Neuroblastoma (NB) is an aggressive lethal pediatric cancer of the developing sympatho-adrenergic nervous system and characterised by a low mutation burden while exhibiting recurrent DNA copy number alterations including chromosome 2p gain and MYCN amplification. Rare amplifications have previously allowed to identify additional oncogenes implicated in NB such as ALK and LIN28B.

Here we report on three NB tumours and two NB cell lines with high level focal gain containing the SRY-related HMG-box transcription factor 11 (SOX11) as only protein-coding gene in the smallest region of overlap. The high expression levels of SOX11 in NB and the developing sympathetic nervous system, and high correlation of SOX11 mRNA and protein levels with survival outcome, suggested a role for SOX11 as oncogene and prompted us to further investigate its role in MYCN driven NB formation. SOX11 knock down in NB cell lines showed reduced colony formation capacity and G1-S cell cycle arrest. We observed increased SOX11 levels upon MYCN induction in NB cell lines, in MYCN overexpressing mouse neuroblastomas compared to normal ganglia as well as a high correlation of SOX11 and MYCN mRNA and protein levels in cell lines and tumors. As these data could indicate direct MYCN regulation of SOX11, we performed MYCN ChIPseq and indeed confirmed binding of MYCN to the SOX11 promotor. Next, we demonstrated MYCN and SOX11 cooperative binding to common targets using SOX11 and H3K27ac ChIP-sequencing. First, we showed localisation of more than half (62%) of the SOX11 binding sites at enhancers. Moreover, 19% of SOX11 targets contained an E-Box motif, typically known to be targeted by MYCN, and we showed overlap of 30% of SOX11 and MYCN binding targets. In a further step to unravel SOX11 function in NB cells, we analysed SOX11 binding partners using IP-MS and identified 9 robust interaction partners in multiple NB cell lines. These included MYCN which was confirmed by reciprocal co-IP, as well as WEE1, a tyrosine kinase critically implicated in G2-M checkpoint control for which multiple potent and specific small molecule inhibitors are available. Remarkably, upon testing of the AZD-1775 WEE1 inhibitor in 10 NB cell lines, we observed the strongest effects in cells with the highest SOX11 protein levels indicating that SOX11 expression levels can serve as predictive biomarker for AZD-1775 treatment response.

In conclusion we identified high-level focal gain of SOX11 in NB tumors and cell lines and demonstrated the oncogenic role of SOX11 in MYCN driven neuroblastoma with therapeutic opportunities through interaction with WEE1.

Citation Format: Bieke Decaesteker, Sara De Brouwer, Fanny De Vloed, Geertrui Denecker, Suzanne Vanhauwaert, Jolien De Wyn, Geneviève Laureys, Bjorn Menten, Pauline Depuydt, Patrick Reynolds, Jo Vandorpe, Kris Gevaert, Jan Koster, Sara Ek, Frank Speleman, Katleen De Preter. SOX11 acts as part of the MYCN-WEE1 regulatory protein complex implicated in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5506. doi:10.1158/1538-7445.AM2017-5506