A cell with a torn or perforated membrane has to close the breach fast. To heal wounds inflicted by bacteria, cells rely on endocytosis, Idone et al. show.
An injury or even a workout at the gym can tear the plasma membranes of our cells. Earlier work showed that a wounded cell makes repairs through exocytosis, extruding lysosomes whose membranes help close the rip. But this mechanism alone can't explain how cells heal all injuries. Some bacterial toxins and defensive proteins such as the complement system embed themselves in the membrane, forming a pore that can't be closed by exocytosis. Idone et al. wanted to nail down how cells mend these types of perforations.
The team exposed cells to Streptococcus toxin that bores into the plasma membrane. Repairs were quick—the membranes resealed in less than 30 seconds. Cells wouldn't have time to disassemble the pores in that time, ruling out one possible mechanism. The team also discounted the possibility that injury-induced blebs on the cell membrane somehow dislodge the pores—cells still healed when the team blocked blebbing.
A third possibility is that cells use endocytosis to remove the pores from the membrane. To test the idea, Idone et al. followed labeled pores that were stuck in the membrane. Within a few seconds, endosomes carrying tagged toxin began showing up inside the cells. The results indicate that injury stimulates the formation of endosomes that engulf pores that have penetrated the membrane. The team also discovered that cells use the same method to excise membrane abrasions.