PRMT5 as a Key Driver of Stemness and Metastatic Potential in Triple-Negative Breast Cancer

Protein arginine methyltransferase 5 (PRMT5) mediates arginine methylation of a wide range of proteins and plays context-dependent oncogenic or tumor-suppressive roles. In cancer, PRMT5 represses several tumor suppressor genes, including E-cadherin, TP53BP1, ST7, PTEN, and RB (retinoblastoma). Elevated PRMT5 expression has been reported across multiple cancer types, notably triple-negative breast cancer (TNBC). In TNBC, high PRMT5 levels are associated with enhanced cancer stem cell self-renewal, increased tumor growth and metastasis, and reduced patient survival. Mechanistically, PRMT5 promotes breast cancer stem cell maintenance and proliferation through stabilization of the transcription factors KLF4 and KLF5. Disruption of the PRMT5–KLF4 axis results in significant tumor reduction in TNBC models. Moreover, increased PRMT5 expression has been linked to resistance to chemotherapy and immunotherapy in TNBC. Notably, PRMT5 inhibitors demonstrate synergistic anticancer activity when combined with inhibitors of key oncogenic signaling pathways, including EGFR, PARP, and AKT. While several PRMT5 inhibitors are currently being evaluated in clinical trials for other malignancies, no clinical trials have yet been initiated specifically for TNBC.