MYCN acts as a direct co-regulator of p53 in MYCN amplified neuroblastoma

Abstract

The MYC oncogenes and p53 have opposing yet interrelated roles in normal development and tumorigenesis. How MYCN expression alters the biology and clinical responsiveness of pediatric neuroblastoma remains poorly defined. Neuroblastoma is p53 wild type at diagnosis and repression of p53 signaling is required for tumorigenesis. Here, we tested the hypothesis that MYCN amplification alters p53 transcriptional activity in neuroblastoma. Interestingly, we found that MYCN directly binds to the tetrameric form of p53 at its C-terminal domain, and this interaction is independent of MYCN/MAX heterodimer formation. Chromatin analysis of MYCN and p53 targets reveals dramatic changes in binding, as well as co-localization of the MYCN-p53 complex at p53-REs and E-boxes of genes critical to DNA damage responses and cell cycle progression. RNA sequencing studies show that MYCN-p53 co-localization significantly modulated the expression of p53 target genes. Furthermore, MYCN-p53 interaction leads to regulation of alternative p53 targets not regulated in the presence of low MYCN levels. These novel targets include a number of genes involved in lipid metabolism, DNA repair, and apoptosis. Taken together, our findings demonstrate a novel oncogenic role of MYCN as a transcriptional co-regulator of p53 in high-risk MYCN amplified neuroblastoma. Targeting this novel oncogenic function of MYCN may enhance p53-mediated responses and sensitize MYCN amplified tumors to chemotherapy.

The MDM2 inhibitor CGM097 combined with the BET inhibitor OTX015 induces cell death and inhibits tumor growth in models of neuroblastoma

“…Though the lack of p53 induction in combination treated SH‐SY5Y cells compared to single‐agent CGM097 treated cells is surprising, the level of p53 expression in the combination treated cells may be adequate to mediate its downstream effects. In single‐agent CGM097 treated SH‐SY5Y cells, the overexpression of MYC family proteins may alter the p53 response, as has been previously reported 27 . MDM2 protein expression increased with CGM097 treatment in SMS‐KCNR and SH‐SY5Y, which is not entirely unexpected as increased p53 expression induces MDM2 in a negative feedback loop, which has been observed in the literature 18‐20 .…”

“…Experimentally, the most sensitive NB cells to MDM2 inhibition have been shown to have MYCN amplification, suggesting that MYCN may play a prominent role in the MDM2/p53 axis 21,25,26 . Additionally, activation of p53 in the presence of abundant MYCN leads to nuclear co‐localization of the two proteins which alters the p53 stress response, further intertwining these pathways in NB 27 . Taken together, MDM2 dysregulation in NB and the role of MYC family proteins in high risk disease has led us to hypothesize that targeting both the MDM2 and MYC family pathways simultaneously may result in a synergistic increase in cytotoxicity in NB models, and present a possible novel therapeutic option.…”

Emerging roles of Myc in stem cell biology and novel tumor therapies

“…Amplified N-Myc directly binds with the tetrameric form of p53 at the C-terminal domain in this neuroendocrine tumor. N-Myc and p53 exhibit the co-localization in the nucleus and alter p53-dependent transcriptional responses that are necessary for DNA repair, anti-apoptosis, and lipid metabolic reprogramming [ 81 ].…”

“…A lipid metabolism gene signature tends to be enriched in patients with TNBC according to TCGA [ 154 , 155 ]. It is notable that the interaction between wild-type p53 and amplified N-Myc causes the lipid metabolic reprogramming [ 81 ]. The degree of AMP-activated protein kinase (AMPK) signal activation exhibits the inversed relationship with c-Myc [ 156 , 157 ].…”

The roles of glucose metabolic reprogramming in chemo- and radio-resistance

“…In MUC1-expressing pancreatic cancer cells, the metabolite levels in glycolysis, PPP and nucleotide biosynthetic pathways increased to enhance the DNA damage repair and inhibit the sensibility of radiation therapy and chemotherapy [64–67]. Furthermore, amplified N-Myc can directly bind with the tetrameric form of p53 at the C-terminal domain in the nucleus to alter p53-dependent transcriptional responses in neuroblastoma patients with wild-type p53, but wild-type p53 negatively regulates G6PD activity, a rate-limiting enzyme of the pentose phosphate pathway that is the most important sources of nucleotides, and then decreases dNTP synthesis, ultimately influencing the DNA repair [46, 68, 69]. Therefore, N-Myc directly suppresses the transcriptional responses of wild-type p53 to inhibit the pentose phosphate pathway and increase the DNA repair.…”