G-quadruplexes as pivotal components of cis-regulatory elements in the human genome

Abstract

Cis-regulatory elements have the ability to precisely regulate gene expression in cells, and G-quadruplexes (G4s), as non-canonical secondary structures, may potentially play a role in this regulation. However, a lack of systematic studies exists to uncover the connection between these two elements. Here, we comprehensively characterized the associations between G4s and human candidate cis-regulatory elements (cCREs) inferred from the Encyclopedia of DNA Elements (ENCODE) data. Our findings demonstrate that G4s are prominently enriched in most types of cCREs, particularly in elements with promoter-like signatures (PLS). Furthermore, we observed that the co-occurrence of CTCF signals with H3K4me3 or H3K27ac signals significantly strengthens the association between cCREs and G4s. This association becomes more pronounced when examining cell type-specific cCREs and G4s. Interestingly, compared to cCREs, genetic variants occurring in G4s, especially within their G-runs, often exhibit higher regulatory potential and deleterious effects. Runs of several consecutive guanines (G-runs) in the vicinity of transcriptional start sites tend to be more constrained in mammalian evolution than cCREss G-runs. Besides, the presence of G4s, is often linked to a more favorable local chromatin environment for the activation and execution of regulatory functions of cCREs, potentially attributable to the formation of G4 secondary structures. Finally, we discovered that G4-associated cCREs exhibit widespread activation in a variety of cancers. Altogether, our study suggests that G4s are integral components of human cis-regulatory elements, and the G4 primary sequences are associated with the localization of the cCREs, while the G4 structures are linked to the activation of the cCREs. Therefore, we propose to define G4s as pivotal regulatory elements in the human genome.