A novel role for α‐Snap in autophagy regulation

Autophagy is a process of intracellular protein degradation that involves a continuous formation and lysosomal fusion of membrane vesicles (autophagosomes), whose biogenesis remains poorly understood. This study addressed the role of a key vesicle fusion regulator, soluble N‐ethylmaleimide sensitive factor attachment protein alpha (α‐SNAP), in autophagy. Small interfering (si)RNA downregulation of α‐SNAP expression in epithelial cells increased the level of an autophagy marker microtubule‐associated protein light chain 3 (LC3‐II) and the number of autophagosomes. These events were further enhanced after blocking lysosomal fusion, thereby indicating the increase in the autophagic flux. Autophagy induction in α‐SNAP‐depleted cells was accompanied by down‐regulation of the mammalian target of rapamycin (mTOR) protein but was independent with an α‐SNAP binding partner N‐ethylmaleimide‐sensitive factor and the Beclin‐1/Vps15 complex. α‐SNAP depletion caused disruption of the Golgi complex and downregulation of Golgi‐specific GTP exchange factor GBF1. Pharmacological and genetic inhibition of GBF1 activity mimicked effects of α‐SNAP‐depletion on the autophagic flux. We conclude that α‐SNAP negatively regulates autophagy by mechanisms involving GBF1‐depended stabilization of the Golgi complex and stimulation of mTOR expression. Supported by NIH grants DK083968 and DK084953 to AII.