A PP2A Regulatory Nexus Modulating Hippo Signalling and Growth

在发育和成年期间组织的生长是细胞增殖、分化和死亡之间的精细平衡行为的结果。了解调节组织生长的机制是生物学中尚未回答的关键问题之一。越来越清楚的是，生长与组织结构密切相关，在病理条件下，组织结构受到严重影响，导致组织异常。Hippo通路是控制组织生长的最重要的信号级联之一，它响应组织结构的改变。这种信号级联包括几个步骤，其中一些步骤由蛋白质介导，蛋白质的功能可以通过连接不同的化学和生物化学实体来修饰，这一过程称为翻译后修饰。磷酸化是细胞中的一种这样的翻译后过程，其由磷酸基团与其他蛋白质的连接组成。这是一个可逆的过程，涉及一种复杂的蛋白质机制，可以附着或去除其他蛋白质的修饰。磷酸化通过影响蛋白质的稳定性、在细胞中的定位或功能来改变蛋白质的性质。我们以前发现磷酸酶PP2A阻断Hippo途径的活性，作为大蛋白复合物的一部分。最近，在详细研究组织结构如何控制Hippo信号传导时，我们发现PP2A磷酸酶在调节组织生长方面具有额外的作用，并且在某些条件下，它可以激活而不是阻断Hippo信号传导。然而，PP2A激活或阻断Hippo通路的信号和机制尚不清楚。我们将以果蝇为模型生物，研究PP2A磷酸酶如何调控组织生长。果蝇是一种非常灵活和高度相关的生物工具，由于其易于操作和快速的生命周期，已被广泛用于遗传研究。许多已知对人类发育重要的基因首先是在果蝇遗传研究中发现和鉴定的。由于果蝇和哺乳动物之间基因的显著保守性，果蝇研究的发现已经转化为我们对人类重要生物过程的理解的进步。因此，我们也将在人类组织培养细胞中研究果蝇中鉴定出的基因的功能，以精确地研究该过程的分子细节。本项目将揭示磷酸酶PP2A如何控制组织生长，以及调节其活性并将其功能从生长促进蛋白转换为生长抑制蛋白的信号是什么，反之亦然。我们将在正常发育条件下和组织对其结构变化做出反应时研究这一关键问题。我们将使用遗传学和生物化学方法相结合的方法来揭示相关基因的功能，通过关闭它们来确定细胞增殖和产生正确大小的组织的能力是否受损。我们将阐明磷酸酶PP2A的活性是如何调节的，控制其活性的信号是什么，以及如何利用它。许多参与组织生长的基因在人类疾病中发生突变，导致发育异常和癌症。因此，鉴定参与组织生长调节的基因可能与未来的治疗干预有关。此外，由于我们将研究我们感兴趣的基因在组织损伤反应中的作用，我们的项目也将与未来的组织再生和组织工程研究非常相关。

The growth of tissues during development and adult life is the result of a fine balancing act between cell proliferation, differentiation and death. Understanding the mechanisms that regulate tissue growth is one of the key unanswered questions in biology. It is increasingly clear that growth is tightly connected with tissue structure and that, in pathological conditions, tissue structure is severely affected, leading to tissue abnormalities.The Hippo pathway is one of the most important signalling cascades controlling tissue growth, and it responds to alterations in tissue architecture. This signalling cascade includes several steps, some of which are mediated by proteins whose function can be modified by the attachment of different chemical and biochemical entities, in a process termed post-translational modification. Phosphorylation is one such post-translational process in the cell, which consists of the attachment of a phosphate group to other proteins. This is a reversible process that involves a complex machinery of proteins that attach or remove the modification from other proteins. Phosphorylation changes the properties of proteins by affecting their stability, localisation in the cell or function.We have previously found that the phosphatase PP2A blocks the activity of the Hippo pathway as part of a large protein complex. Recently, when studying in detail how tissue structure controls Hippo signalling, we discovered that the PP2A phosphatase has an additional role in the regulation of tissue growth and, in certain conditions, it can activate rather than block Hippo signalling. However, it is still unknown what are the signals and mechanisms that control whether PP2A activates or blocks the Hippo pathway.Using the fruit fly Drosophila as a model organism, we will investigate how tissue growth is regulated by the phosphatase PP2A. The fruit fly is an extremely flexible and highly relevant biological tool that has been widely used in genetic studies due to its ease of manipulation and fast life cycle. Many of the genes known to be important for human development were first identified and characterised as a result of fruit fly genetic studies. Due to the remarkable conservation of genes between flies and mammals, findings from fruit fly studies have been translated to advances in our understanding of important biological processes in humans. Thus, our work will also examine the function of genes identified in Drosophila in human tissue culture cells to precisely study the molecular details of the process.This project will reveal how the phosphatase PP2A controls tissue growth and what are the signals that regulate its activity and switch its function from a growth-promoting to a growth-suppressive protein, and vice versa. We will study this crucial question both in normal developmental conditions and when tissues respond to changes in their architecture. We will use a combination of genetic and biochemical approaches to uncover the function of the genes involved by switching them off and determining whether cells are impaired in their ability to proliferate and give rise to tissues of the correct size.We will elucidate how the activity of the phosphatase PP2A is regulated, what are the signals that control its activity, and how it can be exploited. Numerous genes involved in tissue growth are mutated in human disease, leading to developmental abnormalities and cancer. Therefore, identification of genes involved in the regulation of tissue growth may be potentially relevant for future therapeutic interventions. In addition, as we will study the role of our genes of interest in the context of the response to tissue damage, our project will also be very relevant for future studies into tissue regeneration and tissue engineering.