Dissecting a novel mechanism of drug-induced death in Toxoplasma gondii

描述(由申请人提供)：Apicomexa包括一个医学上重要的专性细胞内寄生虫门，包括疟疾的病原体恶性疟原虫，引起胃肠道疾病的隐孢子虫，以及B类弓形虫，它可以在免疫功能低下的宿主和发育中的胎儿中致病。目前缺乏有效治疗这些寄生虫所有阶段的药物疗法，在许多情况下，由于出现抗药性寄生虫菌株，现有药物正迅速变得无效。因此，发现新的药物设计靶点和了解耐药机制是顶端复合体寄生虫研究的首要任务。我们应对这一挑战的方法一直是分离和鉴定对特定抗寄生虫药物具有抗药性的弓形虫突变株。我们最近发现线粒体MutS同源物(MSH)TgMSH-1的破坏直接导致弓形虫的多药耐药性。MSHS是真核细胞DNA错配修复机制的重要组成部分，也参与了细胞周期停滞和细胞凋亡对DNA损伤剂的反应。有趣的是，我们观察到某些抗寄生虫药物以TgMSH1依赖的方式导致细胞周期标记物的表达中断。因此，我们在弓形虫中发现了一条新的途径，当被某些药物诱导时，会导致寄生虫死亡。我们的假设是，某些药物直接或间接影响寄生虫的线粒体，这种作用导致包括TgMSH1在内的信号通路的激活，导致寄生虫死亡。我们的目标是剖析这种依赖TgMSH1的死亡机制，以表征一种新的杀死顶端复合体寄生虫的模式。结合细胞生物学、生物化学和基因组学方法，我们将确定TgMSH1依赖药物对线粒体功能的影响，确定TgMHS1的信号伙伴，并确定TgMSH1依赖药物对细胞周期的影响。这些目标的完成将阐明可诱导死亡途径的细节和机制。这构成了在这种重要病原体中发现药物靶点的创新方法。 公共卫生相关性：弓形虫是人类常见的寄生虫感染。针对这种寄生虫的药物是有限的，而且往往会引起严重的副作用。因此，迫切需要新的抗弓形虫药物。我们发现了一种可以诱导寄生虫死亡的机制。我们的目标是了解参与这一可诱导死亡途径的所有参与者和事件，以此作为发现药物开发新靶点的一种手段。

DESCRIPTION (provided by applicant): The Apicomplexa comprise a medically important phylum of obligate intracellular parasites, including Plasmodium falciparum, the causative agent of malaria, Cryptosporidium, which causes gastrointestinal disease, and the category B agent Toxoplasma gondii, which can be pathogenic in immunocompromised hosts and the developing fetus. Drug therapies that effectively treat all stages of some of these parasites are currently lacking and in many cases existing drugs are quickly becoming ineffective due to the emergence of drug-resistant parasite strains. Thus, the discovery of new targets for drug design and the understanding of resistance mechanisms are high priorities in the studies of apicomplexan parasites. Our approach to this challenge has been to isolate and characterize T. gondii mutants that are resistant to specific anti- parasitic drugs. We have recently discovered that disruption of a mitochondrial MutS homologue (MSH), TgMSH-1, directly confers multi-drug resistance in T. gondii. MSHs are critical components of the eukaryotic DNA mismatch repair machinery and are also involved in signaling cell cycle arrest and apoptosis in response to DNA damaging agents. Interestingly, we have observed that certain anti-parasitic drugs cause disruption in the expression of cell cycle markers in a TgMSH1 dependent manner. Thus, we have identified a novel pathway in T. gondii, that when induced by certain drugs leads to parasite death. It is our hypothesis that that certain drugs affect the mitochondrion of the parasite directly or indirectly and that this effect results in the activation of a signaling pathway, which includes TgMSH1 and results in parasite death. It is our goal to dissect this TgMSH1 dependent death mechanism as to characterize a novel mode of killing apicomplexan parasites. Using a combination of cell biology, biochemistry and genomic approaches we will determine the effect of TgMSH1-dependent drugs on mitochondrial function, identify signaling partners of TgMHS1 and determine the effect of TgMSH1 dependent drugs on cell cycle. The completion of these aims will elucidate the details and mechanisms of an inducible death pathway. This constitutes an innovative approach to the discovery of drug targets in this important pathogen. PUBLIC HEALTH RELEVANCE: Toxoplasma gondii is a common parasitic infection in humans. Drugs against this parasite are limited and can often cause severe side effects. Thus, new drugs against Toxoplasma are critically needed. We have discovered a mechanism by which the parasite can be induced to die. It is our goal to understand all the players and events involved in this inducible death pathway as a means to discover novel targets for drug development.