Figure 1.

Autophagosome formation and underlying signaling events. (A) Autophagy is a cellular stress response that can be induced inter alia by nutrition and growth factor deprivation. Active mTORC1 inhibits autophagosome generation, whereas active ULK- and VPS34 class III PI3K-complexes are prerequisites for autophagosome formation. The phagophore enraptures cytoplasm and matures to an autophagosome, also fusing with endosomes. Acidic hydrolases degrade the constituents in autolysosomes enabling a recycling of bio-molecules (green: stimulatory signals; pink: inhibitory signals; figure not complete). (B) Under growth conditions mTOR is active inhibiting the ULK-complex and by this autophagy. (C) Under starvation conditions mTOR is inactive and ULK active, phosphorylating itself and its binding partners and translocating to pre-autophagosomal structures.