cardiac myocyte hypertrophy in response to growth stimuli. The hypothesis is that Syvn1 decreases toxic protein misfolding by targeting terminally misfolded proteins made in the SR/ER for degradation. Moreover, Syvn1 can target select signaling proteins for degradation, such as the cytosolic growth-promoting kinase, serum/glucocorticoid-regulated kinase 1, SGK1, and that these functions contribute to the ability of Syvn1 to moderate cardiac hypertrophy. The approach will use viral-mediated gene transfer to cultured cardiac myocytes and to mouse hearts, in vivo, to examine the effects of Syvn1 gain- and loss-of-function. The specific aims are to examine the effects of Syvn1- gain- or loss-of-function on 1) cardiac hypertrophy, 2) the degradation of misfolded SR/ER proteins during cardiac myocyte hypertrophy, and 3) the level, location and activity of SGK1, and its impact on cardiac myocyte hypertrophy. The proposed studies are expected to show that, as a regulator of PQQC, Syvn1 contributes to balancing protein synthesis and protein folding capacity. These results will be significant because they will reveal novel mechanisms of inhibiting hypertrophy, and they will identify new targets for HF therapy. The proposed research is innovative because roles for the SR/ER PQQC and, specifically, SR/ER TM E3 Ub ligases in growth regulation have not been examined in any tissue.