Immunology and Oncology Unit, Calvary Mater Newcastle Hospital, Newcastle, New South Wales, Australia.
Mol Cancer Ther. 2010 Dec;9(12):3363-74. doi: 10.1158/1535-7163.MCT-10-0646.
Wild-type p53 is commonly expressed in melanoma but does not appear to be effective in the induction of apoptosis. One explanation is that p53 is targeted for degradation by the E3 ligase MDM2. However, we found in this study that blockade of the interaction of p53 and MDM2 by the MDM2 antagonist nutlin-3 in melanoma cells did not induce apoptosis, even though it upregulated p53 and its proapoptotic targets. Nevertheless, nutlin-3 enhanced TRAIL-induced apoptosis as a result of p53-mediated upregulation of TRAIL-R2. Unexpectedly, nutlin-3 upregulated Mcl-1, which attenuated apoptotic signaling triggered by TRAIL, and inhibited apoptosis induced by the microtubule-targeting drug docetaxel. The increase in Mcl-1 was related to a p53-independent transcriptional mechanism, but stabilization of the Mcl-1 protein played a dominant role, as nutlin-3 upregulated the Mcl-1 protein to a much greater extent than the Mcl-1 mRNA, and this was associated with prolonged half-life time and reduced ubiquitination of the protein. Knockdown of p53 blocked the upregulation of the Mcl-1 protein, indicating that p53 plays a critical role in the stabilization of Mcl-1. The contrasting effects of nutlin-3 on TRAIL- and docetaxel-induced apoptosis were confirmed in fresh melanoma isolates. Collectively, these results show that nutlin-3 may be a useful agent in combination with TRAIL and, importantly, uncover a novel regulatory effect of p53 on the expression of Mcl-1 in melanoma cells on treatment with nutlin-3, which may antagonize the therapeutic efficacy of other chemotherapeutic drugs in addition to docetaxel in melanoma.
野生型 p53 在黑色素瘤中通常表达，但似乎不能有效诱导细胞凋亡。一种解释是 p53 被 E3 连接酶 MDM2 靶向降解。然而，我们在这项研究中发现，在黑色素瘤细胞中，MDM2 拮抗剂 nutlin-3 阻断 p53 和 MDM2 的相互作用，即使它上调了 p53 和其促凋亡靶标，也不会诱导细胞凋亡。然而，nutlin-3 通过 p53 介导的 TRAIL-R2 的上调增强了 TRAIL 诱导的细胞凋亡。出乎意料的是，nutlin-3 上调了 Mcl-1，这减弱了 TRAIL 触发的凋亡信号，并抑制了微管靶向药物多西紫杉醇诱导的细胞凋亡。Mcl-1 的增加与 p53 无关的转录机制有关，但 Mcl-1 蛋白的稳定起主要作用，因为 nutlin-3 上调 Mcl-1 蛋白的程度远大于 Mcl-1 mRNA，这与蛋白半衰期延长和泛素化减少有关。p53 的敲低阻断了 Mcl-1 蛋白的上调，表明 p53 在 Mcl-1 蛋白的稳定中起关键作用。nutlin-3 对 TRAIL 和多西紫杉醇诱导的细胞凋亡的相反作用在新鲜黑色素瘤分离物中得到了证实。总的来说，这些结果表明 nutlin-3 可能与 TRAIL 联合使用是有用的，重要的是，揭示了 p53 在黑色素瘤细胞中对 nutlin-3 处理时 Mcl-1 表达的新的调节作用，除了多西紫杉醇之外，这可能拮抗其他化疗药物的治疗效果在黑色素瘤中。
