RNA-Seq to assess the transcriptional effects of G quadruplex stabilization by the G4 ligand PhenDC3 in HT-1080 cells

G-quadruplex motifs are frequently located near TSS and in the first introns of transcribed genes. We investigated the role that G4 structures play in transcription by stabilizing G4 DNA with the selective G4 ligand PhenDC3 in the HT-1080 human fibrosarcoma cell line. After treatment of triplicate samples with PhenDC3 or a negative control (DMSO carrier only), we performed RNA-Seq after poly-dT selection to assess changes in gene expression. Heme is an essential cofactor for many enzymes, but free heme is toxic and its levels are tightly regulated. G-quadruplexes bind heme avidly in vitro, raising the possibility that they may sequester heme in vivo. If so, then treatment that displaces heme from quadruplexes is predicted to induce expression of genes involved in iron and heme homeostasis. Here we show that PhenDC3, a G-quadruplex ligand structurally unrelated to heme, displaces quadruplex-bound heme in vitro and alters transcription in cultured human cells, up-regulating genes that support heme degradation and iron homeostasis, and most strikingly causing a 30-fold induction of heme oxidase 1, the key enzyme in heme degradation. We propose that G-quadruplexes sequester heme to protect cells from the pathophysiological consequences of free heme. This identifies a new function for G-quadruplexes and a new mechanism for protection of cells from heme. 6 samples total; 2 gene expression conditions (treated and untreated) in triplicate; 4 raw sequencing files per sample