Connecting the dots: combined control of endocytic recycling and degradation

Abstract

Endocytosis is an essential process where proteins and lipids are internalised from the plasma membrane in membrane-bound carriers, such as clathrin-coated vesicles. Once internalised into the cell these vesicles fuse with the endocytic network where their contents are sorted towards degradation in the lysosome or recycling to their origin. Initially, it was thought that cargo recycling is a passive process, but in recent years the identification and characterisation of specialised recycling complexes has established a hitherto unthought-of level of complexity that actively opposes degradation. This review will summarise recent developments regarding the composition and regulation of the recycling machineries and their relationship with the degradative pathways of the endosome.

Keywords: endosomal sorting; endosome; microfilaments; ubiquitin signalling.

Figure 1.. Organelles involved in endosomal trafficking.

Schematic diagram of the organelles and carriers known to be involved in endocytic trafficking. Internalised cargo from the plasma membrane reaches the sorting endosome stage from which it can be transported to one of three destinations.

Figure 2.. Members of the endosomal recycling machinery.

Schematic representation of the protein complexes known to be involved in cargo recycling from the endosome. The spatial distribution of these complexes on the endosome is only partially known and this schematic does not reflect their sequence on endosome.