Department of Radiation Oncology, The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei 050011, P.R. China.
Department of Clinical Laboratory, The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei 050011, P.R. China.
Oncol Rep. 2018 Feb;39(2):667-678. doi: 10.3892/or.2017.6136. Epub 2017 Dec 5.
B-cell‑specific Moloney murine leukaemia virus integration site-1 (BMI-1) contributes to the growth of tumour cells post-irradiation (IR). The aim of the present study was to characterize the effects of BMI-1 on cell viability, radiosensitivity and its mechanisms of action in oesophageal squamous cell cancer (ESCC). Western blotting and immunohistochemistry were employed to evaluate the protein expression of BMI-1 in ESCC cells and specimens, respectively. Additionally, the protein expression levels of BMI-1, H2AK119ub and γH2AX in ESCC cells were detected following different doses of IR and at different times after IR. The protein expression levels of MDC1 and 53BP1 were also measured. Flow cytometry and MTT assays were used to determine cell cycle progression, apoptosis and cell viability. The phosphatidylinositol 3-kinase inhibitor LY294002 and the agonist IGF-1 were employed to suppress or induce the phosphorylation of Akt to determine whether BMI-1 induces radioresistance in ESCC cells via activation of the PI3K/Akt pathway. The expression of BMI-1 was higher in ESCC tissues and cells compared with that in normal oesophageal tissues and cells. In addition, BMI-1 was positively related to tumour size and lymph node metastases and negatively to the overall survival of ESCC patients. IR induced the expression of BMI-1, H2AK119ub and γH2AX in a dose- and time-dependent manner. BMI-1 knockdown lowered the expression of γH2AX, MDC1 and 53BP1, suppressed cell viability and increased radiosensitivity. G2/M phase arrest was eliminated; this was followed by an increased proportion of cells entering the G0/G1 phase after IR and BMI-1 knockdown via the upregulation of P16 and downregulation of cyclin D2 and cyclin-dependent kinase-4. Moreover, BMI-1 knockdown increased cell apoptosis, downregulated MCL-1 and p-Akt and upregulated Bax. Additionally, the inhibitory effect of the downregulation of p-Akt by LY294002 on tumour cell viability was identical to that of BMI-1 knockdown, while the kinase agonist IGF-1 reversed the effects of BMI-1 knockdown on cell viability and radiosensitivity. Taken together, BMI-1 knockdown induces radiosensitivity in ESCC and significantly inhibits cell viability, which may contribute to an increased proportion of cells in the G0/G1 phase and cell apoptosis via suppression of the PI3K/Akt signalling pathway.
B 细胞特异性 Moloney 鼠白血病病毒整合位点 1（BMI-1）有助于肿瘤细胞在辐照后（IR）的生长。本研究旨在探讨 BMI-1 对食管鳞状细胞癌（ESCC）细胞活力、放射敏感性及其作用机制的影响。Western blot 和免疫组化分别用于评估 ESCC 细胞和标本中 BMI-1 的蛋白表达。此外，还检测了不同剂量 IR 后和 IR 后不同时间 ESCC 细胞中 BMI-1、H2AK119ub 和 γH2AX 的蛋白表达水平。还测量了 MDC1 和 53BP1 的蛋白表达水平。流式细胞术和 MTT 测定用于确定细胞周期进程、细胞凋亡和细胞活力。使用磷脂酰肌醇 3-激酶抑制剂 LY294002 和激动剂 IGF-1 抑制或诱导 Akt 的磷酸化，以确定 BMI-1 是否通过激活 PI3K/Akt 通路诱导 ESCC 细胞的放射抗性。ESCC 组织和细胞中的 BMI-1 表达高于正常食管组织和细胞。此外，BMI-1 与肿瘤大小和淋巴结转移呈正相关，与 ESCC 患者的总生存率呈负相关。IR 以剂量和时间依赖的方式诱导 BMI-1、H2AK119ub 和 γH2AX 的表达。BMI-1 敲低降低了 γH2AX、MDC1 和 53BP1 的表达，抑制了细胞活力并增加了放射敏感性。G2/M 期阻滞消除；随后，IR 和 BMI-1 敲低后，通过上调 P16 和下调细胞周期蛋白 D2 和细胞周期蛋白依赖性激酶 4，进入 G0/G1 期的细胞比例增加。此外，BMI-1 敲低增加了细胞凋亡，下调了 MCL-1 和 p-Akt，并上调了 Bax。此外，LY294002 下调 p-Akt 对肿瘤细胞活力的抑制作用与 BMI-1 敲低的作用相同，而激酶激动剂 IGF-1 逆转了 BMI-1 敲低对细胞活力和放射敏感性的影响。总之，BMI-1 敲低可诱导 ESCC 放射敏感性，并显著抑制细胞活力，这可能通过抑制 PI3K/Akt 信号通路增加 G0/G1 期细胞比例和细胞凋亡。
