Figure 2.

The classical process of autophagy. (1) Initiation/nucleation: autophagy induced by nutrient starvation initiates isolation membrane formation to engulf proteins and damaged organelles in the cytoplasm. This process is referred to as phagophore formation. (2) Elongation and maturation: the phagophore gradually elongates into a mature, closed autophagosome. (3) Fusion and degradation: the autophagosome fuses with a lysosome to form an autolysosome, and then cargoes are degraded by lysosomal enzymes such as proteases and lipases.