title: Autophagy pathways activated in response to PDT contribute to cell resistance against ROS damage.
abstract: Reactive oxygen species (ROS) concurrently instigate apoptosis and autophagy pathways, but the link between these processes remains unclear. Because cytotoxic ROS formation is exploited in anticancer therapy, such as in photodynamic therapy (PDT), a better understanding of the complex interplay between autophagy and apoptosis is urgently required. Previously, we reported that ROS generated by PDT with an endoplasmic reticulum (ER)-associated sensitizer leads to loss of ER-Ca(2+) homeostasis, ER stress and apoptosis. Here we show that PDT prompted Akt-mTOR (mammalian target of rapamycin) pathway down-regulation and stimulated macroautophagy (MA) in cancer and normal cells. Overexpression of the antioxidant enzyme glutathione peroxidase-4 reversed mTOR down-regulation and blocked MA progression and apoptosis. Attenuating MA using Atg5 knockdown or 3-methyladenine, reduced clearance of oxidatively damaged proteins and increased apoptosis, thus revealing a cytoprotective role of MA in PDT. Paradoxically, genetic loss of MA improved clearance of oxidized proteins and reduced photokilling. We found that up-regulation of chaperone-mediated autophagy (CMA) in unstressed Atg(-/-) cells compensated for MA loss and increased cellular resistance to PDT. CMA-deficient cells were significantly sensitized to photokilling but were protected against the ER stressor thapsigargin. These results disclose a stress-specific recruitment of autophagy pathways with cytoprotective function and unravel CMA as the dominant defence mechanism against PDT.
authors.affiliation: Cell Death Research and Therapy Laboratory, Department of Molecular Cell Biology, Faculty of Medicine, Katholieke Universiteit Leuven, Leuven, Belgium.
authors.forename: Michael
authors.initials: M
authors.lastname: Dewaele
authors.forename: Wim
authors.initials: W
authors.lastname: Martinet
authors.forename: Noemí
authors.initials: N
authors.lastname: Rubio
authors.forename: Tom
authors.initials: T
authors.lastname: Verfaillie
authors.forename: Peter A
authors.initials: PA
authors.lastname: de Witte
authors.forename: Jacques
authors.initials: J
authors.lastname: Piette
authors.forename: Patrizia
authors.initials: P
authors.lastname: Agostinis
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000873:Anthracenes; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D000071187:Autophagy-Related Protein 5; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000172:deficiency / Q000235:genetics; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000235:genetics / Q000378:metabolism*; D010569:Perylene / Q000031:analogs & derivatives / Q000494:pharmacology; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: C502778:ATG5 protein, human; D000873:Anthracenes; C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species; C025946:3-methyladenine; D010569:Perylene; D019284:Thapsigargin; C004965:hypericin; D005979:Glutathione Peroxidase; D051058:Oncogene Protein v-akt; D058570:TOR Serine-Threonine Kinases; D000225:Adenine