GABARAPs regulate PI4P-dependent autophagosome:lysosome fusion

Abstract

The Atg8 autophagy proteins are essential for autophagosome biogenesis and maturation. The γ-aminobutyric acid receptor-associated protein (GABARAP) Atg8 family is much less understood than the LC3 Atg8 family, and the relationship between the GABARAPs' previously identified roles as modulators of transmembrane protein trafficking and autophagy is not known. Here we report that GABARAPs recruit palmitoylated PI4KIIα, a lipid kinase that generates phosphatidylinositol 4-phosphate (PI4P) and binds GABARAPs, from the perinuclear Golgi region to autophagosomes to generate PI4P in situ. Depletion of either GABARAP or PI4KIIα, or overexpression of a dominant-negative kinase-dead PI4KIIα mutant, decreases autophagy flux by blocking autophagsome:lysosome fusion, resulting in the accumulation of abnormally large autophagosomes. The autophagosome defects are rescued by overexpressing PI4KIIα or by restoring intracellular PI4P through "PI4P shuttling." Importantly, PI4KIIα's role in autophagy is distinct from that of PI4KIIIβ and is independent of subsequent phosphatidylinositol 4,5 biphosphate (PIP 2 ) generation. Thus, GABARAPs recruit PI4KIIα to autophagosomes, and PI4P generation on autophagosomes is critically important for fusion with lysosomes. Our results establish that PI4KIIα and PI4P are essential effectors of the GABARAP interactome's fusion machinery.autophagy | GABARAP | PI4P | PI4KIIα | autophagosome:lysosome fusion

Interactions between neurotropic pathogens, neuroinflammatory pathways, and autophagic neural cell death

“…In contrast to dengue virus, the autophagic vacuole shows no evidence of being the site of replication for JEV. However, this finding is not consistent with the experiments conducted by Jin et al [48] and Wang et al [49] , who stated that the accumulation of the autophagosome and the autophagosome-lysosome fusion are essential to promote JEV replication [47][48][49] . In addition to initiating autophagy, viral intrusion also affects the intermediate step of the event.…”

New insights into autophagosome–lysosome fusion

“…Phosphatidylinositol 4-kinase type 2-alpha (PI4KIIα) normally localizes to the perinuclear region and the trans-Golgi network (TGN). Upon starvation, PI4KIIα exits the TGN and disperses into the cytoplasm, with some PI4KIIα localizing to autophagosomes in a palmitoylationdependent manner with a similar redistribution of PI4P (Wang et al, 2015). Consistent with this, depletion of PI4KIIα reduces the concentration of PI4P in autophagosomes.…”

“…Knockdown of either GABARAP or PI4KIIα creates defective, large autophagosomes and impairs the degradation of LC3 and p62, owing to defective autophagosomal fusion with the lysosome. Importantly, this fusion defect is rescued by introduction of PI4P, but not of phosphatidylinositol (4,5)-bisphosphate, suggesting that the generation of PI4P specifically -and not its downstream metabolites -is essential for autophagosome-lysosome fusion (Wang et al, 2015). However, the exact role of PI4P in the fusion process needs to be clarified in future studies.…”

“…Interestingly, PI4KIIα interacts with the Atg8 homologs GABARAP and GABARAPL2, but not with LC3. Depletion of GABARAP inhibits translocation of PI4KIIα to autophagosomes, whereas depletion of PI4KIIα does not affect GABARAP distribution, indicating that GABARAP functions upstream of PI4KIIα in this context (Wang et al, 2015). Knockdown of either GABARAP or PI4KIIα creates defective, large autophagosomes and impairs the degradation of LC3 and p62, owing to defective autophagosomal fusion with the lysosome.…”

“…The generation of PI4P [ phosphatidylinositol (4)-phosphate] on autophagosomes is crucial for autophagosome-lysosome fusion in mammals (Wang et al, 2015) (Fig. 4).…”