Formation of a unique end-to-end stacked pair of G-quadruplexes in the hTERT core promoter with implications for inhibition of telomerase by G-quadruplex-interactive ligands

Sun Mi L. Palumbo, Scot W. Ebbinghaus, Laurence H. Hurley

Research output: Contribution to journalArticle

146 Scopus citations

Abstract

The hTERT core promoter contains a G-rich region of 12 consecutive G-tracts, embracing 3 Sp1 binding sites, and has the potential to form multiple G-quadruplexes. From the 12 runs of guanines, 9 putative hTERT G-quadruplex-forming sequences were selected to assay for G-quadruplex formation and stability using circular dichroism and a Taq polymerase stop assay. Results from biophysical and chemical assays demonstrate an approximate inverse correlation between total loop size and structure stability. Investigation of the full-length hTERT G-rich sequence using a Taq polymerase stop assay and dimethyl sulfate footprinting revealed the formation of a unique end-to-end stacked G-quadruplex structure from this sequence. This structure consists of an all parallel G-quadruplex, formed by four consecutive G-tracts, linked to another, atypical G-quadruplex, formed by two pairs of consecutive G-tracts separated by a 26-base loop. This 26-base loop likely forms a stable hairpin structure, which would explain the unexpected stability of this G-quadruplex. Significantly, the formation of this tandem G-quadruplex structure in the full-length sequence masks all three Sp1 binding sites, which is predicted to produce significant inhibition of hTERT promoter activity. Furthermore, our study implies that inhibition of telomerase activity by some G-quadruplex ligands is not only produced by targeting telomeric G-quadruplexes but also by stabilization of the hTERT promoter G-quadruplexes.

Original languageEnglish (US)
Pages (from-to)10878-10891
Number of pages14
JournalJournal of the American Chemical Society
Volume131
Issue number31
DOIs
StatePublished - Aug 12 2009

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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