Expression of the human telomerase reverse transcriptase gene is modulated by quadruplex formation in its first exon due to DNA methylation
Journal
Journal of Biological Chemistry
Journal Volume
292
Journal Issue
51
Pages
20859 20870
Date Issued
2017
Author(s)
Abstract
DNA secondary structures and methylation are two wellknown mechanisms that regulate gene expression. The catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT), is overexpressed in -90% of human cancers to maintain telomere length for cell immortalization. Binding of CCCTC-binding factor (CTCF) to the first exon of the hTERT gene can down-regulate its expression. However, DNA methylation in the first exon can prevent CTCF binding in most cancers, but the molecular mechanism is unknown. TheNMRanalysis showed that a stretch of guanine-rich sequence in the first exon of hTERT and located within the CTCF-binding region can form two secondary structures, a hairpin and a quadruplex. A key finding was that the methylation of cytosine at the specific CpGdinucleotides will participate in quartet formation, causing the shift of the equilibrium from the hairpin structure to the quadruplex structure. Of further importance was the finding that the quadruplex formation disrupts CTCF protein binding, which results in an increase in hTERT gene expression. Our results not only identify quadruplex formation in the first exon promoted by CpG dinucleotide methylation as a regulator of hTERT expression but also provide a possible mechanistic insight into the regulation of gene expression via secondary DNA structures. ? 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
SDGs
Other Subjects
Alkylation; Biochemistry; Diseases; DNA; Methylation; Positive ions; CCCTC binding factors; DNA secondary structures; Guanine rich sequence; Human telomerase reverse transcriptase; Human telomerase reverse transcriptase (hTERT); Quadruplex formation; Quadruplex structures; Secondary structures; Gene expression; cytosine; guanine; guanine quadruplex; telomerase reverse transcriptase; transcription factor CTCF; CTCF protein, human; DNA; guanine quadruplex; telomerase; TERT protein, human; transcription factor CTCF; Article; controlled study; DNA methylation; DNA sequence; down regulation; exon; gene expression; gene location; hTERT gene; human; human cell; melting temperature; molecular dynamics; nuclear magnetic resonance spectroscopy; priority journal; protein binding; protein secondary structure; binding site; cell line; chemistry; conformation; CpG island; DNA methylation; genetics; inverted repeat; kinetics; metabolism; mutagenesis; nuclear magnetic resonance; nucleotide sequence; promoter region; thermodynamics; Base Sequence; Binding Sites; CCCTC-Binding Factor; Cell Line; CpG Islands; DNA; DNA Methylation; Exons; G-Quadruplexes; Gene Expression; Humans; Inverted Repeat Sequences; Kinetics; Mutagenesis; Nuclear Magnetic Resonance, Biomolecular; Nucleic Acid Conformation; Promoter Regions, Genetic; Telomerase; Thermodynamics
Type
journal article