Transcription poisoning by topoisomerase I is controlled by gene length, splice sites and miR-142-3p

DNA topoisomerase I (Top1) is required for transcription as it relaxes positive and negative supercoils by forming transient Top1 cleavage complexes (Top1cc) up- and down-stream of transcription complexes. However, Top1cc can also be trapped by endogenous DNA lesions and by camptothecin (CPT) and its anticancer derivatives, which results in transcription blocks. Here, we undertook a genome-wide analysis of the effects of CPT on gene expression at exon resolution. We tested the impact of Top1 inhibition on gene expression at the genome-wide level in human colon carcinoma HCT116 and human breast carcinoma MCF7 cells. The RNA of cells treated with camptothecin (CPT) for various times was analyzed with Affy Exon array (GeneChip Human Exon 1.0 ST array). Moreover, we tested the impact of Top1 down-regulation on gene expression at the genome-wide level in human colon carcinoma HCT116 cells. The RNA of cells treated transfected with a Top1 siRNA was analyzed with Affy Exon array (GeneChip Human Exon 1.0 ST array).