1) (4–6) Autophagy has an intracellular anti-viral function, the

1) (4–6). Autophagy has an intracellular anti-viral function, the targeting of viral components or virions to degrade them via the lysosomes during viral infection; it also plays a role in the initiation of innate and adaptive immune system responses to viral infections (7–12). Some viruses encode virulence factors that interact with the host autophagy machinery and block autophagy. In contrast, other viruses utilize some autophagy components to facilitate their intracellular growth or cellular budding. Taking advantage of yeast genetics, autophagy-defective

HKI-272 purchase (atg/apg/aut) mutants of Saccharomyces cerevisiae were isolated in 1993 (the nomenclature of autophagy related genes has been unified to ATG) (13, 14). The ATG (A uT ophaG y-related) genes were later isolated and characterized (Table 1) (5, 13, 15). Most ATG genes

contribute to autophagosome formation, many being well conserved from yeast to mammals. Although the molecular mechanisms and cellular functions of mammalian autophagy were being ITF2357 datasheet elucidated within a decade, our molecular understanding of autophagy is still far from complete. In this review, we describe the molecular mechanism of action of mammalian Atg proteins and their cellular functions in autophagy. In mammals, the “core” Atg proteins are divided into five subgroups: the ULK1 protein kinase complex (16), Vps34-beclin1 class III PI3-kinase complex (17), Atg9-WIPI-1 complex (18–20), Atg12 conjugation system (21, 22), and LC3 conjugation system (23, 24). Autophagy is impaired without any of these “core” Atg gene products, indicating that a sequential reaction of many protein complexes, including kinases, phosphatases, lipids, and ATP-dependent conjugation, are indispensable for the whole process of autophagy. Upstream of the autophagy machinery, Aspartate class I PI3-kinase and mTor kinase contribute to the induction of autophagy (25). The Vps34-beclin1 class

III PI3-kinase complex is divided into at least three types, the Atg14-Vps34-Vps15-beclin1, UVRAG-Vps34-Vps15-beclin1, and Rubicon-UVRAG-Vps34-Vps15-beclin1 complexes (26–29). Each complex contributes to a different function during autophagy. The Atg9-WIPI-1 complex is composed of an Atg9 membrane-protein and WIPI-1 (18, 30). Two ubiquitylation-like reactions, the Atg12 and LC3 conjugation systems, are essential for the initiation and formation of autophagosomes (Fig. 1, Initiation, elongation, and maturation). The ULK1 protein kinase complex is composed of ULK1 (a protein kinase), Atg13, FIP200, and Atg101 (Fig. 1, Initiation) (16, 31–35). The mTOR kinase directly phosphorylates Atg13 to negatively regulate autophagy (33). Atg101 is important for the stability and basal phosphorylation of Atg13 and ULK1 (34, 35).

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