Genome-wide chromatin accessibility analysis in T-INT2 WT and KO isogenic HCT116 cells (ATAC-seq)

Transcriptional re-activation of hTERT is the limiting step in tumorigenesis. While mutations in hTERT promoter seen in 19% of all cancers are recognized as key drivers of hTERT reactivation, mechanisms by which the wildtype hTERT (WT-hTERT) promoter is reactivated, as observed in the majority of cancers, remain unknown. We report that unlike with the mutant-hTERT promoters, a T-INT2 (Tert INTeracting region 2) region located ~120kb upstream of the hTERT proximal promoter is essential to uniquely reactivate the WT-hTERT promoter, via long-range chromatin interactions. Unlike mutant-hTERT promoters, which are driven by GABPa/b tetramers tethered between T-INT1 (Tert-INTeracting-region 1) and de-novo ETS sites created by promoter mutations, WT-hTERT promoter firing is initiated by 2 events a) elevated JunD mediated recruitment of CTCF and b) ß-catenin and CBP mediated recruitment of Sp1 tetramers between T-INT2 and WT-hTERT proximal-promoter, leading to chromatin-openness, pol2 recruitment and productive transcription. Overall design: The Sp1 cluster in T-INT2 region has been deleted using Crispr-Cas9 editing (450bp deletion). WT and KO HCT116 isogenic cell lines were analyzed for ATAC-seq. 2 clones were used for WT and KO cells with 2 technical replicates.