Mechanism of EGFR activation by a novel fungal pore-forming toxin

粘膜（口腔、阴道、胃肠道）上皮在保护人类免受多种感染方面具有巨大的重要性，因为它是大多数微生物遇到的初始组织。这种微生物-上皮的接触导致在无害的“肠道”微生物的情况下的静止，或者在致病的“病原性”微生物的情况下的免疫和损伤保护机制的激活。当这些正常的宿主反应被破坏时，可能会出现大量的并发症，这些并发症的影响超出了感染的范围，因为包括癌症和自身免疫性疾病在内的疾病与微生物及其宿主之间的异常相互作用有关。鉴于这些相互作用的重要性，上皮细胞具有独特的机制，使粘膜组织能够区分真菌和病原微生物。真菌白色念珠菌是一种微生物的例子，它可以在健康人中作为真菌存在，但在不健康的人中成为一种危险的病原体，导致严重和潜在的致命疾病。事实上，念珠菌感染现在是第三大常见的医院获得性血流感染，是医疗保健提供的严重负担。由于绝大多数C。虽然白色念珠菌感染是通过粘膜表面获得的，但理解这些表面的上皮组织如何检测并将这种医学上重要的病原体限制在粘膜状态是至关重要的。确定这些机制不仅对真菌感染而且对控制粘膜表面的其他微生物具有相当大的价值。我们最近的工作有助于理解上皮细胞识别致病性C。白色念珠菌以及这如何导致宿主的损伤诱导和免疫激活。我们以前证明了C。白念珠菌感染导致上皮细胞损伤，分泌免疫激活剂诱导局部粘膜免疫以抵抗念珠菌。白色念珠菌感染最近，我们发现，为了激活这种保护性免疫过程，上皮细胞靶向一种特定的蛋白质（Ece 1 p）对“侵入性”形式的C。称为菌丝的白色念珠菌。我们现在证明，一个特定区域的Ece 1 p蛋白（命名为Ece 1-III）作为一种新的孔形成毒素（PFT）时，存在于高浓度。这是在人类致病真菌中发现的第一个PFT。Ece 1-III的成孔能力使C.白色念珠菌引起上皮损伤，并被上皮细胞识别以激活免疫力。此外，我们表明，这种新发现的真菌PFT激活一种特异性上皮表面受体（EGFR），从而诱导上皮免疫和保护性反应，防止真菌引起的损伤。我们已经证明，免疫激活是由于Ece 1-III和EGFR之间的直接相互作用而发生的。然而，我们发现Ece 1-III也能够通过一系列复杂的事件间接激活EGFR，这些事件发生在上皮细胞表面，作为对细胞损伤的反应的一部分。间接导致EGFR活化的这些表面事件的性质尚不清楚，尽管孔形成似乎对其活化至关重要。鉴于EGFR是介导上皮免疫和损伤保护的关键受体，本提案的目的是精确确定这种新型真菌PFT的孔形成如何间接激活EGFR，并证明这些激活事件在C.该项目将为真菌PFT的作用机制提供新的见解，并为我们理解粘膜免疫过程中上皮组织对“致病”真菌的反应提供新的见解。此外，它将确定新的宿主-微生物相互作用，这些相互作用不仅可以用于新的，更有效的抗真菌疗法，而且可以用于定义创新方法来对抗细菌PFT和粘膜感染的作用。

The mucosal (oral, vaginal, gastrointestinal) epithelium is of immense importance in protecting humans against a multitude of infections as it is the initial tissue encountered by the majority of microbes. This microbial-epithelial encounter results in either quiescence in the case of harmless 'commensal' microbes, or activation of immunity and damage protection mechanisms in the case of disease-causing 'pathogenic' microbes. When these normal host responses are disrupted, a plethora of complications can arise that have implications beyond infection, as conditions including cancer and autoimmune disease are associated with abnormal interactions between a microbe and its host. Given the importance of these interactions, epithelial cells possess distinct mechanisms enabling mucosal tissues to distinguish between commensal and pathogenic microbes.The fungus Candida albicans is an example of a microbe that can exist as a commensal in healthy people but becomes a dangerous pathogen causing severe and potentially fatal disease in unhealthy people. Indeed, Candida infections are now the third most common hospital-acquired bloodstream infection and are a serious burden to healthcare provision. Given that the vast majority of C. albicans infections are acquired through mucosal surfaces, it is of paramount importance to understand how epithelial tissues at these surfaces detect and restrict this medically-important pathogen to the commensal state. Identifying these mechanisms is of considerable value not only for fungal infections but also for controlling other microbes at mucosal surfaces. Our recent work has been instrumental in understanding the mechanisms by which epithelial cells identify disease-causing C. albicans and how this causes damage induction and immune activation in the host. We previously showed that C. albicans infection leads to epithelial damage and the secretion of immune activators to induce local mucosal immunity to protect against C. albicans infection. Recently, we found that to activate this protective immune process, epithelial cells target a specific protein (Ece1p) on the 'invasive' form of C. albicans known as hyphae. We now demonstrate that a specific region of the Ece1p protein (named Ece1-III) acts as a novel pore-forming toxin (PFT) when present at high concentration. This is the first PFT identified in a human pathogenic fungus. The pore forming abilities of Ece1-III enable C. albicans to cause epithelial damage and are recognised by epithelial cells to activate immunity. Furthermore, we show that this newly identified fungal PFT activates a specific epithelial surface receptor (EGFR), which induces epithelial immunity and the protective responses that protect against fungal-induced damage. We have demonstrated that immune activation occurs as a result of direct interaction between Ece1-III and EGFR. However, we found that Ece1-III is also able to activate EGFR indirectly through a complex series of events that take place at the epithelial cell surface as part of a response to cell damage. The nature of these surface events leading indirectly to EGFR activation is unknown, although pore formation seems to be essential for their activation. Given that EGFR is the key receptor mediating both epithelial immunity and damage protection, the aim of this proposal is to determine precisely how pore-formation by this novel fungal PFT indirectly activates EGFR and to demonstrate the importance of these activation events during C. albicans mucosal infection in vivo.This project will provide new insights into the mechanism of action of fungal PFTs and to our understanding of epithelial tissue responses to 'pathogenic' fungi during mucosal immunity. Further, it will identify novel host-microbe interactions that can be targeted not only for new, more effective antifungal therapies, but also for defining innovative approaches to combat the action of bacterial PFTs and mucosal infections in general.