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

描述（由申请人提供）：结核病（TB）是一种持续的肺部感染，已困扰人类几个世纪，是当今世界卫生最严重的威胁之一。每年有200万至300万人死于结核病，以及出现了对所有现有化疗药物都具有耐药性的菌株，这些都迫切要求开发治疗结核病的新疗法。此外，耐药结核病作为一种生物恐怖主义制剂的威胁已导致它被列为NIAID生物防御研究的C类优先病原体。该研究的主要目的是了解这种病原体操纵其人类宿主以逃避免疫系统杀死的机制。我们之前的研究表明，结核分枝杆菌利用ESX-1蛋白分泌系统输出毒力因子，解除宿主巨噬细胞的武装。我们发现EspR是小鼠分泌和毒力所必需的ESX-1的关键调节因子。EspR激活包含三种ESX-1成分的操纵子的转录，其表达反过来促进ESX-1底物的分泌。令人惊讶的是，dna结合调节因子本身的外排最终导致转录减少，从而减少ESX-1的分泌。我们的研究结果揭示了一个直接的负反馈回路，滴定了一个分泌系统的活性，对一个主要的人类病原体的毒力至关重要。我们假设这种调控方案提供了一种定时机制，允许感染后早期毒力因子分泌的脉冲，然后抑制分泌。这是一个很有吸引力的假设，因为许多ESX-1毒力因子也是适应性免疫反应识别的主要抗原。因此，这些研究将验证结核分枝杆菌在感染早期激活该途径以传递毒力因子的假设，但随后为了躲避免疫系统而使该途径失活。这些研究的结果可能揭示出设计更好的结核病疫苗的方法。

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.