Patch repair protects cells from the small pore-forming toxin aerolysin

Abstract

Small pore-forming toxins in the aerolysin family lyse cells by damaging the membrane, but membrane repair responses used to resist them, if any, remain controversial. Four membrane repair mechanisms have been proposed: toxin removal by caveolar endocytosis, clogging by annexins, microvesicle shedding catalyzed by MEK, and patch repair. Which of these repair mechanisms aerolysin triggers is unknown. Furthermore, Ca2+ flux triggered by aerolysin is controversial, yet membrane repair responses require Ca2+. Here, we determined Ca2+ influx and repair mechanisms activated by aerolysin. In contrast to cholesterol-dependent cytolysins (CDCs), removal of extracellular Ca2+ protected cells from aerolysin. Aerolysin triggered sustained Ca2+ influx. Since aerolysin triggered Ca2+ flux, we investigated Ca2+-dependent repair pathways. Caveolar endocytosis failed to protect cells from aerolysin or CDCs. MEK-dependent repair did not protect against aerolysin. Aerolysin triggered slower annexin A6 membrane recruitment compared to CDCs. In contrast to CDCs, expression of the patch repair protein dysferlin potently protected cells from aerolysin. We propose that aerolysin triggers a Ca2+-dependent death mechanism that obscures repair responses, and the primary repair mechanism used to resist aerolysin is patch repair. We conclude that different classes of bacterial toxins trigger distinct repair mechanisms.