Autophagy inSaccharomyces cerevisiaerequires the monomeric GTP-binding proteins, Arl1 and Ypt6

Abstract

Macroautophagy/autophagy is a cellular degradation process that sequesters organelles or proteins into a double-membrane structure called the phagophore; this transient compartment matures into an autophagosome, which then fuses with the lysosome or vacuole to allow hydrolysis of the cargo. Factors that control membrane traffic are also essential for each step of autophagy. Here we demonstrate that 2 monomeric GTP-binding proteins in Saccharomyces cerevisiae, Arl1 and Ypt6, which belong to the Arf/Arl/Sar protein family and the Rab family, respectively, and control endosome-trans-Golgi traffic, are also necessary for starvation-induced autophagy under high temperature stress. Using established autophagy-specific assays we found that cells lacking either ARL1 or YPT6, which exhibit synthetic lethality with one another, were unable to undergo autophagy at an elevated temperature, although autophagy proceeds normally at normal growth temperature; specifically, strains lacking one or the other of these genes are unable to construct the autophagosome because these 2 proteins are required for proper traffic of Atg9 to the phagophore assembly site (PAS) at the restrictive temperature. Using degron technology to construct an inducible arl1Δ ypt6Δ double mutant, we demonstrated that cells lacking both genes show defects in starvation-inducted autophagy at the permissive temperature. We also found Arl1 and Ypt6 participate in autophagy by targeting the Golgi-associated retrograde protein (GARP) complex to the PAS to regulate the anterograde trafficking of Atg9. Our data show that these 2 membrane traffic regulators have novel roles in autophagy.

The Arl3 and Arl1 GTPases co‐operate with Cog8 to regulate selective autophagy via Atg9 trafficking

“…Together, these results further support the notion that Arl1 activation at the Golgi exerts distinct biological activities, which may be involved in regulating the Cvt pathway. Although it has been shown that the Cvt pathway may be affected by dysfunction of Arl1 at non‐permissive temperature, in our study, arl1 Δ cells only exhibited a minor defect in Ape1 processing. Interestingly, this defect was strengthened by Cog8 malfunction.…”

Yeast dynamin and Ypt6 function in parallel for the endosome‐to‐Golgi retrieval of Snc1

“…Similarly, in ypt6 Δ cells, Snc1 traffic toward the Golgi was negatively affected ( Siniossoglou et al, ; Liu et al, ). It is clear that Ypt6 functions as a GTPase to facilitate endosome‐to‐Golgi retrograde transport as well as autophagy (Siniossoglou et al, ; Luo and Gallwitz, ; Yang and Rosenwald, ). Codeletion of VPS1 and YPT6 genes led to synthetic lethality (Figure ), suggesting the possibility of a functional link between Vps1 and Ypt6.…”

Multiple activities of Arl1 GTPase in the trans-Golgi network

“…In addition to acting as a transport regulator between endosomes and the Golgi, yeast Arl1 − together with the Rab GTPase Ypt6 − is required for starvation-induced autophagy under high-temperature stress (Yang and Rosenwald, 2016). Interestingly, a novel role of Arl1 in regulation of fungal morphogenesis and virulence has recently been revealed in a Candida-albicans-infected oropharyngeal candidiasis mouse model (Labbaoui et al, 2017).…”

“…In mammalian cells, these functions affect a wide range of fundamental cellular processes, including cell polarity (Lock et al, 2005), innate immunity (Bremond et al, 2009;Lieu et al, 2008;Murray and Stow, 2014;Stanley et al, 2012), lipid droplet and chylomicron formation (Hesse et al, 2013;Jaschke et al, 2012), as well as the secretion of insulin (Gehart et al, 2012), chromogranin A (CruzGarcia et al, 2013) and matrix metalloproteinases (MMPs) (Eiseler et al, 2016). In yeast, Arl1 and its effectors are also involved in numerous functions, such as maintenance of cell wall integrity (Liu et al, 2006), ion homeostasis (Marešová and Sychrová, 2010;Munson et al, 2004;Rosenwald et al, 2002), tolerance to stress factors (Jaime et al, 2012;Marešova et al, 2012;Yang and Rosenwald, 2016), regulation of cell proliferation (Benjamin et al, 2011), the unfolded protein response (UPR) (Hsu et al, 2016) and also in the ability of yeast to cause disease (Labbaoui et al, 2017). In addition, these factors regulate the quality control of the endoplasmic reticulum (ER) (Lee et al, 2011), tissue development (Eisman et al, 2006;Torres et al, 2014) and neuronal growth in Drosophila (Chang et al, 2015), and control cell viability in parasites (Price et al, 2005).…”

“…Genetic alterations of Arl1 as well as its effectors were used to characterize developmental and physiological phenotypes (summarized in Fig. 1) (Chang et al, 2015;Cruz-Garcia et al, 2013;Eiseler et al, 2016;Gehart et al, 2012;Hesse et al, 2013;Hsu et al, 2016;Labbaoui et al, 2017;Lieu et al, 2008;Liu et al, 2006;Lock et al, 2005;Marešová and Sychrová, 2010;Marešová et al, 2012;Murray and Stow, 2014;Price et al, 2005;Torres et al, 2014;Yang and Rosenwald, 2016). In mammalian cells, these functions affect a wide range of fundamental cellular processes, including cell polarity (Lock et al, 2005), innate immunity (Bremond et al, 2009;Lieu et al, 2008;Murray and Stow, 2014;Stanley et al, 2012), lipid droplet and chylomicron formation (Hesse et al, 2013;Jaschke et al, 2012), as well as the secretion of insulin (Gehart et al, 2012), chromogranin A (CruzGarcia et al, 2013) and matrix metalloproteinases (MMPs) (Eiseler et al, 2016).…”