The ATM protein kinase, mutations of which are associated with the human disease ataxia-telangiectasia, mediates responses to ionizing radiation in mammalian cells. Here we show that ATM is held inactive in unirradiated cells as a dimer or higher-order multimer, with the kinase domain bound to a region surrounding serine 1981 that is contained within the previously described 'FAT' domain. Cellular irradiation induces rapid intermolecular autophosphorylation of serine 1981 that causes dimer dissociation and initiates cellular ATM kinase activity. Most ATM molecules in the cell are rapidly phosphorylated on this site after doses of radiation as low as 0.5 Gy, and binding of a phosphospecific antibody is detectable after the introduction of only a few DNA double-strand breaks in the cell. Activation of the ATM kinase seems to be an initiating event in cellular responses to irradiation, and our data indicate that ATM activation is not dependent on direct binding to DNA strand breaks, but may result from changes in the structure of chromatin.

DNA damage activates ATM through intermolecular autophosphorylation and dimer dissociation

The inability to repair DNA damage properly in mammals leads to various disorders and enhanced rates of tumour development. Organisms respond to chromosomal insults by activating a complex damage response pathway. This pathway regulates known responses such as cell-cycle arrest and apoptosis (programmed cell death), and has recently been shown to control additional processes including direct activation of DNA repair networks.

https://faculty.missouri.edu/~gatesk/DNADamageResponse.pdf

The DNA damage response: putting checkpoints in perspective

DNA damage is a relatively common event in the life of a cell and may lead to mutation, cancer, and cellular or organismic death. Damage to DNA induces several cellular responses that enable the cell either to eliminate or cope with the damage or to activate a programmed cell death process, presumably to eliminate cells with potentially catastrophic mutations. These DNA damage response reactions include: (a) removal of DNA damage and restoration of the continuity of the DNA duplex; (b) activation of a DNA damage checkpoint, which arrests cell cycle progression so as to allow for repair and prevention of the transmission of damaged or incompletely replicated chromosomes; (c) transcriptional response, which causes changes in the transcription profile that may be beneficial to the cell; and (d) apoptosis, which eliminates heavily damaged or seriously deregulated cells. DNA repair mechanisms include direct repair, base excision repair, nucleotide excision repair, double-strand break repair, and cross-link repair. The DNA damage checkpoints employ damage sensor proteins, such as ATM, ATR, the Rad17-RFC complex, and the 9-1-1 complex, to detect DNA damage and to initiate signal transduction cascades that employ Chk1 and Chk2 Ser/Thr kinases and Cdc25 phosphatases. The signal transducers activate p53 and inactivate cyclin-dependent kinases to inhibit cell cycle progression from G1 to S (the G1/S checkpoint), DNA replication (the intra-S checkpoint), or G2 to mitosis (the G2/M checkpoint). In this review the molecular mechanisms of DNA repair and the DNA damage checkpoints in mammalian cells are analyzed.

Molecular Mechanisms of Mammalian DNA Repair and the DNA Damage Checkpoints

Maintenance of genome stability is essential for avoiding the passage to neoplasia. The DNA-damage response--a cornerstone of genome stability--occurs by a swift transduction of the DNA-damage signal to many cellular pathways. A prime example is the cellular response to DNA double-strand breaks, which activate the ATM protein kinase that, in turn, modulates numerous signalling pathways. ATM mutations lead to the cancer-predisposing genetic disorder ataxia-telangiectasia (A-T). Understanding ATM's mode of action provides new insights into the association between defective responses to DNA damage and cancer, and brings us closer to resolving the issue of cancer predisposition in some A-T carriers.

ATM and related protein kinases: safeguarding genome integrity

Reactive oxygen species (ROS), whether produced endogenously as a consequence of normal cell functions or derived from external sources, pose a constant threat to cells living in an aerobic environment as they can result in severe damage to DNA, protein, and lipids. The importance of oxidative damage to the pathogenesis of many diseases as well as to degenerative processes of aging has becoming increasingly apparent over the past few years. Cells contain a number of antioxidant defenses to minimize fluctuations in ROS, but ROS generation often exceeds the cell's antioxidant capacity, resulting in a condition termed oxidative stress. Host survival depends upon the ability of cells and tissues to adapt to or resist the stress, and repair or remove damaged molecules or cells. Numerous stress response mechanisms have evolved for these purposes, and they are rapidly activated in response to oxidative insults. Some of the pathways are preferentially linked to enhanced survival, while others are more frequently associated with cell death. Still others have been implicated in both extremes depending on the particular circumstances. In this review, we discuss the various signaling pathways known to be activated in response to oxidative stress in mammalian cells, the mechanisms leading to their activation, and their roles in influencing cell survival. These pathways constitute important avenues for therapeutic interventions aimed at limiting oxidative damage or attenuating its sequelae.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jcp.10119

Cellular response to oxidative stress: signaling for suicide and survival.

There are provided antibodies directed against
the ATM protein are peptide derivatives of the protein are
also provided. Also provided is a diagnostic tool for
determining the presence of A-T having a detector for
detecting ATM protein levels and quantification tools for
analyzing the ATM protein levels. A kit for detecting the
presence of A-T containing a detector for detecting ATM
protein levels and a quantificator for analyzing ATM
protein levels is also provided.

https://science.sciencemag.org/content/sci/281/5383/1674.full.pdf

Enchanced phosphorylation of P53 by ATM in response to DNA damage

PROBLEM TO BE SOLVED: To obtain an antibody effective for improving the DNA stability in normal cell and genetically compromised cell and useful for gene therapy, diagnosis, or the like, by recognizing an ATM protein (peptide derivative). SOLUTION: The antibody is effective against an ATM protein (peptide derivative). The antibody is further characterized by the capability of recognizing an intrinsic recombinant-type ATM translated in vitro and separated by immunoprecipitation with other anti-ATM antibody and further by the capability of recognizing a protein of 379 kD expressed by the ectopic expression of ATM in a cell. A diagnostic tool for the determination of the existence of ATM is produced by using a means for detecting an ATM protein level and a quantitative determination means for the analysis of ATM protein activity. Preferably, an antibody against ATM-originated peptide is produced, ATM protein is separated from cultured cell by immunoprecipitation and the precipitated product is assayed to perform the research on the ATM activity.

Nehama I. Smorodinsky

Papers

Enchanced phosphorylation of P53 by ATM in response to DNA damage

Increased phosphorylation of p53 with atm against dna damage