Shigella Targets Epithelial Tricellular Junctions and Uses a Noncanonical Clathrin-Dependent Endocytic Pathway to Spread Between Cells

SummaryBacteria move between cells in the epithelium using a sequential pseudopodium-mediated process but the underlying mechanisms remain unclear. We show that during cell-to-cell movement, Shigella-containing pseudopodia target epithelial tricellular junctions, the contact point where three epithelial cells meet. The bacteria-containing pseudopodia were engulfed by neighboring cells only in the presence of tricellulin, a protein essential for tricellular junction integrity. Shigella cell-to-cell spread, but not pseudopodium protrusion, also depended on phosphoinositide 3-kinase, clathrin, Epsin-1, and Dynamin-2, which localized beneath the plasma membrane of the engulfing cell. Depleting tricellulin, Epsin-1, clathrin, or Dynamin-2 expression reduced Shigella cell-to-cell spread, whereas AP-2, Dab2, and Eps15 were not critical for this process. Our findings highlight a mechanism for Shigella dissemination into neighboring cells via targeting of tricellular junctions and a noncanonical clathrin-dependent endocytic pathway.

Graphical AbstractFigure optionsDownload high-quality image (173 K)Download as PowerPoint slideHighlights
► Shigella targets tricellular junctions for epithelial cell-to-cell spread
► Tricellular junction protein tricellulin is essential for Shigella cell-cell spread
► Clathrin, Epsin-1, and Dynamin-2 mediate pseudopodia engulfment by adjacent cells
► Shigella cell-to-cell spread occurs via noncanonical clathrin-mediated endocytosis