ABSTRACT

Although previous studies have shown anti-cancer activity of betulinic acid (BA), a pentacyclic triterpenoid, against various cancer lines, the underlying molecular mechanisms are not well elucidated. In this study, we evaluated the mechanisms involved in the anti-cancer efficacy of BA in U937 human myeloid leukemia cells. BA exerted a significant cytotoxic effect on U937 cells through blocking cell cycle arrest at the G2/M phase and inducing apoptosis, and that the intracellular reactive oxygen species (ROS) levels increased after treatment with BA. The down-regulation of cyclin A and cyclin B1, and up-regulation of cyclin-dependent kinase inhibitor p21WAF1/CIP1 revealed the G2/M phase arrest mechanism of BA. In addition, BA induced the cytosolic release of cytochrome c by reducing the mitochondrial membrane potential with an increasing Bax/Bcl-2 expression ratio. BA also increased the activity of caspase-9 and -3, and subsequent degradation of the poly (ADP-ribose) polymerase. However, quenching of ROS by N-acetyl-cysteine, an ROS scavenger, markedly abolished BA-induced G2/M arrest and apoptosis, indicating that the generation of ROS plays a key role in inhibiting the proliferation of U937 cells by BA treatment. Taken together, our results provide a mechanistic rationale that BA exhibits anti-cancer properties in U937 leukemia cells through ROS-dependent induction of cell cycle arrest at G2/M phase and apoptosis.

摘要

尽管先前的研究表明五环三萜类化合物桦木酸（BA）对多种癌症细胞具有抗癌活性，但其潜在的分子机制仍未得到很好的阐明。在这项研究中，我们评估了BA对U937人髓样白血病细胞的抗癌功效所涉及的机制。BA通过阻断G2 / M期的细胞周期阻滞并诱导凋亡而对U937细胞产生明显的细胞毒性作用，BA处理后细胞内活性氧（ROS）水平升高。细胞周期蛋白A和细胞周期蛋白B1的下调，以及细胞周期蛋白依赖性激酶抑制剂p21WAF1 / CIP1的上调揭示了BA的G2 / M期阻滞机制。此外，BA诱导细胞色素c的胞质释放通过降低Bax / Bcl-2表达比率来降低线粒体膜电位。BA还增加了caspase-9和-3的活性，并随后降解了聚（ADP-核糖）聚合酶。然而，用ROS清除剂N-乙酰基-半胱氨酸淬灭ROS可明显消除BA诱导的G2 / M停滞和凋亡，这表明ROS的产生在通过BA处理抑制U937细胞增殖中起关键作用。两者合计，我们的结果提供了一种机制学说，即BA通过ROS依赖性诱导的G2 / M期细胞周期停滞和凋亡而在U937白血病细胞中表现出抗癌特性。