An integrated genomic approach identifies that the PI3K/AKT/FOXO pathway is involved in breast cancer tumor initiation

// Linda Smit 1,5 , Katrien Berns 1 , Katherine Spence 2 , W. David Ryder 3 , Nik Zeps 4 , Mandy Madiredjo 1 , Roderick Beijersbergen 1 , René Bernards 1 and Robert B. Clarke 2 1 Division of Molecular Carcinogenesis and Cancer Genomics Center Netherlands, The Netherlands Cancer Institute, Plesmanlaan, CX, Amsterdam, The Netherlands 2 Breast Biology Group, Breast Cancer Now Research Unit, Institute of Cancer Sciences, University of Manchester, Manchester, UK 3 Department of Medical Statistics, The Christie NHS Trust, Manchester, UK 4 St John of God Subiaco Hospital, Subiaco, Perth, WA, Australia 5 Department of Hematology, VU University Medical Center, Cancer Center Amsterdam, De Boelelaan, Amsterdam, The Netherlands Correspondence to: Robert B. Clarke, email: // René Bernards, email: // Keywords : breast cancer, stem cells, FOXO, AKT, genetic screen Received : October 14, 2015 Accepted : October 18, 2015 Published : November 22, 2015 Abstract Therapy resistance is one of the major impediments to successful cancer treatment. In breast cancer, a small subpopulation of cells with stem cell features, named breast cancer stem cells (BCSC), is responsible for metastasis and recurrence of the tumor. BCSC have the unique ability to grow under non-adherent conditions in “mammospheres”. To prevent breast cancer recurrence and metastasis it will be crucial to eradicate BCSC. We used shRNA genetic screening to identify genes that upon knockdown enhance mammosphere formation in breast cancer cells. By integration of these results with gene expression profiles of mammospheres and NOTCH-activated cells, we identified FOXO3A. Modulation of FOXO3A activity results in a change in mammosphere formation, expression of mammary stem cell markers and breast cancer initiating potential. Importantly, lack of FOXO3A expression in breast cancer patients is associated with increased recurrence rate. Our findings provide evidence for a role for FOXO3A downstream of NOTCH and AKT that may have implications for therapies targeting BCSCs.