ULK

The ULK (UNC51-like) enzymes are a family of mammalian kinases that have critical roles in autophagy and development. The ULK family of kinases comprises 5 genes in mammals: ULK1 through ULK4 and STK36. In mammals, ULK1 and ULK2 have been shown to be necessary for the proper autophagy induction and contribute to various developmental, physiological, and pathological processes.

The serine/threonine-protein kinases ULK1 and ULK2 are evolutionarily conserved serine/threonine kinase orthologs of the yeast autophagy related (Atg) family member Atg1, that have redundant roles in the regulation of autophagy. Autophagy targets long-lived proteins or organelles for degradation in lysosomes, and the products of this process are then recycled for other cellular pathways. The canonical ULK/Atg1 complex is composed of ULK1, ATG13, RB1CC1/FIP200/ATG17, and ATG101. It initiates autophagosome formation, at least in part by phosphorylating components of the autophagy-inducing class III phosphatidylinositol 3-kinase complex (e.g., PI3K3C/Vps34, PIK3R4/Vps15, BECN1/Vps30/ATG6, ATG14). ULK/Atg1 also promotes membrane recycling via ATG9. Consistent with the established role of ULK1/2 in autophagy, disrupting ULK1 expression in mice results in a defect in autophagy-mediated clearance of mitochondria during red blood cell maturation, and mice lacking both ULK1 and ULK2 expression die shortly after birth due to a defect in glycogen metabolism, which is similar to other autophagy-defective mice.