Beclin 1-interacting autophagy protein Atg14L targets SNARE-associated protein Snapin to coordinate endocytic trafficking

Abstract

SummaryAutophagy is a highly regulated membrane remodeling process that allows the lysosome-mediated degradation of cytoplasmic entities by sequestrating them in double-membrane autophagosomes. Autophagy is hence highly intertwined with the endocytic trafficking pathway, sharing similar molecular machinery. Atg14L, also known as Beclin 1-associated autophagy-related key regulator (Barkor), directly interacts with Beclin 1 through its coiled-coil domain and enhances phosphatidylinositol 3-phosphate kinase class III (PI3KC3) activity to induce autophagosome membrane nucleation, highlighting its essential role in the early stage of mammalian autophagy. Here, we report a novel function of Atg14L in the endocytic trafficking pathway wherein Atg14L binds to and colocalizes with the fusogenic SNARE effector protein Snapin to facilitate endosome maturation. Atg14L specifically binds to Snapin and this interaction effectively facilitates endosomal maturation without affecting autophagic cargo degradation. Consequently, atg14l knockdown significantly delayed the late stage of endocytic trafficking, as evidenced by the retarded kinetics of internalized surface receptor degradation. This phenotype was effectively complemented by wild-type Atg14L or Beclin 1-binding mutant, but not by its Snapin-binding mutant. Taken together, our study demonstrates that Atg14L functions as a multivalent trafficking effector that regulates endosome maturation as well as autophagosome formation, reflecting the complexity of the crosstalk between autophagic and endocytic vesicle trafficking in higher eukaryotes.

Bcl-xL Affects Group A Streptococcus-Induced Autophagy Directly, by Inhibiting Fusion between Autophagosomes and Lysosomes, and Indirectly, by Inhibiting Bacterial Internalization via Interaction with Beclin 1-UVRAG

“…Finally, we investigated the involvement of Atg14L and UVRAG in the internalization process and autophagy during GAS infection, because both proteins are shown to positively stimulate starvation-induced autophagy [18–21] and also to regulate the endocytic process through their interaction with Beclin 1 [22–25, 36]. In Atg14L knockdown cells (S4A Fig), LC3 puncta formation was suppressed under starvation conditions (S4B and S4C Fig), but GcAV formation was not affected during GAS infection (Fig 4A and 4B).…”

“…In mammalian cells, Atg14L is required to recruit PI3KC3 to the formation site of autophagosomes [48]. Atg14L is traditionally considered to be an autophagy specific factor, but a recent study shows that it may be involved in the regulation of endocytosis [36]. Despite a clear contribution of Atg14L in autophagosome formation under starvation conditions, knockdown of Atg14L did not affect GcAV formation or the internalization of GAS.…”

Focal Adhesion Kinase-mediated Phosphorylation of Beclin1 Protein Suppresses Cardiomyocyte Autophagy and Initiates Hypertrophic Growth

“…The blockade of this basal bulk catabolic program likely primes cardiomyocytes for ensuing hypertrophic growth that occurs via de novo synthesis of proteins. Interestingly, very recent studies indicate that autophagy may compete with endocytic recycling as these pathways share common vesicle trafficking machinery (48,49). Thus, it is also formally possible that a temporary block of autophagy in the face of continued secretory/ endocytic recycling vesicle trafficking could promote plasma membrane expansion, an event that could ultimately prevent growth-induced stress on the plasma membrane and/or de-repress a growth-inhibitory negative feedback system.…”

Sphingosine Kinase 1 Cooperates with Autophagy to Maintain Endocytic Membrane Trafficking

“…Autophagy is regulated by over 30 identified autophagy-related ( Atg ) genes (Feng et al, 2014). Autophagic degradation requires functional late endosomes and lysosomes, and thus it is not surprising that several components of the autophagic machinery positively regulate the endocytic pathway (Lamb et al, 2013), including Beclin1 (Liang et al, 2008; Ruck et al, 2011), Atg14L (Kim et al, 2012), Atg5 (Peng et al, 2014) and Atg3 (Murrow et al, 2015). Bidirectional crosstalk also occurs between autophagy and sphingolipids, as sphingolipids positively and negatively regulate autophagy (Young et al, 2013) and accumulate in autophagy-deficient cells (Alexaki et al, 2014).…”