Wang Shulin, El-Deiry Wafik S
Laboratory of Molecular Oncology and Cell Cycle Regulation, Howard Hughes Medical Institute, Department of Medicine, and Abramson Cancer Center, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 2003 Dec 9;100(25):15095-100. doi: 10.1073/pnas.2435285100. Epub 2003 Nov 26.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits specific tumoricidal activity and is under development for cancer therapy. Mismatch-repair-deficient colonic tumors evade TRAIL-induced apoptosis through mutational inactivation of Bax, but chemotherapeutics including Camptosar (CPT-11) restore TRAIL sensitivity. However, the signaling pathways in restoring TRAIL sensitivity remain to be elucidated. Here, we imaged p53 transcriptional activity in Bax-/- carcinomas by using bioluminescence, in vivo, and find that p53 is required for sensitization to TRAIL by CPT-11. Small interfering RNAs directed at proapoptotic p53 targets reveal TRAIL receptor KILLER/DR5 contributes significantly to TRAIL sensitization, whereas Bak plays a minor role. Caspase 8 inhibition protects both CPT-11 pretreated wild-type and Bax-/- HCT116 cells from TRAIL-induced apoptosis, whereas caspase 9 inhibition only rescued the wild-type HCT116 cells from death induced by TRAIL. The results suggest a conversion in the apoptotic mechanism in HCT116 colon carcinoma from a type II pathway involving Bax and the mitochondria to a type I pathway involving efficient extrinsic pathway caspase activation. In contrast to Bax-/- cells, Bak-deficient human cancers undergo apoptosis in response to TRAIL or CPT-11, implying that these proteins have nonoverlapping functions. Our studies elucidate a mechanism for restoration of TRAIL sensitivity in MMR-deficient Bax-/- human cancers through p53-dependent activation of KILLER/DR5 and reconstitution of a type I death pathway. Efforts to identify agents that up-regulate DR5 may be useful in cancer therapies restoring TRAIL sensitivity.
肿瘤坏死因子相关凋亡诱导配体（TRAIL）具有特异性杀瘤活性，目前正处于癌症治疗的研发阶段。错配修复缺陷的结肠肿瘤通过Bax的突变失活逃避TRAIL诱导的凋亡，但包括喜树碱（CPT-11）在内的化疗药物可恢复TRAIL敏感性。然而，恢复TRAIL敏感性的信号通路仍有待阐明。在此，我们利用生物发光技术在体内对Bax基因敲除的癌组织中的p53转录活性进行成像，发现p53是CPT-11使肿瘤对TRAIL敏感所必需的。针对促凋亡p53靶点的小干扰RNA显示，TRAIL受体KILLER/DR5对TRAIL致敏有显著贡献，而Bak作用较小。半胱天冬酶8抑制可保护CPT-11预处理的野生型和Bax基因敲除的HCT116细胞免受TRAIL诱导的凋亡，而半胱天冬酶9抑制仅能使野生型HCT116细胞免于TRAIL诱导的死亡。结果表明，HCT116结肠癌的凋亡机制从涉及Bax和线粒体的II型途径转变为涉及高效外源性途径半胱天冬酶激活的I型途径。与Bax基因敲除细胞不同，Bak缺陷的人类癌症对TRAIL或CPT-11有凋亡反应，这意味着这些蛋白具有不重叠的功能。我们的研究阐明了错配修复缺陷的Bax基因敲除的人类癌症中通过p53依赖的KILLER/DR5激活和I型死亡途径的重建恢复TRAIL敏感性的机制。寻找上调DR5的药物的努力可能对恢复TRAIL敏感性的癌症治疗有用。
