Knockdown of NR4A1, NR4A2 or Sp1/4 also decrease expression of NR4A1/Sp-regulated genes such as PD-L1, β1- and other integrins in breast cancer cells [20, 40, 42] and similar results were observed for CD71 in this study demonstrating that NR4A1 and NR4A2 in combination with Sp1 and Sp4 regulate basal expression of this key ferroptotic gene. Here, SP4 is linked to breast carcinoma.