Notch3 Transactivates Glycogen Synthase Kinase-3-Beta and Inhibits Epithelial-to-Mesenchymal Transition in Breast Cancer Cells

As a critical transformational process in the attributes of epithelial cells, epithelial-to-mesenchymal transition (EMT) is involved in tumor invasion, metastasis, and resistance to treatment, which contributes to the ultimate death of some patients with breast cancer. Glycogen synthase kinase-3-beta (GSK3 beta) is thought to be an EMT suppressor that down-regulates the protein, snail, a zinc finger transcription inhibitor, and regulates E-cadherin expression and the Wnt signaling pathway. Our previous studies have shown that Notch3 also inhibits EMT in breast cancer. In mammary gland cells, GSK3 beta physically bound and phosphorylated the intracellular domain of two Notch paralogs: N1ICD was positively regulated, but N2ICD was negatively regulated; however, the relationship between Notch3, GSK3 beta, and EMT in breast cancer is still unclear and crosstalk between Notch3 and GSK3 beta has not been widely investigated. In this study, we revealed that Notch3 was an essential antagonist of EMT in breast cancer cells by transcriptionally upregulating GSK3 beta. In breast cancer, MCF-7 and MDA-MB-231 cell lines, the silencing of Notch3 reduced GSK3 beta expression, which is sufficient to induce EMT. Conversely, ectopic Notch3 expression re-activated GSK3 beta and E-cadherin. Mechanistically, Notch3 can bind to the GSK3 beta promoter directly and activate GSK3 beta transcription. In human breast cancer samples, Notch3 expression is positively associated with GSK3 beta (r = 0.416, p = 0.001); moreover, high expressions of Notch3 and GSK3 beta mRNA are correlated to better relapse-free survival in all breast cancer patients via analysis in "the Kaplan-Meier plotter" database. In summary, our preliminary results suggested that Notch3 might inhibit EMT by trans-activating GSK3 beta in breast cancer cells. The suppression of Notch3 expression may contribute to EMT by transcriptionally downregulating GSK3 beta in breast cancer.