Longley D B, Wilson T R, McEwan M, Allen W L, McDermott U, Galligan L, Johnston P G
Drug Resistance Group, Centre for Cancer Research and Cell Biology, Queen's University Belfast, University Floor, Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, UK.
Oncogene. 2006 Feb 9;25(6):838-48. doi: 10.1038/sj.onc.1209122.
c-FLIP inhibits caspase 8 activation and apoptosis mediated by death receptors such as Fas and DR5. We studied the effect of c-FLIP on the apoptotic response to chemotherapies used in colorectal cancer (CRC) (5-fluorouracil, oxaliplatin and irinotecan). Simultaneous downregulation of both c-FLIP splice forms c-FLIP(L) and c-FLIP(S) with siRNA synergistically enhanced chemotherapy-induced apoptosis in p53 wild-type (HCT116p53(+/+), RKO), null (HCT116p53(-/-)) and mutant (H630) CRC cell lines. Furthermore, overexpression of c-FLIP(L), but not c-FLIP(S), potently inhibited apoptosis induced by chemotherapy in HCT116p53(+/+) cells, suggesting that c-FLIP(L) was the more important splice form in mediating chemoresistance. In support of this, siRNA specifically targeted against c-FLIP(L) synergistically enhanced chemotherapy-induced apoptosis in a manner similar to the siRNA targeted against both splice forms. Inhibition of caspase 8 blocked the enhanced apoptosis induced by c-FLIP-targeted (FT) siRNA and chemotherapy. Furthermore, we found that downregulating cell surface DR5, but not Fas, also inhibited apoptosis induced by FT siRNA and chemotherapy. Interestingly, these effects were not dependent on activation of DR5 by its ligand TRAIL. These results indicate that c-FLIP inhibits TRAIL-independent, DR5- and caspase 8-dependent apoptosis in response to chemotherapy in CRC cells. Moreover, targeting c-FLIP in combination with existing chemotherapies may have therapeutic potential for the treatment of CRC.
c-FLIP抑制由死亡受体如Fas和DR5介导的半胱天冬酶8激活和凋亡。我们研究了c-FLIP对结直肠癌（CRC）中使用的化疗药物（5-氟尿嘧啶、奥沙利铂和伊立替康）诱导的凋亡反应的影响。用小干扰RNA（siRNA）同时下调c-FLIP的两种剪接形式c-FLIP(L)和c-FLIP(S)，可协同增强p53野生型（HCT116p53(+/+)、RKO）、缺失型（HCT116p53(-/-)）和突变型（H630）CRC细胞系中化疗诱导的凋亡。此外，c-FLIP(L)而非c-FLIP(S)的过表达可有效抑制HCT116p53(+/+)细胞中化疗诱导的凋亡，这表明c-FLIP(L)是介导化疗耐药性中更重要的剪接形式。支持这一点的是，特异性靶向c-FLIP(L)的siRNA以类似于靶向两种剪接形式的siRNA的方式协同增强化疗诱导的凋亡。半胱天冬酶8的抑制阻断了由靶向c-FLIP（FT）的siRNA和化疗诱导的增强的凋亡。此外，我们发现下调细胞表面DR5而非Fas，也可抑制FT siRNA和化疗诱导的凋亡。有趣的是，这些效应不依赖于DR5被其配体TRAIL激活。这些结果表明，c-FLIP在CRC细胞中抑制对化疗的TRAIL非依赖性、DR5和半胱天冬酶8依赖性凋亡。此外，将靶向c-FLIP与现有化疗联合使用可能对CRC的治疗具有治疗潜力。
