Fig. 1

Exosome biogenesis and secretion within endosomal system. Early endosomes (EEs) are formed by the fusion of endocytic vesicles. Two pathways shown by the EEs: returning to the plasma membrane or conversion into LEs/ MVBs via inward budding of the membrane which pack the cargoes into ILVs. Protein sorting of ILVs can be ESCRT dependent or independent. ESCRT-0, ESCRT-I, ESCRT-II and ESCRT-III are four components of ESCRT machinery which ubiquitinate the substrates on the part of the inward budding endosomal membrane. Later, targeted ILVs are ready to be degraded within lysosome or rescue by DUBs. Rab27A and Rab27B are the essential mediators to lead the MVBs toward the cell periphery. Finally, SNARE complex helps fusion of MVBs with plasma membrane to release ILVs into the extracellular space which now are called exosomes