Recently a noncanonical activity of autophagy proteins has been discovered that targets lipidation of microtubule-associated protein 1 light chain 3 (LC3) onto macroendocytic vacuoles, including macropinosomes, phagosomes, and entotic vacuoles. While this pathway is distinct from canonical autophagy, the mechanism of how these nonautophagic membranes are targeted for LC3 lipidation remains unclear. Here we present evidence that this pathway requires activity of the vacuolar-type H(+)-ATPase (V-ATPase) and is induced by osmotic imbalances within endolysosomal compartments. LC3 lipidation by this mechanism is induced by treatment of cells with the lysosomotropic agent chloroquine, and through exposure to the Heliobacter pylori pore-forming toxin VacA. These data add novel mechanistic insights into the regulation of noncanonical LC3 lipidation and its associated processes, including LC3-associated phagocytosis (LAP), and demonstrate that the widely and therapeutically used drug chloroquine, which is conventionally used to inhibit autophagy flux, is an inducer of LC3 lipidation.
Keywords: ATG, autophagy-related; Baf, bafilomycin A1; CALCOCO2/NDP52, calcium binding and coiled-coil domain 2; CQ, chloroquine; ConA, concanamycin A; FYCO1, FYVE and coiled-coil domain containing 1; GFP, green fluorescent protein; Helicobacter pylori; LAMP1, lysosomal-associated membrane protein 1; LAP; LAP, LC3-associated phagocytosis; LC3; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MTOR, mechanistic target of rapamycin; PIK3C3/VPS34, phosphatidylinositol 3-kinase; PtdIns3K, phosphatidylinositol 3-kinase; PtdIns3P, phosphatidylinositol 3-phosphate; RB1CC1/FIP200, RB1-inducible coiled-coil 1; SQSTM1/p62, sequestosome 1; TEM, transmission electron microscopy; TLR, toll-like receptor; ULK1/2, unc-51 like autophagy activating kinase 1/2; V-ATPase; V-ATPase, vacuolar-type H+-ATPase; VacA, vacuolating toxin A; autophagy; catalytic subunit type 3; chloroquine; entosis; lysosome; phagocytosis.