RBBP5 drives cancer stem cell-like characteristics by suppressing the hippo signaling pathway through WNT5A downregulation in breast cancer

Background Cancer stem cells (CSCs) are a major contributor to breast cancer recurrence and therapeutic resistance. This study investigates the oncogenic role of Retinoblastoma Binding Protein 5 (RBBP5) in driving CSC-like properties in breast cancer.Methods Genetic alterations in RBBP5 and their correlation with patient survival were analyzed using multiple breast cancer cohorts, including METABRIC, TCGA, and Kaplan-Meier (KM) plotter datasets. The impact of RBBP5 on CSC-like traits was assessed through tumorsphere formation and ALDEFLUOR assays, and in vivo xenograft models. To elucidate the underlying molecular mechanism, RNA sequencing (RNA-seq) was performed.Results Elevated RBBP5 expression was significantly associated with poor prognosis in breast cancer. (METABRIC: OS, p = 0.007; DFS, p = 0.049; TCGA: OS, p < 0.001; KM plotter: RFS, p < 0.001). RBBP5 overexpression enhanced tumorsphere-forming capacity, CSC-like population and tumor-initiating cell frequency. RNA-seq results revealed an enrichment of gene sets associated with negative regulation of cell growth, invasiveness, and stem cell population in RBBP5-knockdown cells. RBBP5 knockdown upregulated WNT5A, a non-canonical Wnt ligand, leading to Hippo pathway activation and subsequent suppression of YAP signaling. Pharmacological inhibition of YAP1 abrogated RBBP5-induced CSC-like properties, while suppression of MST1/2 in RBBP5-knockdown cells restored YAP activity and CSC traits.Conclusions These findings indicate that RBBP5 promotes CSC-like properties in breast cancer by repressing WNT5A-mediated Hippo signaling. We suggest RBBP5 as a potential biomarker for poor prognosis and propose that targeting YAP or activating the Hippo pathway could represent a promising therapeutic approach for patients with RBBP5-overexpressing tumors.