Department of Molecular Biology, Yokohama City University Graduate School of Medical Science, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan.
Department of Molecular Biology, Yokohama City University Graduate School of Medical Science, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan.
Cell Rep. 2020 Apr 7;31(1):107407. doi: 10.1016/j.celrep.2020.02.088.
Epithelial cells establish apicobasal polarity by forming tight junctions (TJs) at the apical-lateral boundary, which play fundamental roles in physiological functions. An evolutionarily conserved atypical protein kinase C (aPKC)-partitioning defective (PAR) complex functions as a platform for TJ assembly during cell polarity establishment. However, how this complex converts the spatial cues into a subsequent active unit is unclear. Here, we identify an epithelial isoform of Shank2 as a mediator of the aPKC-PAR complex. Shank2 binds to and colocalizes with aPKC at apical junctional regions of polarized epithelial cells. Shank2 knockdown results in defects in TJ formation. Mechanistically, we find that the N-terminal SPN domain is required for the junctional localization of Shank2 and binds to the active form of Rap1 small GTPase, which is involved in TJ formation. Our findings suggest that a close physical and functional relationship between aPKC and Shank2-active Rap1 signaling serves as the platform for TJ assembly to regulate epithelial cell polarity.
上皮细胞通过在顶端-侧边界形成紧密连接 (TJ) 来建立顶端-基底极性，这在生理功能中起着重要作用。进化保守的非典型蛋白激酶 C (aPKC)-分隔缺陷 (PAR) 复合物作为细胞极性建立过程中 TJ 组装的平台发挥作用。然而，该复合物如何将空间线索转化为后续的活性单元尚不清楚。在这里，我们确定 Shank2 的上皮同工型是 aPKC-PAR 复合物的介体。Shank2 与 aPKC 结合并在极化上皮细胞的顶端连接区域共定位。Shank2 的敲低导致 TJ 形成缺陷。从机制上讲，我们发现 SPN 结构域的 N 端对于 Shank2 的连接定位是必需的，并与参与 TJ 形成的 Rap1 小 GTPase 的活性形式结合。我们的研究结果表明，aPKC 和 Shank2-活性 Rap1 信号之间的紧密物理和功能关系可作为 TJ 组装的平台，以调节上皮细胞极性。
