Wei SJ, Nguyen TH, Yang IH, Mook DG, Makena MR, Verlekar D, Hindle A, Martinez GM, Yang S, Shimada H, Reynolds CP, Kang MH
Despite the improvement in clinical outcome with 13-cis-retinoic acid (13-cisRA) + anti-GD2 antibody + cytokine immunotherapy given in first response ~40% of high-risk neuroblastoma patients die of recurrent disease. MYCN genomic amplification is a biomarker of aggressive tumors in the childhood cancer neuroblastoma. MYCN expression is downregulated by 13-cisRA, a differentiating agent that is a component of neuroblastoma therapy. Although MYC amplification is rare in neuroblastoma at diagnosis, we report transcriptional activation of MYC medicated by the transcription factor OCT4, functionally replacing MYCN in 13-cisRA-resistant progressive disease neuroblastoma in large panels of patient-derived cell lines and xenograft models. We identified novel OCT4-binding sites in the MYC promoter/enhancer region that regulated MYC expression via phosphorylation by MAPKAPK2 (MK2). OCT4 phosphorylation at the S111 residue by MK2 was upstream of MYC transcriptional activation. Expression of OCT4, MK2, and c-MYC was higher in progressive disease relative to pre-therapy neuroblastomas and was associated with inferior patient survival. OCT4 or MK2 knockdown decreased c-MYC expression and restored the sensitivity to 13-cisRA. In conclusion, we demonstrated that high c-MYC expression independent of genomic amplification is associated with disease progression in neuroblastoma. MK2-mediated OCT4 transcriptional activation is a novel mechanism for activating the MYC oncogene in progressive disease neuroblastoma that provides a therapeutic target.