Macropinosomes are Key Players in Early Shigella Invasion and Vacuolar Escape in Epithelial Cells

PLoS Pathog. 2016 May 16;12(5):e1005602. doi: 10.1371/journal.ppat.1005602. eCollection 2016 May.

Abstract

Intracellular pathogens include all viruses, many bacteria and parasites capable of invading and surviving within host cells. Key to survival is the subversion of host cell pathways by the pathogen for the purpose of propagation and evading the immune system. The intracellular bacterium Shigella flexneri, the causative agent of bacillary dysentery, invades host cells in a vacuole that is subsequently ruptured to allow growth of the pathogen within the host cytoplasm. S. flexneri invasion has been classically described as a macropinocytosis-like process, however the underlying details and the role of macropinosomes in the intracellular bacterial lifestyle have remained elusive. We applied dynamic imaging and advanced large volume correlative light electron microscopy (CLEM) to study the highly transient events of S. flexneri's early invasion into host epithelial cells and elucidate some of its fundamental features. First, we demonstrate a clear distinction between two compartments formed during the first step of invasion: the bacterial containing vacuole and surrounding macropinosomes, often considered identical. Next, we report a functional link between macropinosomes and the process of vacuolar rupture, demonstrating that rupture timing is dependent on the availability of macropinosomes as well as the activity of the small GTPase Rab11 recruited directly to macropinosomes. We go on to reveal that the bacterial containing vacuole and macropinosomes come into direct contact at the onset of vacuolar rupture. Finally, we demonstrate that S. flexneri does not subvert pre-existing host endocytic vesicles during the invasion steps leading to vacuolar rupture, and propose that macropinosomes are the major compartment involved in these events. These results provide the basis for a new model of the early steps of S. flexneri epithelial cell invasion, establishing a different view of the enigmatic process of cytoplasmic access by invasive bacterial pathogens.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Dysentery, Bacillary / microbiology*
  • Endosomes / microbiology*
  • Endosomes / ultrastructure
  • Epithelial Cells / microbiology*
  • Epithelial Cells / ultrastructure
  • Host-Pathogen Interactions / physiology
  • Humans
  • Image Processing, Computer-Assisted
  • Microscopy / methods
  • Pinocytosis / physiology
  • Shigella flexneri / pathogenicity*
  • Vacuoles / ultrastructure*

Grants and funding

This work was supported by the Institut Pasteur (PTR 460); by fellowships from the Pasteur-Weizmann Council, EMBO and the Fondation pour la Recherche Médicale (FRM) to AW; by a fellowship from the FRM to NM; by a L’Oreal fellowship to YC; by an EMBO short term fellowship to NM; by a grant from the Region Ile de France to JE (DIM-Malinf); JE is member of the LabEx consortium IBEID, and is supported by the Institut Pasteur CARNOT-MIE programme. JE also acknowledges support of an ERC starting grant (Rupteffects, Nr. 261166). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.