Uncovering the molecular machinery driving caspase-2 activation

凋亡是细胞程序性死亡的一种形式，具有独特的形态学和生化特征，包括半胱天冬酶的活化，半胱天冬酶分为启动剂和效应剂。引发剂半胱天冬酶被招募到多聚体蛋白复合物中进行二聚化和活化。caspase -2是caspase家族中一个独特的成员，它同时具有caspase的启动物和效应物的特性。尽管是第一个克隆的哺乳动物caspase，但caspase-2的作用仍然是谜，激活caspase-2作为caspase启动物的独特凋亡刺激仍然未知。我们已经发现caspase-2在孔隙形成毒素（pft）介导的细胞凋亡过程中作为启动剂caspase被激活。pft（例如-溶血素和溶气素）是由致病菌分泌的主要细菌毒力因子，它们主要通过在宿主细胞膜上形成孔而引起细胞毒性作用。我们已经发现caspase-2是介导α溶血素和溶血素介导的人上皮细胞凋亡所必需的。Caspase-2以PIDDosome独立的方式被激活，通过高分辨率凝胶过滤层析，我们发现在pft处理的细胞中，Caspase-2被募集到一个新的高分子量复合物（Castosome）中。caspase-2向这种高分子量复合物的募集及其激活依赖于pft诱导的钾外排，从而揭示了钾离子在调节caspase-2激活中的关键作用。我们的目标是破译castosome复合物的组成，并进一步阐明caspase-2激活背后的机制。这些结果将使我们能够设计出合理的治疗药物来对抗几种细菌感染和癌症。

Apoptosis is a form of programmed cell death characterized by unique morphological and biochemical features including activation of proteases called caspases, which are classified into initiator and effector caspases. Initiator caspases are recruited to multimeric protein complexes for their dimerization and activation. Caspase-2 is a unique member of the caspase family as it exhibits features of both initiator and effector caspases. Despite being the first cloned mammalian caspase the role of caspase-2 remained enigmatic and the unique apoptotic stimuli that activate caspase-2 as an initiator caspase remained unknown. We have uncovered that caspase-2 is activated as an initiator caspase during Pore forming toxins (PFTs)-mediated apoptosis. PFTs (for instance alpha-hemolysin and aerolysin) are major bacterial virulence factors secreted by pathogenic bacteria and they elicit cytotoxic effects primarily by forming pores on the host cell membranes. We have sown that caspase-2 is required for mediating both alpha-hemolysin and aerolysin-mediated apoptosis in human epithelial cells. Caspase-2 is activated in a PIDDosome independent manner and by employing high-resolution gel filtration chromatography, we have identified that caspase-2 is recruited to a novel high molecular weight complex (Castosome) in PFT-treated cells. Recruitment of caspase-2 to this high molecular weight complex and its activation are dependent on PFT-induced potassium efflux thus revealing a crucial role for potassium ions in regulating caspase-2 activation. We aim to decipher the components of castosome complex and further elucidate mechanisms behind caspase-2 activation. These results will enable us to design rational therapeutic drugs to combat several bacterial infections and cancer.