Department of Biological Sciences, Centre for Cell Biology, Development, and Disease, Simon Fraser University, Burnaby, British Columbia, Canada.
Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada.
mBio. 2020 Jan 21;11(1):e02857-19. doi: 10.1128/mBio.02857-19.
moves from one cell to another using actin-rich membrane protrusions that propel the bacterium toward neighboring cells. Despite cholesterol being required for this transfer process, the precise host internalization mechanism remains elusive. Here, we show that caveolin endocytosis is key to this event as bacterial cell-to-cell transfer is severely impaired when cells are depleted of caveolin-1. Only a subset of additional caveolar components (cavin-2 and EHD2) are present at sites of bacterial transfer, and although clathrin and the clathrin-associated proteins Eps15 and AP2 are absent from the bacterial invaginations, efficient spreading requires the clathrin-interacting protein epsin-1. We also directly demonstrated that isolated membrane protrusions can trigger the recruitment of caveolar proteins in a neighboring cell. The engulfment of these bacterial and cytoskeletal structures through a caveolin-based mechanism demonstrates that the classical nanometer-scale theoretical size limit for this internalization pathway is exceeded by these bacterial pathogens. moves from one cell to another as it disseminates within tissues. This bacterial transfer process depends on the host actin cytoskeleton as the bacterium forms motile actin-rich membranous protrusions that propel the bacteria into neighboring cells, thus forming corresponding membrane invaginations. Here, we examine these membrane invaginations and demonstrate that caveolin-1-based endocytosis is crucial for efficient bacterial cell-to-cell spreading. We show that only a subset of caveolin-associated proteins (cavin-2 and EHD2) are involved in this process. Despite the absence of clathrin at the invaginations, the classical clathrin-associated protein epsin-1 is also required for efficient bacterial spreading. Using isolated protrusions added onto naive host cells, we demonstrate that actin-based propulsion is dispensable for caveolin-1 endocytosis as the presence of the protrusion/invagination interaction alone triggers caveolin-1 recruitment in the recipient cells. Finally, we provide a model of how this caveolin-1-based internalization event can exceed the theoretical size limit for this endocytic pathway.
它通过富含肌动蛋白的膜突起从一个细胞移动到另一个细胞，这些突起推动细菌向邻近的细胞移动。尽管胆固醇是这种转移过程所必需的，但确切的宿主内化机制仍然难以捉摸。在这里，我们表明 caveolin 内吞作用是关键，因为当细胞耗尽 caveolin-1 时，细菌的细胞间转移严重受损。只有一小部分其他 caveolar 成分（cavin-2 和 EHD2）存在于细菌转移部位，尽管 clathrin 和 clathrin 相关蛋白 Eps15 和 AP2 不存在于细菌内陷部位，但有效的扩散需要 clathrin 相互作用蛋白 epsin-1。我们还直接证明，分离的膜突起可以在邻近细胞中触发 caveolar 蛋白的募集。通过 caveolin 为基础的机制吞噬这些细菌和细胞骨架结构表明，这些细菌病原体超过了这个内化途径的经典纳米级理论大小限制。当它在组织内传播时，它会从一个细胞转移到另一个细胞。这个细菌转移过程依赖于宿主肌动蛋白细胞骨架，因为细菌形成运动性富含肌动蛋白的膜突起，将细菌推进邻近的细胞，从而形成相应的膜内陷。在这里，我们检查了这些膜内陷，并证明 caveolin-1 为基础的内吞作用对于有效的细菌细胞间扩散是至关重要的。我们表明，只有一小部分 caveolin 相关蛋白（cavin-2 和 EHD2）参与了这个过程。尽管在凹陷处没有 clathrin，但经典的 clathrin 相关蛋白 epsin-1 也需要有效的细菌扩散。使用添加到幼稚宿主细胞上的分离突起，我们证明了 actin 为基础的推进对于 caveolin-1 内吞作用是可有可无的，因为突起/内陷相互作用的存在本身就会触发受体细胞中 caveolin-1 的募集。最后，我们提供了一个模型，说明这个 caveolin-1 为基础的内化事件如何超过这个内吞途径的理论大小限制。
