Adacan Kaan, Obakan-Yerlikaya Pınar, Arisan Elif Damla, Coker-Gurkan Ajda, Kaya Resul Ismail, Palavan-Unsal Narçın
Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Bakirkoy, 34156, Istanbul, Turkey.
Institute of Biotechnology, Gebze Technical University, 41400, Gebze, Kocaeli, Turkey.
Amino Acids. 2020 Jul;52(6-7):871-891. doi: 10.1007/s00726-020-02857-w. Epub 2020 May 24.
Epibrassinolide (EBR), a polyhydroxysteroid belongs to plant growth regulator family, brassinosteroids and has been shown to have a similar chemical structure to mammalian steroid hormones. Our findings indicated that EBR could trigger apoptosis in cancer cells via induction of endoplasmic reticulum (ER) stress, caused by protein folding disturbance in the ER. Normal cells exhibited a remarkable resistance to EBR treatment and avoid from apoptotic cell death. The unfolded protein response clears un/misfolded proteins and restore ER functions. When stress is chronic, cells tend to die due to improper cellular functions. To understand the effect of EBR in non-malign cells, mouse embryonic fibroblast (MEF) cells were investigated in detail for ER stress biomarkers, autophagy, and polyamine metabolism in this study. Evolutionary conserved autophagy mechanism is a crucial cellular process to clean damaged organelles and protein aggregates through lysosome under the control of autophagy-related genes (ATGs). Cells tend to activate autophagy to promote cell survival under stress conditions. Polyamines are polycationic molecules playing a role in the homeostasis of important cellular events such as cell survival, growth, and, proliferation. The administration of PAs has been markedly extended the lifespan of various organisms via inducing autophagy and inhibiting oxidative stress. Our data indicated that ER stress is induced following EBR treatment in MEF cells as well as MEF Atg5 cells. In addition, autophagy is activated following EBR treatment by targeting PI3K/Akt/mTOR in wildtype (wt) cells. However, EBR-induced autophagy targets ULK1 in MEF cells lacking Atg5 expression. Besides, EBR treatment depleted the PA pool in MEF cells through the alterations of metabolic enzymes. The administration of Spd with EBR further increased autophagic vacuole formation. In conclusion, EBR is an anticancer drug candidate with selective cytotoxicity for cancer cells, in addition the induction of autophagy and PA metabolism are critical for responses of normal cells against EBR.
表油菜素内酯（EBR）是一种多羟基类固醇，属于植物生长调节剂家族油菜素甾醇类，其化学结构已被证明与哺乳动物甾体激素相似。我们的研究结果表明，EBR可通过诱导内质网（ER）应激触发癌细胞凋亡，这种应激是由内质网中蛋白质折叠紊乱引起的。正常细胞对EBR处理表现出显著抗性，可避免凋亡性细胞死亡。未折叠蛋白反应可清除未折叠/错误折叠的蛋白质并恢复内质网功能。当应激持续存在时，细胞往往会因细胞功能异常而死亡。为了解EBR对非恶性细胞的影响，本研究详细调查了小鼠胚胎成纤维细胞（MEF）的内质网应激生物标志物、自噬和多胺代谢。进化保守的自噬机制是一个关键的细胞过程，可在自噬相关基因（ATG）的控制下通过溶酶体清除受损细胞器和蛋白质聚集体。细胞在应激条件下倾向于激活自噬以促进细胞存活。多胺是多阳离子分子，在细胞存活、生长和增殖等重要细胞事件的稳态中发挥作用。多胺的施用已通过诱导自噬和抑制氧化应激显著延长了各种生物体的寿命。我们的数据表明，EBR处理后MEF细胞以及MEF Atg5细胞中会诱导内质网应激。此外，在野生型（wt）细胞中，EBR处理通过靶向PI3K/Akt/mTOR激活自噬。然而，EBR诱导的自噬在缺乏Atg5表达的MEF细胞中靶向ULK1。此外，EBR处理通过改变代谢酶消耗了MEF细胞中的多胺池。将亚精胺与EBR一起施用可进一步增加自噬空泡的形成。总之，EBR是一种对癌细胞具有选择性细胞毒性的抗癌药物候选物，此外，自噬的诱导和多胺代谢对于正常细胞对EBR的反应至关重要。
