MYCN safeguards its upregulated expression through negatively controlling its upstream miRNAs

MYCN plays a central role in neuroblastoma development and exerts a pleiotropic role through the regulation of many protein encoding genes and microRNAs (miRNAs). MYCN activity is strictly controlled at multiple levels, including transcription and protein stability. Previous studies already pinpointed several miRNAs controlling MYCN expression levels. To fully elucidate this regulation, we further explored the MYCN-miRNA interactome upstream of MYCN. Therefore, we used the powerful combination of an unbiased high-throughput luciferase reporter screen for the 3'UTR of MYCN, and a unique dynamic expression dataset, generated from the TH-MYCN mouse model. First, the unbiased MYCN 3’UTR-miRNA library screen identified 29 miRNAs potentially targeting MYCN. Next, we determined which of these miRNAs were relevant in neuroblastoma context. Therefore we have evaluated the expression of these MYCN targeting miRNAs in a murine MYCN-driven neuroblastoma progression model. Interestingly, the majority of MYCN targeting miRNAs showed a decreasing expression pattern during tumor development, suggesting that MYCN induces their downregulation. Further, miRNAs downregulated during murine tumor development showed anti-correlation to MYCN expression in a large cohort of primary neuroblastoma tumors, supporting their role in regulation of MYCN expression. In conclusion, our data strongly suggest that MYCN negatively controls the expression levels of miRNAs binding to it's 3'UTR, thereby safeguarding its own upregulated expression levels.