Epithelial cells aggregate into spheroids when deprived of matrix, and the proclivity for spheroid formation and survival is a hallmark of normal and tumorigenic mammary stem cells. We show here that Nuclear Respiratory Factor 1 (NRF1) is a spheroid promoter by in silico identification of this transcription factor as highly connected to top shRNA-hits deduced from re-iterative selections for shRNAs enriched in MCF10A spheroids. NRF1-promoted spheroid survival is linked to its stimulation of mitochondrial OXPHOS, cell migration, invasion, and mesenchymal transition. Conversely, NRF1 knockdown in breast cancer MDA-MB-231 cells reduced spheroids, migration, invasion, and mesenchymal marker expression. NRF1 knockdown also reduced tumor burden in mammary fat pads and lungs of orthotopic- or tail vein-transplanted mice. With the Luminal A subtype of breast cancer, higher NRF1 expression is associated with lower survival. These results show that NRF1, an activator of mitochondrial metabolism, supports mammary spheroid survival and tumor development.
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We thank J. Dai, Q. Wang, Z. Zhang, and G. Cheng for insightful comments on the study, and X. He for technical assistance. Nano-Bio-Chem Centre in Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO) is acknowledged for professional assistance of cell imaging and FACS assay. This study was initiated as a pilot project in the San Diego Systems Biology Center (NIH P50GM085764) that supported G.S., D.Q., O. H., and J.Y.J.W.; D.Q. was also supported by a grant to J.Y.J.W. (NIH R01CA043054). The study of NFR1 was supported by National Natural Science Foundation of China (Grant No. 31471307), Ministry of Science and Technology (MOST) (Grant No. 2014CB965003, and 2017YFA0104301) to G.S., who is also supported by Hundred Talent Program of Chinese Academy of Sciences. The study was also supported by the CAS/SAFEA International Innovation Teams program.
Conflict of interest
The authors declare that they have no conflict of interest.
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BMB Reports (2019)
International Journal of Molecular Sciences (2019)