Enhanced elimination of oxidized guanine nucleotides inhibits oncogenic RAS-induced DNA damage and premature senescence

Abstract

Approximately 20% of tumors contain activating mutations in the RAS family of oncogenes. As tumors progress to higher grades of malignancy, the expression of oncogenic RAS has been reported to increase, leading to an oncogene-induced senescence (OIS) response. Evasion of this senescence barrier is a hallmark of advanced tumors indicating that OIS serves a critical tumorsuppressive function. Induction of OIS has been attributed to either RAS-mediated production of reactive oxygen species (ROS) or to induction of a DNA damage response (DDR). However, functional links between these two processes in triggering the senescent phenotype have not been explicitly described. Our previous work has shown that, in cultured untransformed cells, preventing elimination of oxidized guanine deoxyribonucleotides, which was achieved by suppressing expression of the cellular 8-oxodGTPase, human MutT homolog 1 (MTH1), sufficed to induce a DDR as well as premature senescence. Here, we demonstrate that overexpression of MTH1 can prevent the oncogenic H-RAS-induced DDR and attendant premature senescence, although it does not affect the observed elevation in ROS levels produced by RAS oncoprotein expression. Conversely, we find that loss of MTH1 preferentially induces an in vitro proliferation defect in tumorigenic cells overexpressing oncogenic RAS. These results indicate that the guanine nucleotide pool is a critical target for intracellular ROS produced by oncogenic RAS and that RAS-transformed cells require robust MTH1 expression to proliferate.

Parallel pathways in RAF-induced senescence and conditions for its reversion

“…These results are thus consistent with the suggestion that activation of DNA-damage checkpoint pathways during oncogene-induced senescence is restricted to S-phase cells (replicative stress). Two possible sources of DNA damage have been invoked for oncogene-induced senescence: ROS that could introduce oxidative lesions in DNA that impede replication fork progression (Moiseeva et al, 2009;Rai et al, 2011), and overexpression of DNA replication factors that could lead to perturbations of DNA replication (Bartkova et al, 2006;Di Micco et al, 2006). We found that RAF-induced senescence was accompanied by the generation of significant ROS when cells were cultivated in ambient 21% oxygen, as has been described for RASval12-induced senescence (Lee et al, 1999;Moiseeva et al, 2009).…”

Metformin Reduces Endogenous Reactive Oxygen Species and Associated DNA Damage

“…While mitochondrial ROS production would be expected to preferentially damage mitochondrial as compared with nuclear DNA, nuclear DNA mutations are related to ROS levels (31). This does not necessarily require direct action of ROS on nuclear DNA, as it has been shown that nuclear mutation may arise due to direct oxidation of the nucleotide pool by ROS (31). Using gH2AX staining, we quantified DNA double-strand breaks in AMPKa þ/þ and AMPKa À/À fibroblasts following exposure to H 2 O 2 or paraquat, with or without metformin (Fig.…”

Addiction to MTH1 protein results in intense expression in human breast cancer tissue as measured by liquid chromatography-isotope-dilution tandem mass spectrometry

“…Suppression of the mutator phenotype in mismatch repair-defective colorectal cancer cells has been achieved by overexpressing MTH1 [26]. Reversal of RAS-induced senescence by reducing the level of DNA damage has also been demonstrated [27]. MTH1 overexpression promoted longevity, reduced anxiety [28], and protected from neurodegeneration [29].…”