Role of Par-3 in E-cadherin recycling and signalling

将我们体内相邻的单位或细胞相互连接的机制被称为细胞-细胞粘附。最近的研究表明，细胞间的粘附对于邻近细胞之间的交流也很重要，从而决定何时分裂、迁移或死亡。特异性细胞粘附蛋白确保细胞间的粘附：一个细胞表面的蛋白质直接与相邻细胞表面的类似蛋白质结合。一种主要的细胞粘附蛋白叫做e -钙粘蛋白。e -钙粘蛋白在上皮细胞之间提供细胞间的黏附，上皮细胞是勾勒出身体所有腔体和表面结构的细胞。e -钙粘蛋白对于身体早期的正常发育至关重要，而e -钙粘蛋白的错误粘附通过增加生长和转移来促进癌症的进展。有两个原因使得细胞能够控制其表面e -钙粘蛋白的数量非常重要。首先，更多的E-cadherin导致相邻细胞之间的粘附更强，并逆转。为了防止上皮细胞破裂，需要增加粘附强度，而当细胞决定交换邻居时，则需要降低粘附强度。机械拉伸和邻居交换都参与了生物体的正常发育及其在成年期的维持，并发生在疾病中。第二个原因是，细胞表面e -钙粘蛋白的数量决定了e -钙粘蛋白分子的数量，这些分子可以与参与细胞间交流的其他蛋白质相互作用。为了能够根据细胞当前的需要快速调整细胞表面e -钙粘蛋白的数量，一部分e -钙粘蛋白不断地在细胞表面和细胞内部循环，这一过程被称为循环。到目前为止，人们对e -钙粘蛋白的循环是如何调节的知之甚少，例如，为什么e -钙粘蛋白在细胞内移动后，然后返回细胞表面，而不是在细胞内被破坏。我选择了一种简单的动物来研究这个问题，果蝇。果蝇使用e -钙粘蛋白的方式和我们一样。例如，如果果蝇胚胎缺乏e -钙粘蛋白，它们就会在发育早期死亡，因为上皮细胞不能保持彼此的接触，组织就会分裂。我最近发现，回收的e -钙粘蛋白与果蝇胚胎中一种叫做Bazooka/Par-3的蛋白质有特殊的联系。Bazooka/Par-3是一种大型蛋白质，它有许多部分，可以与其他蛋白质结合。在我过去的研究中，我获得了一份与Bazooka/Par-3相互作用的所有蛋白质的列表，并发现它包括几种已知参与细胞表面和内部之间蛋白质运输或参与细胞之间通信的蛋白质。因此，Bazooka/Par-3是将e -钙粘蛋白与循环利用和细胞-细胞通信机制联系起来的一个很好的候选物，而本提案的重点是发现Bazooka/Par-3如何做到这一点。了解Bazooka/Par-3如何调节e -钙粘蛋白循环并将其与细胞间的通讯联系起来，可以用来调节e -钙粘蛋白的水平、分布或作用。我期望发现所有动物共有的基本机制。在未来，我将能够将这些知识应用于治疗由e -钙粘蛋白功能缺陷引起的疾病，如上皮源性肿瘤。例如，如果我发现Bazooka/Par-3结合了一种特定的蛋白质，这种蛋白质允许e-钙粘蛋白重新传递到细胞表面，而不是在细胞内部被破坏，那么这种蛋白质的缺失可能被用来标记可能破坏细胞-细胞粘附并开始入侵其他组织的细胞，或者这种蛋白质可能被用作药物靶标，以防止细胞在其他组织中重新建立粘附并形成继发性肿瘤。

The mechanism that attaches neighbouring units, or cells, in our body to each other is known as cell-cell adhesion. Recent work has demonstrated that cell-cell adhesion is also important for communication between neighbouring cells to decide when to divide, migrate or die. Specific cell adhesion proteins ensure cell-cell adhesion: the proteins on the surface of one cell bind directly to similar proteins on the surface of adjacent cell. One of the major cell adhesion proteins is called E-cadherin. E-cadherin provides cell-cell adhesion between epithelial cells: the cells that outline all cavities and surface structures of the body. E-cadherin is vital for proper development of the body from very early stages, whereas faulty E-cadherin adhesion contributes to cancer progression by increasing growth and metastasis. Two reasons make it important for a cell to be able to control amounts of E-cadherin at its surface. First, more E-cadherin results in stronger adhesion between neighbouring cells, and reverse. Increasing strength of adhesion is required in response to mechanical forces to prevent rapture of epithelia, whereas reducing strength of adhesion is needed when cells decide to exchange neighbours. Both mechanical stretching and neighbour exchange participate in normal development of an organism and its maintenance during adult life, and occur in disease. The second reason is that the amount of E-cadherin at the cell surface determines the number of E-cadherin molecules available to interact with other proteins that are involved in communication between cells. To be able to rapidly adjust the amount of E-cadherin at the cell surface according to the current needs of a cell, a portion of E-cadherin constantly circulates between cell surface and cell's interior, a process called recycling. To date, little is known about how E-cadherin recycling is regulated, for example why after E-cadherin moves inside the cell, it is then returned back to the cell surface instead of being destroyed inside the cell. I have chosen a simple animal to study this problem, the fruit fly Drosophila. Fruit flies use E-cadherin in the same way as we do. For example, if fruit fly embryos lack E-cadherin they die early in development because epithelial cells cannot maintain contacts to each other and tissues fall apart. I have recently discovered that recycled E-cadherin is specifically associated with the protein called Bazooka/Par-3 in Drosophila embryos. Bazooka/Par-3 is a large protein that has many parts, which bind other proteins. During my past research I obtained a list of all proteins that interact with Bazooka/Par-3, and found that it includes several proteins that are known to either participate in transport of proteins between cell's surface and interior, or in communication between cells. Therefore, Bazooka/Par-3 is a good candidate to link E-cadherin to recycling and cell-cell communication machineries, and it is the focus of this proposal to discover how Bazooka/Par-3 does this. The knowledge of how Bazooka/Par-3 regulates E-cadherin recycling and links it to communication between cells may be used to regulate the levels, distribution or action of E-cadherin. I anticipate to discover basic mechanisms that are shared between all animals. In future, I will be able to apply this knowledge to treatment of medical conditions arising from defects in E-cadherin function such as epithelia-derived tumours. For example, if I find that Bazooka/Par-3 binds a particular protein that allows E-cadherin to be re-delivered to the cell surface instead of being destroyed inside cells, absence of this protein might be used to mark cells that are likely to break down cell-cell adhesion and start invading other tissues, or this protein might be used as a drug target to prevent cells from re-building adhesion and forming secondary tumours in other tissues.