Apoptotic and autophagic responses to Bcl-2 inhibition and photodamage.
Among the cellular responses to photodamage initiated by photodynamic therapy (PDT) are autophagy and apoptosis. While autophagy is a reversible process that can be both a survival and a death pathway, apoptosis is irreversible, leading only to cell death. In this study, we followed the fate of mouse leukemia L1210 cells after photodamage to the endoplasmic reticulum (ER) using a porphycene photosensitizer, where Bcl-2 was among the PDT targets. In wild-type cells, we observed a rapid wave of autophagy, presumed to represent the recycling of some damaged organelles, followed by apoptosis. Using shRNA technology, we created a Bax knockdown line (L1210/Bax(-)). In the latter cell line, we found a marked decrease in apoptosis after photodamage or pharmacologic inactivation of Bcl-2 function, but this did not affect PDT efficacy. Loss of viability was associated with a highly-vacuolated morphology consistent with autophagic cell death. Previous studies indicated pro-survival attributes of autophagy after low-dose PDT, suggesting that autophagy may be responsible for the 'shoulder' on the dose-response curve. It appears that attempts at extensive recycling of damaged organelles are associated with cell death, and that this phenomenon is amplified when apoptosis is suppressed.
Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
David
D
Kessel
Adelaida Segarra
AS
Arroyo
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D000071193:Autophagy-Related Protein 7; D015153:Blotting, Western; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000473:pathology; D017353:Gene Deletion; D007939:Leukemia L1210 / Q000188:drug therapy* / Q000473:pathology*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010778:Photochemotherapy / Q000009:adverse effects*; D017319:Photosensitizing Agents / Q000494:pharmacology; D011166:Porphyrins / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000378:metabolism; D013997:Time Factors
C502661:Atg7 protein, mouse; D008869:Microtubule-Associated Proteins; D017319:Photosensitizing Agents; D011166:Porphyrins; D019253:Proto-Oncogene Proteins c-bcl-2; C051407:porphycene; D000071193:Autophagy-Related Protein 7