A novel ataxia-telangiectasia mutated autoregulatory feedback mechanism in murine embryonic stem cells

Abstract

Ataxia-telangiectasia mutated (ATM) is known to play a central role in effecting the DNA damage response that protects somatic cells from potentially harmful mutations, and in this role it is a key anti-cancer agent. However, it also promotes repair of therapeutic damage (e.g. radiotherapy) and so frustrates the efficacy of some treatments. A better understanding of the mechanisms of ATM regulation is therefore important both in prevention and treatment of disease. While progress has been made in elucidating the key signal transduction pathways that mediate damage response in somatic cells, relatively little is known about whether these function similarly in pluripotent embryonic stem (ES) cells where ATM is also implicated in our understanding of adult stem cell ageing and in improvements in regenerative medicine. There is some evidence that different mechanisms may operate in ES cells and that our understanding of the mechanisms of ATM regulation is therefore incomplete. We investigated the behaviour of the damage response signalling pathway in mouse ES cells. We subjected the cells to the DNA-damaging agent doxorubicin, a drug that induces double-strand breaks, and measured ATM expression levels. We found that basal ATM gene expression was unaffected by doxorubicin treatment. However, following ATM kinase inhibition using a specific ATM inhibitor, we observed a significant increase in ATM and ataxia-telangiectasia and Rad3 related transcription. We demonstrate the use of a dynamical modelling approach to show that these results cannot be explained in terms of known mechanisms. Furthermore, we show that the modelling approach can be used to identify a novel feedback process that may underlie the anomalies in the data. The predictions of the model are consistent both with our in vitro experiments and with in vivo studies of ATM expression in somatic cells in mice, and we hypothesize that this feedback operates in both somatic and ES cells in vivo. The results point to a possible new target for ATM inhibition that overcomes the restorative potential of the proposed feedback.

The DNA-Damage Response to γ-Radiation Is Affected by miR-27a in A549 Cells

“…At both time points after irradiation, notably, the level of ATM was significantly decreased in cells over-expressing miR-27a. Besides the action of miR-27a on ATM -3′UTR, such mRNA reduction could be due to an ATM autoregulatory feedback mechanism in response to DNA damage, as recently proposed by Clyde et al [28]. According to these authors, cells have evolved a sensor mechanism that results in rapid induction of the ATM transcript to compensate for ATM chemical inhibition through a negative feedback.…”

The effect of ataxia-telangiectasia mutated kinase-dependent hyperphosphorylation of checkpoint kinase-2 on oligodeoxynucleotide 7909 containing CpG motifs-enhanced sensitivity to X-rays in human lung adenocarcinoma A549 cells

“…Therefore, an effective approach would be to increase the radiosensitivity of tumors and improve therapeutic efficacy by promoting tumor cell cycle progression then arrest at G 2 /M phase. However, regulation of cell cycle is closely related to DDRs, and studies have shown that DDR signaling pathways are initiated well by phosphoinositide 3-kinase-like kinase family members, including ATM kinase and ataxia-telangiectasia and Rad3-related kinase, which recognize different types of DNA lesions 25. Importantly, it is well demonstrated that ATM kinase is activated by double-stranded DNA breaks (DSBs) induced by irradiation.…”

“…However, regulation of cell cycle is closely related to DDRs, and studies have shown that DDR signaling pathways are initiated well by phosphoinositide 3-kinase-like kinase family members, including ATM kinase and ataxia-telangiectasia and Rad3-related kinase, which recognize different types of DNA lesions. 25 Importantly, it is well demonstrated that ATM kinase is activated by double-stranded DNA breaks (DSBs) induced by irradiation. In response to IR-induced DNA damage, ATM kinase is recruited to the sites of DSBs and is activated by autophosphorylation at Ser-1981 and binding to heterotrimeric Mre11/Rad50/Nbs1 adaptor complex, resulting in phosphorylation of downstream substrates such as Chk2 and p53 protein and eventually inducing cell cycle checkpoint activation to arrest cells at G 2 /M phase by initiating downstream cascade reactions.…”

DNA repair systems

“…Under certain condi ons, however, the pa ern of expression of ATM may be altered, which is accompanied by a corresponding change in ATM ac vity [778][779][780]. ATM may be subject to transcrip onal regula on at promoter as well as at mRNA level [781][782][783]. ATM is one of the major targets of novel an cancer therapies.…”