Schematic overview of the autophagy process.

Initially, a precursor form of the autophagosome, a phagophore is formed by various sources including ER, Golgi, mitochondria, endosomes, and plasma membrane. This cup-shaped and double membrane structure extends its edges to form an autophagosome. Closed autophagosomes containing engulfed cytoplasmic proteins or organelles migrate toward the perinuclear part of the cells where lysosomes are clustered to enable autophagosome-lysosome fusion. Alternatively, autophagosomes can generate amphisomes by fusion with endosomes. Ultimately, autophagosomes or amphisomes fuse with lysosomes where their contents are degraded.