A small-molecule inhibitor of UBE2N induces neuroblastoma cell death via activation of p53 and JNK pathways

J Cheng,Y Yu,E S Kim,Y Rojas,J Yang,X Chen,Y-H Fan,H Zhang,Y Tang,X Xu,J G Nuchtern,S A Vasudevan,X Zhong,J Dou,F Lu,Y Zhao

doi:10.1038/cddis.2014.54

Abstract

Neuroblastoma (NB) is the most common extracranial neoplasm in children. In NB, loss of p53 function is largely due to cytoplasmic sequestration rather than mutation. Ubiquitin-conjugating enzyme E2 N (UBE2N), also known as Ubc13, is an E2 ubiquitin-conjugating enzyme that promotes formation of monomeric p53 that results in its cytoplasmic translocation and subsequent loss of function. Therefore, inhibition of UBE2N may reactivate p53 by promoting its nuclear accumulation. Here, we show that NSC697923, a novel UBE2N inhibitor, exhibits potent cytotoxicity in a panel of NB cell lines evidenced by its ability to induce apoptosis. In p53 wild-type NB cells, NSC697923 induced nuclear accumulation of p53, which led to its increased transcriptional activity and tumor suppressor function. Interestingly, in p53 mutant NB cells, NSC697923 induced cell death by activating JNK pathway. This effect was reversible by blocking JNK activity with its selective inhibitor, SP600125. More importantly, NSC697923 impeded cell growth of chemoresistant LA-N-6 NB cell line in a manner greater than conventional chemotherapy drugs doxorubicin and etoposide. NSC697923 also revealed in vivo antitumor efficacy in NB orthotopic xenografts. Taken together, our results suggest that UBE2N is a potential therapeutic target in NB and provide a basis for the rational use of UBE2N inhibitors like NSC697923 as a novel treatment option for NB patients.

Highlights

The p53 protein has been studied extensively due to its key role in tumor suppression
ubiquitin-conjugating enzyme E2 N (UBE2N) forms an obligate heterodimer with Uev1A to positively regulate nuclear factor kappa B (NF-kB) signal– transduction pathway, while in complex with Mms[2], UBE2N is required for DNA damage repair.[18]
With regard to p53, UBE2N associates with p53 and increases the cytoplasm pool of monomeric p53, thereby inhibiting nuclear tetramerization of p53.14,20 Owing to the critical role of UBE2N in cytosolic sequestration of wild-type p53 and the fact that cytosolic sequestration of wild-type p53 is present in most NB cases, we hypothesized that pharmacological inhibition of UBE2N would promote p53 nuclear translocation and its subsequent activation in NB

Summary

Introduction

The p53 protein has been studied extensively due to its key role in tumor suppression It functions as a transcription factor and induces cell cycle arrest, apoptosis and cellular senescence by controlling a variety of signaling pathways in response to stress signals.[7] Upon its activation, p53 will dissociate with mouse double minute 2 homolog (MDM2), an E3 ubiquitin ligase, and translocate to the nucleus, where it activates the target genes.[8,9,10] As the majority of p53 tumor suppressor functions are achieved by its transcriptional activity, nuclear localization of the protein is essential. Our findings shed light on the viability of UBE2N as a potential molecular target in the treatment of NB and suggest that NSC697923 may serve as a novel antitumor drug for NB patients

Methods

Results

Conclusion