TP53 and neoplasm: In fact, the dominant-negative FoxO Eμ-myc tumours arose as rapidly as those on a p53+/− background.26 FoxO3 and MYC compete for binding to some promoters and appear to antagonise each other's activity.27, 28, 29 FoxO3 directly regulates expression of the MYC inhibitor MXI1, whereas other Max-interacting protein (MXD) family members are regulated indirectly.30