Oral Presentation Advances in Neuroblastoma Research Congress 2016

The role of PRC2 in the early neuroblastoma tumorigenesis in MYCN-Tg mice (#2)

Shoma Tsubota 1 , Satoshi Kishida 1 , Miki Ohira 2 , Satoshi Yamashita 3 , Toshikazu Ushijima 3 , Kenji Kadomatsu 1
  1. Department of Biochemistry, Nagoya Graduate School of Medicine, Nagoya, Aichi, Japan
  2. Research Institute for Clinical Oncology, Saitama Cancer Center, Saitama, Japan
  3. Division of Epigenomics, National Cancer Center Research Institute, Tokyo, Japan

[Introduction] The aim of this study is to better understand the regulatory mechanisms of early neuroblastoma (NB) tumorigenesis. To this end, we used MYCN-Tg mice and primarily looked at sympathoadrenal progenitors during embryogenesis.

[Methods] We established a spheroid culture method, in which undifferentiated neuroblasts could form spheres, and evaluated sphere-forming and tumor-forming ability of neuroblasts. We further analyzed transcriptome and epigenome of E13.5 spheres from wild-type and MYCN-Tg mice using microarray and methyl-CpG binding domain (MBD) protein-enriched genome sequencing (MBD-seq).

[Results] Firstly, we observed that E13.5 spheres from MYCN-Tg but not from wild-type mice were passageable and were able to develop subcutaneous tumors, suggesting that NB tumorigenesis has started as early as E13.5 in MYCN-Tg mice. MYCN expression was confirmed by means of in situ hybridization in a subset of neuroblasts at E13.5 in MYCN-Tg mice. Consistent with this, microarray expression analysis and GSEA revealed that MYCN target genes were upregulated in E13.5 MYCN-Tg spheres, validating the usefulness of the spheroid culture as a tool reflecting in vivo tumorigenesis. Importantly, it was also revealed that polycomb repressive complex 2 (PRC2) target genes were broadly downregulated while its components were slightly upregulated. Moreover, MBD-seq revealed that the number of promoter-methylated genes was increased in MYCN-Tg spheres. Genes related to development were enriched in the promoter-methylated genes. We identified a group of genes whose promoters were methylated and expressions were simultaneously downregulated in MYCN-Tg spheres. Expressions of these genes were downregulated in high-risk and stage 4 NBs, and could predict patient’s prognosis.

[Conclusion] Our study demonstrates the importance of epigenome, particularly PRC2 activation, in impaired developmental program in the early NB pathogenesis. Investigation of the epigenetic intervention potential is currently being undertaken in our laboratory to cure NB. Further study about PRC2 and its epigenetic regulatory mechanism may open a new therapeutic avenue.