Abstract 261: Akt1 and Cyclin D1 govern polarity of self-renewing divisions in breast cancer stem cells

Abstract Background. Stem-like cells contribute to the development and progression of human cancers. Genes that control symmetric cell divisions have an evolutionarily conserved role in the regulation of cell polarity and in tumorigenesis. Two cells generated by asymmetric divisions have reduced proliferative potential compared with symmetric divisions. The cell survival oncoprotein Akt (Protein Kinase B) is encoded by three isoforms that are altered in human cancers. The Akt isoform-specific impact on breast cancer stem cell function and polarity is controversial, with Akt1 either reducing (1) or promoting (2) cell polarity and migration in tissue culture. Deletion of Akt1 reduced mammary tumor progression and metastasis in transgenic mice (2, 3). Methods. Analysis of Akt1, cyclin D1 and Notch signaling was conducted from public databases, and human as well as murine breast cancer samples. Cells derived from Akt1 gene deletion MMTV-ErbB2 breast oncomice (MMTV-ErbB2/Akt1+/+ and MMTV-ErbB2/Akt1−/−) and from the human MCF-7 breast cancer cell line with regulated expression of cyclin D1 and p53 were analyzed for the symmetry of cell division, stem cell function, and signaling pathways. Results. In breast tumors derived from MMTV-ErbB2 transgenics, associated with reduced metastasis, Akt1 genetic deletion reduced the frequency of symmetric cell divisions and the production of mammospheres. Akt1 deletion increased p53 and reduced cyclin D1. Pharmacological reactivation of p53 with Nutlin correlated with the reinduction of asymmetric cellular divisions and reduction in mammospheres in murine and human BCa cells. Akt1 deletion abrogated Nutlin-mediated induction of asymmetric cell divisions. Cyclin D1 induced symmetrical cell divisions, mammosphere formation and reduced p53 and Numb. Conclusions. Akt1 promoted symmetrical cell division at least in part via cyclin D1 suppression of Numb, and induction of γ secretase activity and thereby Notch signaling. Reference. (1) Irie HY, Pearline RV, Grueneberg D, Hsia M, Ravichandran P, Kothari N, et al. Distinct roles of Akt1 and Akt2 in regulating cell migration and epithelial-mesenchymal transition. J Cell Biol 2005;171: 1023-34. (2) Ju X, Katiyar S, Wang C, Liu M, Jiao X, Li S, et al. Akt1 governs breast cancer progression in vivo. Proc Natl Acad Sci U S A 2007;104: 7438-43. (3) Chen X, Ariss MM, Ramakrishnan G, Nogueira V, Blaha C, Putzbach W, et al. Cell-Autonomous versus Systemic Akt Isoform Deletions Uncovered New Roles for Akt1 and Akt2 in Breast Cancer. Mol Cell 2020;80: 87-101 e5 Citation Format: Xuanmao Jiao, Xin Sun, Zhiping Li, Xiaoming Ju, Danni Li, Ritika Harish, Gordon Robertson, Anthony W. Ashton, Richard G. Pestell. Akt1 and Cyclin D1 govern polarity of self-renewing divisions in breast cancer stem cells abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 261.