State Key Laboratory of Oncology in South China, Sun Yat-Sen University Cancer Center, Guangzhou, China.
J Pineal Res. 2012 Aug;53(1):77-90. doi: 10.1111/j.1600-079X.2012.00973.x. Epub 2012 Feb 16.
Melatonin exhibits anti-inflammatory and anticancer effects and could be a chemopreventive and chemotherapeutic agent against cancers, but the precise mechanisms involved remain largely unresolved. In this study, we evaluated the mechanism of action of melatonin in human MDA-MB-361 breast cancer cells. Melatonin at pharmacological concentrations (10(-3) m) significantly suppressed cell proliferation and induced apoptosis in a dose-dependent manner. The observed suppression of proliferation was accompanied by the melatonin-mediated inhibition of COX-2, p300, and NF-κB signaling. Melatonin significantly inhibited COX-2 expression and prostaglandin E(2) (PGE2) production, abrogated p300 histone acetyltransferase activity and p300-mediated NF-κB acetylation, thereby blocking NF-κB binding and p300 recruitment to COX-2 promoter. Pretreatment with a COX-2- or p300-selective inhibitor abrogated the melatonin-induced inhibition of cell proliferation, whereas PGE2 treatment or COX-2 transfection reversed the inhibition by melatonin. Moreover, melatonin markedly inhibited phosphorylation of PI3K, Akt, PRAS40, and GSK-3 proteins, thereby inactivating the PI3K/Akt signaling pathway. Pretreatment with a PI3K- or an Akt-selective inhibitor or an Akt-specific siRNA blocked the melatonin-mediated inhibition of cell proliferation. Conversely, gene delivery of a constitutively active Akt effectively reversed the inhibition by melatonin. Furthermore, melatonin induced Apaf-1 expression, triggered cytochrome C release, and stimulated caspase-3 and caspase-9 activities and cleavage, leading to an activation of the Apaf-1-dependent apoptotic pathway. Pretreatment with an Apaf-1-specific siRNA effectively attenuated the melatonin-induced apoptosis. These results therefore indicate that melatonin inhibits cell proliferation and induces apoptosis in MDA-MB-361 breast cancer cells in vitro by simultaneously suppressing the COX-2/PGE2, p300/NF-κB, and PI3K/Akt/signaling and activating the Apaf-1/caspase-dependent apoptotic pathway.
褪黑素具有抗炎和抗癌作用，可能是预防和治疗癌症的化学预防剂和化疗药物，但涉及的确切机制在很大程度上仍未解决。在这项研究中，我们评估了褪黑素在人 MDA-MB-361 乳腺癌细胞中的作用机制。褪黑素在药理浓度（10(-3) m）下显著抑制细胞增殖并呈剂量依赖性诱导细胞凋亡。观察到的增殖抑制伴随着褪黑素介导的 COX-2、p300 和 NF-κB 信号的抑制。褪黑素显著抑制 COX-2 表达和前列腺素 E2（PGE2）的产生，阻断 p300 组蛋白乙酰转移酶活性和 p300 介导的 NF-κB 乙酰化，从而阻断 NF-κB 结合和 p300 募集到 COX-2 启动子。用 COX-2 或 p300 选择性抑制剂预处理可阻断褪黑素诱导的细胞增殖抑制，而 PGE2 处理或 COX-2 转染可逆转褪黑素的抑制作用。此外，褪黑素显著抑制 PI3K、Akt、PRAS40 和 GSK-3 蛋白的磷酸化，从而使 PI3K/Akt 信号通路失活。用 PI3K 或 Akt 选择性抑制剂或 Akt 特异性 siRNA 预处理可阻断褪黑素介导的细胞增殖抑制。相反，组成型激活 Akt 的基因转染可有效逆转褪黑素的抑制作用。此外，褪黑素诱导 Apaf-1 表达，触发细胞色素 C 释放，并刺激 caspase-3 和 caspase-9 的活性和裂解，从而激活 Apaf-1 依赖性凋亡途径。用 Apaf-1 特异性 siRNA 预处理可有效减弱褪黑素诱导的凋亡。因此，这些结果表明，褪黑素通过同时抑制 COX-2/PGE2、p300/NF-κB 和 PI3K/Akt/信号通路并激活 Apaf-1/caspase 依赖性凋亡途径，抑制 MDA-MB-361 乳腺癌细胞的体外增殖并诱导细胞凋亡。
