Barakat David J, Mendonca Janet, Barberi Theresa, Zhang Jing, Kachhap Sushant K, Paz-Priel Ido, Friedman Alan D
Department of Oncology, Johns Hopkins University, Baltimore, Maryland, USA.
Department of Oncology, Johns Hopkins University, Baltimore, Maryland, USA.
Cancer Lett. 2016 May 28;375(1):152-161. doi: 10.1016/j.canlet.2016.03.005. Epub 2016 Mar 8.
The purpose of this study was to ascertain the mechanisms by which advanced prostate cancer cells resist bortezomib therapy. Several independent studies have shown that cells are protected from proteasome inhibition by increased autophagic activity. We investigated whether C/EBPβ, a transcription factor involved in the control of autophagic gene expression, regulates resistance to proteasome inhibition. In PC3 cells over-expressing C/EBPβ, turnover of autophagic substrates and expression of core autophagy genes were increased. Conversely, C/EBPβ knockdown suppressed autophagosome-lysosome fusion. We also found that C/EBPβ knockdown suppressed REDD1 expression to delay early autophagy, an effect rescued by exogenous REDD1. Cells with suppressed C/EBPβ levels showed delayed autophagy activation upon bortezomib treatment. Knockdown of C/EBPβ sensitized PC3 cells to bortezomib, and blockade of autophagy by chloroquine did not further increase cell death in cells expressing shRNA targeting C/EBPβ. Lastly, we observed a decreased growth of PC3 cells and xenografts with C/EBPβ knockdown and such xenografts were sensitized to bortezomib treatment. Our results demonstrate that C/EBPβ is a critical effector of autophagy via regulation of autolysosome formation and promotes resistance to proteasome inhibitor treatment by increasing autophagy.
本研究的目的是确定晚期前列腺癌细胞抵抗硼替佐米治疗的机制。多项独立研究表明，细胞通过增强自噬活性来抵御蛋白酶体抑制。我们研究了参与自噬基因表达调控的转录因子C/EBPβ是否调节对蛋白酶体抑制的抗性。在过表达C/EBPβ的PC3细胞中，自噬底物的周转和核心自噬基因的表达增加。相反，敲低C/EBPβ会抑制自噬体-溶酶体融合。我们还发现，敲低C/EBPβ会抑制REDD1表达以延迟早期自噬，外源性REDD1可挽救这种效应。C/EBPβ水平受抑制的细胞在硼替佐米处理后自噬激活延迟。敲低C/EBPβ使PC3细胞对硼替佐米敏感，用氯喹阻断自噬不会进一步增加表达靶向C/EBPβ的短发夹RNA（shRNA）的细胞的死亡。最后，我们观察到敲低C/EBPβ后PC3细胞及其异种移植物的生长减缓，且此类异种移植物对硼替佐米治疗敏感。我们的结果表明，C/EBPβ通过调节自噬溶酶体形成是自噬的关键效应因子，并通过增加自噬促进对蛋白酶体抑制剂治疗的抗性。
