Regulation of Vps4 during MVB sorting and cytokinesis.

Multivesicular body (MVB) formation is the result of invagination and budding of the endosomal limiting membrane into its intralumenal space. These intralumenal vesicles (ILVs) contain a subset of endosomal transmembrane cargoes destined for degradation within the lysosome, the result of active selection during MVB sorting. Membrane bending and scission during ILV formation is topologically similar to cytokinesis in that both events require the abscission of a membrane neck that is oriented away from the cytoplasm. The endosomal sorting complexes required for transport (ESCRTs) represent cellular machinery whose function makes essential contributions to both of these processes. In particular, the AAA-ATPase Vps4 and its substrate ESCRT-III are key components that seem to execute the membrane abscission reaction. This review summarizes current knowledge about the Vps4-ESCRT-III system and discusses a model for how the recruitment of Vps4 to the different sites of function might be regulated.