Intercellular junctions and cell polarity

所有上皮细胞通过三种主要类型的连接相互连接-紧密连接(TJ)、黏附连接 连接(AJ)和桥粒(DSM)。在单纯性上皮中，这些连接沿着根尖定位。 细胞侧膜末端，在那里形成顶端连接复合体(AJC)。AJS和DSM，但是 而不是TJ，也存在于基底侧质膜上，在那里它们的大小要小得多。这 连接组织的不对称性是单纯上皮的一个显著的结构特征。这种不对称性是 由一组保守的极性蛋白质控制。我们在这项提案中要解决的主要问题是 IS：两种极性的蛋白质，基侧蛋白ScriB和顶端蛋白Par3是如何与蛋白质相互联系的 调节AJC中细胞-细胞连接的位置。 我们最近发表的研究结果表明，Scrib是如何维持简单上皮细胞的“基侧特性”的 膜，多年来一直难以捉摸的机制。我们发现Scrib的这个功能是基于 关于磷酸酶PP1和Rho/Rac鸟嘌呤核苷酸交换因子两种酶的调节， 全环基金-H1。我们的结果表明，Scrib将PP1保持在非活性状态，并通过 与其他极性蛋白质的相互作用，Llg1，Dlg，和带4.1。我们还展示了一种连接 带有DSM组装的极性装置是一种手臂蛋白，Pkp3。我们提供证据证明这一点 蛋白质储存在TJ周围的“休眠”池中，该池是在顶端极性蛋白质的控制下建立的 第3段。从这个池中释放出来的活性形式的Pkp3，使用以下机制驱动DSM的形成 与进化相关的连接AJs的组装机制截然不同。此外，我们 目前的一些证据表明，连接组装也涉及类似的依赖PKP的机制 形成一种以前未被识别的AJ亚型，我们在这里称之为依赖Pkp4的AJ。这个 前几年取得的进展使我们能够提出这项建议，其中包括调查： (I)Scrib如何调控Pp1，这一途径的效应者是什么；(Ii)Pkp3如何调控黏附 桥粒钙粘附素的活性及其DSM组装活性如何受极性系统的调节；以及 (3)Pkp4是如何调控经典钙粘附素在特定AJ亚群组装中的黏附活性的。这部作品 将为开发调节粘附性和阻隔性的试剂铺平道路 上皮组织。

All epithelial cells are interconnected through three major types of junctions – Tight Junctions (TJs), Adherens Junctions (AJs), and Desmosomes (DSMs). In simple epithelia, these junctions are positioned along the apical end of the cell lateral membrane, where they form the Apical Junctional Complex (AJC). AJs and DSMs, but not TJs, are also present along the basolateral plasma membrane, where they are much smaller in size. This asymmetry of junction organization is a distinctive architectural feature of simple epithelia. Such asymmetry is controlled by a set of conserved polarity proteins. The main question that we set out to address in this proposal is: how are two polarity proteins, basolateral protein Scrib and apical protein Par3, interconnected with proteins regulating the positioning of the cell-cell junctions in AJC. Our recently published results suggested how Scrib maintains “basolateral identity” of simple epithelial cell membrane, the mechanism that has been elusive for many years. We found that this function of Scrib is based on regulation of two enzymes, phosphatase PP1 (PP1) and Rho/Rac Guanine Nucleotide Exchange Factor, GEF-H1. Our results suggest that Scrib holds PP1 in inactive state and releases it in an active form through interactions with other polarity proteins, Llgl, Dlg, and Band 4.1. We also show that a protein that links the polarity apparatus with DSM assembly is an ARM protein, plakophilin 3 (Pkp3). We provide evidence that this protein is stored around TJs in a “dormant” pool that is established under control of the apical polarity protein Par3. The active form of Pkp3, released from this pool, drives formation of DSMs using the mechanism that is radically distinct from the assembly mechanism of the evolutionary related junctions, AJs. Furthermore, we present some evidence suggesting that a similar Pkp-dependent mechanism of junction assembly is involved in formation of a previously unrecognized subtype of AJs, which we call here Pkp4-dependent AJs. The advances made in previous years allow us to come up with this proposal, which includes the investigation of: (i) how Scrib regulates PP1 and what are the effectors of this pathway; (ii) how Pkp3 regulates adhesion activity of desmosomal cadherins and how its DSM assembly activity is regulated by the polarity system; and (iii) how Pkp4 controls adhesion activity of classic cadherins in assembly of specific subset of AJs. This work will pave the way toward the development of reagents modulating the adhesive and barrier properties of epithelial tissues.