A novel HECT-type E3 ubiquitin protein ligase NEDL1 enhances the p53-mediated apoptotic cell death in its catalytic activity-independent manner

NEDL1 (NEDD4-like ubiquitin protein ligase-1) is a newly identified HECT-type E3 ubiquitin protein ligase highly expressed in favorable neuroblastomas as compared with unfavorable ones. In this study, we found that NEDL1 cooperates with p53 to induce apoptosis. During cisplatin (CDDP)-mediated apoptosis in neuroblastoma SH-SY5Y cells, p53 was induced to accumulate in association with an increase in expression levels of NEDL1. Enforced expression of NEDL1 resulted in a decrease in number of G418-resistant colonies in SH-SY5Y and U2OS cells bearing wild-type p53, whereas NEDL1 had undetectable effect on p53-deficient H1299 and SAOS-2 cells. Similarly, enforced expression of NEDL1 increased number of U2OS cells with sub-G1 DNA content. Co-immunoprecipitation and in vitro binding assays revealed that NEDL1 binds to the COOH-terminal region of p53. Luciferase reporter assay showed that NEDL1 has an ability to enhance the transcriptional activity of p53. Small interfering RNA-mediated knockdown of the endogenous NEDL1 conferred the resistance of U2OS cells to adriamycin. It is noteworthy that NEDL1 enhanced pro-apoptotic activity of p53 in its catalytic activity-independent manner. Taken together, our present findings suggest that functional interaction of NEDL1 with p53 might contribute to the induction of apoptosis in cancerous cells bearing wild-type p53.