Involved in the endosomal multivesicular bodies (MVB) pathway. MVBs contain intraluminal vesicles (ILVs) that are generated by invagination and scission from the limiting membrane of the endosome and mostly are delivered to lysosomes enabling degradation of membrane proteins, such as stimulated growth factor receptors, lysosomal enzymes and lipids. Thought to be a cofactor of VPS4A/B, which catalyzes disassembles membrane-associated ESCRT-III assemblies (By similarity). Involved in the sorting and down-regulation of EGFR. Interacts with VPS4B. Interacts with CHMP1B. Interacts with CHMP2A; the interaction probably involves the open conformation of (polymerized) CHMP2A. Interacts with CHMP3. Interacts with CHMP5; the interaction involves soluble CHMP5. Interacts with IST1 (By similarity). Widely expressed. Expressed in brain, liver, kidney, spleen, lung and heart (at protein level). Belongs to the VTA1 family.