Xue Liang-yan, Chiu Song-mao, Azizuddin Kashif, Joseph Sheeba, Oleinick Nancy L
Department of Radiation Oncology, The Case Comprehensive Cancer Center, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
Photochem Photobiol. 2007 Sep-Oct;83(5):1016-23. doi: 10.1111/j.1751-1097.2007.00159.x.
Photodynamic therapy (PDT) is an efficient inducer of apoptosis in many types of cells, except in cells deficient in one or more of the factors that mediate apoptosis. Recent reports have identified autophagy as a potential alternative cell death process following PDT. Here we investigated the occurrence of autophagy after PDT with the photosensitizer Pc 4 in human cancer cells that are deficient in the pro-apoptotic factor Bax (human prostate cancer DU145 cells) or the apoptosis mediator caspase-3 (human breast cancer MCF-7v cells) and in apoptosis-competent cells (MCF-7c3 cells that stably overexpress human pro-caspase-3 and Chinese hamster ovary CHO 5A100 cells). Further, each of the cell lines was also studied with and without stably overexpressed Bcl-2. Autophagy was identified by electron microscopic observation of the presence of double-membrane-delineated autophagosomal vesicles in the cytosol and by immunoblot observation of the Pc 4-PDT dose- and time-dependent increase in the level of LC3-II, a component of the autophagosomal membrane. Autophagy was observed in all of the cell lines studied, whether or not they were capable of typical apoptosis and whether or not they overexpressed Bcl-2. The presence of stably overexpressed Bcl-2 in the cells protected against PDT-induced apoptosis and loss of clonogenicity in apoptosis-competent cells (MCF-7c3 and CHO 5A100 cells). In contrast, Bcl-2 overexpression did not protect against the development of autophagy in any of the cell lines or against loss of clonogenicity in apoptosis-deficient cells (MCF-7v and DU145 cells). Furthermore, 3-methyladenine and wortmannin, inhibitors of autophagy, provided greater protection against loss of viability to apoptosis-deficient than to apoptosis-competent cells. The results show that autophagy occurs during cell death following PDT in human cancer cells competent or not for normal apoptosis. Only the apoptosis-competent cells are protected by Bcl-2 against cell death.
光动力疗法（PDT）是许多类型细胞凋亡的有效诱导剂，但在缺乏一种或多种介导凋亡因子的细胞中除外。最近的报告已将自噬确定为PDT后一种潜在的替代性细胞死亡过程。在此，我们研究了在缺乏促凋亡因子Bax的人癌细胞（人前列腺癌DU145细胞）或凋亡介质半胱天冬酶-3（人乳腺癌MCF-7v细胞）以及具有凋亡能力的细胞（稳定过表达人原半胱天冬酶-3的MCF-7c3细胞和中国仓鼠卵巢CHO 5A100细胞）中，用光敏剂Pc 4进行PDT后自噬的发生情况。此外，还对每种细胞系在稳定过表达Bcl-2和未稳定过表达Bcl-2的情况下进行了研究。通过电子显微镜观察细胞质中双膜界定的自噬体囊泡的存在以及通过免疫印迹观察自噬体膜成分LC3-II水平的Pc 4-PDT剂量和时间依赖性增加来鉴定自噬。在所研究的所有细胞系中均观察到了自噬，无论它们是否能够进行典型凋亡以及是否过表达Bcl-2。细胞中稳定过表达的Bcl-2的存在可防止具有凋亡能力的细胞（MCF-7c3和CHO 5A100细胞）中PDT诱导的凋亡和克隆形成能力的丧失。相比之下，Bcl-2过表达并不能防止任何细胞系中自噬的发生，也不能防止凋亡缺陷细胞（MCF-7v和DU145细胞）中克隆形成能力的丧失。此外，自噬抑制剂3-甲基腺嘌呤和渥曼青霉素对凋亡缺陷细胞活力丧失的保护作用比对具有凋亡能力的细胞更大。结果表明，在人癌细胞中，无论是否具有正常凋亡能力，自噬都发生在PDT后的细胞死亡过程中。只有具有凋亡能力的细胞受到Bcl-2的保护而免于细胞死亡。
