Fig. 2.

Intracellular trafficking checkpoints involved in MVB transport and fusion. Of note, as the release of exosomes requires tightly regulated steps of transport, tethering and fusion of MVBs to the plasma membrane. Moreover, MVB acidification and PTMs (mainly ubiquitination) of membrane proteins of MVBs play important roles in the regulation of MVB fate. The core factors involved in MVB trafficking are shown in the figure, where the factor labelled with ^* is mainly involved in MVB-targeted lysosomal degradation