title: Autophagosome-lysosome fusion depends on the pH in acidic compartments in CHO cells.
abstract: Autophagy is the bulk degradation of cytoplasmic constituents in response to starvation and other environmental or intracellular cues. During this process, most of the cytoplasm is sequestered into autophagosomes, which then fuse with lysosomes where the degradation of the sequestered material proceeds. We investigated the relationship between autophagosome-lysosome fusion and the pH in acidic compartments by visualizing the fusion process using fluorescence in CHO cells. In this experiment, mitochondria were labeled with GFP by transfecting CHO cells with the presequence of ornithine transcarbamylase, and lysosomes were labeled with Texas Red Dextran; any fusion was identified by the colocalization of mitochondria (in autophagosomes) and lysosomes using fluorescence microscopy. When CHO cells were treated with rapamycin or starvation medium to induce autophagy, the colocalization of fluorescence was observed. Whereas when they were treated with 3-MA, an inhibitor of autophagy, the colocalization disappeared. We conclude that the colocalization reflects the fusion of autophagosomes and lysosomes. Moreover, when the CHO cells were treated with drugs that increase the pH of acidic compartments, the colocalization disappeared. This suggests that the autophagosome-lysosome fusion is inhibited by increasing pH in acidic compartments independently of V-ATPase activity in CHO cells.
authors.affiliation: Division of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Kawai
authors.forename: Hiromi
authors.initials: H
authors.lastname: Uchiyama
authors.forename: Syuichi
authors.initials: S
authors.lastname: Takano
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nakamura
authors.forename: Shoji
authors.initials: S
authors.lastname: Ohkuma
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects; D016466:CHO Cells; D002451:Cell Compartmentation / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007425:Intracellular Membranes / Q000187:drug effects; D007476:Ionophores / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D008561:Membrane Fusion / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects; D010588:Phagosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D007476:Ionophores