ATG4B (Autophagin-1) Phosphorylation Modulates Autophagy

• Published in: The Journal of biological chemistry 2015-10, Vol.290 (44), p.26549-26561
• Main Authors: Yang, Zhifen, Wilkie-Grantham, Rachel P., Yanagi, Teruki, Shu, Chih-Wen, Matsuzawa, Shu-ichi, Reed, John C.
• Format: Article
• Language: English
• Subjects: Animals; autophagy; Autophagy - physiology; Autophagy-Related Proteins; Cells, Cultured; Cysteine Endopeptidases - genetics; Cysteine Endopeptidases - metabolism; Enzymology; Lipoylation - physiology; Mice, Knockout; Microtubule-Associated Proteins - genetics; Microtubule-Associated Proteins - metabolism; phosphorylation; Phosphorylation - physiology; protease; protein kinase; protein-protein interaction; Proteolysis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.658088

Autophagy is a catabolic cellular mechanism for entrapping cellular macromolecules and organelles in intracellular vesicles and degrading their contents by fusion with lysosomes. Important roles for autophagy have been elucidated for cell survival during nutrient insufficiency, eradication of intracellular pathogens, and counteracting aging through clearance of senescent proteins and mitochondria. Autophagic vesicles become decorated with LC3, a protein that mediates their fusion with lysosomes. LC3 is a substrate of the cysteine protease ATG4B (Autophagin-1), where cleavage generates a C-terminal glycine required for LC3 conjugation to lipids in autophagosomes. ATG4B both cleaves pro-LC3 and also hydrolyzes lipids from cleaved LC3. We show here that phosphorylation of ATG4B at Ser-383 and Ser-392 increases its hydrolyase activity as measured using LC3 as a substrate. Reconstituting atg4b−/− cells with phosphorylation-deficient ATG4B showed a role of ATG4B phosphorylation in LC3 delipidation and autophagic flux, thus demonstrating that the cellular activity of ATG4B is modulated by phosphorylation. Proteolytic conversion of pro-LC3 to LC3-I was not significantly impacted by ATG4B phosphorylation in cells. Phosphorylation-deficient ATG4B also showed reduced interactions with the lipid-conjugated LC3 but not unconjugated LC3. Taken together, these findings demonstrate a role for Ser-383 and Ser-392 phosphorylation of ATG4B in control of autophagy. Background: ATG4B mediates the cleavage of pro-LC3 and removes lipid conjugates from LC3 during autophagy. Results: We determined that defects in phosphorylation of ATG4B reduced its hydrolyase activity and impaired autophagic flux. Conclusion: Phosphorylation of ATG4B plays an important role in modulating its hydrolyase activity. Significance: This is the first report showing a role for phosphorylation of an ATG4-family protease in control of autophagy.