Departments of Dermatology and Cell & Molecular Biology and.
Departments of Pathology and Dermatology, Northwestern University, The Feinberg School of Medicine, Chicago, IL 60611.
Mol Biol Cell. 2021 Sep 1;32(19):1824-1837. doi: 10.1091/mbc.E21-01-0001. Epub 2021 Jul 14.
Desmosomes (DSMs), together with adherens junctions (AJs) and tight junctions (TJs), constitute the apical cell junctional complex (AJC). While the importance of the apical and basolateral polarity machinery in the organization of AJs and TJs is well established, how DSMs are positioned within the AJC is not understood. Here we use highly polarized DLD1 cells as a model to address how DSMs integrate into the AJC. We found that knockout (KO) of the desmosomal ARM protein Pkp3, but not other major DSM proteins, uncouples DSMs from the AJC without blocking DSM assembly. DLD1 cells also exhibit a prominent extraDSM pool of Pkp3, concentrated in tricellular (tC) contacts. Probing distinct apicobasal polarity pathways revealed that neither the DSM's association with AJC nor the extraDSM pool of Pkp3 are abolished in cells with defects in Scrib module proteins responsible for basolateral membrane development. However, a loss of the apical polarity protein, Par3, completely eliminates the extraDSM pool of Pkp3 and disrupts AJC localization of desmosomes, dispersing these junctions along the entire length of cell-cell contacts. Our data are consistent with a model whereby Par3 facilitates DSM assembly within the AJC, controlling the availability of an assembly competent pool of Pkp3 stored in tC contacts.
桥粒（DSMs）与黏着连接（AJs）和紧密连接（TJs）一起构成了顶端细胞连接复合体（AJC）。虽然顶端和基底外侧极性机制在 AJs 和 TJs 的组织中的重要性已得到充分证实，但 DSMs 在 AJC 中的定位方式尚不清楚。在这里，我们使用高度极化的 DLD1 细胞作为模型来解决 DSMs 如何整合到 AJC 中的问题。我们发现，桥粒 ARM 蛋白 Pkp3 的敲除（KO），而不是其他主要的 DSM 蛋白，会使 DSMs 与 AJC 解偶联，而不会阻止 DSM 组装。DLD1 细胞还表现出大量的 Pkp3 位于桥粒之外（extraDSM），集中在三叶形（tC）接触处。探测不同的顶端基底极性途径表明，无论是 DSM 与 AJC 的关联还是 Pkp3 的 extraDSM 池，在负责基底外侧膜发育的 Scrib 模块蛋白缺陷的细胞中都不会被消除。然而，顶端极性蛋白 Par3 的缺失完全消除了 Pkp3 的 extraDSM 池，并破坏了桥粒在 AJC 中的定位，使这些连接沿着细胞-细胞接触的全长分散。我们的数据与 Par3 促进 DSM 在 AJC 内组装的模型一致，控制储存在 tC 接触处的具有组装能力的 Pkp3 池的可用性。
