Mechanism of Ca²⁺-triggered ESCRT assembly and regulation of cell membrane repair.

In muscle and other mechanically active tissue, cell membranes are constantly injured, and their repair depends on the injury-induced increase in cytosolic calcium. Here, we show that injury-triggered Ca(2+) increase results in assembly of ESCRT III and accessory proteins at the site of repair. This process is initiated by the calcium-binding protein-apoptosis-linked gene (ALG)-2. ALG-2 facilitates accumulation of ALG-2-interacting protein X (ALIX), ESCRT III and Vps4 complex at the injured cell membrane, which in turn results in cleavage and shedding of the damaged part of the cell membrane. Lack of ALG-2, ALIX or Vps4B each prevents shedding, and repair of the injured cell membrane. These results demonstrate Ca(2+)-dependent accumulation of ESCRT III-Vps4 complex following large focal injury to the cell membrane and identify the role of ALG-2 as the initiator of sequential ESCRT III-Vps4 complex assembly that facilitates scission and repair of the injured cell membrane.