As APP-BP1 catalyses the rate-limiting step of NEDDylation20, we, next, determined APP-BP1 and NEDD8 expression in tissue microarrays from breast cancer patients and the result revealed that both APP-BP1 and NEDD8 are upregulated in breast cancer (Fig. 1f, g), suggesting breast cancer cells exhibit higher levels of NEDDylation than normal cells. This evidence concerns the gene NAE1 and breast cancer.