Phosphorylation of Atg9 regulates movement to the phagophore assembly site and the rate of autophagosome formation

Abstract

Macroautophagy is primarily a degradative process that cells use to break down their own components to recycle macromolecules and provide energy under stress conditions, and defects in macroautophagy lead to a wide range of diseases. Atg9, conserved from yeast to mammals, is the only identified transmembrane protein in the yeast core macroautophagy machinery required for formation of the sequestering compartment termed the autophagosome. This protein undergoes dynamic movement between the phagophore assembly site (PAS), where the autophagosome precursor is nucleated, and peripheral sites that may provide donor membrane for expansion of the phagophore. Atg9 is a phosphoprotein that is regulated by the Atg1 kinase. We used stable isotope labeling by amino acids in cell culture (SILAC) to identify phosphorylation sites on this protein and identified an Atg1-independent phosphorylation site at serine 122. A nonphosphorylatable Atg9 mutant showed decreased autophagy activity, whereas the phosphomimetic mutant enhanced activity. Electron microscopy analysis suggests that the different levels of autophagy activity reflect differences in autophagosome formation, correlating with the delivery of Atg9 to the PAS. Finally, this phosphorylation regulates Atg9 interaction with Atg23 and Atg27.

KIF1A/UNC-104 Transports ATG-9 to Regulate Neurodevelopment and Autophagy at Synapses

“…ATG-9 is required for autophagosome biogenesis (Feng et al, 2016; He et al, 2009; Lang et al, 2000; Orsi et al, 2012; Reggiori and Tooze, 2012; Wang et al, 2013; Yamamoto et al, 2012; Young et al, 2006). In yeast, Atg9 localizes to small vesicles that nucleate to form the phagophore (Suzuki et al, 2015; Wang et al, 2013; Yamamoto et al, 2012).…”

“…ATG-9 is known for its role in autophagosome biogenesis (Feng et al, 2016; Lang et al, 2000; Noda et al, 2000; Reggiori et al, 2004; Stanley et al, 2013; Wang et al, 2013; Yamamoto et al, 2012). Through genetic and cell biological approaches, we determined that the autophagy pathway is required cell-autonomously to promote presynaptic assembly in the interneuron AIY.…”

Mechanisms of Autophagy Initiation

“…The amount of Atg9 expressed in cells appears to control the frequency of autophagosome formation (138). Phosphorylation of the N-terminal domain of Atg9 by an unknown kinase upregulates the recruitment of Atg9 to the PAS and its ability to initiate autophagy (139). Clearly, the bulk lipid contributed by such a small number of vesicles is a miniscule fraction of what is needed to generate an autophagosome.…”

Autophagic membrane delivery through ATG9

“…Previous studies have identified phosphorylation as an important posttranslational modification that controls Atg9 trafficking in yeast [8,9]. The work by Zhou et al [10] reveals a novel mechanism of mammalian ATG9 trafficking regulation in basal and induced autophagy that involves both adaptor protein sorting signals and phosphorylation.…”