Forever Young: Structural Stability of Telomeric Guanine Quadruplexes in the Presence of Oxidative DNA Lesions**

Abstract

Human telomeric DNA, in G‐quadruplex (G4) conformation, is characterized by a remarkable structural stability that confers it the capacity to resist to oxidative stress producing one or even clustered 8‐oxoguanine (8oxoG) lesions. We present a combined experimental/computational investigation, by using circular dichroism in aqueous solutions, cellular immunofluorescence assays and molecular dynamics simulations, that identifies the crucial role of the stability of G4s to oxidative lesions, related also to their biological role as inhibitors of telomerase, an enzyme overexpressed in most cancers associated to oxidative stress.

Impact of G-Quadruplexes and Chronic Inflammation on Genome Instability: Additive Effects during Carcinogenesis

“…Using this approach, the lab revealed that chronic 8oxoG formation and persistence at telomeres impairs replication, resulting in telomere shortening and genome instability [85]. An immunofluorescence study showed that non-tumorigenic MCF-10A breast epithelial cells express elevated G4 levels that colocalize with 8oxoG upon H 2 O 2 treatment [80]. These results support the above in vitro studies that G4s largely remain formed and stabilized upon oxidation.…”

“…However, the telomeric G4 motif containing 8oxoG could still bond with other nucleotides, resulting in rearrangement of base conformations that have minor impacts on structure in vitro. In fact, biophysical measurements showed no change in the parallel structure and only slightly reduced peaks in the hybrid structure upon H 2 O 2 addition, suggesting that this oxidant does not create lesions that change the overall G4 structure [80].…”

“…K + or Na + are favorable in maintaining G4 formation, and steric hindrance and charges associated with different lesions would necessarily interrupt the metal cation coordination. Miclot, et al observed instances of cation expulsion in a telomeric G4 via molecular dynamics simulations, particularly when two 8oxoG lesions were present [80], suggesting oxidative lesions may impact cation arrangement and coordination. However, the telomeric G4 motif containing 8oxoG could still bond with other nucleotides, resulting in rearrangement of base conformations that have minor impacts on structure in vitro.…”

Never Cared for What They Do: High Structural Stability of Guanine-Quadruplexes in the Presence of Strand-Break Damage

“…Although the h-telo sequence is characterized by high polymorphism, hybrid conformations are also possible [ 55 ], the parallel arrangement represents a suitable model for assessing stability in the presence of strand break lesions. Furthermore, we have previously shown that hybrid sequences show even higher stability to oxidative lesions than parallel arrangements [ 31 ]. In addition to the undamaged quadruplex used as a reference, 27 different structures harboring strand breaks have been taken into account.…”

“…In particular, oxidative damage has been scrutinized due to the fact that G4s are inherently composed of guanine-rich sequences, and the latter is the most easily oxidized nucleotide, and 8-oxo-guanine (8-OxoG) is its most common oxidation product [ 27 , 28 , 29 , 30 ]. Although G4s are clearly considered hotspots for oxidative DNA damage, they have shown strong structural resistance to this class of lesion [ 31 ], depending on the amount of oxidative lesions and their position in the DNA backbone [ 31 , 32 , 33 , 34 ].…”