PRMT1 and cancer: For instance, protein arginine methyltransferase PRMT1 encodes eight different isoforms that can differ by their catalytic activity as well as substrate specificity and it is assumed that catalytically inactive isoform lacking dimerization arm could act as a competitive inhibitor for PRMT1 in cancer cells by shielding substrates from access to active isoform oligomers [36,37].