Reciprocal interactions between apoptosis pathway and cell size

通过程序性细胞死亡清除不需要的细胞对细胞发育和维持细胞稳态至关重要。程序性细胞死亡的错误调控可导致包括癌症在内的疾病。细胞凋亡是一种程序性细胞死亡，在动物物种中是保守的，在过去的30-40年里被广泛研究。这些研究已经鉴定和表征了形成“细胞凋亡途径”的少数因素，这些因素在细胞中被激活时，会引发细胞凋亡。这些因子包括促和抗凋亡的bcl -2样蛋白，apaf -1样蛋白和半胱天冬酶，这些酶可以切割其他蛋白质。正是这些半胱天冬酶的激活超过了临界的“致死活性”阈值，才会引发细胞凋亡。重要的是，我们对细胞凋亡途径的全面理解导致了被称为“BH3模拟物”的癌症治疗药物的发展，自2016年以来，该药物已用于临床治疗慢性淋巴细胞白血病和其他类型的癌症患者。BH3模拟物靶向抗凋亡bcl -2样蛋白。然而，基于BH3模拟物的治疗仍然存在挑战，这些挑战是毒性和耐药性的发展。这些挑战反映了我们对细胞凋亡途径理解的两个缺陷。首先，我们仍然缺乏对细胞凋亡途径在体内如何被控制的全面理解。其次，越来越多的证据表明，细胞凋亡途径除了清除不需要的细胞之外还有其他功能，我们仍然缺乏对这些“非规范”功能的足够了解。拟议的项目解决了这两个缺点。有人认为，细胞的大小可以引发细胞凋亡。然而，缺乏明确的证据，特别是在体内。Aim 1的目的是在动物发育的背景下，研究细胞大小对细胞凋亡途径激活的贡献。为此，我们将使用秀丽隐杆线虫，一种被广泛用于研究细胞凋亡的模式生物。事实上，通过对秀丽隐杆线虫（apaf -1样蛋白，caspases）的凋亡研究，初步确定了凋亡途径的许多组成部分。秀丽隐杆线虫的发育具有高度的可重复性，在每条发育中的线虫中，同样有131个细胞通过凋亡死亡。其中两个细胞是左、右NSM姐妹细胞（NSMsc），我的小组对这两个细胞的死亡进行了近20年的研究。重要的是，我们现在已经确定了允许我们增加或减少NSMsc大小的突变。利用这些突变，我们已经确定了细胞大小与NSMsc死亡能力之间的负相关关系。这支持了细胞的物理大小可以在体内触发细胞凋亡的观点。在提议的项目中，我们将检验这一假设。此外，我们将确定细胞凋亡途径的哪些组成部分是由细胞大小控制的，以及细胞大小如何与该组成部分“沟通”。NSMsc是通过母细胞的“不平等”细胞分裂产生的，是两个子细胞中较小的一个。在我们的研究中，我们惊奇地发现凋亡通路在控制NSMsc的大小方面具有非规范的功能。具体来说，凋亡途径在NSMsc的母体中起作用，并导致其不平等分裂。这确保了NSMsc的大小获得了一个临界的“致命大小”阈值。此外，我们有证据表明，在这种情况下，半胱天冬酶直接与控制肌动球蛋白细胞骨架网络的因子相互作用，而肌动球蛋白在不均匀细胞分裂中起着关键作用。Aim 2的目的是研究caspase在NSMsc细胞母细胞分裂过程中影响肌动球蛋白网络的机制，从而控制NSMsc的大小。

The removal of unwanted cells through programmed cell death is critical for development and the maintenance of cellular homeostasis. Misregulation of programmed cell death can lead to disease, including cancer. Apoptosis is a type of programmed cell death that is conserved across animal species and that has been studied intensely over the past 30-40 years. These studies have resulted in the identification and characterization of a handful of factors that form the 'apoptosis pathway', which when activated in a cell, triggers apoptosis. These factors include pro- and anti-apoptotic Bcl-2-like proteins, Apaf-1-like proteins and caspases, enzymes that can cleave other proteins. It is the activation of these caspases above a critical 'lethal activity' threshold that triggers apoptosis. Importantly, our comprehensive understanding of the apoptosis pathway has led to the development of cancer therapeutics referred to as 'BH3 mimetics', which since 2016, have been used in the clinic to treat patients with chronic lymphocytic leukemia and other types of cancer. BH3 mimetics target anti-apoptotic Bcl-2-like proteins. However, challenges remain with BH3 mimetic-based treatments and these are toxicity and the development of resistance. These challenges reflect two shortcomings of our understanding of the apoptosis pathway. First, we are still lacking a comprehensive understanding of how the apoptosis pathway is controlled in vivo. Second, there is increasing evidence that the apoptosis pathway has functions other than in the removal of unwanted cells and we still lack sufficient knowledge of these 'non-canonical' functions. The proposed project addresses both of these shortcomings.It has been suggested that the size of a cell can trigger apoptosis. However, definitive evidence is lacking especially in vivo. The goal of Aim 1 is to investigate, in the context of animal development, the contribution of cell size to the activation of the apoptosis pathway. To that end, we will use the nematode Caenorhabditis elegans, a model organism that has been extensively used to study apoptosis. Indeed, a number of components of the apoptosis pathway were initially identified through studies of apoptosis in C. elegans (Apaf-1-like proteins, caspases). C. elegans development is highly reproducible and in every developing nematode worm, the same 131 cells die through apoptosis. Two of these cells are the left and right NSM sister cell (NSMsc), and my group has studied the deaths of these two cells for almost 20 years. Importantly, we have now identified mutations that allow us to either increase or decrease the size of the NSMsc. Using these mutations, we have identified an inverse correlation between cell size and the ability of the NSMsc to die. This supports the view that the physical size of a cell can trigger apoptosis in vivo. In the proposed project, we will test this hypothesis. In addition, we will determine which component(s) of the apoptosis pathway are controlled by cell size and how cell size is 'communicated' to this component.The NSMsc are generated through an 'unequal' cell division of a mother cell and are the smaller of the two daughter cells generated. During our studies, we have made the surprising discovery that the apoptosis pathway has a non-canonical function in the control of the size of the NSMsc. Specifically, the apoptosis pathway acts in the mother of the NSMsc and contributes to its unequal division. This ensures that the size of the NSMsc acquires a critical 'lethal size' threshold. In addition, we have evidence that in this context, the caspase directly interacts with a factor that controls the actomyosin cytoskeletal network, which is known to play a critical role during unequal cell divisions. The goal of Aim 2 is to investigate the mechanism(s) through which the caspase affects the actomyosin network during division of the mother of the NSMsc cell, thereby controlling NSMsc size.