Fig. 1.

Overview of the autophagy process. In response to cellular stimuli such as starvation and immune signals, the class I PI(3)K (phosphoinositide 3-kinases)-induced Atg1 complex and a class III PI(3)K complex involving Beclin-1 activate downstream ATG proteins in a series of steps that guide the induction, elongation, maturation, and degradation of the autophagosome. Two ubiquitin-like conjugation systems involving Atg12 (a) and LC3 (b) direct the vesicle elongation of the isolation membrane, which forms a crescent shape to sequester the cytoplasmic cargo. Upon completion, the autophagosome then undergoes the maturation step through a series of remodeling processes including fusion with endosomes/lysosomes. Fusion with lysosome helps the autophagosome mature into an autolysosome in which the autophagic vacuole along with its content is degraded.