A threshold of endogenous stress is required to engage cellular response to protect against mutagenesis

Abstract

Endogenous stress represents a major source of genome instability, but is in essence difficult to apprehend. Incorporation of labeled radionuclides into DNA constitutes a tractable model to analyze cellular responses to endogenous attacks. Here we show that incorporation of [3H]thymidine into CHO cells generates oxidative-induced mutagenesis, but, with a peak at low doses. Proteomic analysis showed that the cellular response differs between low and high levels of endogenous stress. In particular, these results confirmed the involvement of proteins implicated in redox homeostasis and DNA damage signaling pathways. Induced-mutagenesis was abolished by the anti-oxidant N-acetyl cysteine and plateaued, at high doses, upon exposure to L-buthionine sulfoximine, which represses cellular detoxification. The [3H]thymidine-induced mutation spectrum revealed mostly base substitutions, exhibiting a signature specific for low doses (GC > CG and AT > CG). Consistently, the enzymatic activity of the base excision repair protein APE-1 is induced at only medium or high doses. Collectively, the data reveal that a threshold of endogenous stress must be reached to trigger cellular detoxification and DNA repair programs; below this threshold, the consequences of endogenous stress escape cellular surveillance, leading to high levels of mutagenesis. Therefore, low doses of endogenous local stress can jeopardize genome integrity more efficiently than higher doses.

An adaptive pre-DNA-damage-response protects genome integrity

“…Although they are continuously exposed to such chronic low-level endogenous stresses, cells still proliferate and replicate their genome, suggesting that the DDR is not or not fully activated. Thus, this implies that a stress threshold is needed to be reached to fully activate the DDR, as previously proposed (Saintigny et al, 2016;Wilhelm et al, 2014Wilhelm et al, , 2016, and, as a corollary, that cells either do not respond to low-level stresses, or have developed specific alternative responses.…”

A Proteomic Study Suggests Stress Granules as New Potential Actors in Radiation-Induced Bystander Effects

“…Gel spots 2D were manually cut and prepared, as previously described [ 38 ]. The LC-MS/MS experiments were performed using a U3000 NCS nano-high-performance liquid chromatography (Thermo Fisher Scientific Inc, Waltham, MA, USA) system and a Q-Exactive Plus Orbitrap mass spectrometer.…”

Significance of Wild-Type p53 Signaling in Suppressing Apoptosis in Response to Chemical Genotoxic Agents: Impact on Chemotherapy Outcome

“…Recent studies have revealed that a threshold level of genotoxic stress must be reached to trigger the DNA damage surveillance network [ 5 ]. This response is initiated by rapid stabilization of p53, its nuclear accumulation, and activation of its transcriptional and biological functions [ 24 ].…”

“…Constitutively available DNA repair processes deal with low levels of genomic injury and assist in ameliorating the detrimental effects of such agents. An increase in DNA damage above a threshold level activates the DNA damage surveillance network, which involves multiple signaling pathways that protect against genomic instability and restrict aberrant cell growth in response to genotoxic stress [ 5 ]. The wild-type p53 tumor suppressor functions at the hub of this network [ 6 , 7 ].…”