Promoter G-quadruplex favours epigenetic reprogramming-induced atypical expression of ZEB1 in cancer cells

• Published in: Biochimica et biophysica acta. General subjects 2021-08, Vol.1865 (8), p.129899-129899, Article 129899
• Main Authors: Dutta, Anindya, Maji, Nilanjana, Sengupta, Pallabi, Banerjee, Nilanjan, Kar, Swarnali, Mukherjee, Gopeswar, Chatterjee, Subhrangsu, Basu, Moitri
• Format: Article
• Language: English
• Subjects: Cancer cells; Epigenetic modification; G-quadruplex; Invasion; Transcription; Transcription factor; ZEB1
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/j.bbagen.2021.129899

Aberrant expression of Zinc-finger E-box binding homeobox 1 (ZEB1), which remains repressed in normal cells, is frequently associated with cancer aggressiveness. However, transcriptional mechanism underlying such atypical ZEB1 expression in cancer is not yet well-understood. ZEB1 promoter G-quadruplexes were studied and modeled extensively using circular dichroism, fluorescence spectroscopy, ITC and DMS protection assay. Luciferase assay, qPCR, FAIRE, ChIP, western blotting, confocal microscopy was used to access the regulation of ZEB1 transcription. Our study unravels the occupancy of nucleolin to ZEB1 promoter as a crucial determinant which facilitates the binding of SP1 transcription factor to chromatin, by locally remodelling the region. SP1, subsequently, recruits P300 acetyl transferase leading to enriched acetyl-histone H3 at promoter and activates ZEB1 transcription. ZEB1 promoter analysis identifies presence of four putative G-quadruplex (G4) forming motifs within 700 bp of TSS; each quadruplex is characterized structurally in details with an array of biophysical techniques. Surprisingly, stabilization of G4 with cationic porphyrin TMPyP4 represses its transcription and eventually impedes cell invasiveness. TMPyP4 binding to a selected G4 motif (5′ -534/−511–3′ from TSS), where nucleolin/SP1/P300 co-occupies, prevents the association of nucleolin which consequently hinders SP1 binding, leading to chromatin compactness and transcriptional repression. Our findings demonstrate an epigenetic mechanism of ZEB1 reactivation where dynamic occupancy of transcription regulators encompassing a G4 motif is crucial and thus, small molecule induced G-quadruplex stabilization may act as a potential molecular switch to turn-off gene expression. •Four G-quadruplex (G4) motifs are formed on ZEB1 promoter.•Stabilizing G4s represses ZEB1 transcription and impedes cancer cell invasion.•Binding of Nucleolin facilitates SP1 occupancy by local chromatin remodelling.•SP1 recruits P300, acH3 is enriched at promoter and activates ZEB1 transcription.•A specific G4 motif is key player in epigenetic and transcription control of ZEB1.