Su Jung-Chen, Tseng Ping-Hui, Hsu Cheng-Yi, Tai Wei-Tien, Huang Jui-Wen, Ko Ching-Huai, Lin Mai-Wei, Liu Chun-Yu, Chen Kuen-Feng, Shiau Chung-Wai
Institute of Biopharmaceutical Sciences, National Yang-Ming University, Taipei, Taiwan.
Department of Medical Research, National Taiwan University Hospital, Taipei, Taiwan; National Center of Excellence for Clinical Trial and Research, National Taiwan University Hospital, Taipei, Taiwan.
Oncotarget. 2014 Jul 15;5(13):4909-19. doi: 10.18632/oncotarget.2054.
Obatoclax is a small molecule which targets the Bcl-2 family, and is to treat leukemia, lymphoma and lung carcinoma. Previously, an obatoclax analogue, SC-2001, was found to disrupt the protein-protein interactions of the Bcl-2 family and also repress Bcl-XL and Mcl-1 expression via STAT3 inactivation. Here, we report a novel mechanism of autophagy induction by SC-2001 in liver cancer cells. The findings indicate that SC-2001 induced the autophagy marker LC3-II in four hepatocellular carcinoma (HCC) cells. Autophagosomes induced by SC-2001-treated cells were confirmed by electron microscopy. SC-2001 activated SHP-1, dephosphorylated STAT3 and Mcl-1, and subsequently released free beclin 1. Overexpression of STAT3 and Mcl-1 in PLC5 cells attenuated the induction of SC-2001 on autophagy. Abolishment of SHP-1 by a specific inhibitor aboragated the autophagic effects induced by SC-2001. In addition, it was further revealed that RFX-1, a transcription factor of SHP-1, is a critical regulator in SC-2001-mediated autophagy. Downregulation of RFX-1 by si-RNA protected cells from SC-2001-induced autophagy. Importantly, Huh7 tumor-bearing nude mice treated with SC-2001 showed downregulation of Mcl-1 and p-STAT3 protein expression and upregulation of SHP-1, LC3II, and RFX-1 protein expression. In summary, our data suggest that SC-2001 induces autophagic cell death in a RFX1/SHP-1/STAT3/Mcl-1 signaling cascade.
obatoclax是一种靶向Bcl-2家族的小分子，用于治疗白血病、淋巴瘤和肺癌。此前，发现一种obatoclax类似物SC-2001可破坏Bcl-2家族的蛋白质-蛋白质相互作用，并通过STAT3失活抑制Bcl-XL和Mcl-1的表达。在此，我们报告了SC-2001在肝癌细胞中诱导自噬的新机制。研究结果表明，SC-2001在四种肝癌（HCC）细胞中诱导了自噬标志物LC3-II。通过电子显微镜证实了SC-2001处理的细胞诱导的自噬体。SC-2001激活SHP-1，使STAT3和Mcl-1去磷酸化，随后释放游离的beclin 1。PLC5细胞中STAT3和Mcl-1的过表达减弱了SC-2001对自噬的诱导作用。一种特异性抑制剂消除SHP-1可消除SC-2001诱导的自噬效应。此外，进一步揭示，SHP-1的转录因子RFX-1是SC-2001介导的自噬中的关键调节因子。通过si-RNA下调RFX-1可保护细胞免受SC-2001诱导的自噬。重要的是，用SC-2001处理的荷Huh7肿瘤裸鼠显示Mcl-1和p-STAT3蛋白表达下调，SHP-1、LC3II和RFX-1蛋白表达上调。总之，我们的数据表明，SC-2001在RFX1/SHP-1/STAT3/Mcl-1信号级联中诱导自噬性细胞死亡。
