Flotillin-1 is Hijacked by Listeria monocytogenes to Drive Cell-to-Cell Spreading

Listeria monocytogenes spreads intercellularly by creating actin-rich projections that are endocytosed into recipient cells. Caveolin-mediated endocytosis has been implicated in this process, accounting for ∼70% in cell-to-cell spread in cells depleted of caveolin-1. Thus, additional mechanisms may contribute for the remaining spread and we examined the role of flotillin-based endocytosis. We found flotillin-1 localized to L. monocytogenes invaginations in recipient cells and depletion of flotillin-1 significantly impaired bacterial transfer. Similarly, preventing endogenous flotillin-1 from membrane association significantly reduced bacterial spread. To evaluate whether an interplay between flotillin-1 and caveolin-1-mediated endocytosis were functioning at L. monocytogenes invagination sites, we measured the area of spread in cells knocked-down for both caveolin-1 and flotillin-1 and found a further significant decrease in spread and many cells with complete blockage. This work demonstrates that flotillin-based endocytosis is crucial for cell-to-cell spreading of L. monocytogenes and that this endocytic strategy can internalize large-sized membrane protrusions.