A pore-forming toxin initiates ABI1 complex switching to promote bacterial cell-to-cell spread

Listeria monocytogenes (Lm), a prototypical intracellular bacterial pathogen, expresses ActA to initiate ARP2/3-mediated actin-based motility in the cytosol of host cells. Motile bacteria generate Lm-containing protrusions at the cell surface, facilitating direct cell-to-cell spread and dissemination within the host. Protrusion formation is an active, spatially regulated process, yet how Lm coordinates bacterial and host factors to orchestrate this process remains unclear. Here, we identify Abelson-interactor 1 (ABI1) as a host factor required for efficient Lm protrusion formation and cell-to-cell spread. Conditional knockout of Abi1 in mice significantly reduces susceptibility to Lm infection, while deletion of actA abrogates the protective effect of Abi1 knockout. During Lm infection, ABI1 is uncoupled from spectrin at the cell cortex and binds to EPS8 within protrusions. This ABI1 "complex switching" is initiated by the pore-forming toxin LLO, which perforates the host plasma membrane and triggers Ca²⁺ influx, leading to calpain-mediated cleavage of the spectrin cytoskeleton. Spectrin cleavage mobilizes ABI1, allowing ABI1 to bind EPS8 and activate EPS8's actin capping activity to facilitate local actin recycling necessary for efficient protrusion elongation and cell-to-cell spread. These findings reveal an unrecognized host-pathogen interaction, in which a bacterial pore-forming toxin induces spatially confined cytoskeletal remodeling to promote cell-to-cell spread.