Abstract
Autophagy has been well documented to play an important role in maintaining genomic stability. However, in addition to directly engulfing and digesting the damaged organelles and chromatin fragments, autophagy can affect many cellular processes including DNA damage response, regulation of redox homeostasis, and cell division; it remains to be determined to what extent each of those processes contributes to the maintenance of genomic stability. We here examined the role of autophagy-dependent redox regulation in the maintenance of genomic stability in two cancer cell lines (HT1080 and U2OS) and mesenchymal stem cells (MSCs) using micronuclei MN, also referred to as cytoplasmic chromatin fragments, as a marker. Our results showed that the spontaneous and genotoxic stress-induced frequencies of MN in cancer cells were significantly reduced by autophagy activators rapamycin and Torin1, and the reduction in MN was accompanied by a reduction in reactive oxygen species (ROS). Increased micronucleation in senescent MSCs, in which autophagic flux is blocked, was also attenuated by rapamycin, together with a reduction in ROS. Inhibition of autophagy by chloroquine (CQ) or ATG5 depletion, on the other hand, resulted in an increased frequency of MN, though a ROS elevation in response to autophagy inhibition was only observed in MSCs. Importantly, the induction of MN by autophagy inhibition in MSCs could be abrogated by antioxidant N-acetylcysteine (NAC). In contrast to the reported impairment of CHK1 activation in Atg7-deficient mouse embryonic fibroblasts, we found that the level of phosphorylated CHK1 was increased by CQ or ATG5 depletion but decreased by rapamycin or Torin1, suggesting that the increased genomic instability by defective autophagy is not caused by insufficient activation of CHK1-homologous recombination cascade. Together, our findings suggest that redox homeostasis regulated by autophagy contributes substantially to the maintenance of genomic stability in certain contexts.
Highlights
Macroautophagy, hereafter known as autophagy, is a lysosomal-dependent degradation pathway that involves in degrading and recycling redundant or damaged substances to protect cells from various types of stress [1]
To determine whether the contribution of autophagy to genomic stability is related to redox homeostasis, we examined the reactive oxygen species (ROS) level in HT1080 cells and U2OS cells after rapamycin treatment
In order to explore the role of the autophagy-redox link in the formation of MN in more contexts, we evaluated the effect of autophagy on micronucleation in senescent human umbilical cord mesenchymal stem cells
Summary
Macroautophagy, hereafter known as autophagy, is a lysosomal-dependent degradation pathway that involves in degrading and recycling redundant or damaged substances to protect cells from various types of stress [1]. It is crucial to understand how autophagy contributes to the maintenance of genomic stability. The micronucleation is usually exacerbated in cells with defective autophagy [10, 11]. These autophagic micronuclei account for only a very small proportion of the MN [9]. In addition to directly disposing and recycling the damaged organelles, proteins, and chromatin fragments, autophagy is known to affect other cellular processes that may affect genome stability. It remains to be determined to what extent each of those processes regulated by autophagy contributes to the maintenance of genomic stability
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