NONO as a Sensor of Intracellular Oxidation: Relevance to Neuroblastoma Cell Death
Neuroblastoma, a transcriptionally driven pediatric malignancy, exhibits a remarkable clinical and biological heterogeneity. Two major subtypes, the adrenergic and mesenchymal, are differentially governed by a subset of transcription factors that comprise the core regulatory circuit (CRC). The former subtype is often associated with MYCN amplification and is particularly aggressive and therapy-resistant, underscoring the need for novel targets. Here, we identify the multifunctional non-POU domain-containing octamer-binding (NONO) protein as a guardian of individual CRC genes, thereby contributing to survival of neuroblastoma cells with different MYCN copy numbers. Intracellular oxidation in response to auranofin, an inhibitor of thioredoxin reductase 1, rapidly down-regulated the amounts of NONO mRNA and protein in MYCN-amplified Kelly cell line. Conversely, NONO knockdown with RNA interference (siNONO) also triggered intracellular oxidation. These effects were less pronounced in the SK-N-AS cell line carrying a single MYCN copy, as well as in non-malignant HS5 fibroblasts. In Kelly cells, siNONO attenuated auranofin-induced activation of CRC genes HAND2 and PHOX2B. In line with preferential effects on NONO abundance, the Kelly cells were more sensitive than single MYCN copy counterparts to combinations of a sublethal concentration of auranofin with siNONO. Importantly, MYCN-amplified cells demonstrated a significantly suppressed clonogenic survival 14 days after transient exposure to these combinations compared with each agent alone; HS5 fibroblasts were largely spared. Our findings 1) establish NONO as a redox sensor, a non-trivial role for transcriptional proteins, and 2) justify the strategy of therapeutic targeting of MYCN-amplified tumors vulnerable to oxidative stress. Key pointsO_LINONO, a master regulator of the core regulatory circuit (CRC) in MYCN-amplified neuroblastoma, is rapidly down-regulated by auranofin-induced intracellular oxidation. C_LIO_LINONO knockdown synergizes with auranofin in triggering individual CRC gene deregulation and lethal oxidative stress preferentially in MYCN-amplified cells. C_LI