MYCN and breast carcinoma: In breast cancer cells, modulation of BMI1 did not significantly change p53 protein levels.44 In contrast, BMI-1 has been shown to have a negative impact on p53 expression in neuroblastoma cell lines.37, 45 Calao et al.37 showed that BMI-1 promotes p53 ubiquitination and degradation, and Cui et al.45 demonstrated that BMI-1 blocks MYCN-driven p53 induction.