凋亡抑制蛋白XIAP和促凋亡因子Smac在胰腺癌化疗抵抗中的调控作用

目的探讨凋亡抑制蛋白XIAP和促凋亡因子Smac在胰腺癌细胞化疗抵抗中的作用及其分子机制。方法应用流式细胞术检测顺铂、5-FU介导的Panc-1、BXPC-3的凋亡率及胞浆染色分析细胞XIAP表达变化,Western-blot分析XIAP、Smac、Caspase-3表达水平；构建pEGFP-N1／Smac真核表达载体并转染胰腺癌Panc-1细胞,流式细胞术检测转染胞浆表达型 Smac基因对Panc-1细胞凋亡敏感性的作用。结果与BXPC-3细胞相比,Panc-1对顺铂或5-FU介导的凋亡具有较强抵抗性,Western blot分析显示Panc-1细胞高表达XIAP,在化疗药物作用下化疗敏感细胞BXPC-3胞浆内XIAP水平下降明显多于Panc-1细胞,而且凋亡的BXPC-3细胞释放入胞浆内的成熟 Smac蛋白水平明显高于Panc-1细胞。转染胞浆表达型Smac基因至化疗抵抗Panc-1细胞,可明显下调其XIAP表达水平,促进效应 Caspase-3分子活化,显著提高顺铂、5-FU诱导的细胞凋亡率。结论在化疗药物诱导的凋亡中,线粒体释放Smac下调XIAP是胰腺癌化疗敏感性的重要决定因素,而上调Smac活性蛋白的胞浆表达作为一种有效调节信号,通过拮抗XIAP的凋亡抑制作用协同化疗药物促进胰腺癌细胞凋亡。

Regulatory Effects of X-linked Inhibitor of Apoptosis Protein and Pro-apoptotic Protein Smac on Apoptosis Resistance to Chemotherapy in Pancreatic Cancer Cells

To investigate the relation of X-linked inhibitor of apoptosis (XIAP) and second mitochondria-derived activator of caspase (Smac) signaling pathway to chemoresistance in human pancreatic cancer Panc-1 and BXPC-3 cells. Methods: Apoptosis and the changes of XIAP expression in permeabilized cells induced by cisplatin and 5-fluorouracil (FU) were measured by flow cytometry. The cytosolic expression of XIAP, Smac and caspase-3 was detected by Western blot. A recombinant plasmid vector pEGFP-N1/Smac was constructed and transfected into of Pane-1 cells. The effect of cytosolic overexpression of Smac on apoptosis of Pane-1 cells was evaluated by flow cytometry. Results: Pane-1 was more resistant to cisplatin or 5-FU induced apoptosis than BXPC-3. Western blot revealed that chelnoresistant Panc-1 highly expressed XIAP, and increased cytosolic expression of Smac might be responsible for the marked down-regulation of XIAP in chemo-sensitive BXPC-3 cells after exposure to cisplatin or 5-FU. Furthermore, cytosolic overexpression of Smac could significantly down-regulate the levels of XIAP and promote the activity of caspase-3, as well as sensitize Pane-1 cells to anticancer drug-induced apoptosis. Conclusion: Anticancer drug-induced apoptosis requires mitochondrial release of Smac and downregulation of XIAP, which may be an important determinant of chemo-sensitivity in pancreatic cancer cells. Up-regulation of cytosolic expression of Smac may act as an effective modifying signal to overcome apoptosis resistance to chemotherapy in pancreatic cancer cells.