Regulation of ESX-1 secretion and its role in M. tuberculosis virulence

描述（由申请人提供）：结核病（TB）是一种持续性肺部感染，已困扰人类数百年，是当今世界健康最严重的威胁之一。每年有200万至300万人死于结核病，并且出现了对所有可用化疗剂具有耐药性的菌株，这迫切需要开发新的治疗结核病的疗法。此外，耐药结核病作为生物恐怖主义制剂的威胁已导致其被列为NIAID生物防御研究的C类优先病原体。这项研究的主要目的是了解这种病原体操纵人类宿主以逃避免疫系统杀死的机制。我们之前已经证明了M。结核病利用ESX-1蛋白分泌系统输出解除宿主巨噬细胞的毒力因子。我们发现EspR是ESX-1的关键调节因子，是小鼠分泌和毒力所必需的。EspR激活包括三个ESX-1组分的操纵子的转录，其表达反过来促进ESX-1底物的分泌。令人惊讶的是，DNA结合调节剂本身的流出最终导致转录减少，从而减少ESX-1分泌。我们的研究结果揭示了一个直接的负反馈回路，该回路刺激了一种主要人类病原体毒力所必需的分泌系统的活性。我们假设，这样的调控机制提供了一个定时机制，允许脉冲的毒力因子分泌感染后早期，随后抑制分泌。这是一个吸引人的假设，因为许多ESX-1毒力因子也是适应性免疫应答识别的主要抗原。因此，这些研究将测试的假设，M。结核病在感染早期激活这一途径以传递毒力因子，但随后使这一途径失活以躲避免疫系统。这些研究的结果可能会揭示如何设计更好的疫苗来对抗结核病。 公共卫生相关性：目前预防结核病感染的疫苗根本不起作用。我们已经确定了一种潜在的机制，通过这种机制，结核病细菌可以通过关闭我们免疫细胞最好检测到的蛋白质的产生来隐藏免疫系统。我们的工作可能允许合理地设计更好的结核病疫苗株。

DESCRIPTION (provided by applicant): Tuberculosis (TB) is a persistent lung infection that has plagued mankind for centuries and ranks as one of the most serious threats to world health today. The 2-3 million deaths attributed yearly to the disease, as well as the emergence of strains resistant to all of the available chemotherapeutic agents, urgently call for the development of new therapies to treat TB. Furthermore, the threat of drug-resistant TB as a bioterrorism agent has led to it's listing as a NIAID Category C Priority Pathogen for biodefense research. The primary objective of the proposed research is to understand the mechanisms by which this pathogen manipulates its human host to evade killing by the immune system. We showed previously that M. tuberculosis utilizes the ESX-1 protein secretion system to export virulence factors that disarm host macrophages. We found that EspR is a key regulator of ESX-1 that is required for secretion and virulence in mice. EspR activates transcription of an operon that includes three ESX-1 components, whose expression in turn promotes secretion of ESX-1 substrates. Surprisingly, efflux of the DNA-binding regulator itself eventually results in reduced transcription, and thus reduced ESX-1 secretion. Our results reveal a direct negative feedback loop that titrates the activity of a secretion system essential for virulence of a major human pathogen. We hypothesize that such a regulatory scheme provides a timing mechanism that allows for a pulse of virulence factor secretion early after infection, followed by inhibition of secretion. This is an appealing hypothesis as many of the ESX-1 virulence factors are also major antigens recognized by the adaptive immune response. Thus, these studies will test the hypothesis that M. tuberculosis activates this pathway early during infection to deliver virulence factors, but then inactivates the pathway in order to hide from the immune system. Results from these studies may reveal ways to engineer better vaccines to fight TB. PUBLIC HEALTH RELEVANCE: Current vaccines to prevent TB infection simply don't work. We have identified a potential mechanism by which TB bacteria may hide from the immune system by turning off the production of the proteins that are best detected by our immune cells. Our work may allow for the rational engineering of a better TB vaccine strain.