Listeria monocytogenes Co-opts Caveolin-Mediated E-cadherin Trafficking and Macropinocytosis for Epithelial Cell-to-Cell Spread

Abstract

Listeria monocytogenes is an intracellular bacterial pathogen that spreads directly between adjacent host cells without exposure to the extracellular space. Recent studies have identified several host cell factors that promote L. monocytogenes cell-to-cell spread in epithelial monolayers, but details of the mechanism remain unclear. We find that the adherens junction protein, E-cadherin, promotes L. monocytogenes cell-to-cell spread at the recipient side of cell contacts. In particular, two point mutations in E-cadherins cytoplasmic domain that prevent its ubiquitination hinder bacterial cell-to-cell spread efficiency without reducing the extent of contact between neighboring cells. As ubiquitination induces E-cadherin endocytosis, we hypothesize that E-cadherin promotes protrusion engulfment, where donor cell protrusions containing L. monocytogenes are taken up by the recipient cell concurrently with E-cadherin internalization. In support of this hypothesis, we show that inhibiting caveolin-mediated membrane trafficking reduces L. monocytogenes cell-to-cell spread only under conditions where E-cadherin can be ubiquitinated. Additionally, we demonstrate that macropinocytosis also contributes to dissemination of L. monocytogenes through an epithelial monolayer.