Multifunctional protein involved in endocytosis, multivesicular body biogenesis, membrane repair, cytokinesis, apoptosis and maintenance of tight junction integrity. Class E VPS protein involved in concentration and sorting of cargo proteins of the multivesicular body (MVB) for incorporation into intralumenal vesicles (ILVs) that are generated by invagination and scission from the limiting membrane of the endosome. Binds to the phospholipid lysobisphosphatidic acid (LBPA) which is abundant in MVBs internal membranes. The MVB pathway requires the sequential function of ESCRT-O, -I,-II and -III complexes (PubMed:14739459). The ESCRT machinery also functions in topologically equivalent membrane fission events, such as the terminal stages of cytokinesis (PubMed:17853893, PubMed:17556548). Adapter for a subset of ESCRT-III proteins, such as CHMP4, to function at distinct membranes. Required for completion of cytokinesis (PubMed:17853893, PubMed:17556548, PubMed:18641129). May play a role in the regulation of both apoptosis and cell proliferation. Regulates exosome biogenesis in concert with SDC1/4 and SDCBP (PubMed:22660413). By interacting with F-actin, PARD3 and TJP1 secures the proper assembly and positioning of actomyosin-tight junction complex at the apical sides of adjacent epithelial cells that defines a spatial membrane domain essential for the maintenance of epithelial cell polarity and barrier (By similarity). (Microbial infection) Involved in HIV-1 virus budding. Can replace TSG101 it its role of supporting HIV-1 release; this function requires the interaction with CHMP4B. The ESCRT machinery also functions in topologically equivalent membrane fission events, such as enveloped virus budding (HIV-1 and other lentiviruses). Self-associates (PubMed:14505570, PubMed:14519844). Interacts with SH3KBP1/CIN85 (By similarity). Interacts with PDCD6 in a calcium -dependent manner (PubMed:16957052, PubMed:18256029, PubMed:18940611). Interacts with TSG101 in a calcium-dependent manner; PDCD6IP homooligomerization may be required for TSG101-binding (PubMed:14505570, PubMed:14519844, PubMed:18641129, PubMed:19520058, PubMed:17350572). Interacts with SGSM3 (PubMed:15849434). Directly interacts with CHMP4A, CHMP4B and CHMP4C (PubMed:12860994, PubMed:14505569, PubMed:14505570, PubMed:14519844, PubMed:14678797, PubMed:14583093, PubMed:17428861, PubMed:17350572, PubMed:18511562). Directly interacts with CEP55 in a 1:2 stoechiometry (PubMed:17853893, PubMed:17556548, PubMed:18641129, PubMed:18948538). The interaction with CEP55 is required for PDCD6IP targeting to the midbody (PubMed:18641129). May interact with PDGFRB (PubMed:20494825). Interacts with SH3GL1 and SH3GL2/endophilin-1 (PubMed:17350572). Forms a complex with SDCBP and SDC2 (PubMed:22660413). Found in a complex with F-actin, TJP1/ZO-1 and PARD3 (By similarity). Interacts with CD2AP (PubMed:17853893). Interacts with ARRDC1 (PubMed:21191027). (Microbial infection) Interacts with HIV-1 p6 (PubMed:14505569, PubMed:17350572, PubMed:17277784, PubMed:18066081). Interacts with HIV-1 p9 (PubMed:18066081). (Microbial infection) Interacts with EIAV p9. (Microbial infection) Interacts with Murine leukemia virus Gag polyprotein (via LYPX(n)L motif). (Microbial infection) Interacts with ebola virus protein VP40 (via YPx(n)L/I motif). Identified by mass spectrometry in melanosome fractions from stage I to stage IV. Colocalized with CEP55 at centrosomes of non-dividing cells. Component of the actomyosin-tight junction complex (By similarity). PDCD6IP targeting to the midbody requires the interaction with CEP55 (PubMed:18641129). May be phosphorylated on tyrosine residues by activated PDGFRB. Truncated N-terminus.