Arginine methylation of DDX3 by PRMT1 mediates mitochondrial homeostasis to promote breast cancer metastasis

Dysregulated mitochondrial dynamics and metabolism play important roles in tumorigenesis. Metastasizing tumor cells predominantly utilize mitochondrial metabolism, and regulators of metabolic reprogramming may provide reliable biomarkers for diagnosing cancer metastasis. Here, we identified a type I arginine methyltransferase-DEAD-box polypeptide 3, X-linked (PRMT1-DDX3) axis that promotes breast cancer metastasis by coordinating mitochondrial biogenesis and mitophagy to ensure mitochondrial quality control. Mechanistically, PRMT1 induces arginine methylation of DDX3, which enhances its protein stability and prevents proteasomal degradation. DDX3 mediates mitochondrial homeostasis by translocating to mitochondria where it facilitates phosphatase and tensin homology-induced kinase 1 translation in response to mitochondrial stress. Inhibition of DDX3 suppresses mitochondrial biogenesis and mitophagy, resulting in diminished cancer stemness and metastatic properties. Overall, this study uncovers a mechanism by which the PRMT1-DDX3 axis regulates mitochondrial homeostasis to support breast cancer metastasis, suggesting strategies for targeting metabolic vulnerabilities to treat metastatic breast cancer. Significance: DDX3 is stabilized by PRMT1-mediated arginine methylation and coordinates mitophagy and mitochondrial biogenesis by upregulating PINK1 to facilitate breast cancer progression.