New Roles of the Primary Cilium in Autophagy

Figure 2

Overview of the autophagic pathway. Autophagy can be divided into five stages: initiation, nucleation, elongation, fusion, and degradation. “Initiation” refers to the activation of the ULK1 (ATG1) complex, which can be achieved by increased activity of AMP-dependent kinase (AMPK) and/or inhibition of the mechanistic target of rapamycin complex 1 (mTORC1). The “nucleation” indicates the process of recruitment of proteins of the autophagic machinery at the autophagosome formation sites, which are required for the formation of the new autophagosome, which occurs during the “elongation” stage. Then the complete autophagosome is loaded with the material that needs to be removed from the cell and degraded. The autophagosome fuses with a lysosome, thus activating the lysosomal acidic hydrolases, which degrade the cargo sequestered in the autophagic vesicle. See the main text for additional details.