Figure 1.

The steps of autophagosome formation. Macroautophagy begins with the formation of a cup-shaped structure called a phagophore as a consequence of the activity of the ULK1/2 complex. In the sequence, the ATG5-ATG12-ATG16L1 complex, Class III PtdIns3K, ATG9, and LC3 assist in the formation of the autophagosome. Autophagosomes completely wrap their cargo and fuse with endosomes (forming an amphisome, which will later fuse with lysosomes) or directly with lysosomes, forming an autolysosome. Upon fusion, the cargo is degraded by lysosomal hydrolases and exported back to the cytosol to be used by the cell.