School of Life Sciences, Zhengzhou University, Zhengzhou 450001, China.
Department of Pharmaceutical Engineering, School of Chemistry, Wuhan University of Technology, Wuhan 430070, China.
J Biol Chem. 2018 May 25;293(21):7982-7992. doi: 10.1074/jbc.RA117.001321. Epub 2018 Mar 27.
Liver tumor–initiating cells (TICs) form small subsets of cells in hepatocellular tumors and account for tumorigenesis, metastasis, recurrence, and drug resistance. Recently, we found that the transcription factor Zic family member 2 (ZIC2) is highly expressed in liver TICs and required for their self-renewal. However, the molecular mechanisms underlying self-renewal of liver TICs remain unclear. Here, using expression profiling and CRISPR-interference assays with clinical samples of human liver cancers, we identified a long noncoding RNA (lncRNA), lncZic2, that is located near the ZIC2 locus and was highly expressed in liver cancer and liver TICs. We found that lncZic2 is required for the self-renewal of liver TICs in a ZIC2-independent manner. lncZic2 drove the expression of myristoylated alanine-rich protein kinase C substrate (MARCKS) and MARCKS-like 1 (MARCKSL1), whose expression levels were increased during liver tumorigenesis and liver TIC self-renewal. Mechanistically, lncZic2 interacted with BRM/SWI2-related gene 1 (BRG1) and recruited this transcriptional regulator to the promoters of the MARCKS and MARCKSL1 gene, which activated expression of these genes. Moreover, we noted that depletion of lncZic2 and BRG1 decreases MARCKS and MARCKSL1 expression and diminishes liver TIC levels. In conclusion, lncZic2 is required for the self-renewal of liver TICs by up-regulating MARCKS and MARCKSL1 gene expression via the transcription factor BRG1. Our findings suggest that the lncZic2–BRG1–MARCKS/MARCKSL1 signaling cascade might be a potential target for eliminating liver TICs in the management of liver cancer.
肝肿瘤起始细胞（TICs）在肝细胞肿瘤中形成细胞的小亚群，并且负责肿瘤发生、转移、复发和耐药性。最近，我们发现锌指蛋白家族成员 2（ZIC2）转录因子在肝 TIC 中高度表达，并且是其自我更新所必需的。然而，肝 TIC 自我更新的分子机制尚不清楚。在这里，我们使用人类肝癌的临床样本进行表达谱分析和 CRISPR 干扰实验，鉴定出一个长链非编码 RNA（lncRNA）lncZic2，它位于 ZIC2 基因座附近，在肝癌和肝 TIC 中高度表达。我们发现 lncZic2 以 ZIC2 非依赖性方式维持肝 TIC 的自我更新。lncZic2 驱动肌氨酸丰富的蛋白激酶 C 底物（MARCKS）和 MARCKS 样蛋白 1（MARCKSL1）的表达，其表达水平在肝肿瘤发生和肝 TIC 自我更新过程中增加。在机制上，lncZic2 与 BRM/SWI2 相关基因 1（BRG1）相互作用，并将该转录调节剂募集到 MARCKS 和 MARCKSL1 基因的启动子上，从而激活这些基因的表达。此外，我们注意到，lncZic2 和 BRG1 的耗竭降低了 MARCKS 和 MARCKSL1 的表达，并减少了肝 TIC 水平。总之，lncZic2 通过上调 MARCKS 和 MARCKSL1 基因的表达来维持肝 TIC 的自我更新，该过程通过转录因子 BRG1 进行。我们的研究结果表明，lncZic2-BRG1-MARCKS/MARCKSL1 信号级联可能是消除肝癌中肝 TIC 的潜在靶点。
