Phosphorylation of MYCN and MAX by PAK family kinases is a novel tumor-suppressor mechanism in neuroblastoma with potential therapeutic implications

Abstract

High-risk Neuroblastoma (HR-NB) is a very aggressive pediatric cancer, responsible of over 15% of all childhood cancer-associated deaths. Despite very aggressive multimodal interventions, less than 50% of HR-NB patients survive, exhibiting serious long-term sequelae from therapy. Therefore, more efficient, and less toxic interventions are urgently needed. Genomic amplification of the MYCN gene is observed in about 50% of all HR-NB cases, and is the most reliable genomic hallmark associated to a bad prognosis. c-MYC is highly expressed in a significant amount of the remaining (non-MYCN-amplified) HR-NB cases. Here, we investigated an endogenous mechanism mediated by the PAK2 kinase and known to phosphorylate and suppress c-MYC transcriptional activity. We uncovered that PAK2 can also phosphorylate MYCN and its obligate transcriptional partner MAX in two conserved Ser/Thr residues, disrupting MYCN:MAX interaction, transcription, and neuroblastoma cell proliferation. We further provide evidence for a potential mechanism by which PAK kinase activity is blunted in MYCN-amplified neuroblastoma tumors and propose an innovative strategy to circumvent such signaling impairment and potentially suppress HR-NB tumor growth.