MYCN-amplified neuroblastoma maintains an aggressive and undifferentiated phenotype by deregulation of estrogen and NGF signaling

Neuroblastoma (NB) is a remarkably heterogenic childhood tumor of the sympathetic nervous system with clinical behavior ranging from spontaneous regression to poorly differentiated tumors and metastasis. MYCN is amplified in 20% of cases and correlates with an undifferentiated, aggressive phenotype and poor prognosis. Estrogen receptor alpha (ER alpha) and the nerve growth factor (NGF) receptors TrkA and p75(NTR) are involved in neuronal differentiation and survival. We have previously shown that MYCN, via miR-18a, targets ER alpha in NB cells. Here, we demonstrate that interference with miR-18a or overexpression of ER alpha is sufficient to induce NGF signaling and to modulate both basal and NGF-induced neuronal differentiation in MYCN-amplified NB cells. Proteomic analysis confirmed an increase of neuronal features and showed that processes linked to tumor initiation and progression were inhibited upon ER alpha overexpression. Indeed, ectopic ER alpha expression was sufficient to inhibit metabolic activity and tumorigenic processes, including glycolysis, oxidative phosphorylation, cell viability, migration, and anchorage independent growth. Importantly, ER alpha overexpression reduced tumor burden in NB mouse models and high ER alpha levels were linked to improved survival in patients. In addition to ER alpha, several other nuclear hormone receptors (NHRs), including the glucocorticoid and the retinoic acid receptors, correlated with clinical markers for favorable and low-stage NB disease. Our data suggest that MYCN targets ER alpha and thereby NGF signaling to maintain an undifferentiated and aggressive phenotype. Notably, we identified the estrogen-NGF crosstalk, as well as a set of other NHRs, as potential prognostic markers and targets for therapeutic strategies against NB.