Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

ER stress restricts Legionella pneumophila replication in human macrophages. (#103)

Manal H. Alshareef 1 2 3 , Elizabeth L. Hartland 1 2 , Kitty McCaffrey 1 2
  1. Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Clayton, VIC 3168, Australia
  2. Department of Molecular and Translational Science, Monash University, Clayton, VIC 3168, Australia
  3. College of Pharmacy, Umm Al-Qura University, Makkah 24230, Saudi Arabia

L. pneumophila is an environmental Gram-negative bacterium that survives in the environment by replicating within free-living amoebae. When transmitted to humans, it infects phagocytic immune cells within the lung, such as macrophages and monocytes, to cause disease. To survive and replicate within its hosts, Legionella uses a type-IVB secretion system to secrete >330 “effector” proteins into the host cell that manipulate various host processes to evade elimination by phago-lysosomal degradation and establish its intracellular replicative vacuole, the Legionella-containing vacuole (LCV). Legionella hijacks endoplasmic reticulum (ER) membranes to form the LCV and we hypothesise that it causes a loss of ER homeostasis, or ER stress, within the host cell.

The unfolded protein response (UPR) is a homeostatic response to ER stress but also plays an important role in infection and immunity. Legionella effectors have been previously shown to inhibit UPR signalling but whether the UPR restricts Legionella replication remains unknown. In this study, we have shown that pre-treatment of a human macrophage cell line with pharmacological inducers of ER stress, tunicamycin and thapsigargin, inhibits Legionella intracellular replication. Drug pre-treatment did not inhibit Legionella growth in vitro, phagocytic uptake of the bacterium or effector translocation via the type-IVB secretion system. Although tunicamycin was shown to enhance host apoptosis to inhibit bacterial replication, thapsigargin pre-treatment rather protected macrophages from Legionella-induced cytotoxicity. Together, these data suggest that ER stress restricts Legionella replication via a cell intrinsic mechanism, possibly a UPR-dependent mechanism, that is currently being investigated.

Words: 243.

  1. Alshareef, Manal H., Elizabeth L. Hartland, and Kathleen McCaffrey. "Effectors targeting the unfolded protein response during intracellular bacterial infection." Microorganisms 9.4 (2021): 705.
  2. Mondino, Sonia, et al. "Legionnaires’ disease: state of the art knowledge of pathogenesis mechanisms of Legionella." Annual Review of Pathology: Mechanisms of Disease 15 (2020): 439-466.
  3. Celli, Jean, and Renée M. Tsolis. "Bacteria, the endoplasmic reticulum and the unfolded protein response: friends or foes?." Nature Reviews Microbiology 13.2 (2015): 71-82.
  4. Treacy-Abarca, Sean, and Shaeri Mukherjee. "Legionella suppresses the host unfolded protein response via multiple mechanisms." Nature communications 6.1 (2015): 1-10.
  5. Hempstead, Andrew D., and Ralph R. Isberg. "Inhibition of host cell translation elongation by Legionella pneumophila blocks the host cell unfolded protein response." Proceedings of the National Academy of Sciences 112.49 (2015): E6790-E6797.