NR4A1 and malignant colon neoplasm: MC-38 mouse colon cancer cells also express NR4A1 and PD-L1 (Fig. 2A), and knockdown of NR4A1 by RNAi decreased expression of both PD-L1 and NR4A1; Sp1 knockdown or treatment with mithramycin also decreased Sp1 and PD-L1 expression in MC-38 cells (Fig. 2B) as observed in the human colon cancer cell lines, suggesting that PD-L1 may also be regulated by an NR4A1/Sp1 complex in MC-38 cells.