Fulda Simone, Debatin Klaus-Michael
University Children's Hospital, Prittwitzstr. 43, D-89075 Ulm, Germany.
Oncogene. 2002 Apr 4;21(15):2295-308. doi: 10.1038/sj.onc.1205255.
Resistance of tumors to cytotoxic therapy may be due to disrupted apoptosis programs and remains a major obstacle in cancer treatment. Here, we report that IFNgamma sensitizes resistant tumor cells with absent or low caspase-8 expression for apoptosis induced by death-inducing ligands or cytotoxic drugs by upregulating caspase-8 through a Stat1/IRF1 dependent pathway. Combined treatment using IFNgamma with TRAIL, APO1, TNFalpha or cytotoxic drugs cooperated to trigger apoptosis in various resistant tumor cell lines derived from Ewing tumor, neuroblastoma or medulloblastoma, while single agents exerted only a minimal effect. Importantly, IFNgamma induced caspase-8 expression also in cells with inactivation of the caspase-8 gene by hypermethylation, although no direct effect of IFNgamma on the methylation status of regulatory sequences of the caspase-8 gene was found. IFNgamma-mediated facilitation of apoptosis was inhibited by the caspase-8 specific inhibitor zIETD.fmk or in caspase-8 mutant Jurkat cells implying a prominent role of caspase-8 in mediating sensitization by IFNgamma. Upregulation of caspase-8 and sensitization for apoptosis by IFNgamma was blocked by overexpression of dominant-negative mutants of Stat1 or in Stat1-deficient U3A cells, while complementation of Stat1-deficient U3A cells with wild-type Stat1 restored the IFNgamma effect. Moreover, ectopic expression of IRF1 induced caspase-8 expression thereby sensitizing cells for TRAIL-, APO1- or doxorubicin-induced apoptosis. These findings provide evidence that the Stat1/IRF1 pathway is involved in induction of caspase-8 expression and apoptosis initiated by IFNgamma and indicate that IFNgamma might be an effective strategy to sensitize various resistant tumor cells with deficient caspase-8 expression for chemotherapy- or death receptor-induced apoptosis.
肿瘤对细胞毒性疗法产生抗性可能是由于凋亡程序紊乱，这仍然是癌症治疗中的一个主要障碍。在此，我们报告，干扰素γ（IFNγ）通过Stat1/IRF1依赖性途径上调半胱天冬酶-8（caspase-8），使caspase-8表达缺失或低表达的抗性肿瘤细胞对死亡诱导配体或细胞毒性药物诱导的凋亡敏感。IFNγ与肿瘤坏死因子相关凋亡诱导配体（TRAIL）、载脂蛋白1（APO1）、肿瘤坏死因子α（TNFα）或细胞毒性药物联合治疗协同触发源自尤因肉瘤、神经母细胞瘤或髓母细胞瘤的各种抗性肿瘤细胞系中的凋亡，而单一药物仅产生最小的作用。重要的是，IFNγ在因高甲基化导致caspase-8基因失活的细胞中也诱导caspase-8表达，尽管未发现IFNγ对caspase-8基因调控序列的甲基化状态有直接影响。caspase-8特异性抑制剂zIETD.fmk或在caspase-8突变的Jurkat细胞中抑制了IFNγ介导的凋亡促进作用，这意味着caspase-8在介导IFNγ的致敏作用中起重要作用。Stat1显性负突变体的过表达或在Stat1缺陷的U3A细胞中阻断了IFNγ诱导的caspase-8上调和凋亡致敏作用，而用野生型Stat1对Stat1缺陷的U3A细胞进行互补恢复了IFNγ的作用。此外，IRF1的异位表达诱导caspase-8表达，从而使细胞对TRAIL、APO1或阿霉素诱导的凋亡敏感。这些发现提供了证据表明Stat1/IRF1途径参与IFNγ诱导的caspase-8表达和凋亡启动，并表明IFNγ可能是一种有效的策略，使各种caspase-8表达缺陷的抗性肿瘤细胞对化疗或死亡受体诱导的凋亡敏感。
