The Repressive Effect of miR-148a on TGF beta-SMADs Signal Pathway Is Involved in the Glabridin-Induced Inhibition of the Cancer Stem Cells-Like Properties in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related mortality worldwide. Current standard practices for treatment of HCC are less than satisfactory because of cancer stem cells (CSCs)-mediated post-surgical recurrence. For this reason, targeting the CSCs or the cancer cells with CSCs-like properties has become a new approach for the treatment of HCC. GLA exhibits anti-tumor effects in that it attenuates the proliferation, migration, invasion, and angiogenesis of human cancer cells. However, the functions of GLA in the regulation of CSCs-like properties in HCC cells, and the molecular mechanisms underlying in remain obscure. Here we found that GLA attenuated the CSCs-like properties by the microRNA-148a (miR-148a)-mediated inhibition of transforming growth factor beta (TGF-β)/SMAD2 signal pathway in HCC cell lines (HepG2, Huh-7, and MHCC97H). Indeed, GLA inhibited the activations/expressions of both TGFβ-induced and the endogenous SMAD2. Further, GLA improved the expression of miR-148a in a dose/time-dependent manner. MiR-148a, which targeted the SMAD2-3′UTR, decreased the expression and function of SMAD2. Knockdown of miR-148a abolished the GLA-induced inhibition of TGF-β/SMAD2 signal pathway and the CSCs-like properties in HCC cells. Our study found a novel mechanism that GLA inhibits the CSCs-like properties of HCC cells by miR-148a-mediated inhibition of TGF-β/SMAD2 signal pathway, which may help to identify potential targets for the therapies of HCC.

肝细胞癌（Hepatocellular carcinoma, HCC）是全球范围内第三大癌症相关死亡病因。当前针对HCC的标准治疗方案疗效欠佳，究其根源在于癌症干细胞（cancer stem cells, CSCs）介导的术后复发。正因如此，靶向CSCs或具备CSCs样特性的肿瘤细胞，已成为HCC治疗的新兴策略。GLA在抗肿瘤方面展现出明确功效，可抑制人类肿瘤细胞的增殖、迁移、侵袭及血管生成过程。然而，GLA在调控HCC细胞CSCs样特性中的具体作用，及其潜在分子机制至今仍不明晰。本研究发现，在HCC细胞系（HepG2、Huh-7及MHCC97H）中，GLA通过microRNA-148a（miR-148a）介导的转化生长因子β（transforming growth factor beta, TGF-β）/SMAD2信号通路抑制作用，削弱了细胞的CSCs样特性。实验证实，GLA可同时抑制TGF-β诱导激活及内源性的SMAD2激活与表达。进一步研究表明，GLA能够以剂量依赖性及时间依赖性方式上调miR-148a的表达水平。靶向SMAD2 3'非翻译区（3'UTR）的miR-148a，可降低SMAD2的表达与功能。敲低miR-148a可抵消GLA诱导产生的、对HCC细胞中TGF-β/SMAD2信号通路及CSCs样特性的抑制作用。本研究揭示了一种全新机制：GLA通过miR-148a介导的TGF-β/SMAD2信号通路抑制，削弱HCC细胞的CSCs样特性，这一发现可为HCC治疗的潜在靶点筛选提供新的理论依据。