PADI4 and breast cancer: In breast cancer cells, PADI4-mediated citrullination of the transcription factor Elk-1 happens upon stimulation with Epidermal Growth Factor (EGF), suggesting that PADI4 may be activated by a component of EGF signalling [16], although it is yet unclear from this study whether it is the catalytic activity of PADI4, or its association with Elk-1 that is regulated in this manner.