title: Bcl-2 increases emptying of endoplasmic reticulum Ca2+ stores during photodynamic therapy-induced apoptosis.
abstract: Photodynamic therapy (PDT) is clinically approved for the treatment of several types of cancer as well as age-related macular degeneration, the leading cause of blindness in the elderly. PDT using the photosensitizer verteporfin has been previously shown to induce rapid apoptosis via a mitochondrial-caspase activation pathway. The impact of PDT on other cellular organelles such as the endoplasmic reticulum (ER) is undefined. The effect of PDT on intracellular Ca2+ ([Ca2+]i) in control and Bcl-2-overexpressing HeLa cells was assessed. A greater [Ca2+]i transient was observed for Bcl-2 overexpressing cells in response to PDT. The PDT-induced Ca2+ release was due to the emptying of Ca2+ from ER and possibly mitochondrial stores and was not due to an influx of Ca2+ from the medium. For Bcl-2-transfected cells, the release of Ca2+ was incomplete as determined by a further [Ca2+]i transient produced by the addition of the Ca2+ ionophore ionomycin after PDT. Furthermore, extrusion of Ca2+ was not hindered while ER-mediated sequestration of Ca2+ was impaired after PDT. Impairment of ER-mediated sequestration of Ca2+ may be due to the immediate caspase-independent depletion of sarco/endoplasmic reticulum Ca2+ ATPase-2 (SERCA2) that occurred in response to PDT in birth HeLa/Neo and Bcl-2 overexpressed HeLa cells. In summary, PDT induced the rapid degradation of SERCA2 and release of ER and mitochondrial Ca2+ stores. Although overexpression of Bcl-2 did not protect against SERCA2 degradation, it may influence the release of Ca2+ from ER and mitochondrial stores in PDT-treated cells.
authors.affiliation: UBC McDonald Research Laboratories and the iCAPTURE Centre/, St. Paul's Hospital ed.-University of British Columbia, Vancouver, BC, Canada.
authors.forename: D J
authors.initials: DJ
authors.lastname: Granville
authors.forename: D O
authors.initials: DO
authors.lastname: Ruehlmann
authors.forename: J C
authors.initials: JC
authors.lastname: Choy
authors.forename: B A
authors.initials: BA
authors.lastname: Cassidy
authors.forename: D W
authors.initials: DW
authors.lastname: Hunt
authors.forename: C
authors.initials: C
authors.lastname: van Breemen
authors.forename: B M
authors.initials: BM
authors.lastname: McManus
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001692:Biological Transport / Q000187:drug effects / Q000528:radiation effects; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008928:Mitochondria / Q000378:metabolism; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology; D011166:Porphyrins / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000077362:Verteporfin
chemical_list: D003574:Cytochrome c Group; D017319:Photosensitizing Agents; D011166:Porphyrins; D019253:Proto-Oncogene Proteins c-bcl-2; D000077362:Verteporfin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506946:ATP2A2 protein, human; D000252:Calcium-Transporting ATPases; D002118:Calcium