PHLPP1 depletion promotes tumorigenesis and stemness in triple-negative breast cancer cells through AKT signaling

Breast cancer, particularly triple-negative breast cancer (TNBC), is a major cause of women's mortality, and effective treatment options are still lacking due to the absence of known mechanisms and biomarkers. Therefore, unveiling novel molecular mechanisms to identify potential biomarkers is urgently needed to ensure an effective TNBC treatment. In this study, we investigated the role of PHLPP1, a tumor suppressor gene, in the tumorigenesis and induction of cancer stem cells in TNBC using publicly available data and experimental protocols. Our study found that lower levels of PHLPP1 contributed negatively to patient overall survival. In addition, loss of PHLPP1 increased breast cancer cell proliferation, long-term colony regrowth ability, and the number of migrated and invaded cells. Consequently, we designed a stable PHLPP1 knockdown (KD) cell line to understand its impact through its stemness potential. As expected, PHLPP1 KD dramatically upregulated breast cancer stemness markers (NANOG, OCT4, and SOX2) expression and significantly increased cancer stem cell frequencies in TNBC cells. Mechanistically, PHLPP1 loss enhanced AKT phosphorylation at Ser473, thus activating AKT signaling, leading to larger tumor formation in vivo and elevated stemness expression. This study concludes that PHLPP1 has the capability to reduce the expression of cancer stemness genes by negatively regulating the AKT signaling pathway. Therefore, these findings may pave the way for discoveries in the context of cancer stemness and future strategies for developing effective treatment options for TNBC patients.