Listeriolysin O is necessary and sufficient to induce autophagy during Listeria monocytogenes infection.
BACKGROUND
Recent studies have suggested that autophagy is utilized by cells as a protective mechanism against Listeria monocytogenes infection.


RESULTS
However we find autophagy has no measurable role in vacuolar escape and intracellular growth in primary cultured bone marrow derived macrophages (BMDMs) deficient for autophagy (atg5-/-). Nevertheless, we provide evidence that the pore forming activity of the cholesterol-dependent cytolysin listeriolysin O (LLO) can induce autophagy subsequent to infection by L. monocytogenes. Infection of BMDMs with L. monocytogenes induced microtubule-associated protein light chain 3 (LC3) lipidation, consistent with autophagy activation, whereas a mutant lacking LLO did not. Infection of BMDMs that express LC3-GFP demonstrated that wild-type L. monocytogenes was encapsulated by LC3-GFP, consistent with autophagy activation, whereas a mutant lacking LLO was not. Bacillus subtilis expressing either LLO or a related cytolysin, perfringolysin O (PFO), induced LC3 colocalization and LC3 lipidation. Further, LLO-containing liposomes also recruited LC3-GFP, indicating that LLO was sufficient to induce targeted autophagy in the absence of infection. The role of autophagy had variable effects depending on the cell type assayed. In atg5-/- mouse embryonic fibroblasts, L. monocytogenes had a primary vacuole escape defect. However, the bacteria escaped and grew normally in atg5-/- BMDMs.


CONCLUSIONS
We propose that membrane damage, such as that caused by LLO, triggers bacterial-targeted autophagy, although autophagy does not affect the fate of wild-type intracellular L. monocytogenes in primary BMDMs.
Meyer-Morse
Nicole
N
Department of Molecular and Cellular Biology, University of California, Berkeley, California, United States of America.
Robbins
Jennifer R
JR
Rae
Chris S
CS
Mochegova
Sofia N
SN
Swanson
Michele S
MS
Zhao
Zijiang
Z
Virgin
Herbert W
HW
Portnoy
Daniel
D
D000818:Animals; D001343:Autophagy / Q000502:physiology*; D001427:Bacterial Toxins; D002478:Cells, Cultured; D006360:Heat-Shock Proteins / Q000502:physiology*; D006460:Hemolysin Proteins / Q000502:physiology*; D008081:Liposomes; D008088:Listeriosis / Q000276:immunology* / Q000503:physiopathology; D051379:Mice
D001427:Bacterial Toxins; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; D008081:Liposomes; C038705:hlyA protein, Listeria monocytogenes