title: Listeria monocytogenes evades killing by autophagy during colonization of host cells.
abstract: Listeria monocytogenes is an intracellular pathogen that is able to colonize the cytosol of macrophages. Here we examined the interaction of this pathogen with autophagy, a host cytosolic degradative pathway that constitutes an important component of innate immunity towards microbial invaders. L. monocytogenes infection induced activation of the autophagy system in macrophages. At 1 h post infection (p.i.), a population of intracellular bacteria ( approximately 37%) colocalized with the autophagy marker LC3. These bacteria were within vacuoles and were targeted by autophagy in an LLO-dependent manner. At later stages in infection (by 4 h p.i.), the majority of L. monocytogenes escaped into the cytosol and rapidly replicated. At these times, less than 10% of intracellular bacteria colocalized with LC3. We found that ActA expression was sufficient to prevent autophagy of bacteria in the cytosol of macrophages. Surprisingly, ActA expression was not strictly necessary, indicating that other virulence factors were involved. Accordingly, we also found a role for the bacterial phospholipases, PI-PLC and PC-PLC, in autophagy evasion, as bacteria lacking phospholipase expression were targeted by autophagy at later times in infection. Together, our results demonstrate that L. monocytogenes utilizes multiple mechanisms to avoid destruction by the autophagy system during colonization of macrophages.
authors.affiliation: Cell Biology Program, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Birmingham
authors.forename: Veronica
authors.initials: V
authors.lastname: Canadien
authors.forename: Edith
authors.initials: E
authors.lastname: Gouin
authors.forename: Erin B
authors.initials: EB
authors.lastname: Troy
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Yoshimori
authors.forename: Pascale
authors.initials: P
authors.lastname: Cossart
authors.forename: Darren E
authors.initials: DE
authors.lastname: Higgins
authors.forename: John H
authors.initials: JH
authors.lastname: Brumell
mesh_terms: D000818:Animals; D001343:Autophagy / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001427:Bacterial Toxins; D002460:Cell Line; D005798:Genes, Bacterial; D006360:Heat-Shock Proteins / Q000502:physiology; D006460:Hemolysin Proteins / Q000502:physiology; D008089:Listeria monocytogenes / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D008264:Macrophages / Q000382:microbiology* / Q000502:physiology* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D051379:Mice; D046529:Microscopy, Electron, Transmission; D008954:Models, Biological; D009154:Mutation; D010454:Peptide Termination Factors / Q000235:genetics / Q000502:physiology; D010738:Type C Phospholipases / Q000502:physiology; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; D008565:Membrane Proteins; D010454:Peptide Termination Factors; C072980:actA protein, Listeria monocytogenes; D010738:Type C Phospholipases; C105598:phosphatidylcholine-specific phospholipase C; C038705:hlyA protein, Listeria monocytogenes