Centre for Cancer Therapeutics, Ottawa Hospital Research Institute, Ottawa, ON, Canada; Faculty of Medicine and the Department of Biochemistry, University of Ottawa, Ottawa, ON, Canada.
Int J Cancer. 2014 Jan 15;134(2):268-79. doi: 10.1002/ijc.28369. Epub 2013 Aug 1.
We have previously demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to induce tumor-specific apoptosis. The apoptotic effects of lovastatin were regulated in part by the integrated stress response (ISR) that regulates cellular responses to a wide variety of stress inducers. A key regulator of the ISR apoptotic response is activating transcription factor 3 (ATF3) and its target gene CHOP/GADD153. In our study, we demonstrate that in multiple lovastatin-resistant clones of the squamous cell carcinoma (SCC) cell line SCC9, lovastatin treatment (1-25 μM, 24 hr) in contrast to the parental line failed to significantly induce ATF3 expression. Furthermore, the SCC-derived cell lines SCC25 and HeLa that are sensitive to lovastatin-induced apoptosis also preferentially induce ATF3 expression compared to resistant breast (MCF-7) and prostate carcinoma (PC3)-derived cell lines. In HeLa cells shRNA targeting ATF3 expression as well as in ATF3-deficient murine embryonic fibroblasts, lovastatin-induced cytotoxicity and apoptosis were attenuated. In ex vivo HNSCC tumors, lovastatin also induced ATF3 mRNA expression in two of four tumors evaluated. Salubrinal, an agent that can sustain the activity of a key regulator of the ISR eIF2α, further increased the expression of ATF3 and demonstrated synergistic cytotoxicity in combination with lovastatin in SCC cells. Taken together, our results demonstrate preferential induction of ATF3 in lovastatin-sensitive tumor-derived cell lines that regulate lovastatin-induced apoptosis. Importantly, combining lovastatin with salubrinal enhanced ATF3 expression and induced synergistic cytotoxicity in SCC cells.
我们之前已经证明了洛伐他汀（一种强效的甲羟戊酸合成抑制剂）能够诱导肿瘤特异性细胞凋亡。洛伐他汀的凋亡作用部分受到整合应激反应（ISR）的调节，ISR 调节细胞对各种应激诱导物的反应。ISR 凋亡反应的一个关键调节因子是激活转录因子 3（ATF3）及其靶基因 CHOP/GADD153。在我们的研究中，我们证明在鳞状细胞癌（SCC）细胞系 SCC9 的多个洛伐他汀耐药克隆中，与亲本系相比，洛伐他汀处理（1-25 μM，24 小时）未能显著诱导 ATF3 表达。此外，对洛伐他汀诱导凋亡敏感的 SCC 衍生细胞系 SCC25 和 HeLa 也比耐药的乳腺（MCF-7）和前列腺癌（PC3）衍生细胞系更优先诱导 ATF3 表达。在 HeLa 细胞中，靶向 ATF3 表达的 shRNA 以及 ATF3 缺陷型鼠胚胎成纤维细胞中，洛伐他汀诱导的细胞毒性和凋亡作用减弱。在体外 HNSCC 肿瘤中，在评估的四个肿瘤中的两个中，洛伐他汀也诱导了 ATF3 mRNA 的表达。Salubrinal 是一种可以维持 ISR eIF2α关键调节剂活性的药物，它进一步增加了 ATF3 的表达，并在与洛伐他汀联合应用于 SCC 细胞时表现出协同细胞毒性。总之，我们的研究结果表明，洛伐他汀敏感的肿瘤衍生细胞系中优先诱导 ATF3，从而调节洛伐他汀诱导的细胞凋亡。重要的是，将洛伐他汀与 Salubrinal 联合使用可增强 SCC 细胞中 ATF3 的表达并诱导协同细胞毒性。
