The role of Jam-C trafficking in endothelial vascular function

身体对病原体或组织损伤的反应对于生存至关重要。循环系统中存在的白色血细胞通过内皮细胞上存在的信号靶向损伤部位，所述内皮细胞排列在损伤或感染部位附近的血管中。这导致白细胞在内皮上滚动，随后在白细胞找到合适的点穿过内皮进入感染组织之前牢固粘附和爬行。这种多步骤级联反应受到严格调控，白细胞和内皮细胞上的许多不同蛋白质受体控制着每一步。 存在于内皮细胞上的蛋白质家族（连接粘附分子或JAM）已被证明在该炎症级联反应的最后步骤中具有重要作用，即白细胞通过内皮细胞层并进入感染组织。Jam-C是该家族的一员，是这种迁移所必需的，并且已被证明可以保持白细胞运动的方向性以及帮助控制内皮层的渗透性。Jam-C功能的抑制导致白细胞犹豫地通过内皮细胞单层和/或返回血流。重要的是，Jam-C表达和功能与多种炎性疾病状态相关，包括关节炎和心脏病等。Jam-C主要定位于内皮细胞之间的连接处，在那里它与存在于相邻细胞上的Jam-C或Jam-B分子结合，从而有助于产生紧密连接。这种连接限制了一些分子和蛋白质通过内皮细胞层。当白细胞穿过内皮时，内皮细胞上存在的Jam-C被认为会转变为结合白细胞表面存在的受体。最近的研究表明，Jam-C也存在于细胞内囊泡池中，并且存在于表面、细胞连接处和细胞内囊泡中的Jam-C的量在炎症刺激后变化，这也适用于培养中生长的内皮细胞。这表明Jam-C的内部池可能根据细胞暴露的刺激而动态调节。Jam-C的内化或再分布可能是调节已知Jam-C功能的一种手段：通过阻止受体结合和信号传导，或通过将其浓缩在可能使用的特定池中，即在迁移的白细胞周围。 我们建议开发方法来监测Jam-C的内部贩运和这样做所需的细胞机制。通常，表面受体的这种内化和细胞内路由取决于受体的细胞内部分中存在的氨基酸基序。这些基序与细胞机械结合，并决定蛋白质是否被内化，以及现在的细胞内蛋白质随后发生什么。受体可能在溶酶体中降解，或者受体可能通过许多不同的途径再循环回到细胞表面。 一旦我们对Jam-C如何内在化和在细胞周围运输有了更好的机械概念，我们打算利用这些信息找到新的方法来抑制这一过程，方法是敲除关键的机械部分或改变图案本身。这种方法应该允许我们定义细胞内Jam-C交通对Jam-C已知功能的重要性。它在白细胞迁移或增加细胞渗透性中起什么作用？任何新的信息都可以转化为控制这些过程的新方法。这些信息最终可能在慢性炎症情况下控制不适当的白细胞迁移或在患者免疫受损的情况下提高白细胞流入率方面很重要。

The body's response to a pathogen or tissue injury is essential for survival. White blood cells present in the circulatory system are targeted to the site of injury by signals present on the endothelial cells that line the blood vessels near to the site of injury or infection. This results in rolling of the leukocytes on the endothelium followed by subsequent firm adhesion and crawling before the leukocyte finds a suitable point to pass through the endothelium into the infected tissue. This multi-step cascade is tightly regulated and a number of different protein receptors on both the leukocyte and the endothelium govern each step. A family of proteins present on the endothelial cells (the junctional adhesion molecules or JAMs) have been shown to have important roles in the final step of this inflammatory cascade, the passage of leukocytes through the endothelial cell layer and into the infected tissue. Jam-C, a member of this family, is necessary for this transmigration and has been demonstrated to maintain the directionality of leukocyte movement as well as helping to control the permeability of the endothelial layer. Inhibition of Jam-C function results in leukocytes passing hesitantly through the endothelial cell monolayer and/or returning to the blood flow. Importantly Jam-C expression and function has been associated with multiple inflammatory disease states including, amongst others, arthritis and heart disease. Jam-C is primarily localised to the junctions between endothelial cells where it binds to Jam-C or Jam-B molecules present on neighbouring cells thus helping to create a tight junction. This junction restricts the passage of some molecules and proteins through the endothelial cell layer. When a leukocyte passes through the endothelium the Jam-C present on the endothelial cell is thought to switch to bind a receptor present on the leukocyte surface. Recent research has demonstrated that Jam-C is also present in intracellular vesicular pools and that the amount of Jam-C present at the surface, the cellular junctions and in intracellular vesicles varies following an inflammatory stimulus and this is also true of endothelial cells grown in culture. This indicates that internal pools of Jam-C might be dynamically regulated depending on the stimulus that the cells are exposed to. Internalisation or redistribution of Jam-C might be a means of regulating known Jam-C functions: either by preventing the receptor binding and signalling or by concentrating it in specific pools where it might be used i.e. around transmigrating leukocytes. We propose to develop approaches to monitor the internal trafficking of Jam-C and the cellular machinery required to do this. Often this internalisation and intracellular routing of a surface receptor depends upon amino acid motifs present in the intracellular portion of the receptor. These motifs bind to cellular machinery and determine if the protein is internalised and also what happens subsequently to the now intracellular protein. The receptor might be degraded in the lysosome or the receptor might be recycled back to the cell surface by a number of different routes. Once we have a better mechanistic idea of how Jam-C gets internalised and traffics around the cell we intend to use this information to find novel ways to inhibit this process by knocking out key pieces of machinery or by changing the motifs themselves. This approach should allow us to define the importance of intracellular Jam-C traffic on the known functions of Jam-C. What role does it play in leukocyte migration or in increasing cell permeability? Any new information could translate into new methods for controlling these processes. Such information could eventually be important in controlling inappropriate leukocyte transmigration in chronic inflammatory situations, or in boosting the rate of leukocyte influx in situations where a patient is immune compromised.