Actin cytoskeleton: Regulation through protein interactions and epigenetic re-programming

人体内每个细胞的形状由一种名为细胞骨架的内部结构决定，细胞骨架是一种相互连接的蛋白质网络，提供了一种能够移动并保护身体免受潜在破坏性外力伤害的“承重”结构。肌动蛋白和肌球蛋白是两种最重要的细胞骨架蛋白。单个肌动蛋白分子可以连接在一起形成长纤维。肌球蛋白是一个大的蛋白质复合体，由2条重链、2条必需轻链和2条调控轻链组成。肌动蛋白纤维和肌球蛋白复合体相互结合，当肌球蛋白被激活时，它会拉动它们所结合的肌动蛋白纤维，缩短肌动蛋白-肌球蛋白纤维的长度，导致细胞骨架网络的紧张。由于细胞骨架负责保护细胞免受外力的破坏，因此细胞调整细胞骨架的体力以适应不断变化的环境是很重要的。细胞加强细胞骨架的一个重要方式是激活肌球蛋白复合体，以缩短肌动蛋白-肌球蛋白纤维的长度。这种肌动蛋白-肌球蛋白纤维的缩短会产生细胞骨架的张力，从而使细胞变得更加僵硬。除了肌球蛋白的激活，与细胞骨架相关的蛋白质的收集可能会发生变化。在这个方案中，我们将确定细胞骨架放松时属于其一部分的蛋白质，并发现当细胞骨架变得紧张时，相关蛋白质的集合是如何变化的。如果环境对细胞施加压力的方式经历了长期的变化，细胞可能会通过迅速改变特定基因的表达方式来进行补偿，甚至通过修改它们的DNA来改变有助于细胞骨架体力的基因的长期表达。在这项提案中，我们将确定如果细胞骨架张力延长，细胞是否会重新连接他们的DNA以改变基因表达模式，并将识别由于这些DNA变化而不同表达的细胞骨架相关基因。这项计划中的实验将首次系统地研究细胞骨架中的蛋白质复合体如何在松弛和收缩状态之间变化，以及持续的细胞骨架收缩如何改变与细胞骨架组织和功能相关的蛋白质编码基因的表达。拟议中的研究将从以下方面惠及加拿大人：1)在细胞生物学和细胞骨架调控方面的新发现，这将提高加拿大的科学声誉和创新潜力；2)培训高素质的人员，以扩大他们的职业前景，并增加他们未来在学术或工业生物医学研究中的就业能力，以便他们可能为加拿大的知识经济做出贡献；3)开发新颖的多学科方法，并产生独特的生物研究工具，将与加拿大研究界共享。

The shape of each cell in the human body is determined by an internal structure called the cytoskeleton, which is a network of interconnected proteins that provides a "load-bearing" structure that enables movement and provides protection from potentially damaging external forces. Two of the most important cytoskeleton proteins are actin and myosin. Individual actin molecules can be joined together to form long fibres. Myosin is a large protein complex, composed of 2 heavy chains, 2 essential light chains and 2 regulatory light chains. Actin fibres and myosin complexes bind to each other, and when myosin is activated it pulls on the actin fibres they are bound to, shortening the length of actin-myosin fibres and leading to tension in the cytoskeleton network. Since the cytoskeleton is responsible for protecting cells from damaging external forces, it is important for cells to adjust the physical strength of their cytoskeleton to adapt to changing environments. An important way that cells reinforce their cytoskeleton is to activate the myosin complex to shrink the length of actin-myosin fibres. This actin-myosin fibre shortening produces cytoskeleton tension that makes cells physically stiffer. In addition to myosin activation, there may be changes in the collection of proteins that are associated with the cytoskeleton. In this proposal, we will identify the proteins that are part of the cytoskeleton when it is relaxed, and discover how the collection of associated proteins changes when the cytoskeleton becomes tense. If the environment undergoes long term changes in how it exerts pressure on cells, cells may compensate by rapidly changing how specific genes are expressed, and even by modifying their DNA to alter the long-term expression of genes that contribute to the cytoskeleton's physical strength. In this proposal, we will determine if cells "re-wire" their DNA to change gene expression patterns if cytoskeleton tension is prolonged, and we will identify the cytoskeleton-related genes that are expressed differently as a result of these DNA alterations. The experiments in this proposal will be the first to systematically examine how the complex of proteins in the cytoskeleton changes between the relaxed and contracted states, and how sustained cytoskeleton contraction alters the expression of genes encoding for proteins related to cytoskeleton organization and function. The proposed research will benefit Canadians by: 1) Leading to novel discoveries in cell biology and cytoskeleton regulation that will enhance Canada's scientific reputation and innovation potential; 2) Training of highly-qualified personnel to expand their career perspectives and increase future employability in academic or industrial biomedical research so that they may contribute to Canada's knowledge economy; 3) Development of novel multi-disciplinary approaches and generation of unique biological research tools that will be shared with the Canadian research community.