Abstract 264: Circular chromosome conformation capture analysis of MYCN downregulation during retinoic acid-induced differentiation of neuroblastoma
Authors: Yoshioka Masahiro , Takeuchi Kenneth , Higa Kelly , Tanaka Royden , Bryan Chena , Tuthill Matthew , Wada Randal 
Published: June 2012

Abstract
The purpose of this study was to identify interactions of the human MYCN promoter with other chromosomal loci as potential mediators of MYCN downregulation in response to the retinoic acid (RA)-induced differentiation of neuroblastoma cells. Neuroblastoma is a common deadly childhood malignancy. Activation of MYCN through genomic amplification identifies patients at highest risk, for which cure has remained elusive. RA is one of the few agents found to improve survival in this large subgroup, and appears to achieve its therapeutic benefit by inducing differentiation of residual tumor cells. Transcriptional downregulation of MYCN is a key step in this process, but the mechanism through which this occurs is poorly understood. Recently nuclear architecture and chromatin geography have been recognized as important factors in the regulation of individual gene expression. Chromosome looping allows distant segments of DNA from the same chromosome, or regions from different chromosomes, to interact, so that the expression of genes may be controlled by regulatory components that are otherwise separated by great distances. These long range interactions may serve to gather related genes at specific assembly sites within the nucleus, where their expression can be coordinated through the sharing of transcription factors and/or machinery. The RA effect on MYCN transcription was therefore analyzed using circular chromosome conformation capture. RA was found to trigger an interaction between the basal MYCN promoter on chromosome 2, and a 2-300 bp region that was a 100% match to sequence from chromosome 7. This association was only observed in RA treated cells. The partnering region mapped to 7q11.2, and covered sequence upstream from the AUTS2 gene. The function of this gene is unknown; however translocations and mutations involving AUTS2 have been reported in association with autism and mental retardation, suggesting that it may play a role in neural development. AUTS2 lies within a region of 7q known to contain ultra-conserved non-coding regions. Between 40-45% of neuroblastoma tumors have been reported to have gains of genetic material involving 7q. While this abnormality is correlated with a lack of MYCN amplification, its significance is unknown. AUTS2 was expressed in LA-N-5 neuroblastoma cells, and was downregulated by RA along the same rapid time course as MYCN. Lastly, FISH assays on control and RA-treated neuroblastoma cells showed that co-localization of AUTS2 and MYCN probes was associated with RA treatment, and was only observed in cells that had received RA. These data suggest that RA may induce interactions of the MYCN promoter with regulatory regions on other chromosomes, which may allow for coordinate downregulation of multiple genes.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 264. doi:10.1158/1538-7445.AM2011-264