GSE133419
G-quadruplex roles in transcription deciphered by comparative transcriptomic analyses
G-quadruplexes (G4) are non-canonical nucleic acid structures that can form at certain DNA or RNA guanine-rich sequences. G4 motifs are dispersed throughout the genome and considerably enriched at promoters, where they flank the transcription start site (TSS) and cluster at the 5' end of the first intron, which suggests potential regulatory roles of quadruplexes in transcription. To improve our understanding of these roles, we have associated gene expression with the frequency of canonical G4 motifs near gene promoters and characterized perturbations caused by treatment with three G-quadruplex ligands, Pyridostatin and the two bisquinolinium compounds PhenDC3 and PhenDC6. We show that enrichment of G4 motifs characterizes the most actively transcribed genes, challenging the notion that quadruplexes chiefly exert negative regulation by blocking progress of RNA polymerase. G4 ligand-treatment altered splicing of transcripts at genes enriched for G4 motifs at the 5'-end of intron 1, suggesting that G-quadruplexes in the pre-mRNA can regulate splicing. Furthermore, our analysis also revealed some of the effects of G4 ligand treatment that likely reflect quadruplex-dependent replication stress leading to the induction of transcriptional signatures compatible with impaired cell cycle progression. Collectively, our results support the view that G-quadruplexes typically function as positive regulators of transcription, suggesting that quadruplexes may stabilize promoter architecture to enable efficient transcription. This analysis provides strong support for function of quadruplexes near the promoter as regulators of transcription and splicing. Overall design: RNA-seq data in HT1080-ST fibrosarcoma human cells untreated (DMSO) or treated with G-quadruplex ligands