Listeria monocytogenes Co-Opts the Host Exocyst Complex To Promote Internalin A-Mediated Entry

The bacterial pathogen Listeria monocytogenes induces its internalization (entry) into intestinal epithelial cells through interaction of its surface protein, internalin A (InIA), with the human cell-cell adhesion molecule, E-cadherin. While InIA-mediated entry requires bacterial stimulation of actin polymerization, it remains unknown whether additional host processes are manipulated to promote internalization. Here, we show that interaction of InIA with E-cadherin induces the host membrane-trafficking process of polarized exocytosis, which augments uptake of Listeria. Imaging studies revealed that exocytosis is stimulated at sites of InIA-dependent internalization. Experiments inhibiting human N-ethylmaleimide-sensitive factor (NSF) demonstrated that exocytosis is needed for efficient InIA-mediated entry. Polarized exocytosis is mediated by the exocyst complex, which comprises eight proteins, including Sec6, Exo70, and Exo84. We found that Exo70 was recruited to sites of InIA-mediated entry. In addition, depletion of Exo70, Exo84, or Sec6 by RNA interference impaired entry without affecting surface levels of E-cadherin. Similar to binding of InIA to E-cadherin, homophilic interaction of E-cadherin molecules mobilized the exocyst and stimulated exocytosis. Collectively, these results demonstrate that ligation of E-cadherin induces exocytosis that promotes Listeria entry, and they raise the possibility that the exocyst might also control the normal function of E-cadherin in cell-cell adhesion.

Automated summary

The bacterial pathogen Listeria monocytogenes induces internalization by interacting with the host membrane-trafficking process of polarized exocytosis through its surface protein InIA and the human cell-cell adhesion molecule E-cadherin.