A role for ActA in epithelial cell invasion by Listeria monocytogenes

Monica Suarez, Bruno González Zörn, Yolanda Vega, Isabel Chico-Calero, Jose A Vazquez-Boland

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We assessed the role of the actin-polymerizing protein, ActA, in host cell invasion by Listeria monocytogenes. An in frame DeltaactA mutant was constructed in a hyperinvasive strain of prfA* genotype, in which all genes of the PrfA-dependent virulence regulon, including actA, are highly expressed in vitro. Loss of ActA production in prfA* bacteria reduced entry into Caco-2, HeLa, MDCK and Vero epithelial cells to basal levels. Reintroduction of actA into the DeltaactA prfA* mutant fully restored invasiveness, demonstrating that ActA is involved in epithelial cell invasion. ActA did not contribute to internalization by COS-1 fibroblasts and Hepa 1-6 hepatocytes. Expression of actA in Listeria innocua was sufficient to promote entry of this non-invasive species into epithelial cell lines, but not into COS-1 and Hepa 1-6 cells, indicating that ActA directs an internalization pathway specific for epithelial cells. Scanning electron microscopy of infected Caco-2 human enterocytes suggested that this pathway involves microvilli. prfA* bacteria, but not wild-type bacteria (which express PrfA-dependent genes very weakly in vitro) or prfA* DeltaactA bacteria, efficiently invaded differentiated Caco-2 cells via their apical surface. Microvilli played an active role in the phagocytosis of the prfA* strain, and actA was required for their remodelling into pseudopods mediating bacterial uptake. Thus, ActA appears to be a multifunctional virulence factor involved in two important aspects of Listeria pathogenesis: actin-based motility and host cell tropism and invasion.
Original languageEnglish
Pages (from-to)853-64
Number of pages12
JournalCellular Microbiology
Issue number12
Publication statusPublished - Dec 2001


  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins/genetics
  • Bacterial Proteins/metabolism
  • Bacterial Proteins/physiology
  • Base Sequence
  • COS Cells
  • Caco-2 Cells
  • Cell Line
  • Cercopithecus aethiops
  • DNA, Bacterial
  • Dogs
  • Epithelial Cells/cytology
  • Epithelial Cells/metabolism
  • Epithelial Cells/microbiology
  • Gene Expression
  • HeLa Cells
  • Humans
  • Listeria monocytogenes/isolation & purification
  • Listeria monocytogenes/metabolism
  • Listeria monocytogenes/physiology
  • Listeria monocytogenes/ultrastructure
  • Membrane Proteins/genetics
  • Membrane Proteins/metabolism
  • Membrane Proteins/physiology
  • Microscopy, Electron, Scanning/methods
  • Molecular Sequence Data
  • Mutagenesis
  • Peptide Termination Factors
  • Trans-Activators
  • Vero Cells


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