The G-quadruplex Ligand Telomestatin Inhibits POT1 Binding to Telomeric Sequences In vitro and Induces GFP-POT1 Dissociation from Telomeres in Human Cells

Abstract

Telomestatin is a potent G-quadruplex ligand that specifically interacts with the 3 ¶ telomeric overhang, leading to its degradation and that induces a delayed senescence and apoptosis of cancer cells. Protection of Telomere 1 (POT1) was recently identified as a specific single-stranded telomerebinding protein involved in telomere capping and T-loop maintenance. We showed here that a telomestatin treatment inhibits POT1 binding to the telomeric overhang in vitro. The treatment of human EcR293 cells by telomestatin induces a dramatic and rapid delocalization of POT1 from its normal telomere sites but does not affect the telomere localization of the double-stranded telomere-binding protein TRF2. Thus, we propose that G-quadruplex stabilization at telomeric Goverhang inactivates POT1 telomeric function, generating a telomere dysfunction in which chromosome ends are no longer properly protected. (Cancer Res 2006; 66(14): 6908-12)

In vivo veritas: Using yeast to probe the biological functions of G-quadruplexes

“…Further, the human telomere binding protein POT1, which binds the single stranded telomere overhang, inhibits G4-DNA formation in vitro [44], while treatment of cells with the quadruplex-selective ligand telomestatin displaces POT1 and uncaps telomeres (i.e. causes them to be recognized as DNA breaks) [45,46]. Therefore, POT1 binding and G4-DNA formation at the telomere are likely mutually exclusive states.…”

Differential Effects of the G-Quadruplex Ligand 360A in Human Normal and Cancer Cells

“…Some G-quadruplex ligands (e.g. telomestatin, BRACO19, RHPS4) but nor all (TMPyP4) show selective toxicity towards cancer cells (Gomez et al, 2006;Cheng et al, 2007;Salvati et al, 2007;Rha et al, 2000). Indeed TMPyP4 inhibits the cell proliferation of normal cells (fibroblasts, adult keratinocytes and epithelial cells) and cancer cells (neuroblastoma, breast cancer, cervical cancer, pancreatic cancer, colon cancer and a prostate cancer cell line) (Rha et al, 2000).…”

“…Finally, TRF2 or POT1 overexpression correlates with the resistance to telomestatin and RHSP4 (Salvati et al, 2007;Cheng et al, 2007;Gomez et al, 2006). TRF2 might therefore counteract the effects of Gquadruplex ligands through the formation of a T-loop that would mask the 3' overhang and inhibit the recruitment of helicases which are expected to resolve G-quadruplexes and favour the binding of POT1 (Salvati et al, 2007;Opresko et al, 2002;O'Connor et al, 2006).…”

Telomeric D-loops Containing 8-Oxo-2′-deoxyguanosine Are Preferred Substrates for Werner and Bloom Syndrome Helicases and Are Bound by POT1

“…It also affects the POT1 binding in singlestranded telomeric DNA by stabilizing G-quadruplex structures (42). We investigated the effect of TMS on POT1 binding to damaged and undamaged D-loops.…”