title: Differential responses of Mcl-1 in photosensitized epithelial vs lymphoid-derived human cancer cells.
abstract: The antiapoptotic Bcl-2-family proteins, Bcl-2 and Bcl-xL, are recognized phototargets of photodynamic therapy (PDT) with the mitochondrion-targeting phthalocyanine photosensitizer Pc 4. In the present study, we found that myeloid cell leukemia 1 (Mcl-1), another antiapoptotic member of the Bcl-2 family, was not photodamaged in Pc 4-PDT-treated human carcinoma cells MCF-7c3, MDA-MB468, DU145, and A431, although Mcl-1 turnover was observed after exposure of HeLa or MCF-7c3 cells to a supralethal dose of UVC. In contrast, when human lymphoma U937 and Jurkat cells were treated with Pc 4-PDT, staurosporine (STS) or UVC, Mcl-1 was cleaved to generate a 28-kDa fragment over a 2-4 h period. The cleavage of Mcl-1 was accompanied by the activation of caspases-3, -9, and -8. The broad-specificity caspase inhibitor z-VAD-fmk completely blocked Mcl-1 cleavage induced by PDT, STS or UVC, providing evidence for Mcl-1 as a substrate for caspases. Western blot analysis localized Mcl-1 to mitochondria, ER, and cytosol of both MCF-7c3 and U937 cells, suggesting that Mcl-1 protein, unlike Bcl-2 and Bcl-xL, is not a target for Pc 4-PDT, probably due to its localization to sites removed from those of Pc 4 binding. The 28-kDa cleaved fragment of Mcl-1, which has proapoptotic activity, was produced in PDT-treated lymphoid-derived cells, but not in cells of epithelial origin, suggesting that PDT-induced rapid and extensive apoptosis in lymphoma cells may result in part from the sensitivity of their Mcl-1 to caspase cleavage, removing an important negative control on apoptosis.
authors: Department of Radiation Oncology and the Case Comprehensive Cancer Center, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4942, USA.
authors: Liang-yan
authors: LY
authors: Xue
authors: Song-mao
authors: SM
authors: Chiu
authors: Nancy L
authors: NL
authors: Oleinick
mesh_terms: D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D008221:Lymphoid Tissue / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D013379:Substrate Specificity; D014466:Ultraviolet Rays
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007211:Indoles; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D017319:Photosensitizing Agents; D019253:Proto-Oncogene Proteins c-bcl-2; C107448:phthalocyanine Pc 4; D020169:Caspases; D019311:Staurosporine