Cell–cell junction formation requires actin cytoskeletal remodeling. Here, we show that PLEKHG4B, a Rho-guanine nucleotide exchange factor (Rho-GEF), plays a crucial role in epithelial cell–cell junction formation. Knockdown of PLEKHG4B decreased Cdc42 activity and tended to increase RhoA activity in A549 cells. A549 monolayer cells showed ‘closed junctions’ with closely packed actin bundles along the cell–cell contacts, but PLEKHG4B knockdown suppressed closed junction formation, and PLEKHG4B-knockdown cells exhibited ‘open junctions’ with split actin bundles located away from the cell–cell boundary. In Ca²⁺-switch assays, PLEKHG4B knockdown delayed the conversion of open junctions to closed junctions and β-catenin accumulation at cell–cell junctions. Furthermore, PLEKHG4B knockdown abrogated the reduction in myosin activity normally seen in the later stage of junction formation. The aberrant myosin activation and impairments in closed junction formation in PLEKHG4B-knockdown cells were reverted by ROCK inhibition or LARG/PDZ-RhoGEF knockdown. These results suggest that PLEKHG4B enables actin remodeling during epithelial cell–cell junction maturation, probably by reducing myosin activity in the later stage of junction formation, through suppressing LARG/PDZ-RhoGEF and RhoA–ROCK pathway activities. We also showed that annexin A2 participates in PLEKHG4B localization to cell–cell junctions.

This article has an associated First Person interview with the first author of the paper.

细胞 - 细胞连接的形成需要肌动蛋白细胞骨架重塑。在这里，我们表明 PLEKHG4B，一种 Rho-鸟嘌呤核苷酸交换因子 (Rho-GEF)，在上皮细胞 - 细胞连接形成中起着至关重要的作用。PLEKHG4B 的组合式降低了 Cdc42 活性，并倾向于增加 A549 细胞中的 RhoA 活性。A549 单层细胞显示“闭合连接”，沿着细胞 - 细胞接触处有紧密堆积的肌动蛋白束，但 PLEKHG4B 敲低抑制了闭合连接的形成，而 PLEKHG4B 敲低细胞表现出“开放连接”，分裂的肌动蛋白束远离细胞 - 细胞边界. 在 Ca ²⁺-switch 测定，PLEKHG4B 敲低延迟了开放连接到闭合连接的转化以及细胞 - 细胞连接处的 β-连环蛋白积累。此外，PLEKHG4B 组合式消除了通常在连接形成后期看到的肌球蛋白活性的降低。ROCK 抑制或 LARG/PDZ-RhoGEF 敲低可逆转 PLEKHG4B 敲低细胞中的异常肌球蛋白激活和闭合连接形成受损。这些结果表明 PLEKHG4B 能够在上皮细胞 - 细胞连接成熟过程中实现肌动蛋白重塑，这可能是通过抑制 LARG/PDZ-RhoGEF 和 RhoA-ROCK 通路活性来降低连接形成后期的肌球蛋白活性。我们还表明膜联蛋白 A2 参与 PLEKHG4B 定位到细胞 - 细胞连接。

本文与该论文的第一作者进行了相关的第一人称采访。