Listeria monocytogenes is an intracellular bacterium that utilizes two phospholipases C (PLCs) and a pore-forming cytolysin (listeriolysin O, LLO) to escape the phagosome. However, prior to escape, the bacterium must overcome a number of phagosomal defenses, including autophagy and NOX2 NADPH oxidase production of reactive oxygen species (ROS).
Autophagy, the cellular process of self-digestion, is a key component of innate immunity. Previously, it has been shown that L. monocytogenes is targeted by autophagy (LC3+) at 1 h post infection (p.i.) but the mechanism remains elusive. Here, I show that at 1 h p.i., diacylglycerol (DAG) and ROS production are required for autophagy targeting to the bacteria, which are predominantly in phagosomes. It has been shown that autophagy targeting of cytosolic L. monocytogenes is mediated via protein ubiquitination. However, protein ubiquitination is not associated with LC3+ bacteria at 1 h p.i.. Thus, my data suggest that distinct signals mediate autophagy targeting of L. monocytogenes depending on the location within host cells.
Given that ROS mediate autophagy targeting to L. monocytogenes and that previous studies have demonstrated that ROS production limits bacterial escape, I investigated how L. monocytogenes overcomes ROS production prior to phagosomal escape. I found that LLO inhibits ROS production by preventing NOX2 NADPH oxidase localization to L. monocytogenes-containing phagosomes. LLO-deficient bacteria can be complemented by perfringolysin O, a related cytolysin, suggesting that other pathogens may also use pore-forming cytolysins to inhibit ROS production. While PLCs can activate ROS production, this effect is alleviated by LLO pore-formation. Therefore, the combined activities of PLCs and LLO allow L. monocytogenes to efficiently escape the phagosome while avoiding microbicidal ROS.
Together, this thesis provides a clearer understanding of the balance between host defense versus bacterial evasion. Greater insight into host-bacterial interaction may lead to better therapeutics that can “tip the balance” in the host’s favour.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/32799 |
| Date | 31 August 2012 |
| Creators | Lam, Grace |
| Contributors | Brumell, John |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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