Department of Surgery, Tungs' Taichung Metroharbor Hospital, Taichung, Taiwan, R.O.C.
Department of Nursing, Jen-Teh Junior College of Medicine, Nursing and Management, Miaoli, Taiwan, R.O.C.
Anticancer Res. 2019 Aug;39(8):4149-4164. doi: 10.21873/anticanres.13574.
BACKGROUND/AIM: Signaling regulation of myeloid zinc finger 1 (MZF1) has been implicated in the progression of many human malignancies; however, the mechanistic action of MZF1 in triple-negative breast cancer (TNBC) progression remains elusive. In this study, the aim was to investigate the molecular mechanisms of MZF1 and its functional role in TNBC cellular migration and invasion.
Hs578T and MDA-MB-231 cells were transfected to stably express the acidic domain of MZF1 (MZF1), or were transfected with MZF1-specific or ELK1-specific short hairpin RNA (shRNA). Changes in cell morphology and distributions of cellular proteins were observed and subsequently migration and invasion were measured by wound healing and transwell assays. Expression levels of epithelial-mesenchymal transition (EMT)-related genes were carried out using immunoblotting and quantitative reverse transcription-polymerase chain reaction (RT-PCR) assays. Data of transcriptional regulation were obtained from promoter-luciferase reporter and chromatin immunoprecipitation (ChIP) assays.
Herein, we found that MZF1 in high-level MZF1-expressing TNBC cells is associated with cell migration, invasion, and mesenchymal phenotype. MZF1 interacted with the promoter region of insulin-like growth factor 1 receptor (IGF1R) to drive invasion and metastasis of high-level MZF1-expressing TNBC cells. Exogenous expression of the acidic domain of MZF1 repressed the binding of endogenous MZF1 to IGF1R promoter via blocking the interaction with ETS-like gene 1 (ELK1). This blockage not only caused MZF1 protein degradation, but also restrained ELK1 nuclear localization in high-level MZF1-expressing TNBC cells. MZF1, but not ELK1, was necessary for the retention of mesenchymal phenotype by repressing IGF1R promoter activity in TNBC cells expressing high levels of MZF1. Activation of the IGF1R-driven p38MAPK-ERα-slug-E-cadherin signaling axis mediated the conversion of mesenchymal cell to epithelial phenotype, caused by MZF1 destabilization. These results suggest that MZF1 is an oncogenic inducer.
Blocking of the MZF1/ELK1 interaction to reduce MZF1 protein stability by saturating the endogenous MZF1/ELK1 binding domains might be a promising therapeutic strategy for the treatment of high-level MZF1-expressing TNBC.
背景/目的：髓样锌指 1（MZF1）的信号转导已被牵连到许多人类恶性肿瘤的进展中；然而，MZF1 在三阴性乳腺癌（TNBC）进展中的作用机制仍不清楚。在这项研究中，目的是研究 MZF1 的分子机制及其在 TNBC 细胞迁移和侵袭中的功能作用。
Hs578T 和 MDA-MB-231 细胞被转染以稳定表达 MZF1 的酸性结构域（MZF1），或被转染 MZF1 特异性或 ELK1 特异性短发夹 RNA（shRNA）。观察细胞形态和细胞蛋白分布的变化，然后通过划痕愈合和 Transwell 测定测量迁移和侵袭。使用免疫印迹和定量逆转录聚合酶链反应（RT-PCR）测定法进行上皮-间充质转化（EMT）相关基因的表达水平。转录调节的数据来自启动子-荧光素酶报告基因和染色质免疫沉淀（ChIP）测定。
在此，我们发现高水平 MZF1 表达的 TNBC 细胞中的 MZF1 与细胞迁移、侵袭和间充质表型有关。MZF1 与胰岛素样生长因子 1 受体（IGF1R）的启动子区域相互作用，驱动高水平 MZF1 表达的 TNBC 细胞的侵袭和转移。MZF1 酸性结构域的外源性表达通过阻断与 ETS 样基因 1（ELK1）的相互作用来抑制内源性 MZF1 与 IGF1R 启动子的结合。这种阻断不仅导致 MZF1 蛋白降解，而且还抑制了高水平 MZF1 表达的 TNBC 细胞中 ELK1 的核定位。在高水平表达 MZF1 的 TNBC 细胞中，MZF1 通过抑制 IGF1R 启动子活性来保留间充质表型，而不是 ELK1，对于保留间充质表型是必需的。IGF1R 驱动的 p38MAPK-ERα-slug-E-cadherin 信号轴的激活介导了由 MZF1 不稳定引起的间充质细胞向上皮细胞表型的转化。这些结果表明 MZF1 是一种致癌诱导剂。
通过饱和内源性 MZF1/ELK1 结合域来阻断 MZF1/ELK1 相互作用以减少 MZF1 蛋白稳定性可能是治疗高水平 MZF1 表达的 TNBC 的一种有前途的治疗策略。
