抑癌基因PTEN对肝癌细胞增殖的抑制及作用机制

目的探讨抑癌基因PTEN对肝癌细胞增殖和细胞周期的调控作用。方法构建野生型PTEN基因和突变型PTEN基因的真核表达载体pEGFP—WT—PTEN和pEGFP—PTEN;G129R。采用脂质体介导的基因转染法,分别将上述载体转染不表达PTEN蛋白的人肝细胞肝癌细胞系HHCC,经G418筛选,获得稳定表达PTEN蛋白的细胞克隆。以流式细胞仪测定细胞周期,以Western blot法分析稳定表达PTEN蛋白的肝癌细胞内源性的磷酸化AKT表达水平,同时与未进行基因转染和转染空载体pEGFP-C1的HHCC细胞进行对照。结果稳定表达野生型PTEN蛋白的肝癌细胞,细胞生长受到明显抑制,与转染空载体的HHCC细胞比较,G1期细胞比例显著增高,G2期和S期细胞比例显著降低,且差异有统计学意义（P〈0．05）;而转染突变型PTEN基因的HHCC细胞,与转染空载体的HHCC细胞比较,差异无统计学意义（P〉0.05）。与转染空载体的HHCC细胞比较,稳定表达野生型PTEN蛋白的HHCC细胞,其内源性磷酸化AKT水平明显减低;而转染突变型PTEN基因的HHCC细胞,其AKT水平无明显变化。结论野生型PTEN基因对肝癌细胞周期具有调控作用,而突变型PTEN基因丧失对肝癌细胞周期的调控作用;野生型PTEN基因可能通过降低AKT的活化而实现对肝癌细胞周期的调控。

Inhibitory effect of tumor suppressor gene PTEN on hepatocellular carcinoma cell line HHCC proliferation and its mechanisms of action

Objective To study the effect of tumor suppressor gene PTEN on proliferation and cell cycle of hepatocellular carcinoma cell line HHCC. Methods Firstly, eukaryotic expression vectors of wild type and mutated type of PTEN gene were constructed, named as pEGFP-WT-PTEN and pEGFP-PTEN; G129R, respectively. Lipofectamine2000 was used to transfect the constructed expression vectors into hepatocellular carcinoma cell line HHCC which was PTEN protein negative. G418 was used to select the cell clones constantly expressing PTEN protein. Flow cytometry was used to assay the cell cycle of HHCC transfected by above mentioned eukaryotic expression vectors and non-transfected cell line HHCC. Intrinsic 473-phosphorylated AKT representing the level of active AKT was assayed by Western blot. The nontransfected HHCC served as control. Results The proliferation of HHCC constantly expressing PTEN protein was obviously inhibited compared with HHCC cells transfected with mutated PTEN gene and empty vectors, and non-transfected HHCC cells. The number of HHCC cells transfected with wild type PTEN gene at G1 phase, G2 phase and S phase was 70.8% , 6.8% and 22.4%, respectively. Compared with control group transfected with empty vector, the numbr, of G1 phase HHCC cells constantly expressing wild type-PTEN protein was significantly higher than that of control. The number of cells in G2 and S phase was significantly lower than that of control. However, the number of cells in G1 phase, G2 phase and S phase of HHCC transfected with mutant PTEN was 63. 2%, 10. 1% and 26. 7% , respectively. There was no significant difference compared with control group. Western blot result showed that the intrinsic level of 473- phosphorylated AKT of HHCC constantly expressing wild type PTEN protein was down-regulated, and that of HHCC transfected with mutated PTEN gene was equal to that of control. Conclusion Wild type PTEN gene can inhibit the proliferation of hepatocellular carcinoma cells at G1 phase. The mechanism is possibly relatedwith intrinsic activity of AKT, which is down-regulated by wild type PTEN.