Termination of autophagy and reformation of lysosomes regulated by mTOR

Abstract

Autophagy is an evolutionarily conserved process to catabolize cytoplasmic proteins and organelles1, 2. During starvation, the target of rapamycin (TOR), a nutrient-responsive kinase, is inhibited, thereby inducing autophagy. In autophagy, double-membrane autophagosomes envelop and sequester intracellular components and then fuse with lysosomes to form autolysosomes which degrade their contents to regenerate nutrients. Current models of autophagy terminate with the degradation of autophagosome cargo in autolysosomes3-5, but the regulation of autophagy in response to nutrients and the subsequent fate of the autolysosome are poorly defined. Here we show that mTOR signaling is inhibited during autophagy initiation, but reactivated with prolonged starvation. mTOR reactivation is autophagy-dependent, and requires the degradation of autolysosomal products. Increased mTOR activity attenuates autophagy and generates proto-lysosomal tubules and vesicles that extrude from autolysosomes and ultimately mature into functional lysosomes, thereby restoring the full complement of lysosomes in the cell – a process we identify in multiple animal species. Thus, an evolutionarily-conserved cycle in autophagy governs nutrient sensing and lysosome homeostasis during starvation.

Chronic mTOR inhibition in mice with rapamycin alters T, B, myeloid, and innate lymphoid cells and gut flora and prolongs life of immune‐deficient mice

“…Rapamycin is considered primarily an mTORC1 inhibitor (Laplante & Sabatini, 2012) but can also inhibit mTORC2. Recent studies distinguish mTORC1 versus mTORC2 effects on lifespan (Selman et al ., 2009) in addition to effects on cell proliferation (Dowling et al ., 2010), metabolism (Sengupta et al ., 2010; Lamming et al ., 2012), protein translation (Thoreen et al ., 2012), immunity (Chi, 2012), and other processes (Yu et al ., 2010; Shimobayashi & Hall, 2014). …”

Association and dissociation of autophagy, apoptosis and necrosis by systematic chemical study

“…Autophagosomes are formed and destroyed continuously, establishing the autophagic flux (Mizushima et al, 2010). As a result there are two reasons why autophagosomes (that are detected as GFP-LC3 puncta) can increase in number: (i) an increase in the on-rate, that is, the autophagic sequestration of cytoplasmic material and (ii) a decrease in the off-rate, for instance, as a result of reduced fusion between autophagosomes and lysosomes (Yu et al, 2010). To accurately distinguish between these two possibilities, it is possible to stop the fusion between autophagosomes and lysosomes, for instance, by adding the vacuolar ATPase inhibitor bafilomycin-A1 (BafA1) (Mizushima et al, 2010).…”

Autophagic program is regulated by miR-325

“…45 Enforced expression of miR-155 can increase autophagic activity in human nasopharyngeal cancer and cervical cancer cells, whereas knockdown of miR-155 can inhibit hypoxia-induced autophagy. 46 Autophagy is controlled by a complex interplay between the anti-and pro-autophagic proteins, [47][48][49][50] and more than 800 microRNAs have been identified. 51 The function of miR-325 remains unknown.…”