Silencing RPL9 promotes malignant proliferation in breast cancer cells.

OBJECTIVE: To identify key RNA-binding proteins (RBPs) associated with breast cancer (BRCA) prognosis and to construct an RBP-based prognostic scoring model and clinical nomogram. Additionally, to explore the functional role of RPL9 in BRCA cell proliferation and apoptosis. INTRODUCTION: Breast cancer is a molecularly heterogeneous malignancy in which posttranscriptional dysregulation contributes significantly to tumor progression. RNAbinding proteins regulate multiple steps of RNA metabolism and have emerged as promising prognostic biomarkers and therapeutic targets in BRCA. METHODS: RNA-sequencing data and clinical information of BRCA patients were obtained from TCGA. Differential expressions, Cox, and LASSO regression analyses were performed to identify prognosis-related RBPs and establish a risk scoring model. A clinical nomogram integrating the model with clinicopathological features was generated. Tumor mutational burden (TMB), tumor immune microenvironment (TIME), and immune checkpoint expression were analyzed between risk groups. Functional assays, including CCK-8 proliferation and flow cytometry-based apoptosis analyses, were conducted in BRCA cell lines to determine the role of RPL9. RESULTS: Nine prognosis-related RBPs were identified and used to construct the RBPbased prognostic scoring model, which effectively predicted 3-, 5-, and 9-year survival outcomes. The model remained robust in an external validation cohort. A clinical nomogram based on the model showed strong predictive performance. High-risk patients displayed higher TMB, lower immune scores, reduced CD8⁺ T-cell infiltration, and decreased immune checkpoint expression. RPL9 was markedly downregulated in BRCA tissues and cells, and RPL9 overexpression inhibited cell proliferation and significantly increased apoptosis, supporting its tumor-suppressive role. CONCLUSION: We identified and constructed a 9-RBP based scoring model and a clinical prognostic nomogram for accurately predicting the survival probability and assessing the tumor microenvironment of patients with BRCA. Moreover, our findings firstly demonstrated that RPL9 downregulation correlated with poor clinical outcomes and functionally drives tumor cell proliferation, establishing it as a potential therapeutic target and prognostic biomarker for BRCA.