Neuroblastoma, which arises from the developing sympathetic nervous system, is one of the most aggressive solid tumors of early childhood. Amplification of the MYCN oncogene is found in around 30% of NB patients and is associated with rapid tumor progression and poor prognosis. Our recent findings show that a small chemical molecule, 10058-F4, previously identified as a c-MYC inhibitor also targets the MYCN/MAX complex resulting in apoptosis and neuronal differentiation in MYCN-amplified NB cells. Importantly, we demonstrated that inhibition of MYCN results in metabolic changes including mitochondrial dysfunction leading to accumulation of lipid droplets in NB cells. Similarly, treatment with the bromodamain inhibitor JQ1 leads to MYCN downregulation followed by lipid accumulation.
To investigate downstream effects of MYCN targeting we have performed quantitative proteomics of MYCN-amplified NB cells treated with 10058F4 or JQ1. For comparison, downregulation of MYCN expression using short hairpin RNA against MYCN followed by proteomic analysis was performed. We identified over 7000 proteins of which 6500 have been used for identification of novel pathways involved in NB pathogenesis. We found that primary metabolic processes including protein, lipid and nucleic acid metabolic processes were the most significantly affected activities upon MYCN downregulation. For analysis of the impact of MYCN expression on glycolysis and mitochondrial capacity we performed metabolic flux measurements using a Seahorse XF analyser. These results show that MYCN-amplified NB cells have a high metabolic potential and that they primarily use oxidative phosphorylation for their energy consumption. We also found that MYCN not only positively regulates the respiratory capacity but also significantly enhances glycolysis in NB cells. Importantly, we demonstrate that MYCN positively regulates the ability of NB cells to oxidize exogenous fatty acids.
Taken together, our findings show that MYCN expression enhances the bioenergetic capabilities and that NB cells can shift their metabolic processes depending on the available nutrition. Importantly, MYCN regulates metabolic plasticity in NB cells, which contributes to their aggressiveness.