Abstract
BackgroundThe epithelial–mesenchymal transition (EMT) is crucial for the invasion and metastasis of breast cancer. However, how Notch signaling regulates the EMT process and invasion in breast cancer remains largely unknown.MethodsThe impact of Notch1 silencing by specific shRNAs on the EMT and invasion of human breast cancer MCF-7 and MDA-MB-231 cells as well as xenografts was tested by western blot, real-time polymerase chain reaction (RT-PCR), immunofluorescence, transwell, and immunohistochemistry assays. The effect of Slug silencing or upregulation on the EMT and invasion of breast cancer cells was analyzed, and the effect of Notch1 signaling on Slug expression was determined by the luciferase reporter assay.ResultsThe Notch1 intracellular domain (N1ICD) and Jagged1 were expressed in breast cancer cells. Notch1 silencing reversed the spontaneous EMT process and inhibited the migration and invasion of breast cancer cells and the growth of xenograft breast cancers. The expression of N1ICD was upregulated significantly by Jagged1-mediated Notch signaling activation. Moreover, Jagged1-mediated Notch signaling promoted the EMT process, migration, and invasion of breast cancer cells, which were abrogated by Notch silencing. Furthermore, the N1ICD positively regulated the Slug expression by inducing Slug promoter activation. Importantly, the knockdown of Slug weakened the invasion ability of breast cancer cells and reversed the Jagged1-induced EMT process with significantly decreased expression of vimentin and increased expression of E-cadherin. In addition, Slug overexpression restored the Notch1 knockdown-suppressed EMT process.ConclusionsOur novel data indicate that Notch signaling positively regulates the EMT, invasion, and growth of breast cancer cells by inducing Slug expression. The Notch1–Slug signaling axis may represent a potential therapeutic target for breast cancer therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0295-3) contains supplementary material, which is available to authorized users.
Highlights
The epithelial–mesenchymal transition (EMT) is crucial for the invasion and metastasis of breast cancer
Stable Notch1 knockdown and Jagged1 were applied to inhibit or activate Notch signaling, respectively, in breast cancer cells To investigate the role of Notch1 in Notch signaling, we established stable shRNA-transfected cells termed as MCF-7-shNotch1 and MDA-MB-231-shNotch1, MCF-7-shNC, and MDA-MB-231-shNC
After MCF-7 and MDA-MB-231 cells were incubated with Jagged1 for 48 h, these cells were transfected with Notch1 shRNA lentiviral vectors for another 48 h; the results showed that the enhanced migration and invasion abilities that were due to Jagged1-mediated Notch signaling activation were abolished by Notch1 silencing (Figure 6A–B)
Summary
The epithelial–mesenchymal transition (EMT) is crucial for the invasion and metastasis of breast cancer. How Notch signaling regulates the EMT process and invasion in breast cancer remains largely unknown. Breast cancer is one of the most frequently diagnosed cancers and the leading cause of cancer death in females worldwide. It accounts for 23% of total cancer cases and 14% of cancer deaths [1]. There have been substantial advances in the treatment of localized malignancies, The process of epithelial–mesenchymal transition (EMT) plays a key role in tumor metastasis [4]. E-cadherin is a repressor of cancer invasion and EMT induction [8,9]. Slug, and ZEB2/ SIP1 are direct transcriptional repressors of E-cadherin, whereas Twist and ZEB1 act indirectly on E-cadherin [10]
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