Department of Cell Biology and 2 Imaging Unit, Institute of Ophthalmology, University College London, London EC1V 9EL, England, UK.
J Cell Biol. 2014 Jan 6;204(1):111-27. doi: 10.1083/jcb.201304064. Epub 2013 Dec 30.
Epithelial cells develop morphologically characteristic apical domains that are bordered by tight junctions, the apical-lateral border. Cdc42 and its effector complex Par6-atypical protein kinase c (aPKC) regulate multiple steps during epithelial differentiation, but the mechanisms that mediate process-specific activation of Cdc42 to drive apical morphogenesis and activate the transition from junction formation to apical differentiation are poorly understood. Using a small interfering RNA screen, we identify Dbl3 as a guanine nucleotide exchange factor that is recruited by ezrin to the apical membrane, that is enriched at a marginal zone apical to tight junctions, and that drives spatially restricted Cdc42 activation, promoting apical differentiation. Dbl3 depletion did not affect junction formation but did affect epithelial morphogenesis and brush border formation. Conversely, expression of active Dbl3 drove process-specific activation of the Par6-aPKC pathway, stimulating the transition from junction formation to apical differentiation and domain expansion, as well as the positioning of tight junctions. Thus, Dbl3 drives Cdc42 signaling at the apical margin to regulate morphogenesis, apical-lateral border positioning, and apical differentiation.
上皮细胞在形态上发育出具有特征性的顶端结构域，这些结构域由紧密连接（顶侧边界）所包围。CDC42 及其效应复合物 Par6-非典型蛋白激酶 C（aPKC）调节上皮细胞分化的多个步骤，但是介导 CDC42 特异性激活以驱动顶端形态发生并激活从连接形成到顶端分化的转变的机制还知之甚少。使用小干扰 RNA 筛选，我们鉴定出 Dbl3 是一种鸟嘌呤核苷酸交换因子，它被 ezrin 招募到顶膜，在紧密连接上方的顶侧边缘富集，并驱动空间受限的 CDC42 激活，促进顶端分化。Dbl3 的缺失不影响连接的形成，但确实影响上皮形态发生和刷状缘的形成。相反，活性 Dbl3 的表达驱动 Par6-aPKC 途径的特定过程激活，刺激从连接形成到顶端分化和域扩展的转变，以及紧密连接的定位。因此，Dbl3 驱动顶缘的 CDC42 信号传导，以调节形态发生、顶侧边界定位和顶端分化。
