State Key Laboratory of Natural Medicines, Jiangsu Key Laboratory of Carcinogenesis and Intervention (China Pharmaceutical University), Nanjing, People's Republic of China.
Cell Signal. 2012 Aug;24(8):1722-32. doi: 10.1016/j.cellsig.2012.04.009. Epub 2012 Apr 25.
Autophagy is a tightly-regulated catabolic process that involves the degradation of intracellular components via lysosomes. Although the pivotal role of autophagy in cell growth, development, and homeostasis has been well understood, its function in cancer prevention and intervention remains to be delineated. The aim of this study was to investigate the function and mechanism of autophagy induced by oroxylin A, a natural mono-flavonoid extracted from Scutellariae radix. We found for the first time that oroxylin A induced Beclin 1-mediated autophagy in human hepatocellular carcinoma HepG2 cells. Time-lapse video microscopy and western blotting studies showed that treatment of cells with 80 μM oroxylin A resulted in the conversion of water soluble MAP-LC3 (LC3-I) to the lipidated and autophagosome-associated form (LC3-II) after 12hours; then autophagosome-lysosome fusion and lysosome degradation after 24 hours was required in oroxylin A-mediated cell death. This induction was associated with the suppressing of PI3K-PTEN-Akt-mTOR signaling pathway by oroxylin A. Our results also showed that autophagy took place before noticeable apoptosis can be observed. It was further demonstrated that oroxylin A-triggered autophagy contributed to cell death using over-expression of autophagy-related gene (Atg5 and Atg7) and inhibition of autophagy by siBeclin 1 and 3-methyladenine (3-MA). In vivo study, oroxylin A inhibited xenograft tumor growth and induced obvious autophagy in tumors. Taken together, we conclude that oroxylin A exhibits autophagy-mediated antitumor activity in a dose and time-dependent manner in vivo and in vitro. These findings define and support a novel function of autophagy in promoting death of hepatocellular carcinoma cells.
自噬是一种严格调控的分解代谢过程，涉及通过溶酶体降解细胞内成分。虽然自噬在细胞生长、发育和稳态中的关键作用已经得到很好的理解，但它在癌症预防和干预中的作用仍有待描绘。本研究旨在探讨提取自黄芩的天然单黄酮氧甲素诱导的自噬的功能和机制。我们首次发现氧甲素在人肝癌 HepG2 细胞中诱导 Beclin 1 介导的自噬。时差视频显微镜和 Western blot 研究表明，用 80μM 氧甲素处理细胞 12 小时后，会导致水溶性 MAP-LC3（LC3-I）转化为脂化的和与自噬体相关的形式（LC3-II）；然后在氧甲素介导的细胞死亡中需要 24 小时自噬体-溶酶体融合和溶酶体降解。这种诱导与氧甲素抑制 PI3K-PTEN-Akt-mTOR 信号通路有关。我们的结果还表明，自噬发生在可观察到明显凋亡之前。进一步证明，氧甲素触发的自噬通过过表达自噬相关基因（Atg5 和 Atg7）和抑制自噬通过 siBeclin 1 和 3-甲基腺嘌呤（3-MA）有助于细胞死亡。在体内研究中，氧甲素抑制异种移植肿瘤生长并在肿瘤中诱导明显的自噬。总之，我们得出结论，氧甲素在体内和体外以剂量和时间依赖的方式表现出自噬介导的抗肿瘤活性。这些发现定义并支持自噬在促进肝癌细胞死亡中的新功能。
