An unmet actin requirement explains the mitotic inhibition of clathrin-mediated endocytosis.
An unmet actin requirement explains the mitotic inhibition of clathrin-mediated endocytosis.
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DOI：
10.7554/elife.00829
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发表时间：
2014-02-18
期刊：
影响因子：
7.7
通讯作者：
Royle SJ
中科院分区：
文献类型：
--
作者：
Kaur S;Fielding AB;Gassner G;Carter NJ;Royle SJ
网格蛋白介导的内吞作用（CME）是哺乳动物细胞中许多不同受体类型的主要内化途径。CME在有丝分裂早期被关闭，但这种抑制的机制尚不清楚。在这项研究中，我们表明，有丝分裂关闭是由于未满足的要求肌动蛋白在CME。在有丝分裂细胞中，膜张力增加，这引起了对肌动蛋白细胞骨架的需求，以帮助CME机器克服增加的负荷。然而，肌动蛋白细胞骨架参与有丝分裂细胞中刚性皮质的形成，因此无法部署。我们证明，CME可以'重新启动'有丝分裂细胞，尽管高膜张力，允许肌动蛋白进行内吞作用。内吞蛋白的有丝分裂磷酸化在具有恢复的CME的有丝分裂细胞中维持，表明CME机制的直接磷酸化不能解释关闭。DOI：http://dx.doi.org/10.7554/eLife.00829.001围绕细胞的质膜作为一个保护屏障，调节什么可以进入或离开细胞。然而，大分子和其他“货物”可以通过多种方式进入细胞。其中一种途径被称为网格蛋白介导的内吞作用，它涉及到细胞膜外部的受体抓住货物，而一种叫做网格蛋白的蛋白质在受体下面形成一个“坑”。这个坑变得越来越深，直到货物完全被网格蛋白衬里的膜包围，并被带入细胞内。在过去的50年里，人们已经研究了这个过程，并且已知网格蛋白介导的内吞作用在细胞开始分裂产生新细胞时关闭，然后在细胞分裂结束时重新打开。然而，关于为什么这个过程在细胞分裂开始时停止，有一些相互竞争的理论。现在，Kaur等人通过观察另一种叫做肌动蛋白的蛋白质在关闭网格蛋白介导的内吞作用中所起的作用来研究这些理论。肌动蛋白是一种在细胞内形成一种支架的分子（称为细胞骨架），它也指导细胞内分子和较大结构的运动。此外，当细胞膜被拉伸时，肌动蛋白细胞骨架可以帮助网格蛋白介导的内吞机制将货物拉入细胞。那么，为什么肌动蛋白在细胞分裂过程中不参与内吞作用呢？Kaur等人认为，答案是细胞中的所有肌动蛋白都是细胞分裂过程中细胞骨架所需要的，因此没有肌动蛋白可用于执行其他任务，如网格蛋白介导的内吞作用。进一步的实验表明，这种形式的内吞作用可以通过以释放一些额外肌动蛋白的方式处理细胞而在分裂细胞中“重新启动”。Kaur等人的工作也排除了细胞分裂过程中内吞机制的化学变化使其失效的理论。这些发现对于通过内吞作用将药物递送到与癌症等疾病有关的快速分裂细胞具有意义。DOI：http://dx.doi.org/10.7554/eLife.00829.002网站
Clathrin-mediated endocytosis (CME) is the major internalisation route for many different receptor types in mammalian cells. CME is shut down during early mitosis, but the mechanism of this inhibition is unclear. In this study, we show that the mitotic shutdown is due to an unmet requirement for actin in CME. In mitotic cells, membrane tension is increased and this invokes a requirement for the actin cytoskeleton to assist the CME machinery to overcome the increased load. However, the actin cytoskeleton is engaged in the formation of a rigid cortex in mitotic cells and is therefore unavailable for deployment. We demonstrate that CME can be ‘restarted’ in mitotic cells despite high membrane tension, by allowing actin to engage in endocytosis. Mitotic phosphorylation of endocytic proteins is maintained in mitotic cells with restored CME, indicating that direct phosphorylation of the CME machinery does not account for shutdown. DOI: http://dx.doi.org/10.7554/eLife.00829.001 The plasma membrane that surrounds a cell acts as a protective barrier that regulates what can enter or exit the cell. However, large molecules and other ‘cargo’ can get into a cell in a variety of ways. One of these routes—known as clathrin-mediated endocytosis—involves a receptor on the outside of the membrane grabbing hold of the cargo while a protein called clathrin forms a ‘pit’ beneath the receptor. This pit becomes deeper and deeper until the cargo is completely surrounded by clathrin-lined membrane and is brought inside the cell. This process has been studied over the past 50 years, and it is known that clathrin-mediated endocytosis is turned off when a cell begins to divide to produce new cells, and then turned back on when cell division has come to an end. However, there are competing theories as to exactly why this process stops when cell division starts. Now, Kaur et al. have investigated these theories by looking at the role that another protein, called actin, plays in turning off clathrin-mediated endocytosis. Actin is a molecule that forms a sort of scaffolding within the cell (called the cytoskeleton), and it also guides the movement of molecules and larger structures within the cell. Further, when the cell membrane is being stretched, the actin cytoskeleton can assist the clathrin-mediated endocytosis machinery to pull cargo into the cell. So why doesn’t actin help with endocytosis during cell division? The answer, Kaur et al. suggest, is that all the actin in the cell is needed by the cytoskeleton during cell division, so there is no actin available to perform other tasks such as clathrin-mediated endocytosis. Further experiments demonstrated that this form of endocytosis can be ‘restarted’ in dividing cells by treating the cells in a way that frees up some additional actin. The work of Kaur et al. also ruled out the theory that chemical changes to the endocytosis machinery disabled it during cell division. These findings have implications for the delivery of drugs, via endocytosis, to the rapidly dividing cells that are involved in diseases such as cancer. DOI: http://dx.doi.org/10.7554/eLife.00829.002