1. The Breast Center, the Cancer Hospital of Shantou University Medical College (SUMC), China;
2. ChangJiang Scholar's Laboratory, the Cancer Hospital of Shantou University Medical College (SUMC), China;
3. Department of Medical Oncology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands;
4. Department of Breast and Thyroid Surgery, the First Affiliated Hospital of SUMC;
5. Department of Pathology, the Cancer Hospital of Shantou University Medical College (SUMC), China;
6. Department of Breast Medical Oncology, the Cancer Hospital of Shantou University Medical College (SUMC), China;
7. Institute of Automation, Chinese Academy of Science, China;
8. Department of Surgery, Hong Kong University Li Ka-Tsing faculty of Medicine, Hong Kong, China.
* These authors contributed this work equally.
The luminal A phenotype is the most common breast cancer subtype and is characterized by estrogen receptor α expression (ERα). Identification of the key regulator that governs the luminal phenotype of breast cancer will clarify the pathogenic mechanism and provide novel therapeutic strategies for this subtype of cancer. ERα signaling pathway sustains the epithelial phenotype and inhibits the epithelial-mesenchymal transition (EMT) of breast cancer. In this study, we demonstrate that Notch3 positively associates with ERα in both breast cancer cell lines and human breast cancer tissues. We found that overexpression of Notch3 intra-cellular domain, a Notch3 active form (N3ICD), in ERα negative breast cancer cells re-activated ERα, while knock-down of Notch3 reduced ERα transcript and proteins, with alteration of down-stream genes, suggesting its ability to regulate ERα. Mechanistically, our results show that Notch3 specifically binds to the CSL binding element of the ERα promoter and activates ERα expression. Moreover, Notch3 suppressed EMT, while suppression of Notch3 promoted EMT in cellular assay. Overexpressing N3ICD in triple-negative breast cancer suppressed tumorigenesis and metastasis in vivo. Conversely, depletion of Notch3 in luminal breast cancer promoted metastasis in vivo. Furthermore, Notch3 transcripts were significantly associated with prolonged relapse-free survival in breast cancer, in particular in ERα positive breast cancer patients. Our observations demonstrate that Notch3 governs the luminal phenotype via trans-activating ERα expression in breast cancer. These findings delineate the role of a Notch3/ERα axis in maintaining the luminal phenotype and inhibiting tumorigenesis and metastasis in breast cancer, providing a novel strategy to re-sensitize ERα negative or low-expressing breast cancers to hormone therapy.
Keywords: Notch3, estrogen receptor α, epithelial-mesenchymal transition, breast cancer, luminal phenotype.