Retrofusion of intralumenal MVB membranes parallels viral infection and coexists with exosome release
Priscillia Perrin, Lennert Janssen, Hans Janssen, Bram van den Broek, Lennard M. Voortman, Daphne M. van Elsland, Ilana Berlin, Jacques Neefjes
Abstract
Given the small physical scale, retrofusion of ILVs cannot be measured with conventional techniques. To circumvent this, we designed a chemically tunable cell-based system to monitor retrofusion in real time. Using this system, we demonstrate that retrofusion occurs as part of the natural MVB lifestyle, with attributes parallel to those of viral infection. Furthermore, we find that retrofusion and exocytosis coexist in an equilibrium, implying that ILVs inert to retrofusion comprise a significant fraction of exosomes destined for secretion. MVBs thus contain three types of ILVs: those committed to lysosomal degradation, those retrofusing ILVs, and those subject to secretion in the form of exosomes. VIDEO ABSTRACT.