Institute of Digestive Disease and Department of Medicine and Therapeutics, Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong.
J Pathol. 2013 Aug;230(4):441-52. doi: 10.1002/path.4206.
Smad7 is a principal inhibitor of the TGFβ-Smad signalling pathway. We have investigated the functional significance of Smad7 in hepatocellular carcinoma (HCC). Smad7 knockout (KO) and wild-type (WT) mice were injected with diethylnitrosamine (DEN) to induce HCC. The effects of Smad7 on cellular features were examined in HCC cells, using a Smad7 over-expression or deletion approach. Signalling pathway components modulated by Smad7 in HCC were evaluated using luciferase reporter assay and co-immunoprecipitation. Smad7 was down-regulated in human HCCs compared with the adjacent normal tissues (p < 0.001). Smad7 KO mice were more susceptible to DEN-induced HCC than WT mice (78% versus 22%, p < 0.05). HCCs from KO mice displayed a greater proliferation activity (p < 0.05) and a reduced apoptotic index compared with WT littermates (p < 0.05). Deletion of Smad7 promoted cell proliferation in primary cultured HCC cells. In addition, over-expression of Smad7 in HCC cell lines markedly suppressed cell growth (p < 0.0001) and colony formation (p < 0.01). Cell cycle analysis revealed an increase in the G1 phase and a reduction in the S-phase populations, accompanied by up-regulation of p27(Kip1) and down-regulation of cyclin D1. Smad7 increased cell apoptosis (p < 0.01) by mediating an intrinsic [caspase-9, caspase-3 and poly(ADP-ribose) polymerase] apoptotic pathway. Moreover, Smad7 inhibited NF-κB signalling by interacting with TAB2, an upstream activator of NF-κB, and inhibited TGFβ signalling by suppressing phosphorylation of Smad3. In conclusion, loss of Smad7 enhances susceptibility to HCC. Smad7 suppresses HCC cell growth by inhibiting proliferation and G1 -S phase transition and inducing apoptosis through attenuation of NF-κB and TGFβ signalling. Smad7 acts as a potential tumour suppressor in liver.
Smad7 是 TGFβ-Smad 信号通路的主要抑制剂。我们研究了 Smad7 在肝细胞癌 (HCC) 中的功能意义。使用二乙基亚硝胺 (DEN) 注射 Smad7 敲除 (KO) 和野生型 (WT) 小鼠诱导 HCC。使用 Smad7 过表达或缺失方法在 HCC 细胞中检查 Smad7 对细胞特征的影响。使用荧光素酶报告基因测定和共免疫沉淀评估 Smad7 调节的 HCC 中的信号通路成分。与相邻正常组织相比，Smad7 在人 HCC 中下调 (p < 0.001)。与 WT 小鼠相比，Smad7 KO 小鼠对 DEN 诱导的 HCC 更敏感 (78%对 22%，p < 0.05)。KO 小鼠的 HCC 显示出更高的增殖活性 (p < 0.05) 和降低的凋亡指数与 WT 同窝仔相比 (p < 0.05)。Smad7 的缺失促进原代培养的 HCC 细胞的增殖。此外，在 HCC 细胞系中过表达 Smad7 显著抑制细胞生长 (p < 0.0001) 和集落形成 (p < 0.01)。细胞周期分析显示 G1 期增加，S 期减少，同时 p27(Kip1)上调，cyclin D1 下调。Smad7 通过介导内在 [caspase-9、caspase-3 和多聚 (ADP-核糖) 聚合酶] 凋亡途径增加细胞凋亡 (p < 0.01)。此外，Smad7 通过与 TAB2 相互作用抑制 NF-κB 信号，TAB2 是 NF-κB 的上游激活物，并通过抑制 Smad3 的磷酸化抑制 TGFβ 信号。总之，Smad7 的缺失增强了 HCC 的易感性。Smad7 通过抑制增殖和 G1-S 期转变以及通过减弱 NF-κB 和 TGFβ 信号诱导细胞凋亡来抑制 HCC 细胞生长。Smad7 在肝脏中作为潜在的肿瘤抑制因子发挥作用。
