The mitochondrial intermembrane space protein Smac/DIABLO in signal transduction and immune response

Smac是一种线粒体膜间隙蛋白，在细胞凋亡过程中释放并促进半胱天冬酶激活。许多其他的，潜在的，胞质功能的Smac可以推断的基础上实验胞质表达的Smac和使用的小分子的“Smac-模拟物”，但有很少的证据的功能的Smac蛋白外细胞死亡。越来越明显的是，凋亡信号装置也可以仅被激活到低水平，其中可以检测到一些信号事件，但细胞保持存活。我们最近发现，这种“亚致死”线粒体凋亡信号（“少数MOMP”）是人类和小鼠细胞感染几种细菌和病毒病原体的一个特征。我们的数据表明，这种信号是一种细胞警报机制，并在抗微生物宿主防御中发挥作用。我们最近的数据进一步表明，Smac是重要的线粒体亚致死凋亡信号。我们已经测试了Smac在幽门螺杆菌体外感染中的作用，并发现了Smac在这种感染中在少数MOMP期间释放的证据，是激活替代NF-κ B所需的，并有助于上皮细胞产生细胞因子。我们建议，Smac释放是少数MOMP的一般特征，并且Smac在检测病原体对非专业免疫细胞的感染中具有信号传导功能。在这个项目中，我们将测试这个假设。我们将分析在少数MOMP的情况下Smac和细胞色素c的相对释放，并将确定是否是单个线粒体或更多的线粒体网络释放这些蛋白质。我们将进一步努力区分细胞色素c和Smac对少数MOMP生物效应的相对作用。我们将研究细胞溶质中的Smac依赖性信号传导，重点关注细胞凋亡蛋白抑制剂中和的连续事件，并将更彻底地测试细胞因子的分泌和细菌遏制。我们已经建立了Smac缺陷小鼠系，并将使用这些小鼠的肠道类器官，并用猫螺杆菌和小鼠衣原体感染小鼠，以了解Smac对细菌感染免疫反应的贡献。我们的数据表明，Smac在免疫反应的启动中具有凋亡细胞死亡之外的信号传导功能，我们希望能够在这里确定这些功能的信号传导途径和生理作用。

Smac is a mitochondrial intermembrane space protein that is released and that facilitates caspase-activation during apoptosis. A number of other, potential, cytosolic functions of Smac can be inferred based on experimental cytosolic expression of Smac and on the use of small-molecule ‘Smac-mimetics’ but there is very little evidence of a function of Smac-protein outside cell death. It is becoming evident that the apoptosis signalling apparatus can also be activated only to a low level, where some signalling events can be detected but the cell stays alive. We have recently found that such ‘sub-lethal’ mitochondrial apoptosis signalling (‘minority MOMP’) is a feature of infection of human and mouse cells with any of several bacterial and viral pathogens tested. Our data suggest that this signalling is a mechanism of cell alert and plays a role in anti-microbial host defence. Our recent data further suggest that Smac is important in mitochondrial sub-lethal apoptosis signalling. We have tested for a role of Smac in infection in vitro with Helicobacter pylori and have found evidence that Smac is in this infection released during minority MOMP, is required for the activation of alternative NF-kappaB and contributes to cytokine production by epithelial cells. We propose that Smac-release is a general feature of minority MOMP, and that Smac has a signalling function in the detection of the infection of non-professional immune cells by pathogens. In this project we will test this hypothesis. We will analyse the relative release of Smac and cytochrome c during situations of minority MOMP and will establish whether it is individual mitochondria or more of the mitochondrial network releasing these proteins. We will further endeavour to distinguish the relative roles of cytochrome c and Smac for the biological effects of minority MOMP. We will investigate Smac-dependent signalling in the cytosol, focussing on events consecutive to the neutralisation of inhibitor of apoptosis proteins and will more thoroughly test for the secretion of cytokines and bacterial containment. We have made a Smac-deficient mouse line and will use intestinal organoids from these mice and perform infections of the mice with Helicobacter felis and Chlamydia muridarum to understand the contribution of Smac to the immune response to bacterial infection. Our data suggest that Smac has signalling functions outside apoptotic cell death in the initiation of an immune reaction, and we hope to be able here to work out signalling pathways and physiological roles of such functions.