Georgiou Marios, Marinari Eliana, Burden Jemima, Baum Buzz
MRC Laboratory for Molecular Cell Biology, Division of Life Sciences, University College London, Gower Street, London WC1E 6BT, UK.
Curr Biol. 2008 Nov 11;18(21):1631-8. doi: 10.1016/j.cub.2008.09.029. Epub 2008 Oct 30.
By acting as a dynamic link between adjacent cells in a monolayer, adherens junctions (AJs) maintain the integrity of epithelial tissues while allowing for neighbor exchange. Although it is not currently understood how this combination of AJ stability and plasticity is achieved, junctionally associated actin filaments are likely to play a role, because actin-based structures have been implicated in AJ organization and in the regulation of junctional turnover.
Here, through exploring the role of actin cytoskeletal regulators in the developing Drosophila notum, we have identified a critical role for Cdc42-aPKC-Par6 in the maintenance of AJ organization. In this system, the loss or inhibition of Cdc42-aPKC-Par6 leads to junctional discontinuities, the formation of ectopic junctional structures, and defects in apical actin cytoskeletal organization. Affected cells also undergo progressive apical constriction and, frequently, delamination. Surprisingly, this Cdc42-aPKC-Par6-dependent regulation of junctional stability was found to be independent of several well-known targets of Cdc42-aPKC-Par6: Baz, Lgl, Rac, and SCAR. However, similar AJ defects are observed in wasp, arp2/3, and dynamin mutant cells, suggesting a requirement for actin-mediated endocytosis in the maintenance of junctional stability downstream of Cdc42. This was confirmed in endocytosis assays, which revealed a requirement for Cdc42, Arp2/3, and Dynamin for normal rates of E-cadherin internalization.
By focusing on the molecular mechanisms required to maintain an epithelium, this analysis reveals a novel role for the epithelial polarity machinery, Cdc42-Par6-aPKC, in local AJ remodeling through the control of Arp2/3-dependent endocytosis.
通过作为单层中相邻细胞之间的动态连接，黏着连接（AJs）维持上皮组织的完整性，同时允许相邻细胞之间的物质交换。尽管目前尚不清楚如何实现AJ稳定性和可塑性的这种结合，但与连接相关的肌动蛋白丝可能发挥作用，因为基于肌动蛋白的结构与AJ组织和连接周转的调节有关。
在这里，通过探索肌动蛋白细胞骨架调节因子在发育中的果蝇背板中的作用，我们确定了Cdc42-aPKC-Par6在维持AJ组织中的关键作用。在这个系统中，Cdc42-aPKC-Par6的缺失或抑制会导致连接中断、异位连接结构的形成以及顶端肌动蛋白细胞骨架组织的缺陷。受影响的细胞还会经历渐进性的顶端收缩，并且经常发生脱层。令人惊讶的是，发现这种Cdc42-aPKC-Par6依赖性的连接稳定性调节独立于Cdc42-aPKC-Par6的几个众所周知的靶点：Baz、Lgl、Rac和SCAR。然而，在黄蜂、arp2/3和发动蛋白突变细胞中观察到类似的AJ缺陷，这表明在Cdc42下游维持连接稳定性需要肌动蛋白介导的内吞作用。这在内吞作用实验中得到了证实，该实验揭示了正常E-钙黏蛋白内化速率需要Cdc42、Arp2/3和发动蛋白。
通过关注维持上皮组织所需的分子机制，该分析揭示了上皮极性机制Cdc42-Par6-aPKC在通过控制Arp2/3依赖性内吞作用进行局部AJ重塑中的新作用。
