In lung squamous cell carcinoma and breast carcinoma cells, protein arginine methyltransferase 5 (PRMT5) complexes with MEP50/WDR77, and WDR5 is recruited by the protein complex to target gene promoters, resulting in histone H3K4 trimethylation, target gene transcription and cancer cell invasion (61). The gene discussed is PRMT5; the disease is breast carcinoma.