Biological effects of induced MYCN hyper-expression in MYCN-amplified neuroblastomas

Abstract

Abstract. Neuroblastoma is a childhood malignancy of the sympathetic nervous system. The tumor exhibits two different phenotypes: favorable and unfavorable. MYCN amplification is associated with rapid tumor progression and the worst neuroblastoma disease outcome. We have previously reported that inhibitors of histone deacetylase (HDAC) and proteasome enhance favorable neuroblastoma gene expression in neuroblastoma cell lines and inhibit growth of these cells. In this study, we investigated the effect of Trichostatin A or TSA (an HDAC inhibitor), and Epoxomycin (a proteasome inhibitor) on MYCN and p53 expression in MYCN-amplified neuroblastoma cells. It was found that TSA down-regulated MYCN expression, but Epoxomycin and the TSA/Epoxomycin combination led to MYCN hyper-expression in MYCNamplified neuroblastoma cell lines. Despite their contrasting effects on MYCN expression, TSA and Epoxomycin caused growth suppression and cell death of the MYCN-amplified cell lines examined. Consistent with these data, forced hyperexpression of MYCN in MYCN-amplified IMR5 cells via transfection resulted in growth suppression and the increased expression of several genes known to suppress growth or induce cell death. Furthermore, Epoxomycin as a single agent and its combination with TSA enhance p53 expression in the MYCN-amplified neuroblastoma cell lines. Unexpectedly, cotransfection of TP53 and MYCN in IMR5 cells resulted in high p53 expression but a reduction of MYCN expression. Together our data suggest that either down regulation or hyper-expression of MYCN results in growth inhibition and/ or apoptosis of MYCN-amplified neuroblastoma cells. In addition, elevated p53 expression has a suppressive effect on MYCN expression in these cells.

S(+)-ibuprofen destabilizes MYC/MYCN and AKT, increases p53 expression, and induces unfolded protein response and favorable phenotype in neuroblastoma cell lines

“…Our previous study indicated that elevated p53 expression has a suppressive effect on MYCN expression in MYCN -amplified neuroblastoma cells ( 8 ). We thus investigated whether this was also the case in the S(+)-ibuprofen-treated cells.…”

“…Western blotting was performed as previously described ( 8 , 9 ). Light emission signals were captured by a LAS-3000 (Fujifilm) digital image analyzer.…”

“…Our previous study on the response of neuroblastoma cells to inhibitors of histone deacetylases and proteasomes suggests that enhanced p53 expression is linked to MYCN destabilization ( 8 ). We also showed that inhibition of Hsp90 resulted in the destabilization of AKT, MYC, MYCN and in an increase in p53 levels ( 9 ).…”

Clinical, Genomic, and Pharmacological Study of MYCN-Amplified RB1 Wild-Type Metastatic Retinoblastoma

“…The proteasome inhibitor alters cellular protein homeostasis and has shown to prevent MYCN degradation resulting in its accumulation with a deleterious effect in MYCN-driven neuroblastomas [55,56]. Bortezomib was also selected based on single-agent activity and promising features in combination studies in pediatric preclinical models [20,57,58].…”

Exploitation of chick embryo environments to reprogram MYCN-amplified neuroblastoma cells to a benign phenotype, lacking detectable MYCN expression

“…Protein stability is controlled by a number of signalling pathways including mTOR, 37 whereas mRNA stability may be dependent on a variety of miRNAs and proteins including HuD and members of the p53 family. 35 , 38 , 39 , 40 However, developmentally, MYCN expression will be controlled by suppression of transcription and this is likely to be the principal mechanism by which MYCN is downregulated in the Kelly cells, although a contribution by factors regulating mRNA and protein stability cannot be ruled out. The key factors that initiate suppression of MYCN expression remain to be elucidated.…”