Genetic-epigenetic interactions in neuroblastoma

The solid childhood cancer neuroblastoma arises from cells of the sympathetic nervous system. Neuroblastoma is the most common childhood cancer in children younger than one year old worldwide and accounts for 28% of all cancers diagnosed in Europe and the U.S. in infants. 25% of neuroblastomas bear an amplification of the proto-oncogene MYCN; in addition to this genetic alteration, epigenetic modifications such as transcriptional silencing of tumour suppressor genes by promoter DNA hypermethylation and histone modifications can occur. Previous studies have shown an interaction between MYC and DNA hypermethylation, through recruitment of de novo DNA methyltransferases to the promoter of MYC target genes, in order to repress their transcription. We hypothesised that MYCN might be similarly capable of repressing its target genes. Our results revealed that MYCN interacts with the maintenance and de novo methyltransferase DNMT1 and DNMT3A, respectively in MYCN amplified neuroblastoma cell lines and all three bind the promoter region of the hypermethylated gene RASSF1A. However, only minor changes in DNA methylation of RASSF1A were shown by pyrosequencing analysis upon MYCN knock-down. This probably indicates only a small involvement of MYCN in epigenetically-induced gene silencing by DNA hypermethylation. The important role of MYCN in gene activation was highlighted from DNA methylation microarray studies on neuroblastoma cell lines compared to human neural crest cells. 73% of all hit genes showed hypomethylation, which led to the conclusion that a more open chromatin configuration and thus increased gene expression is favoured in high stage neuroblastoma cell lines, where MYCN and MYC compensate each others protein levels. The same study also led to the discovery of a novel methylated gene MEGF10 in neuroblastoma. The importance of epigenetic silencing in neuroblastoma was also highlighted by the ability of DNA demethylating agent 5-Aza-2'-deoxycytidine to re-sensitise chemotherapeutic resistant neuroblastoma cells to commonly used cytotoxic drugs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo