WIPI β-propellers at the crossroads of autophagosome and lipid droplet dynamics

Macroautophagy (autophagy hereafter) is an evolutionarily highly conserved catabolic process activated by eukaryotes in order to counteract cellular starvation. Autophagy leads to bulk degradation of cytoplasmic content in the lysosomal compartment, thereby clearing the cytoplasm and generating nutrients and energy. Upon autophagy initiation, cytoplasmic material becomes sequestered in newly formed double-membrane vesicles termed 'autophagosomes' that subsequently acquire acidic hydrolases for content destruction. The de novo biogenesis of autophagosomes often occurs at the endoplasmic reticulum (ER) and, in many cases, in close proximity to lipid droplets (LDs), intracellular neutral lipid storage reservoirs. LDs are targets of autophagic destruction, but have recently also been shown to contribute to autophagosome formation. In fact, some autophagy-related (Atg) proteins, such as microtubule-associated protein light chain 3 (LC3), Atg2 and Atg14L, functionally contribute to both LD and autophagosome biogenesis. In the present paper, we discuss Atg proteins, including members of the human WD-repeat protein interacting with phosphoinositides (WIPI) family that co-localize prominently with LC3, Atg2 and Atg14L to conceivably integrate LD and autophagosome dynamics.