Department of Pharmacology, Penn State Hershey Cancer Institute, Pennsylvania State University College of Medicine and Milton S. Hershey Medical Center, Hershey, PA, USA.
Oncogene. 2012 Feb 23;31(8):1055-64. doi: 10.1038/onc.2011.290. Epub 2011 Jul 11.
Nucleus accumbens-1 (NAC1), a nuclear factor belonging to the BTB/POZ gene family, is known to have important roles in proliferation and growth of tumor cells and in chemotherapy resistance. Yet, the mechanisms underlying how NAC1 contributes to drug resistance remain largely unclear. We report here that autophagy was involved in NAC1-mediated resistance to cisplatin, a commonly used chemotherapeutic drug in the treatment of ovarian cancer. We found that treatment with cisplatin caused an activation of autophagy in ovarian cancer cell lines, A2780, OVCAR3 and SKOV3. We further demonstrated that knockdown of NAC1 by RNA interference or inactivation of NAC1 by inducing the expression of a NAC1 deletion mutant that contains only the BTB/POZ domain significantly inhibited the cisplatin-induced autophagy, resulting in increased cisplatin cytotoxicity. Moreover, inhibition of autophagy and sensitization to cisplatin by NAC1 knockdown or inactivation were accompanied by induction of apoptosis. To confirm that the sensitizing effect of NAC1 inhibition on the cytotoxicity of cisplatin was attributed to suppression of autophagy, we assessed the effects of the autophagy inhibitors 3-methyladenosine and chloroquine, and small interfering RNAs (siRNAs) targeting beclin 1 or Atg5 on the cytotoxicity of cisplatin. Treatment with 3-methyladenosine, chloroquine or beclin 1 and Atg5-targeted siRNA also enhanced the sensitivity of SKOV3, A2780 and OVCAR3 cells to cisplatin, indicating that suppression of autophagy indeed renders tumor cells more sensitive to cisplatin. Regulation of autophagy by NAC1 was mediated by the high-mobility group box 1 (HMGB1), as the functional status of NAC1 was associated with the expression, translocation and release of HMGB1. The results of our study not only revealed a new mechanism determining cisplatin sensitivity but also identified NAC1 as a novel regulator of autophagy. Thus, the NAC1-mediated autophagy may be exploited as a new target for enhancing the efficacy of cisplatin against ovarian cancer and other types of malignancies.
伏隔核-1（NAC1）是一种属于 BTB/POZ 基因家族的核因子，已知其在肿瘤细胞的增殖和生长以及化疗耐药性中具有重要作用。然而，NAC1 如何促进耐药性的机制在很大程度上仍不清楚。我们在此报告，自噬参与了 NAC1 介导的顺铂耐药性，顺铂是治疗卵巢癌中常用的化疗药物。我们发现，顺铂处理导致卵巢癌细胞系 A2780、OVCAR3 和 SKOV3 中的自噬激活。我们进一步证明，通过 RNA 干扰敲低 NAC1 或通过诱导仅包含 BTB/POZ 结构域的 NAC1 缺失突变体的表达来失活 NAC1，可显著抑制顺铂诱导的自噬，从而增加顺铂的细胞毒性。此外，NAC1 敲低或失活抑制自噬并使顺铂敏感与凋亡诱导有关。为了证实 NAC1 抑制对顺铂细胞毒性的敏化作用归因于自噬的抑制，我们评估了自噬抑制剂 3-甲基腺苷和氯喹以及针对 beclin 1 或 Atg5 的小干扰 RNA（siRNA）对顺铂细胞毒性的影响。用 3-甲基腺苷、氯喹或 beclin 1 和 Atg5 靶向 siRNA 处理也增强了 SKOV3、A2780 和 OVCAR3 细胞对顺铂的敏感性，表明抑制自噬确实使肿瘤细胞对顺铂更敏感。NAC1 通过高迁移率族框 1（HMGB1）调节自噬，因为 NAC1 的功能状态与 HMGB1 的表达、易位和释放有关。我们的研究结果不仅揭示了决定顺铂敏感性的新机制，而且还确定 NAC1 是自噬的新调节剂。因此，NAC1 介导的自噬可被利用为增强顺铂对卵巢癌和其他类型恶性肿瘤疗效的新靶标。
