title: Distinct autophagosomal-lysosomal fusion mechanism revealed by thapsigargin-induced autophagy arrest.
abstract: Autophagy, a catabolic pathway that delivers cellular components to lysosomes for degradation, can be activated by stressful conditions such as nutrient starvation and endoplasmic reticulum (ER) stress. We report that thapsigargin, an ER stressor widely used to induce autophagy, in fact blocks autophagy. Thapsigargin does not affect autophagosome formation but leads to accumulation of mature autophagosomes by blocking autophagosome fusion with the endocytic system. Strikingly, thapsigargin has no effect on endocytosis-mediated degradation of epidermal growth factor receptor. Molecularly, while both Rab7 and Vps16 are essential regulatory components for endocytic fusion with lysosomes, we found that Rab7 but not Vps16 is required for complete autophagy flux, and that thapsigargin blocks recruitment of Rab7 to autophagosomes. Therefore, autophagosomal-lysosomal fusion must be governed by a distinct molecular mechanism compared to general endocytic fusion.
authors.affiliation: Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
authors.forename: Ian G
authors.initials: IG
authors.lastname: Ganley
authors.forename: Pui-Mun
authors.initials: PM
authors.lastname: Wong
authors.forename: Noor
authors.initials: N
authors.lastname: Gammoh
authors.forename: Xuejun
authors.initials: X
authors.lastname: Jiang
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D019284:Thapsigargin / Q000494:pharmacology*; D020691:rab GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins
chemical_list: D000090802:rab7 GTP-Binding Proteins; C000716465:rab7 GTP-binding proteins, mouse; D019284:Thapsigargin; D020691:rab GTP-Binding Proteins