Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan.
Toxicol Appl Pharmacol. 2012 Dec 15;265(3):325-34. doi: 10.1016/j.taap.2012.08.034. Epub 2012 Sep 12.
Prodigiosin is a bacterial tripyrrole pigment with potent cytotoxicity against diverse human cancer cell lines. Endoplasmic reticulum (ER) stress is initiated by accumulation of unfolded or misfolded proteins in the ER lumen and may induce cell death when irremediable. In this study, the role of ER stress in prodigiosin-induced cytotoxicity was elucidated for the first time. Comparable to the ER stress inducer thapsigargin, prodigiosin up-regulated signature ER stress markers GRP78 and CHOP in addition to activating the IRE1, PERK and ATF6 branches of the unfolded protein response (UPR) in multiple human breast carcinoma cell lines, confirming prodigiosin as an ER stress inducer. Prodigiosin transcriptionally up-regulated CHOP, as evidenced by its promoting effect on the CHOP promoter activity. Of note, knockdown of CHOP effectively lowered prodigiosin's capacity to evoke PARP cleavage, reduce cell viability and suppress colony formation, highlighting an essential role of CHOP in prodigiosin-induced cytotoxic ER stress response. In addition, prodigiosin down-regulated BCL2 in a CHOP-dependent manner. Importantly, restoration of BCL2 expression blocked prodigiosin-induced PARP cleavage and greatly enhanced the survival of prodigiosin-treated cells, suggesting that CHOP-dependent BCL2 suppression mediates prodigiosin-elicited cell death. Moreover, pharmacological inhibition of JNK by SP600125 or dominant-negative blockade of PERK-mediated eIF2α phosphorylation impaired prodigiosin-induced CHOP up-regulation and PARP cleavage. Collectively, these results identified ER stress-mediated cell death as a mode-of-action of prodigiosin's tumoricidal effect. Mechanistically, prodigiosin engages the IRE1-JNK and PERK-eIF2α branches of the UPR signaling to up-regulate CHOP, which in turn mediates BCL2 suppression to induce cell death.
灵菌红素是一种具有强细胞毒性的细菌三吡咯色素，可杀伤多种人类癌细胞系。内质网（ER）应激是由内质网腔中未折叠或错误折叠蛋白的积累引发的，当无法纠正时可能会诱导细胞死亡。在这项研究中，首次阐明了 ER 应激在灵菌红素诱导的细胞毒性中的作用。与 ER 应激诱导剂 thapsigargin 类似，灵菌红素上调了多种人乳腺癌细胞系中 ER 应激标志物 GRP78 和 CHOP 的表达，同时激活了未折叠蛋白反应（UPR）的 IRE1、PERK 和 ATF6 分支，证实灵菌红素是一种 ER 应激诱导剂。灵菌红素转录上调了 CHOP，这一点可以从其促进 CHOP 启动子活性的作用中得到证明。值得注意的是，CHOP 的敲低有效降低了灵菌红素引起 PARP 切割、降低细胞活力和抑制集落形成的能力，突出了 CHOP 在灵菌红素诱导的细胞毒性 ER 应激反应中的重要作用。此外，灵菌红素以 CHOP 依赖的方式下调了 BCL2。重要的是，BCL2 表达的恢复阻断了灵菌红素诱导的 PARP 切割，并大大增强了灵菌红素处理细胞的存活率，表明 CHOP 依赖的 BCL2 抑制介导了灵菌红素诱导的细胞死亡。此外，用 SP600125 抑制 JNK 或用显性负性 PERK 阻断 eIF2α 磷酸化可损害灵菌红素诱导的 CHOP 上调和 PARP 切割。总的来说，这些结果确定了 ER 应激介导的细胞死亡是灵菌红素杀伤肿瘤作用的一种作用机制。从机制上讲，灵菌红素参与了 UPR 信号的 IRE1-JNK 和 PERK-eIF2α 分支，上调了 CHOP，进而介导了 BCL2 的抑制，从而诱导细胞死亡。
