结直肠癌表观沉默蛋白Bmi1与Notch信号通路调控的关系

目的 探讨人结直肠癌中表观沉默蛋白Bmi1和Notch1的蛋白表达与结直肠癌病理特征的关系,观察Notch通路对结直肠癌细胞增殖凋亡及Bmi1表达的影响。方法 应用免疫组织化学技术(SP法)检测85例结直肠癌组织及其邻近正常肠黏膜中Notch1及Bmi1的蛋白表达;将Notch1通路中γ-分泌酶抑制剂DAPT,作用于结肠癌SW480细胞株,运用噻唑蓝(MTT)比色法检测细胞增殖状态;流式细胞仪观察其对细胞凋亡的影响,Western blot检测ICN及Bmi1蛋白的表达。结果 结直肠癌组织中Notch1和Bmi1蛋白表达的阳性率明显高于正常肠黏膜(P＜0.05),分别为61.2％ (52/85)对15.3％ (13/85)和56.5％ (48/85)对17.6％ (15/85);Bmi1表达率与Notch1表达率呈正相关(r =0.625,P＜0.01),并与肿瘤分化程度、分期及淋巴结转移有关(P＜0.05);阻断Notch1通路(DAPT)可抑制SW480细胞的增殖,诱导其凋亡,作用12、24、36 h后其增殖抑制率分别为13.1％、17.5及22.6％,而凋亡率为32.7％、45.6％及67.2％;同时Notch1胞内活性段ICN随作用时间延长而下降,而Bmi1表达水平也逐渐降低。结论 结直肠癌中Bmi1与Notch1表达密切相关,阻断Notch通路可抑制Bmi1表达,同时可抑制结肠癌细胞的增殖,促进其凋亡。

Relationship between Notch signal transduction pathway and expression of Bmi1 in colorectal caner cells

Objective To investigate the Notch1 and Bmi1 protein levels in human colorectal cancer samples and their correlation with clinicopathological parameters of colorectal cancer and reveal the mechanism of Notch signal transduction pathway regulating the expression of Bmi1 in colorecta caner cells.Methods We assessed Notch1 and Bmi1 protein levels in 85 cases of colorectal cancer and adjacent normal tissue by immunohistochemistry. SW480 cells were treated with DAPT (γ-secretase inhibitor) at different time points. MTT assay and flow cytometry were used to measure the proliferation and apoptosis of SW480 cells. The expression of ICN and Bmi1 were measured by Western blotting. Results Notch1 and Bmi1 protein levels were increased in colorectal cancer cells as compared with adjacent normal mucosa (P ＜0. 05 ). The positive rate of Notch1 and Bmi1 expression in gastric cancer tissues was 61.2％ (52/85) and 56. 5％ (48/85), significantly higher than in the adjacent noncancerous tissues15.3％(13/85) and 17. 6％ ( 15/85), respectively]. The overexpression of Notch1 and Bmi1 was related to differentiation and lymph nodes metastasis in colorectal cancer (P ＜ 0. 05 ). There was a positive correlation between Notch1 and Bmi1 protein levels (r =0. 625, P ＜ 0. 01 ). Treating SW480 with DAPT resulted in significant growth inhibition and apoptosis induction. Inhibition ratio for cell proliferation after treatment with DAPT ( 12, 24 and 36 h) was 13.1％, 17. 5％ and 22. 6％, respectively; Apoptosis rate was 32. 7％, 45.6％ and 67. 2％, respectively. DAPT could down-regulated ICN and Bmi1. Conclusion Overexpression of Notch1 and Bmi1 may play a critical role in the development of colorectal cancer. Notch signal transduction pathway regulates the expression of Bmi1 in colorectal cancer cells. Blockade of Notch1 signal pathway can inhibit proliferation and accelerate apoptosis of colorectal cancer cells.