Division of Transfusion Medicine, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan; School of Medicine, National Yang-Ming University, Taipei, Taiwan; Comprehensive Breast Health Center, Taipei Veterans General Hospital, Taipei, Taiwan; Division of Medical Oncology, Center for Immuno-Oncology, Department of Oncology, Taipei Veterans General Hospital, Taipei, Taiwan.
Comprehensive Breast Health Center, Taipei Veterans General Hospital, Taipei, Taiwan.
EBioMedicine. 2019 Feb;40:263-275. doi: 10.1016/j.ebiom.2018.12.032. Epub 2019 Jan 14.
Triple-negative breast cancer (TNBC) remains difficult to be targeted. SET and cancerous inhibitor of protein phosphatase 2A (CIP2A) are intrinsic protein-interacting inhibitors of protein phosphatase 2A (PP2A) and frequently overexpressed in cancers, whereas reactivating PP2A activity has been postulated as an anti-cancer strategy. Here we explored this strategy in TNBC.
Data from The Cancer Genome Atlas (TCGA) database was analyzed. TNBC cell lines were used for in vitro studies. Cell viability was examined by MTT assay. The apoptotic cells were examined by flow cytometry and Western blot. A SET-PP2A protein-protein interaction antagonist TD19 was used to disrupt signal transduction. In vivo efficacy of TD19 was tested in MDA-MB-468-xenografted animal model.
TCGA data revealed upregulation of SET and CIP2A and positive correlation of these two gene expressions in TNBC tumors. Ectopic SET or CIP2A increased cell viability, migration, and invasion of TNBC cells. Notably ERK inhibition increased PP2A activity. ERK activation is known crucial for Elk-1 activity, a transcriptional factor regulating CIP2A expression, we hypothesized an oncogenic feedforward loop consisting of pERK/pElk-1/CIP2A/PP2A. This loop was validated by knockdown of PP2A and ectopic expression of Elk-1, showing reciprocal changes in loop members. In addition, ectopic expression of SET increased pAkt, pERK, pElk-1 and CIP2A expressions, suggesting a positive linkage between SET and CIP2A signaling. Moreover, TD19 disrupted this CIP2A-feedforward loop by restoring PP2A activity, demonstrating in vitro and in vivo anti-cancer activity. Mechanistically, TD19 downregulated CIP2A mRNA via inhibiting pERK-mediated Elk-1 nuclear translocation thereby decreased Elk-1 binding to the CIP2A promoter.
These findings suggested that a novel oncogenic CIP2A-feedforward loop contributes to TNBC progression and targeting SET to disrupt this oncogenic CIP2A loop showed therapeutic potential in TNBC.
三阴性乳腺癌（TNBC）仍然难以靶向。SET 和癌性蛋白磷酸酶 2A 抑制剂（CIP2A）是蛋白磷酸酶 2A（PP2A）的固有蛋白相互作用抑制剂，在癌症中经常过表达，而激活 PP2A 活性已被推测为一种抗癌策略。在这里，我们在 TNBC 中探索了这种策略。
分析了癌症基因组图谱（TCGA）数据库中的数据。使用 TNBC 细胞系进行体外研究。通过 MTT 测定法检查细胞活力。通过流式细胞术和 Western blot 检查凋亡细胞。使用 SET-PP2A 蛋白-蛋白相互作用拮抗剂 TD19 来破坏信号转导。在 MDA-MB-468 异种移植动物模型中测试了 TD19 的体内疗效。
TCGA 数据显示 SET 和 CIP2A 上调，并且这些两种基因在 TNBC 肿瘤中的表达呈正相关。异位 SET 或 CIP2A 增加了 TNBC 细胞的细胞活力、迁移和侵袭。值得注意的是，ERK 抑制增加了 PP2A 活性。ERK 激活对于 Elk-1 活性至关重要，Elk-1 是调节 CIP2A 表达的转录因子，我们假设了一个由 pERK/pElk-1/CIP2A/PP2A 组成的致癌正反馈回路。通过敲低 PP2A 和异位表达 Elk-1 验证了该回路，显示了回路成员的相互变化。此外，异位表达 SET 增加了 pAkt、pERK、pElk-1 和 CIP2A 的表达，表明 SET 和 CIP2A 信号之间存在正联系。此外，TD19 通过恢复 PP2A 活性破坏了这种 CIP2A 正反馈回路，证明了其在体外和体内的抗癌活性。从机制上讲，TD19 通过抑制 pERK 介导的 Elk-1 核易位来下调 CIP2A mRNA，从而减少 Elk-1 与 CIP2A 启动子的结合。
这些发现表明，一种新的致癌性 CIP2A 正反馈回路有助于 TNBC 的进展，靶向 SET 以破坏这种致癌性 CIP2A 循环在 TNBC 中显示出治疗潜力。
