Regulated proteolysis of p62/SQSTM1, nutrient-sensing and human disease

背景：感知营养物质的可用性是帮助细胞保持健康并决定何时生长的基本过程。当没有营养物质时，细胞就会通过“自我吞噬”或自噬的过程来分解和回收旧物质。营养感应和自噬之间的平衡维持了体内平衡。这些过程受到多种因素的调控，包括生长因子、toll样受体（TLRs）、细胞因子和微生物感染。p62或Sequestosome 1（SQSTM1）是一个泛素结合的分子支架，参与许多信号转导途径。重要的是，p62参与感知营养物质，如氨基酸，以及通过自噬细胞质内容物的周转。然而，其在细胞过程中的差异参与的分子基础需要阐明。编码p62蛋白的基因的自然突变与四种人类疾病有关。这些包括额颞叶痴呆（FTD）、肌萎缩性侧索硬化症（ALS）、骨佩吉特病和远端肌病伴边缘空泡（DMRV）。因此，研究p62控制的分子过程应该有助于我们更好地了解其功能障碍如何导致或改变这些疾病，以及是否可以设计新的治疗方法来治疗患者。我们发现caspase-8蛋白水解将p62修饰成更短的p62TRM蛋白，该蛋白在营养传感中具有排他作用，但不参与自噬。重要的是，FTD患者的一种罕见突变消除了p62切割，并特异性地破坏了营养感应。这一突破揭示了p62在自噬和营养感知等不同生理途径中的差异参与的基本过程。然而，p62蛋白水解过程是如何调控的，该过程涉及的基因，p62TRM的更广泛功能及其在疾病中的功能障碍仍有待研究。目标和方法：通过之前的Wellcome Trust种子奖产生的初步数据导致发现控制p62TRM生产的新分子。在本提案中，我们将剖析p62蛋白水解的机制以及p62TRM在细胞中的更广泛作用。我们将研究TLR3和TLR4对p62蛋白的水解作用及其与营养传感的串扰。对SQSTM1自然突变的研究将阐明它们是否特异性地影响p62在自噬和/或营养感知中的作用。此外，我们将部署新的合成策略，控制p62蛋白水解，深入研究其作用以及它如何在其他疾病易感基因的背景下运作。潜在益处：我们的研究重点是确定p62在细胞中的基本生物学功能以及这些功能如何在疾病中受到损害。自噬缺陷与遗传性和自发的人类疾病有关，包括神经退行性疾病、结肠炎、骨骼和肌肉疾病以及各种癌症。因此，这一建议有可能影响基本细胞过程和人类疾病的研究，从长远来看，可能有助于设计更好的治疗方法。

Background: Sensing the availability of nutrients is a fundamental process that helps cells stay healthy and decide when to grow. When nutrients are not available, cells turn on the process of breaking down and recycling old material through the process of 'self-eating' or autophagy. The balance between nutrient-sensing and autophagy maintains homeostasis. These processes are regulated by various cues, including growth-factors, Toll-like receptors (TLRs), cytokines and microbial infection. p62 or Sequestosome 1(SQSTM1) is a ubiquitin-binding molecular scaffold involved in many signal transduction pathways. Importantly, p62 participates in sensing nutrients, e.g. amino acids, and the turnover of cytoplasmic contents through autophagy. However, the molecular basis of its differential involvement in cellular processes need to be elucidated. Natural mutations in the gene that encodes p62 protein are linked to four human diseases. These include frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), Paget's disease of the bone and distal myopathy with rimmed vacuoles (DMRV). Therefore, investigating the molecular processes controlled by p62 should help us better understand how its dysfunction can cause or modify these diseases and whether new therapies could be designed to treat patients. We discovered that caspase-8 proteolytically trims p62 into the shorter p62TRM protein, which has exclusive roles in nutrient-sensing but does not participate in autophagy. Importantly, a rare mutation in an FTD patient abolished p62 cleavage and specifically disrupted nutrient-sensing. This breakthrough uncovered a fundamental process that governed the differential involvement of p62 in physiologically distinct pathways such as autophagy and nutrient-sensing. However, how p62 proteolysis process is regulated and the genes involved in the process, the broader functions of p62TRM and its dysfunction in disease remains to be investigated. Aims and approaches: Preliminary data generated through a previous Wellcome Trust Seed Award led to the discovery of new molecules that control p62TRM production. In this proposal we will dissect the mechanisms of p62 proteolysis and the broader role of p62TRM in cells. We will investigate p62 proteolysis by TLR3 and TLR4 and their crosstalk with nutrient-sensing. Studies on natural mutations in SQSTM1 will clarify whether they specifically affect the roles of p62 in autophagy and/or nutrient-sensing. In addition, we will deploy our new synthetic strategy of controlled p62 proteolysis for in-depth investigation of its roles and how it operates in the context of other disease-susceptibility genes. Potential benefits: Our studies focus on defining the basic biological functions of p62 in cells and how these may be compromised in disease. Defects in autophagy are linked to hereditary and spontaneous human diseases, including neurodegenerative diseases, colitis, bone and muscle disease and types of cancer. This proposal thus has the potential to impact research on fundamental cellular processes and human diseases, and in the long term, may help in the design of better therapeutics.