GENE-17. TOP2B REGULATES CDK4 SPLICE VARIANTS IN GLIOMAS

Topoisomerase IIB (TOP2B) is known to decoil and decatenate DNA, releasing chromatin torsional forces. Whereas TOP2B has been implicated in transcript splicing, direct evidence supporting this function, through localization of TOP2B to specific chromatin sites and in association with specific types of cancer, is modest at best. Here, we report our preliminary activities that are intended to address this knowledge gap. GSEA differential expression analysis using TCGA glioblastoma data showed that high TOP2B expression is associated with elevated expression of cell cycle-related genes (p-value= 1.67E(-05)). To investigate the possible association of TOP2B with specific gene sequences we used TOP2B ChIP-seq in analyzing glioma cell lines TS543 and BT142, and found TOP2B associations with the introns of especially long genes (gen length ≥ 100Kb, p-value= 0.001). Functional annotation analysis for genes with TOP2B intron binding showed a significant enrichment for genes with multiple known splice variants (p-value= 1.9E(-11)). To determine effects of TOP2B inhibition on splice variant expression, we treated BT142 cells with the TOP2 inhibitor ICRF-193 and examined treatment effects on splice variant expression using paired-end RNA-seq. We observed altered splicing of 319 genes following TOP2 inhibition, with increased expression of splice variant CDK4-009 being the most significant of all splice variant expression changes (p-value= 1E(-54)). This result corresponded well with TCGA data whose analysis showed a strong positive correlation between TOP2B and CDK4-009 expression (rho= -0.3 and p-value= 7.28E(-05)). CONCLUSIONS: Our results support TOP2B expression and activity as being influential in regulating the levels of CDK4 splice variant 009 in GBM.