Systems Biology Ireland, School of Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
Cell Death Dis. 2022 Aug 8;13(8):692. doi: 10.1038/s41419-022-05147-3.
Metastatic malignant melanoma is the deadliest skin cancer, and it is characterised by its high resistance to apoptosis. The main melanoma driving mutations are part of ERK pathway, with BRAF mutations being the most frequent ones, followed by NRAS, NF1 and MEK mutations. Increasing evidence shows that the MST2/Hippo pathway is also deregulated in melanoma. While mutations are rare, MST2/Hippo pathway core proteins expression levels are often dysregulated in melanoma. The expression of the tumour suppressor RASSF1A, a bona fide activator of the MST2 pathway, is silenced by promoter methylation in over half of melanomas and correlates with poor prognosis. Here, using mass spectrometry-based interaction proteomics we identified the Second Mitochondria-derived Activator of Caspases (SMAC) as a novel LATS1 interactor. We show that RASSF1A-dependent activation of the MST2 pathway promotes LATS1-SMAC interaction and negatively regulates the antiapoptotic signal mediated by the members of the IAP family. Moreover, proteomic experiments identified a common cluster of apoptotic regulators that bind to SMAC and LATS1. Mechanistic analysis shows that the LATS1-SMAC complex promotes XIAP ubiquitination and its subsequent degradation which ultimately results in apoptosis. Importantly, we show that the oncogenic BRAF mutant prevents the proapoptotic signal mediated by the LATS1-SMAC complex while treatment of melanoma cell lines with BRAF inhibitors promotes the formation of this complex, indicating that inhibition of the LATS1-SMAC might be necessary for BRAF-driven melanoma. Finally, we show that LATS1-SMAC interaction is regulated by the SMAC mimetic Birinapant, which requires C-IAP1 inhibition and the degradation of XIAP, suggesting that the MST2 pathway is part of the mechanism of action of Birinapant. Overall, the current work shows that SMAC-dependent apoptosis is regulated by the LATS1 tumour suppressor and supports the idea that LATS1 is a signalling hub that regulates the crosstalk between the MST2 pathway, the apoptotic network and the ERK pathway.
转移性恶性黑色素瘤是最致命的皮肤癌，其特征是对细胞凋亡具有很高的抗性。主要的黑色素瘤驱动突变是 ERK 通路的一部分，其中 BRAF 突变最为常见，其次是 NRAS、NF1 和 MEK 突变。越来越多的证据表明，MST2/Hippo 通路在黑色素瘤中也失调。虽然突变很少见，但黑色素瘤中 MST2/Hippo 通路核心蛋白的表达水平经常失调。肿瘤抑制因子 RASSF1A 的表达被启动子甲基化沉默，超过一半的黑色素瘤存在这种情况，并且与预后不良相关。在这里，我们使用基于质谱的相互作用蛋白质组学方法鉴定出 Second Mitochondria-derived Activator of Caspases (SMAC) 是 LATS1 的一种新的相互作用蛋白。我们表明，RASSF1A 依赖性激活 MST2 通路促进 LATS1-SMAC 相互作用，并负调控 IAP 家族成员介导的抗凋亡信号。此外，蛋白质组学实验鉴定出一组与 SMAC 和 LATS1 结合的常见凋亡调节剂。机制分析表明，LATS1-SMAC 复合物促进 XIAP 的泛素化及其随后的降解，最终导致细胞凋亡。重要的是，我们表明致癌 BRAF 突变体阻止了由 LATS1-SMAC 复合物介导的促凋亡信号，而黑色素瘤细胞系用 BRAF 抑制剂处理则促进了该复合物的形成，这表明抑制 LATS1-SMAC 可能是 BRAF 驱动的黑色素瘤所必需的。最后，我们表明 LATS1-SMAC 相互作用受 SMAC 模拟物 Birinapant 调节，Birinapant 需要抑制 C-IAP1 和 XIAP 的降解，这表明 MST2 通路是 Birinapant 作用机制的一部分。总的来说，目前的工作表明，SMAC 依赖性凋亡受 LATS1 肿瘤抑制因子调节，并支持 LATS1 是调节 MST2 通路、凋亡网络和 ERK 通路之间串扰的信号枢纽的观点。
