ATG7 deficiency suppresses apoptosis and cell death induced by lysosomal photodamage.
Photodynamic therapy (PDT) involves photosensitizing agents that, in the presence of oxygen and light, initiate formation of cytotoxic reactive oxygen species (ROS). PDT commonly induces both apoptosis and autophagy. Previous studies with murine hepatoma 1c1c7 cells indicated that loss of autophagy-related protein 7 (ATG7) inhibited autophagy and enhanced the cytotoxicity of photosensitizers that mediate photodamage to mitochondria or the endoplasmic reticulum. In this study, we examined two photosensitizing agents that target lysosomes: the chlorin NPe6 and the palladium bacteriopheophorbide WST11. Irradiation of wild-type 1c1c7 cultures loaded with either photosensitizer induced apoptosis and autophagy, with a blockage of autophagic flux. An ATG7- or ATG5-deficiency suppressed the induction of autophagy in PDT protocols using either photosensitizer. Whereas ATG5-deficient cells were quantitatively similar to wild-type cultures in their response to NPe6 and WST11 PDT, an ATG7-deficiency suppressed the apoptotic response (as monitored by analyses of chromatin condensation and procaspase-3/7 activation) and increased the LD(50) light dose by > 5-fold (as monitored by colony-forming assays). An ATG7-deficiency did not prevent immediate lysosomal photodamage, as indicated by loss of the lysosomal pH gradient. However, unlike wild-type and ATG5-deficient cells, the lysosomes of ATG7-deficient cells recovered this gradient within 4 h of irradiation, and never underwent permeabilization (monitored as release of endocytosed 10-kDa dextran polymers). We propose that the efficacy of lysosomal photosensitizers is in part due to both promotion of autophagic stress and suppression of autophagic prosurvival functions. In addition, an effect of ATG7 unrelated to autophagy appears to modulate lysosomal photodamage.
Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI, USA. dhkessel@med.wayne.edu
David H
DH
Kessel
Michael
M
Price
John J
JJ
Reiners
D000588:Amines / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D000071193:Autophagy-Related Protein 7; D001429:Bacteriochlorophylls / Q000737:chemistry / Q000494:pharmacology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects / Q000648:ultrastructure; D048430:Cell Shape / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D005453:Fluorescence; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008027:Light; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000172:deficiency* / Q000378:metabolism; D010539:Permeability / Q000187:drug effects / Q000528:radiation effects; D010588:Phagosomes / Q000187:drug effects / Q000528:radiation effects / Q000648:ultrastructure; D017319:Photosensitizing Agents / Q000494:pharmacology; D011166:Porphyrins / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects / Q000528:radiation effects; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects
D000588:Amines; C502661:Atg7 protein, mouse; D001429:Bacteriochlorophylls; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D017319:Photosensitizing Agents; D011166:Porphyrins; D011993:Recombinant Fusion Proteins; C493330:Red DND-99; D049452:Green Fluorescent Proteins; D000071193:Autophagy-Related Protein 7; C503696:padeliporfin; C053434:Talaporfin