NEDD8 and breast cancer: 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.