Oncogenic Role of SAMD4B in Breast Cancer Progression by Activating Wnt/β-Catenin Pathway

The Sterile alpha motif domain-containing protein 4 (SAMD4) family consists of two evolutionarily conserved and highly homologous RNA-binding proteins, SAMD4A and SAMD4B. Previous studies have established SAMD4A as a tumor suppressor that is downregulated in breast cancer, while the function of SAMD4B in tumorigenesis remains poorly defined. In this study, we observed that SAMD4B expression is upregulated in breast cancer. Functional assays demonstrated that SAMD4B facilitated breast cancer cell proliferation, migration, and invasion by inducing epithelial-mesenchymal transition (EMT). Furthermore, SAMD4B accelerated G1-to-S phase cell cycle progression by modulating p53 expression, collectively supporting an oncogenic function of SAMD4B in breast cancer. Mechanistically, we found that SAMD4B enhanced TCF/LEF transcriptional activity and upregulated the expression of β-catenin, Cyclin D1, c-Myc, and Axin2. Further investigations confirmed that SAMD4B activated the Wnt/β-catenin pathway by stabilizing β-catenin mRNA and increasing β-catenin protein expression level. Importantly, treatment with XAV-939, a specific Wnt/β-catenin pathway inhibitor, abrogated the pro-oncogenic effects of SAMD4B overexpression, including Wnt/β-catenin pathway activation, enhanced proliferation, and increased metastatic capacity. These results confirm that SAMD4B promotes the malignant phenotypes of breast cancer cells in a manner dependent on the Wnt/β-catenin pathway. In summary, our findings clarify that SAMD4B exerts an oncogenic role in breast cancer progression by activating the Wnt/β-catenin pathway. These data identify SAMD4B as a potential therapeutic target in breast cancer, although further in vivo investigations are required to validate its clinical relevance.