Zhu Hongbo, Guo Wei, Zhang Lidong, Wu Shuhong, Teraishi Fuminori, Davis John J, Dong Fengqin, Fang Bingliang
Department of Surgical Oncology, Sir Run Run Shaw Hospital, Zhejiang University, China.
Cancer Biol Ther. 2005 Jul;4(7):781-6. doi: 10.4161/cbt.4.7.1897. Epub 2005 Jul 6.
Proteasome inhibitors can resensitize cells that are resistant to tumor necrosis factor-related apoptotic-inducing ligand (TRAIL)-mediated apoptosis. However, the underlying mechanisms of this effect are unclear. To characterize the mechanisms of interaction between proteasome inhibitors and TRAIL protein, we evaluated the effects of combined treatment with the proteasome inhibitors bortezomib and MG132 and TRAIL protein on two TRAIL-resistant human colon cancer cell lines, DLD1-TRAIL/R and LOVO-TRAIL/R. Both bortezomib and MG132 in combination with TRAIL enhanced apoptotosis induction in these cells, as evidenced by enhanced cleavage of caspases 8, 9, and 3, Bid, poly(ADP-ribose) polymerase and by the release of cytochrome C and Smac. Subsequent studies showed that combined treatment with bortezomib or MG132 resulted in an increase of death receptor (DR) 5 and Bik at protein levels but had no effects on protein levels of DR4, Bax, Bak, Bcl-2, Bcl-XL or Flice-inhibitory protein (FLIP). Moreover, c-Jun N-terminal kinase (JNK) is activated by these proteasome inhibitors. Blocking JNK activation with the JNK inhibitor SP600125 attenuated DR5 increase, but enhancement of apoptosis induction and increase of Bik protein were not affected. However, bortezomib-mediated TRAIL sensitization was partially blocked by using siRNA to knockdown Bik. Thus, our data suggests that accumulation of Bik may be critical for proteasome inhibitor-mediated resensitization of TRAIL.
蛋白酶体抑制剂可使对肿瘤坏死因子相关凋亡诱导配体（TRAIL）介导的凋亡产生抗性的细胞重新敏感。然而，这种效应的潜在机制尚不清楚。为了阐明蛋白酶体抑制剂与TRAIL蛋白之间的相互作用机制，我们评估了蛋白酶体抑制剂硼替佐米和MG132与TRAIL蛋白联合处理对两种TRAIL抗性人结肠癌细胞系DLD1-TRAIL/R和LOVO-TRAIL/R的影响。硼替佐米和MG132与TRAIL联合使用均增强了这些细胞的凋亡诱导，这通过半胱天冬酶8、9和3、Bid、聚（ADP-核糖）聚合酶的切割增强以及细胞色素C和Smac的释放得以证明。随后的研究表明，硼替佐米或MG132联合处理导致死亡受体（DR）5和Bik的蛋白水平增加，但对DR4、Bax、Bak、Bcl-2、Bcl-XL或FLICE抑制蛋白（FLIP）的蛋白水平没有影响。此外，这些蛋白酶体抑制剂激活了c-Jun氨基末端激酶（JNK）。用JNK抑制剂SP600125阻断JNK激活可减弱DR5的增加，但凋亡诱导的增强和Bik蛋白的增加不受影响。然而，使用小干扰RNA敲低Bik可部分阻断硼替佐米介导的TRAIL致敏作用。因此，我们的数据表明，Bik的积累可能是蛋白酶体抑制剂介导的TRAIL重新致敏的关键因素。
