Abstract
Transcription factor activity of the nuclear respiratory factor 1 protein (NRF1) is increased in breast cancer. Whether this gain of NRF1 activity is directly involved in breast cancer remains unknown. Herein, we report a novel oncogenic function of NRF1 supporting its causative role in breast cancer development and progression. The gain of NRF1 and/or treatment with 17β-estradiol (E2) produced heterogeneous breast cancer stem cells (BCSCs) composed of more than ten distinct cell sub-populations. Flow sorting combined with confocal imaging of markers for pluripotency, epithelial mesenchymal transition (EMT), and BCSCs phenotypically confirmed that the sub-populations of BCSCs arise from cell re-programming. Thus, we determined the molecular actions of NRF1 on its target gene CXCR4 because of its known role in the acquisition of BCSCs through EMT. CXCR4 was activated by NRF1 in a redox dependent manner during malignant transformation. NRF1-induced BCSCs were able to form xenograft tumors in vivo, while inhibiting transcription of CXCR4 prevented xenograft tumor growth. Consistent with our observation of NRF1 driven breast tumorigenesis in the experimental model, higher levels of NRF1 protein expression were also found in human breast cancer tissue specimens. This highly novel role of NRF1 in the stochastic acquisition of BCSCs and their progression to a malignant phenotype may open an entirely new research direction targeting NRF1 signaling in invasive breast cancer. Additionally, the discovery of targeting transcriptional activation of CXCR4 to inhibit NRF1-induced oncogenic transformation provides a mechanistic explanation for estrogen-dependent breast carcinogenesis and opens the new avenues for mechanistic therapeutic strategy against breast cancer.