FZD2 Promotes TGF-β-induced Epithelial-to-Mesenchymal Transition in Breast Cancer via Activating Notch Signaling Pathway

Abstract

Background: Breast cancer (BC) is one of the commonest female cancers, which is characterized with high incidence. Although treatments have been improved, the prognosis of BC patients in advanced stages remains unsatisfactory. Thus, exploration of the molecular mechanisms underneath BC progression is necessary to find novel therapeutic methods. Frizzled class receptor (FZD2) belongs to Frizzled family, which has been proven to promote cell growth and invasion in various human cancers. The purpose of our study was to detect the functions of FZD2 and explore its mechanism in BC.Methods: The level of FZD2 was measured in BC tissues by quantitative real-time polymerase chain reaction (qRT-PCR), western blot, immunohistochemistry (IHC) respectively. Cell Counting Kit-8 (CCK-8), colony formation assay, transwell assays, wound healing assay and flow cytometry analyses were conducted separately to test cell viability, invasion, migration, apoptosis and cell cycle distribution. Epithelial-mesenchymal transition (EMT) biomarkers were determined by using Immunofluorescence assay. Xenograft tumorigenicity assay was performed to assess the effect of FZD2 on tumor growth in vivo.Results: FZD2 mRNA and protein expression was abundant in BC tissues. Moreover, high level of FZD2 had significant correlation with poor prognosis. In vitro functional assays revealed that silencing of FZD2 had suppressive effects on BC cell growth, migration and invasion. Animal study further demonstrated that FZD2 silencing inhibited BC cell growth in vivo. In addition, FZD2 induced EMT in BC cells in a transforming growth factor (TGF)-β1-dependent manner. Mechanistically, knockdown of FZD2 led to the inactivation of Notch signaling pathway.Conclusion: FZD2 facilitates BC progression and promotes TGF-β1-inudced EMT process through activating Notch signaling pathway.