An ectopic enhancer restores CFTR expression through de novo chromatin looping [4C-seq]

Transcription of the cystic fibrosis transmembrane conductance regulator (CFTR) gene is regulated by a set of ubiquitous and cell-type selective cis-regulatory elements (CREs). These elements include extragenic and intronic enhancers that bind cell-type specific transcription factors, as well as architectural protein bound structural elements. We previously reported that loss of the airway-selective -35kb enhancer in 16HBE14o- airway epithelial cells disrupts normal enhancer-promoter looping at the CFTR locus and nearly abolishes its expression. Here we expand on previous work, and explore the effect of relocation of the 500bp -35kb enhancer core to an ectopic site in intron 1 of CFTR on gene expression and chromatin dynamics. We find that although genomic relocation of this element is not able to fully restore CFTR expression to wild-type levels, the -35kb sequence is able establish a de novo enhancer signature at chromatin at the site of insertion. Additionally, the relocated -35kb enhancer is able to form chromatin contacts with known CFTR CREs. These studies reveal important direct chromatin effects, as well as limitations, of CFTR enhancers, and provide important considerations when targeting the CFTR locus for novel therapeutic gene editing. Overall design: Analysis of the 3D chromatin architecture with 4C-seq at the CFTR locus to determine interaction frequencies between elements in response to deletion or relocation of -35kb CRE in 16HBE14o- cells