Coupling intercellular adhesion, polarity and mechanical signals at epidermal junctions

细胞极化对于正常发育、组织稳态和再生至关重要。对低等生物的研究确定了细胞和组织结构的重要调节因子。Par 3-aPKC-Par 6复合物的极性蛋白介导不同的细胞过程，并将细胞形状的控制与调节生长、细胞命运和分化的信号传导途径偶联。然而，这些保守的极性调节剂如何促进哺乳动物组织功能和疾病还不太清楚。皮肤是一种不断受到机械应力的拉伸组织。极性蛋白是否以及如何驱动分层上皮（如皮肤表皮）的极化，以及它们如何在该组织中促进化学和机械信号传导，在很大程度上是未知的。我们最近的工作揭示了Par 3和aPKCl在皮肤癌中的重要作用，其中连接定位而非细胞质Par 3促进生长、存活和最终肿瘤发生。我们进一步表明，小鼠表皮中的Par 3失活导致表皮屏障缺陷、干细胞下降和过早分化。此外，Par 3控制P-cadherin表面表达，从而调节表皮细胞-细胞相互作用。在SPP 1782中，我们将不同的生物物理方法与细胞生物学、遗传学和蛋白质生化方法相结合，以揭示意想不到的机制，通过该机制，连接Par 3将细胞间粘附的机械信号与细胞反应偶联，以确保表皮稳态和屏障完整性。我们破译了Par 3促进Rho驱动的肌动球蛋白收缩性，以促进细胞-细胞接触处的内力产生，这对维持紧密的连接屏障很重要。 此外，我们的数据表明，极性蛋白介导动态连接重塑响应外部机械线索。有趣的是，纠正肌球蛋白激活也足以挽救有丝分裂缺陷和异位分化后，Par 3损失，解开了极性蛋白依赖性表皮自我更新和分化的肌动球蛋白调节的核心作用。在确定了连接Par 3对角质形成细胞力学的重要性后，第二个资助期的主要工作将旨在进一步揭示介导细胞骨架和生化反应的细胞间粘附中机械和极性信号传导之间的分子联系。我们将使用增益和损失的功能的方法，蛋白质组学，生物物理和成像方法来检查三个类的粘附分子的相关性，这些粘附分子在Par 3损失后被解除管制。此外，我们将研究机械化学效应器连接极性蛋白的下游途径，并询问极性网络如何将机械信号传递到细胞内部，以指导应变适应。总之，这个SPP 1782项目将提供对细胞间连接，细胞极性和重要屏障形成上皮细胞中力传递耦合的分子见解。

Cell polarization is essential for proper development, tissue homeostasis and regeneration. Studies in lower organisms identified important regulators of cell and tissue architecture. Polarity proteins of the Par3-aPKC-Par6 complex mediate diverse cellular processes and couple control of cell shape to signalling pathways regulating growth, cell fate and differentiation. Yet, how these conserved polarity regulators contribute to mammalian tissue function and disease is much less clear. The skin is a tensile tissue constantly exposed to mechanical stress. Whether and how polarity proteins drive polarization in stratified epithelia like the skin epidermis and how they contribute to chemical and mechanical signalling in this tissue is largely unknown. Our recent work revealed important roles of Par3 and aPKCl in skin cancer, with junction-localized but not cytoplasmic Par3 promoting growth, survival and ultimately tumorigenesis. We further showed that Par3 inactivation in the mouse epidermis results in epidermal barrier defects, stem cell decline and premature differentiation. Moreover, Par3 controls P-cadherin surface expression, thereby regulating epidermal cell-cell interactions. Within the SPP1782 we combined different biophysical methods with cell biological, genetic and proteinbiochemical approaches to reveal unexpected mechanisms through which junctional Par3 couples mechanical signals at intercellular adhesions with cellular responses to ensure epidermal homeostasis and barrier integrity. We deciphered that Par3 promotes Rho-driven actomyosin contractility to foster intrinsic force generation at cell-cell contacts, important to maintain the tight junctional barrier. Moreover, our data indicate that polarity proteins mediate dynamic junction remodelling in response to external mechanical cues. Intriguingly, correcting myosin activation was also sufficient to rescue mitotic defects and ectopic differentiation upon Par3 loss, unravelling a central role of actomyosin regulation in polarity protein-dependent epidermal self-renewal and differentiation. Having established the importance of junctional Par3 for keratinocyte mechanics, key efforts in the second funding period will aim to unravel further molecular links between mechanical and polarity signalling at intercellular adhesions that mediate cytoskeletal and biochemical responses. We will use gain- and loss-of-function approaches, proteomics, biophysical and imaging methods to examine the relevance of three classes of adhesion molecules that are deregulated following Par3 loss. Moreover, we will investigate mechanochemical effector pathways downstream of junctional polarity proteins and ask how polarity networks transmit mechanical cues to the cell’s interior to instruct strain adaptation. Together, this SPP1782 project will provide molecular insight into the coupling of intercellular junctions, cell polarity and force transmission in an important barrier-forming epithelium.