Autophagy Regulation: Mechanisms and Key Players

Autophagy, a process of self-digestion, is regulated by various physiological and environmental factors. Starvation, for instance, induces autophagy by inhibiting the mTORC1 complex, while growth factors activate the PI3K-AKT-mTOR pathways to regulate autophagy. The inhibition of mTORC1 leads to the activation of a complex comprising ULK1, ATG13, ATG101, and FIP200, which initiates autophagy. Another complex, the Atg1 kinase complex, which contains Atg1, Atg13, Atg17, Atg29, and Atg31, also participates in autophagy initiation. The Class III phosphatidylinositol complex, comprising Atg6, Atg14, Vps15, Vps34, and Beclin 1, plays a crucial role in promoting autophagosomal membrane nucleation. The Atg8 conjugation system is involved in the recruitment of core autophagy machinery and the docking and fusion of autolysosomes for selective degradation. The Atg12 conjugation system, which contains Atg5, Atg12, and Atg16, and the LC3-ATG8 conjugation system are involved in autophagosomal elongation. The conversion of LC3-I to LC3-II indicates autophagosome formation. Although the function of Atg9 is not yet clear, recent research has shown that Atg9 can recruit the PI(3)P-binding Atg2-Atg18 complex and the E3-like Atg12 conjugation system, which promote Atg8 lipidation. Thus, it is speculated that Atg9 may initiate lipid transfer from compartments such as the endoplasmic reticulum for selective degradation.