The molecular mechanisms underlying microtubule participation in autophagy are not known. In this study, we show that starvation-induced autophagosome formation requires the most dynamic microtubule subset. Upon nutrient deprivation, labile microtubules specifically recruit markers of autophagosome formation like class III-phosphatidylinositol kinase, WIPI-1, the Atg12-Atg5 conjugate, and LC3-I, whereas mature autophagosomes may bind to stable microtubules. We further found that upon nutrient deprivation, tubulin acetylation increases both in labile and stable microtubules and is required to allow autophagy stimulation. Tubulin hyperacetylation on lysine 40 enhances kinesin-1 and JIP-1 recruitment on microtubules and allows JNK phosphorylation and activation. JNK, in turn, triggers the release of Beclin 1 from Bcl-2-Beclin 1 complexes and its recruitment on microtubules where it may initiate autophagosome formation. Finally, although kinesin-1 functions to carry autophagosomes in basal conditions, it is not involved in motoring autophagosomes after nutrient deprivation. Our results show that the dynamics of microtubules and tubulin post-translational modifications play a major role in the regulation of starvation-induced autophagy.Macroautophagy (simply referred to here as autophagy) occurs at low basal levels to perform homeostatic functions such as protein and organelle turnover. It is also an adaptive catabolic response to different metabolic stresses, including nutrient deprivation, growth factor depletion, or hypoxia (1, 2). Newly assembled multilayer membranes expand and sequester parts of the cytoplasm to form autophagosomes that subsequently fuse with lysosomes to degrade their content (1, 2). When cells lack nutrients, inhibition of the mammalian target of rapamycin activates the ULK complex (ULK1 and ULK2 are the mammalian orthologs of the yeast Atg1) to initiate the cascade of events leading to the formation of autophagosomes (reviewed in Ref.3). Building of isolation membranes or phagophores involves a complex comprising Beclin 1 (Beclin 1 is the mammalian homolog of the yeast Atg6) and the class III PI3K 4 (PI3K(III), also called hVps34) (4). Newly synthesized phosphatidylinositol 3-phosphate then recruits effectors such as WIPI-1, the homolog of yeast Atg18 (5, 6), to allow the recruitment of other autophagosomal building bricks (4). Atg9 contributes to membrane shuttling that elongates the pre-autophagosomal membrane (reviewed in Ref. 7). Such elongation also involves ubiquitin-like machineries, which in turn allow Atg12-to-Atg5 conjugation, and the modification of LC3 (LC3 is the mammalian ortholog of the yeast Atg8) (8) prior to their recruitment to autophagosomal membranes. LC3 is a light chain of MAP1 first identified in neurons (9, 10). After autophagy induction, the C-terminal region of native LC3 (pro-LC3) is cleaved by Atg4, yielding LC3-I. Atg7 and Atg3 then conjugate LC3-I to phosphatidylethanolamine on its C-terminal glycine, yielding LC3-II that attaches to the autophagosomal membrane ...

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SummaryBoth at a basal level and after induction (especially in response to nutrient starvation), the function of autophagy is to allow cells to degrade and recycle damaged organelles, proteins and other biological constituents. Here, we focus on the role microtubules have in autophagosome formation, autophagosome transport across the cytoplasm and in the formation of autolysosomes. Recent insights into the exact relationship between autophagy and microtubules now point to the importance of microtubule dynamics, tubulin posttranslational modifications and microtubule motors in the autophagy process. Such factors regulate signaling pathways that converge to stimulate autophagosome formation. They also orchestrate the movements of pre-autophagosomal structures and autophagosomes or more globally organize and localize immature and mature autophagosomes and lysosomes. Most of the factors that now appear to link microtubules to autophagosome formation or to autophagosome dynamics and fate were identified initially without the notion that sequestration, recruitment and/or interaction with microtubules contribute to their function. Spatial and temporal coordination of many stages in the life of autophagosomes thus underlines the integrative role of microtubules and progressively reveals hidden parts of the autophagy machinery.