The role of membrane-trafficking small GTPases in the regulation of autophagy.

Macroautophagy is a bulk degradation process characterised by the formation of double-membrane vesicles, called autophagosomes, which deliver cytoplasmic substrates for degradation in the lysosome. It has become increasingly clear that autophagy intersects with multiple steps of the endocytic and exocytic pathways, sharing many molecular players. A number of Rab and Arf GTPases that are involved in the regulation of the secretory and the endocytic membrane trafficking pathways, have been shown to play key roles in autophagy, adding a new level of complexity to its regulation. Studying the regulation of autophagy by small GTPases that are known to be involved in membrane trafficking is becoming a scientific hotspot and may provide answers to various crucial questions currently debated in the autophagy field, such as the origins of the autophagosomal membrane. Thus, this Commentary highlights the recent advances on the regulation of autophagy by membrane-trafficking small GTPases (Rab, Arf and RalB GTPases) and discusses their putative roles in the regulation of autophagosome formation, autophagosome-dependent exocytosis and autophagosome-lysosome fusion.