PO77EXPRESSION OF THE ONCOGENIC SPLICE VARIANT OF CYCLIN D1, CCND1B, IN PAEDIATRIC LOW GRADE GLIOMAS

Abstract

INTRODUCTION: Paediatric low-grade gliomas have genetic mutations that result in activation of the MAPK pathway. A key downstream target of the MAPK pathway is the cell cycle regulator cyclin D1 (CCND1), which is up-regulated and mutated in many cancers. Aberrant alternative splicing at the exon4-intron boundary in CCND1 leads to expression of the CCND1b transcript, producing an oncogenic truncated protein. We have investigated whether CCND1b is expressed in pLGGs and have examined the SNP and DNA methylation status at the exon4-intron boundary. METHOD: Real-time PCR was used to investigate expression levels of CCND1 splice variants in 27 paediatric low-grade gliomas and 4 normal brain controls. DNA methylation was analysed using the Illumina HumanMethylation450K beadchip, and the SNP status determined by PCR and Sanger sequencing. Findings were confirmed in an independent tumour cohort. RESULTS: The oncogenic splice variant, CCND1b, was found to be upregulated together with the non-oncogenic variant, CCND1a, in both pilocytic and diffuse astrocytomas compared to normal brain. CCND1b expression was significantly higher in diffuse astrocytomas than pilocytic astrocytomas. However, no correlation was found between CCND1b expression and methylation or SNP status across the tumour cohort. CONCLUSION: This study is the first to identify the oncogenic CCND1b splice variant in paediatric low-grade gliomas. The mechanism that leads to oncogenic alternative splicing still needs to be elucidated. As aberrant action of splicing machinery is present in many cancers, our findings warrant further investigation in this group of tumours.