Distinct transcriptional MYCN/c-MYC activities are associated with spontaneous regression or malignant progression in neuroblastomas

TLDR

Amplification of MYCN in 20 % of neuroblastomas defines a highly aggressive subtype, whereas in single‑copy tumors elevated MYCN expression paradoxically associates with favorable outcomes and spontaneous regression of disseminated stage 4s disease. The study investigates whether distinct transcriptional MYCN or c‑MYC activities correlate with specific neuroblastoma phenotypes by defining a core set of direct target genes through expression profiling and ChIP in conditional neuroblastoma cell lines. Transcript levels of these MYCN/c‑MYC target genes were quantified in 251 primary neuroblastoma samples. Target gene expression rises progressively from stage 4s‑non‑amplified through stage 4‑non‑amplified to MYCN‑amplified tumors, with MYCN activation driving stage 4s regression and c‑MYC activation driving stage 4 progression, and high expression of a defined MYCN/c‑MYC target set predicts poor survival independent of established risk factors, underscoring c‑MYC‑mediated malignant progression while moderate MYCN activity in stage 4s supports spontaneous regression.

Abstract

Amplified MYCN oncogene resulting in deregulated MYCN transcriptional activity is observed in 20% of neuroblastomas and identifies a highly aggressive subtype. In MYCN single-copy neuroblastomas, elevated MYCN mRNA and protein levels are paradoxically associated with a more favorable clinical phenotype, including disseminated tumors that subsequently regress spontaneously (stage 4s-non-amplified). In this study, we asked whether distinct transcriptional MYCN or c-MYC activities are associated with specific neuroblastoma phenotypes.We defined a core set of direct MYCN/c-MYC target genes by applying gene expression profiling and chromatin immunoprecipitation (ChIP, ChIP-chip) in neuroblastoma cells that allow conditional regulation of MYCN and c-MYC. Their transcript levels were analyzed in 251 primary neuroblastomas. Compared to localized-non-amplified neuroblastomas, MYCN/c-MYC target gene expression gradually increases from stage 4s-non-amplified through stage 4-non-amplified to MYCN amplified tumors. This was associated with MYCN activation in stage 4s-non-amplified and predominantly c-MYC activation in stage 4-non-amplified tumors. A defined set of MYCN/c-MYC target genes was induced in stage 4-non-amplified but not in stage 4s-non-amplified neuroblastomas. In line with this, high expression of a subset of MYCN/c-MYC target genes identifies a patient subtype with poor overall survival independent of the established risk markers amplified MYCN, disease stage, and age at diagnosis.High MYCN/c-MYC target gene expression is a hallmark of malignant neuroblastoma progression, which is predominantly driven by c-MYC in stage 4-non-amplified tumors. In contrast, moderate MYCN function gain in stage 4s-non-amplified tumors induces only a restricted set of target genes that is still compatible with spontaneous regression.